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Assessment of Fish and Plant Communities in Lake Apopka, Florida

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Title:
Assessment of Fish and Plant Communities in Lake Apopka, Florida
Creator:
MURPHY, STEPHEN J.
Copyright Date:
2008

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Subjects / Keywords:
Boxes ( jstor )
Fish ( jstor )
Fisheries ( jstor )
Freshwater bass ( jstor )
Lakes ( jstor )
Macrophytes ( jstor )
Sediments ( jstor )
Species ( jstor )
Sunfish ( jstor )
Vegetation ( jstor )
Lake Apopka ( local )

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University of Florida
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University of Florida
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Copyright Stephen J. Murphy. Permission granted to University of Florida to digitize and display this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
Embargo Date:
4/17/2006
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77080061 ( OCLC )

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Full Text












ASSESSMENT OF FISH AND PLANT COMMUNITIES
IN LAKE APOPKA, FLORIDA
















By

STEPHEN J. MURPHY


A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE

UNIVERSITY OF FLORIDA


2005
































Copyright 2005

By

Stephen J. Murphy















ACKNOWLEDGMENTS

Appreciation is expressed to all those who assisted me with this research. David

Watson and Dan Willis of Florida LAKEWATCH extended their expertise in

electrofishing activities. Alexis Caffrey helped take light meter measurements and

helped survey aquatic plants, along with Heather Hammers and Laura Stockman.

Elizabeth Daneman and Erich Marzolf from the St. Johns River Water Management

District (SJRWMD), William Johnson from the Florida Fish and Wildlife Conservation

Commission (FFWCC), and Mark Hoyer from the University of Florida provided

previous data on the fish and plant communities. Karen Brown from the University of

Florida (UF), Center for Aquatic and Invasive Plants, assisted me in locating journal

articles for my aquatic plant literature review. Dr. Roger Bachmann guided me in

analyzing limnological data. Dr. Daniel E. Canfield, Jr. served as my committee

chairman and advisor, and directed me towards excellence and professionalism in the

scientific field. Finally, Dr. Charles Cichra and Dr. Kenneth Langeland served on my

committee and helped oversee this research.
















TABLE OF CONTENTS



A C K N O W L E D G M E N T S ......... ................................................................................... iii

LIST OF TABLES ............................. .......................... v

LIST OF FIGURES ......... ....... .................... .......... ....... ............ vi

ABSTRACT .............. ..................... .......... .............. vii

INTRODUCTION .............. ................................... ..............

M A TERIALS AN D M ETH OD S...................................................................................8

F ish ....................................................... 8
A aquatic M acrophytes............................................................................ 10
Statistical A analyses ................................................................. ....... .. ...... .... 15

RESULTS AND DISCU SSION ............................................................. ................19

F ish .........................................................................1 9
A aquatic M acrophytes............................................................................ 29

LAKE MANAGEMENT RECOMMENDATIONS ................................ ...............46

L IST O F R E F E R E N C E S .......................................................................... ....................53

B IO G R A PH IC A L SK E TCH ...................................................................... ..................62















LIST OF TABLES


Table page

1 Electrofishing boat setup used by different studies at Lake Apopka, Florida..........17

2 Electrofishing control box settings used by different studies at Lake Apopka,
F lo rid a ........................................................... ................ 17

3 Electrofishing methods used by different studies at Lake Apopka, Florida. ...........18

4 Common and scientific names of fish collected by individual studies at Lake
A p o p k a, F lo rid a ................................ ......... ... .... ................ ................ 3 6

5 Water chemistry parameters measured for Lake Apopka, Florida, in June -
O ctob er 2004 ...................................................... ................. 37

6 Mean electrofishing catch per unit effort and standard error of fish number
(number/hr) and weight (kg/hr) for Lake Apopka, Florida...................................37

7 Mean yearly and combined electrofishing catch per unit effort and standard error
of fish number (number/hr) for Lake Apopka, Florida, by Johnson and
Crum pton (1998) ................................................................ .. ..........38

8 Annual mean electrofishing catch per unit effort number (number/hr) of two size
groups of largemouth bass, bluegill, and redear sunfish collected in Lake
A p opk a, F lorida .............................................................................. ............... 39

9 Occurrence of plant species in twenty evenly-spaced transects around Lake
A p opk a, F lorida, in 2 004 ............................................................... .....................39

10 Location, area (m2), and maximum depth (m) of eel-grass beds in Lake Apopka,
F lorida, in 2004 .................................................... ................. 40















LIST OF FIGURES


Figure p

1 Lake Apopka and surrounding area. ............................................... ............... 7

2 Mean electrofishing catch per unit effort estimates of total fish abundance
(number/hr) for Lake Apopka, Florida................................. ....................... 41

3 Mean electrofishing catch per unit effort estimates of total fish abundance
(number/hr) for the combined data of different studies for Lake Apopka, Florida..41

4 Individual fish species percent of total number collected by electrofishing for
Lake Apopka, Florida, by Johnson and Crumpton (1998) for 1989 1993. ...........42

5 Individual fish species percent of total number collected by electrofishing for
Lake Apopka, Florida, in June August 2004.............. .....................................42

6 Length frequency distribution of bluegill collected by electrofishing for Lake
Apopka, Florida, in June August 2004....................................... ............... 43

7 Length frequency distribution of redear sunfish collected by electrofishing for
Lake Apopka, Florida, in June August 2004.............. .....................................43

8 Mean electrofishing catch per unit effort estimates of largemouth bass
abundance (number/hr) for Lake Apopka, Florida........................................44

9 Mean electrofishing catch per unit effort estimates of largemouth bass
abundance (number/hr) for the data sets of combined years from different
studies for Lake Apopka, Florida. ........................................ ......................... 44

10 Length frequency distribution of largemouth bass collected by electrofishing for
Lake Apopka, Florida, in June August 2004.............. .....................................45

11 Electrofishing catch per unit effort of largemouth bass (kg/hr) versus total
chlorophyll a (tg/L) for 60 Florida lakes...................................... ............... 45















Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Science

ASSESSMENT OF FISH AND PLANT COMMUNITIES IN LAKE APOPKA,
FLORIDA

By

Stephen J. Murphy

December 2005

Chair: Daniel E. Canfield, Jr.
Major Department: Fisheries and Aquatic Sciences

Since the 1960s, an enormous amount of time and resources has been expended

by the State of Florida and other government entities trying to improve the water quality

in Lake Apopka, a hypereutrophic lake in central Florida; however, the lake remains in a

turbid algal state in the early 2000s. The objective of this study was to assess the

effectiveness of the restoration efforts in returning Lake Apopka back to its historic

primary use of recreational fishing for largemouth bass (Micropterus salmoides

floridanus). The assessment was accomplished by surveying the fish populations and

aquatic plant communities in the lake to determine if there has been an increase in the

abundance of largemouth bass or an expansion in the area occupied by aquatic

vegetation. Fish were sampled by electrofishing on three occasions in June August

2004. Submersed macrophyte beds, primarily eel-grass (Vallisneria americana), and

floating-leaved and emergent plants were sampled in October 2004. The mean

largemouth bass catch rate in 2004 was 7 fish/hr. The combined catch rate from 1989 to









1993 was also 7 fish/hr, thus showing that the largemouth bass population did not

increase in relative abundance during the last decade. The abundance of largemouth bass

continues to be lower than expected for Lake Apopka's trophic status in comparison to

other Florida lakes. Submersed, floating-leaved, and emergent plants covered less than

1% of the surface area of the lake in 2004, indicating that the rooted aquatic vegetation

has not expanded in the last several decades. Eel-grass colonized a total lake bottom area

of approximately 900 m2 in 2004 compared with an estimated 11,032 m2 in 1999. Eel-

grass has drastically declined during the past five years since it was replanted around the

shore in 1999. It now occupies only 8% of its former area that it occupied in 1999. The

restoration efforts at Lake Apopka have not yet been successful in restoring the

largemouth bass fishery or in expanding the area occupied by aquatic vegetation.

Reducing the abundance of planktonic algae through nutrient management is the primary

restoration strategy for agencies such as the St. Johns River Water Management District

(SJRWMD). Other factors besides light attenuation by planktonic algae, however, are

involved in limiting the abundance of largemouth bass and expansion of aquatic

macrophytes. The depth and fluidity of sediments, and wind resuspension of sediments,

are also major factors. It could be several more decades before the largemouth bass

fishery is improved while relying on the current restoration strategy unless alternative

management strategies are also utilized. Three alternative management strategies or

ideas that have been discussed are drawdown, artificial reefs or barriers, and stocking.















INTRODUCTION

Lake Apopka is the fourth largest lake in Florida with a surface area of 12,465 ha

(Hoge et al. 2003). It is located northwest of Orlando, Florida, in both Orange and Lake

counties (Figure 1). It is shallow (1.6 m mean depth) and polymictic. It is

hypereutrophic with high nutrient and chlorophyll levels (100 [g/L mean total

phosphorus (TP) and 59 [g/L mean chlorophyll a (chla)), and low transparency (0.35 m

mean Secchi depth (SD)) (Hoge et al. 2003). These limnological parameter values (TP,

chla, and SD) are mean 2004 values obtained from the St. Johns River Water

Management District (SJRWMD). The lake is nearly round except that it is shaped like a

funnel or gourd neck at the southern end of the lake (Figure 1). Vegetable farms (muck

farms) were established on the north end of the lake after 1940 for World War II wartime

food production.

Prior to 1950, Lake Apopka contained clear water, and dense growths of Illinois

pondweed (Potamogeton illinoensis) and eel-grass (Vallisneria americana) down to

depths of 2.4 m (Clugston 1963, Chestnut and Barman 1974). About 80% of the lake

was inhabited by aquatic plants. Clugston (1963) reported that Illinois pondweed began

at about 180 m from the shoreline and extended across the entire length and breath of the

lake except in deep-water areas (> 2.4 m). Water hyacinth (Eichhornia crassipes) grew

profusely around the entire shoreline of the lake (Clugston 1963). Boating around the

lake was restricted to trails through submersed vegetation and to openings not covered by

extensive mats of water hyacinth (Clugston 1963).









Lake Apopka was nationally renowned as a premier largemouth bass

(Micropterus salmoidesfloridanus) fishing lake (Dequine 1950, Dequine and Hall 1951,

Shofner 1982). Anglers came from throughout the United States to fish for trophy-sized

largemouth bass (Davis 1946, Dequine 1950, Clugston 1963, Chestnut and Barman

1974). By the early 1950s, there were an estimated 13 fishing camps with a value to the

local economy of over one million dollars annually (Dequine and Hall 1951, Shofner

1982).

Lake Apopka was changed in the early twentieth century by flood plain alteration,

water level stabilization, and urban and agricultural runoff (Huffstutler et al. 1965). Also,

in the 1940s, farms at the north end of the lake expanded by draining marsh areas.

Following the expansion of the farms, farmers began to pump an increased amount of

nutrient-rich water back into Lake Apopka (Clugston 1963). A hurricane in 1947

uprooted many of the macrophytes in the lake according to Mr. John Dequine (retired

biologist, Florida Game and Fresh Water Fish Commission, personal communication),

Clugston (1963), Schneider and Little (1969), Lake Apopka Restoration Council (1986),

and Bachmann et al. (1999). Within several years, the remaining macrophytes

disappeared in other parts of the lake as well, coinciding with a switch to a turbid algal

state (Clugston 1963). There is controversy about the role of the hurricane in the loss of

the macrophytes and about whether the switch from rooted macrophytes to algae was the

result of natural causes or the result of the numerous human activities (Schelske and

Brezonik 1992, Bachmann et al. 1999, Lowe et al. 1999, 2001, Canfield et al. 2000,

Schelske et al. 2000, Schelske and Kenney 2001). Regardless of the mechanisms, sport









fishing for largemouth bass declined in the late 1950s and early 1960s (Clugston 1963,

Huffstutler et al. 1965, Lake Apopka Restoration Council 1986).

According to Johnson and Crumpton (1998), the largemouth bass fishery and

aquatic vegetation community have been functionally non-existent at Lake Apopka since

the 1960s. Dequine and Hall (1951) estimated that over 9,513 largemouth bass were

harvested in January 1951 alone. Johnson and Crumpton (1998) stated that the combined

harvest over the last two decades (from 1978 to 1998) probably would not equal that one

month's harvest.

Aquatic vegetation in the 1980s and 1990s has only occupied a narrow belt

around the shoreline of the lake, comprising less than 1% of the surface area of lake

(Canfield and Hoyer 1992, Johnson and Crumpton 1998). Dominant emergent plant

species were cattail (Typha spp.) and woody wetland species (red maple (Acer rubrum)

and Carolina willow (Salix caroliniana)), which occupied 38% and 44% of the shoreline,

respectively, in 1997 (Johnson and Crumpton 1998). There were isolated stands of

aquatic grasses (maidencane (Panicum hemitomon), torpedograss (Panicum repens),

Egyptian paspalidium (Paspalidium geminatum)), and soft-stem bulrush (Scirpus

validus), which together occupied 8% of shoreline (Johnson and Crumpton 1998). The

dominant floating-leaved plant species was water hyacinth in 1986, occurring in 27% of

transects (Canfield and Hoyer 1992). The occurrence of floating-leaved or submersed

plant species was not reported by Johnson and Crumpton (1998). The relative species

richness of aquatic macrophytes (10 species) and fish (16 species) in 1986 was low in

comparison with other Florida lakes (Canfield and Hoyer 1992).









A thick layer of flocculent sediments (1.5 m mean thickness) covers 90% of the

lake bottom in almost all areas of the lake (Schneider and Little 1969). There is a firm

bottom in some parts of the west shore and in some parts of the shoreline in the gourd

neck area. These unconsolidated sediments are often resuspended by the wind,

contributing to the high turbidity, and do not allow plants to anchor their roots (Carter et

al. 1985, Doyle 2001, Doyle and Smart 2001) or largemouth bass to successfully nest

(Porak et al. 1999).

Point sources of nutrient loading from sewage and citrus processing plants were

eliminated by the 1980s, and discharges from farming operations were reduced in 1992

(Johnson and Crumpton 1998, Bachmann et al. 1999, Canfield et al. 2000, Hoge et al.

2003). The majority of these farmlands were purchased by the SJRWMD in the late

1990s. The SJRWMD continues to conduct management efforts to restore Lake Apopka

under the Lake Apopka Surface Water Improvement and Management (SWIM) program

(Conrow et al. 1993, Hoge et al. 2003).

The current restoration program strategy, headed by the SJRWMD, is based

primarily on reducing external nutrient loading, focusing primarily on phosphorus (P)

reductions (Hoge et al. 2003). The P criterion proposed by the SJRWMD for the lake is

55 [g/L (Hoge et al. 2003). Other projects of the current restoration program have

included removing gizzard shad (Dorosoma cepedianum) from the lake and planting

macrophytes around the shore in the 1990s. Despite the enormous amount of time and

resources that have been expended trying to improve the water quality in Lake Apopka

and to return the lake to its former clear-water, macrophyte-dominated state, nationally









renowned for its largemouth bass fishery, the lake remains in a turbid algal state

(Bachmann et al. 1999).

There is a lack of unanimity regarding the efficacy of restoration efforts

(Bachmann et al. 1999, 2001a, b, Lowe et al. 1999, 2001, Canfield et al. 2000, Schelske

et al. 2000, Schelske and Kenney 2001). Some authors do not believe that the restoration

program, based primarily on an external P reduction program, will be successful in

improving the water clarity or in expanding the aquatic vegetation needed as habitat for

largemouth bass in the near-future (Bachmann et al. 1999, 2001a, b, Canfield et al. 2000).

Alternative hypotheses regarding the limiting factor responsible for causing the turbidity

of the water, for example wind resuspension of sediments (Bachmann et al. 1999, 2000a,

b), have been put forth but have not yet been acted upon.

Recent management strategies have not included alternative methods and ideas

such as drawdown or artificial barriers that could reduce the turbidity in the water from

resuspended particles and potentially improve the largemouth bass fishery. For example,

a major drawdown could consolidate and compact the sediments (Wegener and Williams

1974, Moyer et al. 1995) if the technical problems, such as the amount of water to be

moved and the length of time that the lake would stay drained, could be resolved (United

States Environmental Protection Agency (USEPA) 1979). Also, placing artificial barriers

around the perimeter of the lake could provide calm, protected waters and improve the

habitat for largemouth bass in those areas (Canfield et al. 2000).

No studies have been conducted to find out if the aquatic plants, which were

planted by the SJRWMD in or before 1999, have expanded in area to determine if the

restoration program has been successful in one of its primary objectives of restoring lake









habitat (Hoge et al. 2003), and to determine if the money that has been expended has

been well spent. For example, more than $100,000,000 in Federal and State funds were

used to purchase farms, with drainage to the lake, to take them out of production. A

marsh flow-way was also constructed to remove phosphorus-rich particles from the lake

water (Conrow et al. 1993, Hoge et al. 2003). A study was needed to assess the response

of the fish and plant communities in Lake Apopka to these restoration activities because

of the controversy over the successfulness of the restoration program.

Previous studies to assess the fish and plant communities in Lake Apopka were

conducted by Canfield and Hoyer (1992) and Johnson and Crumpton (1998). The

objective of this study was to evaluate the effectiveness of the restoration program in

restoring the largemouth bass fishery and the aquatic plant community. This objective

was accomplished by sampling the littoral fish populations and the aquatic macrophyte

community. The criteria, for determining if the restoration program was effective, was

whether or not the largemouth bass population has increased in abundance (catch rate as

number/hr or kg/hr) in the last two decades, or the aquatic macrophyte community, used

as habitat by largemouth bass, has expanded in area (m2 or ha) since 1999. To make this

determination, the abundance and structure of the littoral fish populations and aquatic

macrophyte community, surveyed by this study in 2004, were compared, and tested as

appropriate, to those of previous studies.










Lake County Orange County


Ferndale .": i]
b b.. . . ......b..b..b ..b.. .. .. .. .. .
.. .. .b..b..b..b..b..b..b..b..b..b...b ..b....b..

Ocoee


SR 50


0 1 2 Kilometers W- -E
I I I s


Figure 1. Lake Apopka and surrounding area (modeled using Hoge et al. 2003, page 14).















MATERIALS AND METHODS

Fish

Fish were electrofished in near-shore areas of the main part of Lake Apopka,

excluding the gourd neck area and the adjoining canals. Ten transects were sampled once

monthly in June, July, and August 2004 using a Coffelt Mfg., Inc. control box. Ten

additional transects were sampled in June using a Smith-Root, Inc. control box as part of

a control box comparison study, thus totaling 40 transects. Transects were evenly spaced

around the lake in all habitats. Each transect was 10 minutes in duration, with continuous

current input. Methods were similar to those used by Canfield and Hoyer (1992), Hoyer

(University of Florida (UF), unpublished data), and Johnson and Crumpton (1998).

Fish were collected, identified to species, measured to the nearest mm total length

(TL), and released back into the lake. Individual fish weights were calculated from

measured lengths using total weight to length regression formulas developed for

individual Florida freshwater fish species by Hoyer and Canfield (1994). The total

number and weight of fish were calculated by transect and then averaged across the 40

transects to yield catch per unit electrofishing effort (number or kg/hr of electrofishing)

statistics.

At each electrofishing transect, the depth and dominant vegetation, if present,

were recorded. Dissolved oxygen (DO) concentration (mg/L), Secchi disc depth (SD)

(m), specific conductance ([iS/cm at 25 C), and water temperature (C) were measured at

four near-shore stations, when the electrofishing was conducted (one station in each of









the north, east, south, and west regions of the lake). Dissolved oxygen concentration,

specific conductance, and water temperature were measured by using a Yellow Springs

Instrument Company Model 85 Meter.

Coffelt Mfg., Inc. control boxes were used in collecting fish in previous studies at

Lake Apopka by Canfield and Hoyer (1992) and by Hoyer (UF, unpublished data).

Coffelt Mfg., Inc. recently went out of business and the only company that now

manufactures electrofishing control boxes is now Smith-Root, Inc. The Florida Fish and

Wildlife Conservation Commission (FFWCC) replaced all of its Coffelt Mfg., Inc.

control boxes with control boxes manufactured by Smith-Root, Inc. in the 1990s, but the

UF, Department of Fisheries and Aquatic Sciences (FAS) uses both brands of control

boxes. Because the catch rate of this study (which used both brands of control boxes)

was compared to previous studies by Canfield and Hoyer (1992), Hoyer (UF,

unpublished data), and Johnson and Crumpton (1998) that did not all use the same brand

of control box, it was important to conduct a comparison study to account for any

possible differences that might be due to using different control boxes.

A comparison study was conducted in June 2004 by using control boxes

manufactured by Smith-Root, Inc. and Coffelt Mfg., Inc. to simultaneously collect fish in

10 paired transects in similar habitat. The data from paired transects were used to test for

differences in catch rate between the two control boxes using a paired t test. Each boat

started from the middle of the habitat, 10 m apart, and worked away from each other to

the ends of the habitat. The two boats used in the comparison study were set up

identically except for the control boxes. Both boats were 5 m in length, made of

aluminum, powered by 50-hp Mercury motors, and equipped with 5000-watt Honda









EG5000X generators (Table 1). Both boats had one boom with an attached 62-cm

diameter ring, with six 1-cm diameter, 1.2-m long, stainless steel cables in place, for

transmitting electricity into the water. Both control boxes were set at 7-9 amps, 180-190

volts, 60-80 pulses per second, and (pulsed) alternating current output (Table 2). All

persons participating in the study had prior experience in electrofishing. One person, in

each boat, dipped fish.

Although the equipment and sampling design used in this study were similar to

previous studies on Lake Apopka, there were some differences. Johnson and Crumpton

(1998) was the only study that used two electric booms. A study was not conducted to

determine if having two booms would result in collecting more fish than using only one

boom. Additionally, no studies were found in the literature that compared the efficiency

of using two booms versus one boom.

Johnson and Crumpton (1998) had the most samples (870 transects in 1989 -

1993, and 150 transects in 1996 1997) (Table 3). They collected fish in 5-min transects

using random sampling in 1989 1993, and both random and selected sampling in 1996

- 1997. All the other studies collected fish in 10-min transects using evenly distributed

sampling. Hoyer (UF, unpublished data) sampled only the northern half of the lake,

whereas, all of the other studies sampled the entire lake.

Aquatic Macrophytes

Dominant plant species were recorded at each of the evenly spaced, electrofishing

transects during each sampling occasion. Four fathometer transects (north to south, west

to east, northwest to southeast, and southwest to northeast) were run across the entire

diameter (-17 km) of the lake in August 2004 to record the location and amount, if any,

of submersed vegetation in Lake Apopka. The procedures for using a recording









fathometer and determining quantitative vegetation parameters have been described

previously (Maceina and Shireman 1980). The widths of floating-leaved and emergent

plant zones (m) were estimated by eye at 30 transects evenly spaced around the lake in

October 2004. Estimating fixed distances was practiced just prior to sampling and

consistent methods were used to make and record estimations of distance. Dissolved

oxygen concentration and SD were measured at four near-shore stations, on the date that

vegetation was sampled (one station in each of the north, east, south, and west regions of

the lake).

The 16 largest beds of eel-grass, reported by the SJRWMD (Conrow and Peterson

2000), were sampled in October 2004. Eel-grass was the only submersed macrophyte

sampled in this study because it was the only submersed macrophyte reported to be

abundant (- 1 ha) in the lake besides hydrilla (Hydrilla verticillata, < 0.5 ha) (Conrow

and Peterson 2000). Hydrilla was not sampled during this study because contact

herbicide has been applied regularly by the SJRWMD to keep it from expanding (Erich

Marzolf, environmental scientist, SJRWMD, Palatka, FL, personal communication). The

location and abundance of hydrilla also changes frequently.

All sampled eel-grass beds were located on the west side of the lake, with a few

exceptions. Only a few small beds were reported on the north, east, or south sides of the

lake (Conrow and Peterson 2000). Seven additional sites were sampled in the north (3

sites), east (1 site), and south (3 sites) regions of the lake, even though they were small

(Conrow and Peterson 2000), so that the entire lake would be represented by the locations

that were chosen. Sites were found using GPS coordinates obtained from the SJRWMD.









At each site, the area (m2) of the plant bed was estimated by eye from the boat for

all but the largest beds. Estimating fixed distances was practiced just prior to sampling

and consistent methods were used to make and record estimations of distance. Plant

beds, over 100 m2 in area, were walked around while simultaneously measuring their area

(m2) with a handheld GPS receiver. The percent density (from 0 to 100% for sparse to

dense aggregations) was estimated by eye. The type of soil (sand or some degree of

silt/mud) was determined by pushing on the substrate with a rod. The maximum water

depth (m) that the plant bed was growing in was determined by lowering a Secchi disk

until it rested on the substrate and measuring the vertical distance (m) from the substrate

to the water surface with the attached cord.

Light attenuation in Lake Apopka was measured (in quanta units) using a

photometer (LI-COR model LI-1400 data logger) attached to an underwater quantum

sensor (LI-192SA) and a spherical quantum sensor (LI-193SA). Three samples, spaced

15 m apart, were taken at the center of the lake on three sampling occasions (once

monthly in June, August, and October 2004) for a total of nine samples. Irradiance

measurements were taken at the center of the lake because of depth limitations near

shore. A sample consisted of taking a series of downwelling irradiation measurements

every 0.2 m into the water column starting from the surface until either depth or light

became limited (as seen by negative irradiance measurements), whichever was reached

first. Measurements were taken with the spherical quantum sensor laying facing up on

the deck to measure ambient atmospheric irradiance and with the underwater sensor

attached to a graduated rod that was held straight out and away from the sampler's body

on the sunny side of the boat with the rod aligned vertically.









The maximum depth of colonization (MDC) is the maximum depth at which an

aquatic macrophyte species is capable of colonizing. Mittelboe and Markager (1997)

stated that the MDC was defined by the deepest growing plant observed. Since MDC is

thought to be primarily limited by irradiance (Chambers and Kalff 1985, Carter et al.

1985), measurements of downwelling irradiance in the water column, and calculations of

the percent of downwelling surface irradiance at depth, can be used to determine the

theoretical MDC (Korschgen et al. 1997). One percent of downwelling surface irradiance

(Io) is generally taken as the theoretical MDC of aquatic macrophytes (Dennison 1987,

Valiela 1995) because it is the compensation depth at which photosynthesis and plant

respiration are equivalent (Korschgen et al. 1997).

Aquatic macrophytes are not always able to colonize down to their theoretical

MDC except under optimal conditions (Spence 1972, Barko and Smart 1981, Chambers

and Kalff 1985, Scheffer et al. 1992, Hudon et al. 2000). The lower depth limit, with

some exceptions, more commonly occurs at light levels between 5 and 10% Io (Sheldon

and Boylen 1977, Barko et al. 1982, Chambers and Kalff 1985, Kimber et al. 1995a, b).

Dennison (1987) stated that the maximum depth limit for freshwater macrophytes was

roughly equivalent to the Secchi disc depth, which is often taken as the 10% light level

(Strickland 1958).

The maximum depth of growth (MDG) is defined in this paper as the maximum

depth corresponding to the minimum percent of Io at which an aquatic macrophyte

species predominantly grows down to, as limited by light attenuation (Sheldon and

Boylen 1977, Kenworthy and Fonseca 1996, Nichols 1997, Moore et al. 2003). Other

studies have more strictly defined the MDG as the maximum depth corresponding to the









minimum percent of Io needed for there to be a specified production (number or g) or

elongation (cm) of leaf, meristem, or shoot, or production (g) of biomass, within a

specified period of time (days) (Barko and Smart 1981, Barko et al. 1982, Loreny and

Herderndorf 1982, Dennison 1987, Duarte and Kalff 1987, Sand-Jensen and Madsen

1991, Korschgen et al. 1997, Blanch et al. 1998, Bintz and Nixon 2001, Grimshaw et al.

2002, Nielsen et al. 2002). The theoretical MDG for eel-grass was established in this

study by referencing previous studies on the minimum percent of Io needed for eel-grass

to grow. For example, the maximum depth corresponding to a minimum referenced

percent of lo, needed for eel-grass to grow, was taken as the MDG.

The data from the light meter measurements were used to determine the

theoretical MDC and MDG of eel-grass in Lake Apopka. The theoretical MDC and

MDG were chosen as 1% Io and 8% Io, respectively, because authors in the literature

have reported that eel-grass and other aquatic vascular plants are capable of colonizing

down to depths of 1% Io and that they grow down to about 8% Io (Sheldon and Boylen

1977, Barko et al. 1982, Carter and Rybicki 1985, 1990, Duarte and Kalff 1987,

Goldsborough and Kemp 1988, Sand-Jensen and Madsen 1991, Zimmerman et al. 1994).

For each sample, the ratio of downwelling irradiance at depth (Id) to Io, taken as a percent,

was calculated using Microsoft Office Excel 2003 to determine theoretical MDC and

MDG. For example, the ratio of Id to Io, taken as a percent, yields the percent

downwelling irradiance at a given depth in the water column. Then, the water depth

corresponding to 1% and 8% Io equals the theoretical MDC and MDG, respectively.

The total area (m2) of eel-grass that was found in Lake Apopka during this study

was subtracted from the total area reported by the SJRWMD in 1999 (Conrow and









Peterson 2000) to determine if eel-grass was expanding, remaining constant, or declining.

The observed and theoretical MDC and MDG were compared to determine if the

maximum depth at which eel-grass was found to be growing agrees with the theoretical

depth to which it should be able to grow. The observed MDG used in my analysis was

derived from the maximum depth (m) at which eel-grass was measured to be

predominantly growing. Similarly, the observed MDC used in my analysis was derived

from the maximum depth at which eel-grass was found to be growing at the 23 sites

sampled.

The area of the lake, that was available for eel-grass to colonize and grow based

on the observed MDC and MDG, was calculated using a bathymetric map (Danek and

Tomlinson 1989). This area was compared to the total area of eel-grass found to

determine the percentage of available area that eel-grass inhabited under the current light

regime. The percentage of the total lake area that eel-grass was theoretically able to

colonize and grow, under the current light regime, was also calculated.

Statistical Analyses

The catch rates of total fish and largemouth bass of this study were compared to

the catch rates of previous studies conducted in 1986 by Canfield and Hoyer (1992); in

1987 1996, excluding 1990, by Hoyer (UF, unpublished data); and in 1989 1993 and

1996 1997 (largemouth bass only) by Johnson and Crumpton (1998). Ttests were

used, where appropriate, to determine if there had been a statistical difference in the

abundance of total fish or individual fish species in the near-shore region of Lake

Apopka. Raw data were available only for Johnson and Crumpton (1998) for 1989 -

1993, and not for 1996 1997. Their report and tables were used to determine the catch

rate of largemouth bass, bluegill (Lepomis macrochirus), and redear sunfish (Lepomis









microlophus) for 1996 1997. Microsoft Office Excel 2003 was used to analyze all data

(the fish and plant data collected in this study, as well as data collected by other

individuals).

The population of largemouth bass at Lake Apopka, from 1986 to 2004, was

graphically compared to 60 other Florida lakes sampled by Canfield and Hoyer (1992),

by plotting the mean catch per unit effort (CPUE) (kg/hr) of largemouth bass for all of the

lakes against their corresponding mean chla ([tg/L) value. Four separately identified data

points were given for the individual studies that sampled Lake Apopka from 1986 to

2004. Chlorophyll data points, for the individual studies conducted at Lake Apopka,

were the mean yearly chlorophyll values, for the years in which Lake Apopka was

sampled, obtained from the SJRWMD. Chlorophyll data points, for the 60 lakes sampled

by Canfield and Hoyer (1992) were the mean chlorophyll values reported in Canfield and

Hoyer (1992). Data were transformed to their logarithms (base 10) to reduce

heterogeneity of variance. The resulting plot allows comparison of the mean CPUE of

largemouth bass of all the lakes based on their mean chla values.

The efficiency of collecting total fish using control boxes manufactured by

different companies, Smith-Root, Inc. versus Coffelt Mfg, Inc., was tested for significant

differences using a paired t test. The efficiency of collecting two categories of fish was

also tested using paired t tests. Centrarchids (warmouth (Lepomis gulosus), bluegill,

redear sunfish, and largemouth bass) were lumped into one category. Other non-

centrarchids (Florida gar (Lepisosteus platyrhincus), bowfin (Amia calva), gizzard shad,

blue tilapia (Tilapia aurea), yellow bullhead (Ameiurus natalis), brown bullhead










(Ameiurus nebulosus), and channel catfish (Ictaluruspunctatus)) were lumped into a

second category.

Table 1. Electrofishing boat setup used by different studies at Lake Apopka, Florida.
Number of Persons
Study Generator Model Number of Booms Dipping Fish
This Study (2004) Honda EG5000X 1 1
Johnson & Crumpton (1998) Honda EG5000X 2 1
Hoyer (Unpublished data) Honda EG5000X 1 1
Canfield & Hoyer (1992) Honda EG5000X 1 1

Table 2. Electrofishing control box settings used by different studies at Lake Apopka,
Florida.
Control Box Output Output Output Pulse
Study Model Mode Amps Volts Width Frequency
This Study (2004) Coffelt VVP-15 Pulsed AC 7-9 180 50% 80- 100
Smith-Root VI-A Pulsed AC 6-8 177 2 ms -
Johnson & Crumpton (1998) Smith-Root VI-A Pulsed AC or 5-7 177- 2 5 ms -
Pulsed DC 500
Hoyer (Unpublished data) Coffelt VVP-15 Pulsed AC 7-9 180 50% 80 100
Canfield & Hoyer (1992) Coffelt VVP-15 Pulsed AC 7-9 180 50% 80 100













Table 3. Electrofishing methods used by different studies at Lake Apopka, Florida.
Elapsed Time of Each
Month and Years Number of Samples Transect With
Study Sampled (N) Continuous Current Sampling Method Region of Lake
This Study (2004) Jun 2004 20 10 Proportioned by habitat Entire lake
Jul 2004 Aug 2004 20 10 Evenly distributed Entire lake
Johnson & Crumpton (1998) Mar 1989 -Nov 1993b 870 5 Random Entire lake
Nov 1996 Sept 1997c 180 5 75 random, 75 selected Entire lake
Hoyer (Unpublished data) Mar 1987 Jan 1996d 62 10 Evenly distributed Northern half only
Canfield and Hover (1992) Aug 1986 9 10 Evenly distributed Entire lake


aNot including the gourd neck area or canals.


bTwenty-nine months were sampled bimonthly in the odd months of the year.

CSix months were sampled bimonthly in the odd months of the year.

dSampling was conducted only in January, February, or March.
00


i
















RESULTS AND DISCUSSION

Fish

Twenty species of fish were collected in 2004 (Table 4). Canfield and Hoyer

(1992), Hoyer (UF, unpublished data), and Johnson and Crumpton (1998) collected 16,

22, and 26 species, respectively. These differences in species richness are within a range

that would be expected from a stable fish community when temporal and personnel

differences in sampling are accounted for (Reynolds 1983, Hardin and Conner 1992,

Andrus 2000, Ott and Longnecker 2001, Bayley and Austen 2002).

Since Johnson and Crumpton (1998) took the most number of samples (870),

bimonthly, over a five-year period, using natural laws of probabilities (Ott and

Longnecker 2001), it would be expected for them to encounter more rare species than the

other studies that took less samples or took all of their samples in only one or a few

months, or only in a certain season of the year. Also, since Canfield and Hoyer (1992)

only sampled on one date, it is reasonable that they collected the smallest number of

species.

Differences in the manner in which personnel sample can result in changes in the

number and type of fish collected (Reynolds 1983, Hardin and Conner 1992, Andrus

2000, Bayley and Austen 2002). Personnel, that are meticulous in collecting every fish

regardless of size, are likely to collect a greater quantity of smaller, rare species. Also,

misidentification can result in an incorrect number of fish species being recorded.









There was no significant difference in the number of total fish, centrarchids, or

non-centrarchids collected between Smith-Root, Inc. and Coffelt Mfg., Inc. control boxes

(p > 0.05 for all three tests), although there were some interesting findings. When the

Smith-Root, Inc. control box was used, slightly more fish (23) were collected overall for

all 10 combined transects than when the Coffelt Mfg., Inc. control box was used. There

was higher variation in the total number of fish collected with the Coffelt Mfg., Inc.

control box (standard error = 7.1/hr) than with the Smith-Root, Inc. control box (standard

error = 6.1/hr). Also, when the Coffelt Mfg., Inc. control box was used, proportionally

more centrarchid fish were caught than non-centrarchids compared to the Smith-Root,

Inc. control box.

These results may apply only to conditions present at Lake Apopka during the

time of sampling (Bayley and Austen 2002). For example, the high mean conductivity

(453 pS/cm at 25 C) in Lake Apopka at the time of sampling, decreased the efficiency of

collecting fish, while using either brand of control box (Kolz 1989). Reynolds (2000)

stated that conductivity was the single most important environmental factor in

electrofishing. Temperature is also important. It affects the ability of the fish to float,

respond, and escape (Reynolds 2000). Mean water chemistry parameters during

sampling were 5.9 mg/L DO, 0.37 m SD, and 31.6 C water temperature (Table 5).

The total catch rate in 2004 was 156 fish/hr. Mean catch for Canfield and Hoyer

(1992), Hoyer (UF, unpublished data), and Johnson and Crumpton (1998) (1989 1993

data) were 203, 268, and 365 fish/hr, respectively (Figures 2 and 3). Comparison of the

yearly mean total catch rate over time suggests that the mean total abundance of fish has

declined since 1993 in the near-shore region in Lake Apopka (p < 0.05).









The total catch rate of this study was only tested for differences with Johnson and

Crumpton (1998), for the data from 1989 1993, because the data of that time period

were the most representative, of the different studies, of the fish populations in Lake

Apopka, based on the fact that they took the most samples (870 transects), bimonthly,

over an extended period of time (5 years) (Materials and Methods, Table 3). Canfield

and Hoyer (1992) only sampled on one occasion (9 transects). Hoyer (UF, unpublished

data) only sampled the northern half of the lake (62 transects).

Johnson and Crumpton (1998) was the only study that used two electric booms.

Using two booms could help explain why their mean total catch rate was higher than

Canfield and Hoyer (1992) and Hoyer (UF, unpublished data) during the same, or close

to the same, time period. If using two booms enabled Johnson and Crumpton (1998) to

collect more total fish than they would have collected using just one, it would result in a

larger reported difference in the catch rate of total fish over time.

Additionally, the mean total catch rate remained stable or increased from 1986 -

1993 (Figure 3). In 1993, the total catch rate seems to have declined dramatically.

Johnson and Crumpton (1998) stated that the abundance of open water fish species

(gizzard shad, threadfin shad (Dorosomapetenense), blue tilapia, and black crappie

(Pomoxis nigromaculatus)) as well as centrarchids (bluegill, redear sunfish, and

largemouth bass) all declined from 1989 1993 to 1996 1997. It was appropriate,

therefore, to test for a decrease in the total catch rate from 1993 to 2004.

Part of the reason for the decline in the total abundance of fish may be attributed

to the extensive harvesting of gizzard shad. For example, Crumpton and Godwin (1997)









reported that, from January 1993 through June 1997, commercial fishermen harvested

over 5 million gizzard shad weighing about 2.3 million kg from Lake Apopka.

Secondly, adverse environmental conditions present at the time of sampling could

also have reduced the total catch rate in 2004. For example, Hurricane Charley passed

over central Florida on 13 August (National Oceanic and Atmospheric Administration

(NOAA) 2005), just five days prior to the date that fish were sampled on 18 August. A

widespread mud plume was observed in the center of the lake while sampling fish on that

date. A widespread fish kill was also observed across the entire north half of the lake.

Additionally, the mean DO concentration (3.48 mg/L) for the near-shore stations in

August was low.

Lastly, it is possible that the decrease in mean yearly chla from about 97[g/L in

1990 to 59 [g/L in 2004 could have resulted in decreased productivity in the lake as well

as a reduction in the abundance of open water fish species (Bachmann et al. 1996). These

chla values were based on unpublished data obtained from the SJRWMD.

Because it was suspected that the adverse environmental conditions in August

2004 affected the total catch rate, the 2004 total catch rate was divided by month. The

mean total catch rates for June, July, and August were 149, 285, and 44 fish/hr,

respectively. The mean total catch rate in August was much lower than the two previous

months and contributed to the low total catch rate in 2004. Comparison of total catch rate

among all the studies, by using the same months that were sampled in 2004, would have

provided a direct comparison. Unfortunately, none of the previous studies sampled in

the same months (June, July, and August) as this study in 2004 (see Materials and

Methods, Table 3).









Comparison of the 2004 individual fish species percent of total, with Johnson and

Crumpton (1998), for 1989 1993, suggests that there has been a decrease in percent of

total fish for open water fish species (gizzard shad, threadfin shad, black crappie, blue

tilapia, and brown bullhead) over time (Figures 4 and 5). These open water species

composed 11% of the total fish number in 2004, a decrease from 56% of the total number

in 1989 1993. These values represent a species composition change from open water

species being most abundant in the near-shore region in previous years (1989 1993) to

centrarchids being dominant in 2004. A decrease in gizzard shad and threadfin shad

(from 34 to 5% of total fish numbers) contributed the largest proportion of the change.

No dramatic changes in the abundance of rare species were observed.

Centrarchids (warmouth, bluegill, redear sunfish, and largemouth bass) comprised

78% of the fish collected in 2004, an increase from 29% of the fish in 1989 1993

(Figures 4 and 5). The most abundant species in 2004 were bluegill and redear sunfish

with catch rates of 86 and 16 fish/hr, respectively (Table 6). The catch rates for these

species in 1989 1993 were 73 and 18 fish/hr, respectively (Table 7). Comparison of the

mean catch rate over time suggests that bluegill abundance is similar from previous years,

even though there is a statistical difference (p < 0.05).

This difference in the catch rate of bluegill and redear sunfish over time is within

a range expected from a stable fish population, given the natural fluctuations in fish

populations, and the temporal differences in sampling (Swingle 1950, Latta 1975, Ott and

Longnecker 2001). Latta (1975) stated that the abundance of fish populations changes

dynamically in response to changing environmental (e.g., temperature, wind, dissolved

oxygen, competition, predation) and biological (e.g., reproduction, growth, and mortality)









factors. Swingle (1950) stated that fish populations are regulated by the number of

offspring in the present year, and the number remaining in the population from the

previous year. He also stated that fish populations dynamically change depending on the

number and ratio of predator and forage fish present. Ott and Longnecker (2001) stated,

that as time increases between sampling occasions, greater differences in abundance

between samples can be expected. These changes in the abundance of bluegill and redear

sunfish over time are not very big considering all of the possible stochastic environmental

and biological changes over time, the amount of time that has passed between sampling

occasions, and the natural variation in sampling.

The catch rate of small (< 14 cm total length (TL)) bluegill and redear sunfish was

66 and 2.6 fish/hr, respectively, in 2004 (Table 8). The catch rate of large (> 14 cm TL)

bluegill and redear sunfish was 20 and 14 fish/hr, respectively, in 2004. Bluegill and

redear sunfish were dominated by small length classes in 2004, as in the past, based on

summary data taken from Table 5 in Johnson and Crumpton (1998), and presented in this

study (Table 8). Redear sunfish reached slightly larger mean length than bluegill

(Figures 6 and 7). Johnson and Crumpton (1998) reported that the annual mean catch

rate of large (> 14 cm) bluegill and redear sunfish were lower in 1996 1997 than values

from 1989 1993. Note that Johnson and Crumpton (1998) summary data was from

1989 1992 instead of for 1989 1993. The catch rate of bluegill and redear sunfish >

14 cm seems to have rebounded in 2004 to be similar to values reported for 1989 1993

by Johnson and Crumpton (1998).

The lake-wide largemouth bass catch rate in 2004 was 6.9 fish/hr. Canfield and

Hoyer (1992), Hoyer (UF, unpublished data), and Johnson and Crumpton (1998) (for









1989 1993, and 1996 1997) collected 1.3, 0.8, 6.5, and 3.6 fish/hr, respectively

(Figures 8 and 9). Comparison of the yearly mean largemouth bass catch rate over time

shows that the mean catch rate of 6.9 fish/hr in 2004 was not statistically different from

the combined mean catch rate of 6.5 fish/hr in 1989 1993 (p > 0.05), slightly more than

one decade ago. This indicates that the largemouth bass population has not significantly

increased in abundance over the last decade.

The mean largemouth bass catch rate of this study (6.9 fish/hr) was only tested for

an increase in largemouth bass abundance with that of Johnson and Crumpton (1998) for

1989 1993 because mean catch rate of that study was the highest (6.5 fish/hr) of the

previous studies (as well as the fact that their data were most representative of the fish

populations in Lake Apopka, as explained earlier). Testing for an increase in largemouth

bass abundance with Johnson and Crumpton (1998) for 1989 1993, was more

conclusive than testing for an increase with the other studies, which had lower mean

catch rates. It should be noted, however, that if using two booms enabled Johnson and

Crumpton (1998) to collect more largemouth bass than they would have collected using

just one boom, it would result in a smaller reported difference in the catch rate of

largemouth bass over time.

Largemouth bass collected in 2004 ranged in size from 7.1 to 51.6 cm TL (Figure

10), and in calculated weight from 3.4 to 2096 g. There was a low catch rate of small

(<24 cm) largemouth bass, as in previous years (Table 8). The fact that small fish (< 24

cm) are represented shows that reproduction is occurring in Lake Apopka.

Largemouth bass were absent from the 16 23.9 cm TL size group. This

suggests that juveniles may be particularly vulnerable to predation and other sources of









mortality at this size (Beverton and Holt 1957). On a statewide basis, largemouth bass

that average 24 cm TL are about 1 to 2 years old (Porak et al. 1999). The dominant size

group in 2004 was 24 31.9 cm TL. If one-year-old fish are undergoing extremely high

mortality, this size group would logically be a mixture of two-year-old and older fish.

Largemouth bass that are recruited into the larger size groups (> 24 cm) seem to be less

susceptible to mortality as shown by the greater frequency of fish in those size groups.

An alternative explanation for the absence of 16 23.9 cm fish is that fish in Lake

Apopka have rapid growth (Dr. Charles Cichra, professor, UF, personal communication).

Sampling was conducted from June through August while largemouth bass in Apopka

likely spawn from February through April. The small fish could thus be young-of-the

year fish. Rapid growth could result in fish between one and two years old exceeding 24

cm TL by summer. Largemouth bass from Lake Apopka should thus be aged to

determine whether the low abundance of 16 23.9 cm TL largemouth bass is due to high

mortality or rapid growth.

Largemouth bass are reproducing, growing, and recruiting to large size in Lake

Apopka, but on a population basis, their abundance is low (< 7 fish/hr), especially when

compared with other Florida lakes. Many Florida lakes have mean electrofishing catch

rates of more than 20 largemouth bass/hr. For example, Lakes Okahumpka, Miona,

Wales, Clear, Baldwin, and Susannah were reported to have 26, 60, 92, 232, 42, and 129

fish/hr, respectively (Canfield and Hoyer 1992).

Comparison of largemouth bass populations from Lake Apopka and 60 other

Florida lakes, sampled by Canfield and Hoyer (1992), shows that the abundance of

largemouth bass at Lake Apopka in 2004 continues to be lower than expected for its









trophic status as estimated by its chlorophyll content (Figure 11). The relationship

between largemouth bass and trophic status is positive suggesting that eutrophic and

hypereutrophic Florida lakes will have a high abundance of largemouth bass (Bachmann

et al. 1996). Lake Apopka is a hypereutrophic lake and in the absence of other limiting

factors, it would be expected to have a high abundance of largemouth bass. But the

results of this study as well as two out of three other previous studies on Lake Apopka

indicate that the abundance of largemouth bass is low (Figure 11), suggesting that

something is limiting their abundance. The amount of quality habitat is most likely the

limiting factor (Porak et al. 1999).

The first year of life is critical to the survival of largemouth bass. The structure

provided by aquatic vegetation, terrestrial brush, and rockpiles offers age-zero

largemouth bass protection from predators (Aggus and Elliot 1975, Crowder and Cooper

1979, Savino and Stein 1982, Durocher et al. 1984, Dibble and Kilgore 1994). Suitable

prey such as zooplankton and small forage fish are more readily available in aquatic

vegetation and other structure than in open areas (Durocher et al. 1984, Gutreuter and

Anderson 1985, Dibble and Kilgore 1994).

Availability of food of the proper type and size contributes to differential growth

in young largemouth bass (Aggus and Elliot 1975, Shelton et al. 1979, Timmons et al.

1980, Gutreuter and Anderson 1985, Olson 1996). Faster growing juveniles make the

switch to piscivory earlier than slower growing fish (Gutreuter and Anderson 1985,

Olson 1996). Rate of growth is one of the primary determinants of the recruitment of

largemouth bass to stock size (Kramer and Smith 1962, Aggus and Elliot 1975, Olson

1996). A higher percentage of fast growing largemouth bass that reach a large size in









their first winter are recruited than slow growing fish (Kramer and Smith 1962, Davies et

al. 1982, Gutreuter and Anderson 1985).

Expanding cover in Lake Apopka would result in a decrease in mortality of age-

zero largemouth bass due to decreased predation in their critical first year of life.

Additionally, young-of-the-year largemouth bass would be able to obtain more of the

proper type and size of food, thus enabling them to grow faster to maturity. As a result, a

higher percentage of juvenile largemouth bass would likely be recruited to stock size in

Lake Apopka.

Submersed and emergent aquatic macrophytes provide additional benefits to both

adult and young largemouth bass. They provide spawning substrate (Kramer and Smith

1962, Chew 1974) and protect spawning nests from wind and waves (Kramer and Smith

1962, Holcomb et al. 1975a, b). Aquatic macrophytes are an important component of the

ecosystem of a lake (Durocher et al. 1984, Dibble et al 1996). Plants have the ability to

affect water chemistry. Their abundance is inversely related with phytoplankton biomass

as measured by chlorophyll, and is positively related to water clarity as measured by use

of a Secchi disc (Canfield and Hoyer 1992). However, aquatic plants do not increase the

lake-wide clarity of water nor decrease the phytoplankton biomass until there is 30 to

50% coverage (percent volume inhabited (PVI)) (Canfield and Hoyer 1992). A narrow

belt of aquatic plants will not reduce lake-wide phytoplankton biomass. A 15% coverage

(PVI) could help largemouth bass populations, however, by providing critical habitat

needed by age-0 largemouth bass during their first year of life (Canfield and Hoyer

1992).









Aquatic plants could be particularly helpful in solving problems associated with

fluid sediments in Lake Apopka. They would help stabilize the bottom by anchoring the

sediments (Carter and Rybicki 1985) and they would reduce turbidity from wind

resuspension of the sediments (Canfield and Hoyer 1992, James and Barko 1994). Plants

would additionally tend to retard large waves by baffling wave action and thus provide

protection for less well-anchored species such as coontail (Ceratophyllum demersum)

(Carter and Rybicki 1985) and reduce shoreline erosion (Canfield and Hoyer 1992).

Previous studies have indicated that for some lakes, the lack of aquatic vegetation

can be detrimental to fish populations. For example, Canfield and Hoyer (1992)

demonstrated in a 60-lake study of Florida lakes that there exists a potential for depressed

fish populations at low levels of aquatic macrophytes (< 15% coverage (PVI)). Porak et

al. (1999) suggested that a lack of aquatic plants was detrimental to the survival of young

largemouth bass due to decreased shelter and food supply.

In large, shallow Florida lakes without macrophytes, such as Lake Apopka, the

shoreline habitat is the only refuge from predation for juvenile largemouth bass (Hoyer

and Canfield (1996a, b). The limited shoreline habitat in Lake Apopka may not be

sufficient for adequate largemouth bass recruitment. The addition of about 15% coverage

(PVI) of aquatic macrophytes or other structure would allow sufficient young-of-the-year

largemouth bass to recruit into adulthood to allow Lake Apopka and other similar lakes to

reach their carrying capacity (Hoyer and Canfield 1996a, b).

Aquatic Macrophytes

Lake Apopka continues to have a low abundance of aquatic macrophytes (< 0.9

percent area covered (PAC) and < 0.4% PVI). The plants only occupied a narrow (mean

= 19.4 m) belt around the shoreline in 2004, with a few exceptions. There were some









isolated stands of soft-stem bulrush (8.5 ha) that existed around the perimeter and in the

northern portion of the lake (Hog Island), as previously noted by Johnson and Crumpton

(1998). Remnant stands of aquatic grass, primarily Egyptian paspalidium (1.5 ha), also

existed in various places around the perimeter of the lake.

Vegetated areas are important largemouth bass habitat. Johnson and Crumpton

(1998) reported that soft-stem bulrush and aquatic grass (Egyptian paspalidium,

maidencane, and torpedograss) sites contained the largest total mean biomass for all four

principle sportfish species (largemouth bass, bluegill, redear sunfish, and black crappie)

in both 1989 1993 and 1996 1997 sampling periods for Lake Apopka. Total mean

biomass for sportfish was lowest in open sites.

The most commonly occurring plants in 2004 were cattail, duck potato (Sagittaria

lancifolia), and pickerelweed (Pontederia cordata) (Table 9). No submersed vegetation

existed in the open area of the lake outside of the narrow belt of emergent aquatic plants.

Essentially, the rooted aquatic vegetation in Lake Apopka has not expanded in the last

two decades and remains similar to what the lake had after the loss of its 80% coverage

of aquatic plants in 1947 (Clugston 1963, Schneider and Little 1969, Holcomb 1977,

Lake Apopka Restoration Council 1986, Johnson and Crumpton 1998).

Eel-grass was the only submersed vascular aquatic macrophyte besides hydrilla

that was observed in 2004. Eel-grass is a versatile submersed aquatic plant that is

capable of surviving in a variety of growing conditions (Jaggers 1994). It can inhabit a

variety of sediment types (sand, silty sand, or mud) (Korschgen and Green 1988, Catling

et al. 1994). It is more shade adapted (Meyer et al. 1943) than several other submersed

aquatic plants (e.g., Myriophyllum spp. and Potamogeton spp.) because of its









physiological adaptability to low (1% Io) light regimes (Titus and Adams 1979, Carter

and Rybicki 1985, Korschgen and Green 1988, Catling et al. 1994, Rybicki and Carter

2002). It is capable of surviving and even flourishing in eutrophic water (Catling et al.

1994, Jaggers 1994). It is also capable of making major comebacks after restoration

(Carter and Rybicki 1990, Kimber et al. 1995a, b).

Studies have reported, however, that eel-grass, grown from tubers, did not survive

in greater than 0.25 m of sediment (Carter et al. 1985, Rybicki and Carter 1986,

Korschgen and Green 1988). Studies also found that there were significant population

declines caused by excessive (numerically undefined) turbidity or highly variable

turbidity (Korschgen and Green 1988, Jaggers 1994). Korschgen and Green (1988) noted

that it was subject to uprooting by tropical storms. For example, Tropical Storm Agnes,

which struck the East Coast in 1972, was cited as a factor in the decrease of eel-grass in

different portions of the Chesapeake Bay (Kerwin et al. 1976, Bayley et al. 1978). Carter

et al. (1985) reported that storm damage was also partially responsible for the decline of

eel-grass in the Potomac River in the 1930s. They indicated that deposition of 0.15 -

0.25 m of sediments from storms were sufficient to completely wipe out populations of

eel-grass, naiad (Najas gracillima and N. guadalupensis), and common elodea (Elodea

canadensis). Years or decades may be required for recovery after exceptionally severe

storms (Carter et al. 1985).

The growth of eel-grass in Lake Apopka has been a special concern to Florida

agencies (Jaggers 1994). It is a valuable plant that is used as refuge and habitat for

invertebrates and fish populations (Hoyer et al. 1996). Eel-grass was planted by the

FFWCC to an unknown degree in the 1990s (William Johnson, administrator, FFWCC,









Eustis, FL, personal communication). It was also planted in plots around the shore of

Lake Apopka by the SJRWMD during drought conditions in 1998 and 1999 (Conrow and

Peterson 2000).

Of the 23 eel-grass sites that were sampled, beds were present at 15 sites (Table

10). Twelve of the sites, where eel-grass was present, were located on the west side of

the lake; two closely spaced sites were located on the south side; and one site was located

on the east side. No plants were found at seven of the sites, and only a single plant was

found at one site. All but two of the 15 beds were small (< 100 m2). There was one

medium (279 m2) bed near Smith Island (on the west shoreline). There was another

medium (536 m2) bed near Monteverde Boat Ramp (also on the west shoreline). No

large (> 1000 m2) plant beds were found during this study.

The density of the plant beds ranged from 1 to 100%. The average density of eel-

grass was estimated to be 50%, at those sites where it was present. Hurricane Jeanne

passed over central Florida on 25 September 2004 (NOAA 2005), one week before eel-

grass was sampled on 1 October 2004. An attempt was made to find eel-grass uprooted

by the recent hurricane, but only a couple of plants were observed to be uprooted.

The total lake bottom colonized by eel-grass in 2004 was approximately 900 m2

(Table 10). The SJRWMD reported an area of 11,032 m2 in 1999 (Conrow and Peterson

2000). Therefore, the observed eel-grass area in 2004 was only 8% of that reported by

the SJRWMD. The drought in 1999 2000, followed by rising waters in 2000 should

have created ideal growing conditions for the expansion of eel-grass. The natural

drawdown would have oxidized and compacted the exposed sediments. Oxidation would

have released nutrients from the soil, stimulating plants to regenerate and expand









(Wegener and Williams 1974, Moyer et al. 1995). Compaction of the soil would have

provided a firmer bottom for rooting and holding plants. However, this study shows that

eel-grass drastically declined during the past five years at Lake Apopka. This suggests

that there is a limiting factor that is preventing eel-grass from surviving and expanding.

Studies in the upper Mississippi River and Chesapeake Bay (Carter and Rybicki

1990, Kimber et al. 1995a, b) reported that eel-grass only grew to 12 15% incident light

(I ) because of turbidity in the water column caused by suspended sediments. Later,

when the turbidity from suspended sediments was reduced through restoration efforts,

eel-grass recolonized those study sites, but only grew down to depths of 5 10% Io.

The observed and theoretical MDC and MDG of eel-grass, in Lake Apopka in

2004, were compared to determine if eel-grass was growing to its potential depth, as

referenced by the primary literature. The observed MDC and MDG of eel-grass in June -

August 2004 were 1.3 and 0.8 m, respectively, at a mean lake surface elevation of 20.3 m

(66.5 ft) National Geodetic Vertical Datum 1929 (NGVD 29). Hydrologic data were

obtained from the SJRWMD (2005). The theoretical MDC and MDG were 1.3 and 1.0 m

based on the mean depths corresponding to light meter measurements of 1 and 8% Io.

Eel-grass, therefore, seems to be growing near its potential MDC and MDG because the

observed values of MDC and MDG agree closely to the theoretical values.

However, the four hurricanes (Charlie, Frances, Ivan, and Jeanne, NOAA 2005),

all of which occurred before my sampling, that passed over Florida in the summer of

2004, dropped > 0.4 m of total precipitation, and undoubtedly influenced the results.

When the hurricanes are accounted for by calculating the observed MDC and MDG at a

lower lake level (20.0 m, NGVD 29), eel-grass would be predominantly growing at 12 -









15% Io and reaching a maximum depth at 5% Io. These results indicate that other

environmental factors are limiting the depth of growth of eel-grass other than light

attenuation.

The area of the lake that is available for eel-grass to colonize and grow at the

observed MDC and MDG (at lake surface elevation 20.3 m, NGVD 29) was calculated to

be 3940 and 848 ha, respectively. As a percent, eel-grass is only inhabiting 0.002% of

the 3940 ha available at MDC and 0.011% of the 848 ha available at MDG under the

current light regime, strongly indicating that other factors are involved in limiting the

growth and survival of eel-grass besides light attenuation.

The 3940 and 848 ha, at MDC and MDG, represents an estimated 32% of the lake

available for eel-grass to colonize and 7% of the lake available to grow in under the

current light regime. This indicates that there is enough irradiance in the water column

for eel-grass to colonize in shallow water around the shoreline of the lake but that the

light conditions in the water column need to significantly improve before eel-grass can be

expected to grow well enough to occupy a larger proportion of the total lake area.

There is a general belief that irradiance primarily controls the depth-distribution

of aquatic macrophytes (Barko and Smart 1981, Chambers and Kalff 1985, Carter and

Rybicki 1990). Studies have recognized, however, that other environmental factors

besides nutrient enrichment and phytoplankton shading are also responsible for limiting

aquatic macrophyte colonization. Chambers and Kalff (1985) stated that wave action and

substrate type also play a major role in determining the distribution and abundance of

aquatic macrophytes. Spence (1972) indicated that turbulence and wave action

influenced aquatic macrophyte colonization. Carter et al. (1985) reported that, other than









phytoplankton, storm pressure, grazing pressure, substrate characteristics, and suspended

sediments are all factors that in different circumstances could be individually or jointly

responsible for limiting the depth-distribution (or spatial extent) of aquatic macrophytes.

Eel-grass in this study was only found at sites having firm sediments and not at

any sites with sediments deeper than 0.25 m. These observations agree with studies that

reported that eel-grass, grown from tubers, did not survive in greater than 0.25 m of

sediment (Carter et al. 1985, Rybicki and Carter 1986, Korschgen and Green 1988). The

depth of sediments (1.5 m mean thickness) covering 90% of Lake Apopka's bottom

(Schneider and Little 1969) is too thick to allow eel-grass to inhabit those areas. The

depth and fluidity of sediments, and wind resuspension of sediments, are probably major

factors that are limiting the growth and survival of eel-grass in Lake Apopka. These

hypotheses are supported by the fact that Lake Apopka is a large, shallow, and nearly

round lake with a long fetch (Bachmann et al. 1999). Because of these combined

attributes, the bottom sediments are often resuspended in the lake (Scheffer et al. 1992,

Bachmann et al. 1999). Carter et al. (1985) stated that where fetches are long, eel-grass

plants are easily uprooted from fine sediments.












Table 4. Common and scientific names of fish collected by individual studies at Lake
Apopka, Florida.


Common Name
Florida gar
Longnose gar
Bowfin
Gizzard shad
Threadfin shad
Black crappie
Blue tilapia
Golden shiner
Lake chubsucker
Taillight shiner
Yellow bullhead
Brown bullhead
Channel catfish
White catfish
Tadpole madtom
Seminole killifish
Bluefin killifish
Eastern mosquitofish
Sailfin molly
Pugnose minnow
Brook silverside
Inland silverside
Tidewater silverside
Everglades pygmy
sunfish
Warmouth
Bluegill
Redear sunfish
Spotted sunfish
Largemouth bass
Sunshine bass

Atlantic needlefish


Scientific Name
Lepisosteus platyrhincus
Lepisosteus osseus
Amia calva
Dorosoma cepedianum
Dorosoma petenense
Pomoxis nigromaculatus
Tilapia aurea
Notemigonus crysoleucas
Erimyzon sucetta
Notropis maculatus
Ameiurus natalis
Ameiurus nebulosus
Ictalurus punctatus
Ictalurus catus
Noturus gyrinus
Fundulus seminolis
Lucania goodei
Gambusia holbrooki
Poecilia latipinna
Opsopoeodus emiliae
Labidesthes sicculus
Menidia beryllina
Menidia peninsula
Elassoma evergladei

Lepomis gulosus
Lepomis macrochirus
Lepomis microlophus
Lepomis punctatus
Micropterus salmoides
Morone chrysopsXM.
saxatilis
Strongylura marina


Canfield
and Hoyer
(1992)
(for 1986)
x



x
x
x

x



x
x

x
x
x

x





x




x
x

x

x


Hoyer (UF)
(unpubl. data)
(1987-1989)
(1991-1996)
x



x
x
x
x
x
x
x
x
x
x
x

x
x
x


Johnson and
Crumpton
(1998)
(for 1989-1993)
x
x
x
x
x
x
x
x

x
x
x
x
x
x
x

x
x
x
x
x


This Study
(for 2004)
x
x
x
x
x
x
x




x
x
x

x
x

x



x
x


x x









Table 5. Water chemistry parameters measured for Lake Apopka, Florida, in June -
October 2004.
Number
of
Water Quality Parameter Location Samples Average Range
Dissolved oxygen (mg/L) Near shore stations 16 5.9 (0.8 11.9)
Secchi depth (m) Near shore stations &
18 0.37 (0.20 0.49)
center of the lake
Specific conductance Near shore stations 12 453
S/c at 25 C 12 453 (403 506)
([iS/cm at 25 C)
Water temperature (C) Near shore stations 10 31.6 (29.5 33.7)

Table 6. Mean electrofishing catch per unit effort and standard error of fish number
(number/hr) and weight (kg/hr) for Lake Apopka, Florida. Forty 10-min
transects were sampled in June August 2004.
Calculated
Number Standard Weight Standard
Common Name (number/hr) Error (kg/hr) Error
Florida gar 7.4 1.28 5.6 0.99
Longnose gar 0.6 0.36 0.2 0.11
Bowfin 0.8 0.32 0.9 0.43
Gizzard shad 6.6 2.15 0.8 0.29
Threadfin shad 1.7 0.74 0.0 0.00
Black crappie 6.9 1.30 1.2 0.31
Blue tilapia 0.8 0.38 0.4 0.17
Yellow bullhead 0.2 0.15 0.0 0.03
Brown bullhead 1.7 0.61 0.6 0.22
Channel catfish 0.6 0.47 0.1 0.07
Tadpole madtom 0.5 0.33 0.0 0.00
Seminole killifish 2.7 0.86 0.0 0.01
Eastern mosquitofish 3.5 1.34 0.0 0.00
Brook silverside 0.2 0.15 0.0 0.00
Inland silverside 0.3 0.21 0.0 0.00
Warmouth 12.6 3.85 0.8 0.24
Bluegill 86.4 20.52 4.1 1.05
Redear sunfish 16.4 5.05 1.6 0.47
Largemouth bass 6.9 1.60 4.1 1.11
Atlantic needlefish 0.2 0.15 0.0 0.01

Total 156.5 20.3










Table 7. Mean yearly and combined electrofishing catch per unit effort and standard
error of fish number (number/hr) for Lake Apopka, Florida, by Johnson and
Crumpton (1998). Eight hundred seventy 5-min transects were sampled
bimonthly from March 1989 to November 1993.
Number (number/hr)
Combined Standard
Common Name 1989 1990 1991 1992 1993 1989-1993 Errora
Florida gar 3.9 3.6 5.1 6.1 8.3 5.4 0.85
Longnosegar 0.3 0.5 1.7 0.7 1.1 0.9 0.24
Bowfin 0.8 0.7 0.6 0.7 0.8 0.7 0.04
Gizzard shad 101.8 71.8 59.3 43.4 42.5 63.8 10.96
Threadfin shad 49.4 47.1 107.5 56.0 37.3 59.6 12.38
Black crappie 26.2 33.7 34.8 52.3 68.8 43.2 7.71
Blue tilapia 7.1 7.6 8.5 15.3 17.7 11.2 2.18
Golden shiner 9.2 7.9 7.1 5.2 6.5 7.2 0.67
Taillight shiner 2.6 6.8 4.6 6.5 8.2 5.7 0.98
Yellow bullhead 2.6 1.4 1.4 1.8 2.9 2.0 0.31
Brown bullhead 45.0 25.7 24.8 14.4 22.5 26.5 5.04
Channel catfish 0.1 0.0 0.0 0.0 0.0 0.0 0.0
White catfish 0.6 0.9 1.8 3.8 16.5 4.7 3.00
Tadpole madtom 0.0 0.0 0.0 0.1 0.0 0.0 0.01
Seminole killifish 3.6 7.4 12.8 10.8 9.3 8.8 1.57
Eastern mosquitofish 4.2 10.6 7.3 6.1 7.4 7.1 1.05
Sailfin molly 0.1 0.7 0.5 0.3 0.6 0.4 0.12
Pugnose minnow 0.0 0.0 0.1 0.0 0.0 0.0 0.01
Brook silverside 0.0 0.0 0.0 1.9 0.0 0.4 0.37
Inland silverside 12.3 15.7 15.9 6.1 3.5 10.7 2.53
Warmouth 5.6 6.0 4.3 9.5 11.7 7.4 1.37
Bluegill 62.0 67.3 55.3 97.6 83.2 73.1 7.67
Redear sunfish 11.1 18.1 15.3 21.1 24.6 18.1 2.33
Spotted sunfish 0.5 0.2 0.1 0.0 0.0 0.1 0.09
Largemouth bass 5.6 6.5 5.9 7.9 6.2 6.5 0.41
Atlantic needlefish 0.1 0.1 0.1 0.2 0.3 0.2 0.03

Total 356.0 341.0 375.0 369.0 381.0 364.0 7.17
aThe combined catch per unit effort number (number/hr) was averaged by month and then by year
to obtain the standard error.










Table 8. Annual mean electrofishing catch per unit effort number (number/hr) of two
size groups of largemouth bass, bluegill, and redear sunfish collected in Lake
Apopka, Florida, by Johnson and Crumpton (1998) for June May of 1989 -
1990, 1990 1991, and 1991 1992, and November 1996 September 1997
(bimonthly samples), and by this study for June August 2004 (once monthly
samples).
Common Name 1989-1990a 1990-1991a 1991-1992a 1996-1997 2004
Largemouth bass (> 24 cm) 4.8 4.8 6.0 2.4 6.0
Largemouth bass (< 24 cm) 2.4 1.2 1.2 1.2 0.9

Bluegill (> 14 cm) 22.8 18.0 20.4 15.6 20.0
Bluegill (< 14 cm) 40.8 54.0 66.0 31.2 66.5

Redear sunfish (> 14 cm) 9.6 9.6 9.6 1.2 13.8
Redear sunfish (< 14 cm) 4.8 6.0 12.0 3.6 2.6
a Summary data from 1989 1992 and 1996 1997 were taken from Johnson and Crumpton
(1998), Table 5, which did not report the catch rate of size groups in 1993.

Table 9. Occurrence of plant species in twenty evenly-spaced transects around Lake
Apopka, Florida, in 2004.
Common Name Scientific Name Percent of Transects


Aquatic Plants
Cattail
Duck potato
Pickerelweed
Soft-stem bulrush
Water pennywort
Egyptian paspalidium
Water primrose
Eel-grass
Wild taro
Torpedograss
Hydrilla

Terrestrial Brush
Carolina willow
Elderberry
Wax myrtle

Hardwood Mixture
Red maple
Loblolly-bay
Sweetbay


Typha spp.
Sagittaria lancifolia
Pontederia cordata
Scirpus validus
Hydrocotyle umbellata
Paspalidium geminatum
Ludwigia octovalvis
Vallisneria americana
Colocasia esculenta
Panicum repens
Hydrilla verticillata


Salix caroliniana
Sambucus canadensis
Myrica cerifera


Acer rubrum
Gordonia lasianthus
Magnolia virginiana










Table 10. Location, area (m2), and maximum depth (m) of eel-grass beds in Lake
Apopka, Florida, in 2004.
Area (m2) Reported by
the SJRWMD in 1999 Area (m2) Measured in Maximum Depth
GPS Locations (unpublished data") 2004 of Plant Bed (m)

Twenty three sites where eel-grass beds were sampled on 1 October 2004
X:-81.66268 Y:28.59395 1465.0 None sighted -
X:-81.66999 Y:28.60700 1277.3 (one plant) 1.0 0.9
X:-81.65463 Y:28.59138 885.3 None sighted -
X:-81.67006 Y:28.60724 517.9 Includedb 0.9
X:-81.65359 Y:28.68176 510.9 None sighted -
X:-81.67829 Y:28.61896 494.4 278.9 0.9
X:-81.67803 Y:28.61925 355.7 29.2 0.9
X:-81.60593 Y:28.56912 333.0 2.6 0.9
X:-81.67317 Y:28.61035 310.5 536.0 1.4
X:-81.54957 Y:28.62397 308.0 8.3 0.5
X:-81.65332 Y:28.68184 281.9 None sighted -
X:-81.68426 Y:28.66171 240.8 None sighted -
X:-81.67196 Y:28.60970 237.4 Includedb 1.4
X:-81.66989 Y:28.60720 201.8 Includedb 0.9
X:-81.67787 Y:28.62014 199.5 1.8 0.9
X:-81.65359 Y:28.68210 174.0 None sighted -
X:-81.60584 Y:28.56924 165.2 Includedb 0.9
X:-81.69429 Y:28.64223 93.5 None sighted -
X:-81.68031 Y:28.62056 55.5 10.5 0.9
X:-81.68025 Y:28.62054 54.5 Includedb 0.9
X:-81.66973 Y:28.60674 41.6 Includedb 0.9
X:-81.58700 Y:28.57731 27.0 None sighted -
X:-81.68030 Y:28.62049 12.1 21.0 0.9

Total 8242.7 889.3

Six sites where eel-grass beds were observed while electrofishing in June August 2004
X:-81.64903 Y:28.58658 1.8 0.9
X:-81.64948 Y:28.58717 1.8 0.9
X:-81.64950 Y:28.58781 1.8 0.9
X:-81.67127 Y:28.60920 1.8 0.9
X:-81.67183 Y:28.60972 1.8 0.9
X:-81.66442 Y:28.59677 1.8 0.9

Total 10.8
aThe data shown here for 23 sampling sites are a subset of the unpublished data set obtained from the
SJRWMD. The total area for all the eel-grass beds in the data set is 11032.1 m2, which includes only the
area of the plant beds in the major part of the lake and not the area of those in the gourd neck area, Marsh
Flow-Way, or canals.
b The SJRWMD reported beds that were near each other as separate beds, identified with separate GPS
coordinates. At some of the sites reported by the SJRWMD to have multiple beds, only one bed was found,
or in some instances the boundary separating multiple beds was not distinguishable. In these instances, the
total area (m2) of closely spaced bed locations was recorded only once at the GPS coordinates of one bed.
The area (m2) of any nearby beds was annotated as included.
"The six eel-grass beds observed while electrofishing were nearly identical in area and maximum depth.

























0



Figure 2. Mean electrofishing catch per unit effort estimates of total fish abundance
(number/hr) for Lake Apopka, Florida, sampled by Canfield and Hoyer (1992)
(*), Hoyer (UF, unpublished data) (m), Johnson and Crumpton (1998) (A),
and this study (e). Data were not available for Johnson and Crumpton (1998)
for 1996 1997.


Canfield and
Hoyer (1992)
(for 1986)


Hoyer (unpubl.
data) (for 1987 -
1989, 1991-
1996)


Johnson and
Crumpton (1998)
(for 1989 1993)


This Study (for
2004)


Figure 3. Mean electrofishing catch per unit effort estimates of total fish abundance
(number/hr) for the combined data of different studies for Lake Apopka,
Florida.


















Common Name


Figure 4. Individual fish species percent of total number collected by electrofishing for
Lake Apopka, Florida, by Johnson and Crumpton (1998) for 1989 1993.
55.2


I.


Il


I I


Common Name


Figure 5. Individual fish species percent of total number collected by electrofishing for
Lake Apopka, Florida, in June August 2004.






























0.0-3.9 4.0-7.9 8.0-11.9 12.0-15.9 16.0-19.9 20.0-23.9 24.0-27.9

Total Length (cm)


Figure 6. Length frequency distribution of bluegill collected
Apopka, Florida, in June August 2004.


40

-
2 30
-
20

10

0


by electrofishing for Lake


U


0.0-3.9 4.0-7.9 8.0-11.9 12.0-15.9 16.0-19.9 20.0-23.9


24.0-27.9


Total Length (cm)

Figure 7. Length frequency distribution of redear sunfish collected by electrofishing for
Lake Apopka, Florida, in June August 2004.




























Figure 8. Mean electrofishing catch per unit effort estimates of largemouth bass
abundance (number/hr) for Lake Apopka, Florida, sampled by Canfield and
Hoyer (1992) (+), Hoyer (UF, unpublished data) (m), Johnson and Crumpton
(1998) (A), and this study (e).


7
6
m 5
4
0


o 0
4 -



SCanfield and Hoyer Johnson and Johnson and This Study
Hoyer (1992) (unpubl. data) Crumpton Crumpton (for 2004)
(for 1986) (for 1987- (1998) (for (1998) (for
1989, 1991- 1989- 1993) 1996-1997)
1996)

Figure 9. Mean electrofishing catch per unit effort estimates of largemouth bass
abundance (number/hr) for the data sets of combined years from different
studies for Lake Apopka, Florida.











18
16
14
12
10
8
6
4
2
0
0.0-7.9 8.0-15.9 16.0-23.9 24.0-31.9 32.0-39.9 40.0-47.9 48.0-53.9

Total Length (cm)

Figure 10. Length frequency distribution of largemouth bass collected by electrofishing
for Lake Apopka, Florida, in June August 2004.









0.8 oo
0.6
1.4

0 .2 *
C S* *






1.0
0.0 0.5 1.0 1.5 2.0 2.5

Log Chlorophyll a (ug/L)


Figure 11. Electrofishing catch per unit effort of largemouth bass (kg/hr) versus total
chlorophyll a ([tg/L) for 60 Florida lakes sampled by Canfield and Hoyer
(1992) and Lake Apopka, Florida, sampled by Canfield and Hoyer (1992) (0),
Hoyer (UF, unpublished data) (o), Johnson and Crumpton (1998) (A), and this
study (o). A regression line is included.
study (o). A regression line is included.















LAKE MANAGEMENT RECOMMENDATIONS

Restoration efforts have not yet been successful in increasing the largemouth bass

population or expanding the area occupied by aquatic vegetation in Lake Apopka. It is

up to lake managers to come up with ideas to improve the largemouth bass fishery so that

anglers can enjoy recreational fishing in the lake. A drawdown was proposed by the

USEPA as part of its environmental impact statement in 1978 as a way to improve the

largemouth bass fishery (USEPA 1979). Downdraw has been a successful tool by

increasing the water clarity and littoral vegetation in several Florida lakes including

Lakes Tohopekaliga, Trafford, Hancock, and Griffin (USEPA 1979). However, a

drawdown was not recommended by the SJRWMD for Lake Apopka for several reasons

including the high cost (of at least $20 million) and increased nutrient flow to

downstream lakes (Lowe et al. 1992). Additionally, there were concerns over the

quantity of water to be pumped, the amount of unconsolidated muck, the type of

vegetation that would grow, and the restrictive time schedule (USEPA 1979).

Conditions in Lake Apopka have changed since 1979. Over $100,000,000 in

Federal and State funds was spent to buy out farms, to reduce or eliminate nutrient-rich

pumpage back into the lake, and to construct a marsh flow-way, to remove phosphorus-

rich particles from the lake water (Conrow et al. 1993, Hoge et al. 2003). Mean

phosphorus levels dropped from over 200 [g/L, in 1979, to about 100 [g/L, in 2004. The

Lake County Water Authority also recently proposed building an alum treatment plant for

Lake Apopka that would help reduce phosphorus levels even more. In light of these









improvements, it would be a good idea to reconsider drawdown. The concern over

increased nutrient flow to downstream lakes is no longer as big of an issue in 2004, as it

was in 1979, because nutrient levels are lower now, than they were before.

Since a drawdown was not approved and may never be approved, the next step for

lake managers is to look for other viable alternative strategies that could potentially

improve the largemouth bass fishery in Lake Apopka. Other alternative ideas have been

proposed that could potentially improve the habitat for largemouth bass in Lake Apopka,

but have not been acted upon by the state agencies. For example, artificial reefs could be

placed along the shoreline as habitat for largemouth bass and other littoral fish (Canfield

et al. 2000). Canfield et al. (2000) also suggested allowing hydrilla, a fast-growing exotic

submersed aquatic plant, to grow behind the protective barriers to provide habitat for

largemouth bass. If at least 50% coverage (PVI) of submersed aquatic vegetation

occurred, it would be enough for the water to start to clear in those local areas and

provide additional benefits (Canfield and Hoyer 1992).

Hydrilla is an exotic aquatic plant that has invaded many lakes. It will often

outcompete native aquatic macrophyte species and expand to fill in an entire water body,

and interfere with navigation and other uses of a water body (Hoyer et al. 2005). Control

of hydrilla across lakes has been unsuccessful (Hoyer et al. 2005). It spreads from one

water body to another when fragments and tubers, left attached to vehicles, trailers, or

propellers, are transported from one water body to another. It also spreads when

fragments and tubers, from one water body, drift into another attached water body. It

costs a tremendous amount of money, to purchase herbicides and equipment, and to

provide manpower to control it. Allowing hydrilla to grow anywhere in Florida lakes,









such as suggested by Canfield et al. (2000), is controversial. However, Lake Apopka

historically had about 80% aquatic macrophyte coverage (PVI). So it should not be a big

issue if hydrilla were to expand into the open area of this lake.

Recent studies have stated that in certain situations, native aquatic macrophytes

will grow in close association with hydrilla. For example, Rybicki and Carter (2002)

found populations of eel-grass, Eurasian water milfoil (Myriophyllum spicatum), and

coontail growing within hydrilla and along the edges, in portions of the Potomac River

recovering from poor water transparency and high turbidity. Smart (1992), in

experimental plots, that were monitored for a duration of one year, showed that Illinois

pondweed, eel-grass, and hydrilla, that were planted in randomly assigned plots, could

grow together for one year, as long as Illinois pondweed and eel-grass were planted

before or at the same time as hydrilla. Illinois pondweed and hydrilla grew in the canopy

and eelgrass grew in the understory.

Smart (1992) stated that eel-grass is considered to be a later successional species

than hydrilla. In the long run, eel-grass should theoretically be able to recolonize areas

that were formerly dominated by hydrilla. There is evidence in Florida lakes that native

aquatic macrophyte species recolonized areas that were dominated by hydrilla for several

years. For example, Lake Okahumpka, Florida, was dominated by hydrilla for several

years, in the late 1990s and early 2000s (Mark Hoyer, research manager, UF, personal

communication). A regular maintenance control program, in the early 2000s, using

contact herbicides, put hydrilla into submission. Native submersed aquatic macrophyte

species (e.g., Illinois pondweed and eel-grass) recolonized areas previously dominated by

hydrilla.









Hydrilla is already present in small quantities in Lake Apopka. Erich Marzolf

(environmental scientist, SJRWMD, Palatka, FL, personal communication) stated that

contact herbicide is applied regularly by the SJRWMD to keep it from expanding. Eel-

grass and hydrilla beds were observed near each other during this study at Lake Apopka

in 2004. Eel-grass plants were also observed growing within hydrilla beds and along the

edges.

Evidence from Lake Okahumpka, Florida (a hypereutrophic lake similar to Lake

Apopka), and from Lake Apopka itself, suggests that if hydrilla were allowed to grow in

small quantities (< 15% PVI) around the periphery of Lake Apopka, to provide habitat

for largemouth bass, that no more than the already existing maintenance control program

using contact herbicides would be required to keep hydrilla in check, and that native

submersed aquatic macrophyte species (e.g., Illinois pondweed and eel-grass) could

coexist with hydrilla.

Erich Marzolf also raised concerns about not being able to control hydrilla and it

spreading to downstream lakes, if it were allowed to grow. Hydrilla is already in the

lakes that are downstream of Lake Apopka. Maintenance control of hydrilla, with

contact herbicides, is already needed as well, in those lakes. Lakes Beauclair and Dora,

the nearest downstream lakes from Lake Apopka, are separated from Lake Apopka by the

Apopka-Beauclair Canal that is about 48 km long, and about 10 m average width.

Should hydrilla be allowed to grow in limited areas in Lake Apopka, the likelihood of

invasion by hydrilla, by fragments and tubers drifting to those downstream lakes would

be reduced to minimal risk because the Apopka-Beauclair Canal is a long and narrow

canal. Additional expenditures might be needed to control hydrilla in Lake Apopka and









in downstream lakes, if hydrilla were allowed to grow in limited areas in Lake Apopka.

It might be appropriate for lake managers to perform a cost assessment to balance the

income from a largemouth bass fishery to the surrounding community against the

additional expenditures needed to control hydrilla.

Hypereutrophic lakes function differently than other lakes. Authors have

suggested in recent years that hydrilla can benefit hypereutrophic lakes such as Lake

Apopka where both light attenuation and deep sediments prevent native vegetation from

colonizing major parts of the lake (Moxley and Langford 1982, Canfield and Hoyer 1992,

Porak et al. 1999, Hoyer et al. 2005) by providing habitat, food resources, and refugia for

fish and wildlife (Aggus and Elliot 1975, Durocher et al. 1984, Dibble and Kilgore 1994,

Dibble et al. 1996, Porak et al. 1999). Canfield et al. (2000) suggested that the

combination of light attenuation and wind resuspension of sediments in Lake Apopka

should prevent hydrilla from filling in the open area of the lake in the same way that

native plants are now being prevented from colonizing that area. In a hydrilla workshop

(Hoyer et al. 2005), it was recommended for hypereutrophic lakes like Lake Apopka that

a regular control program such as the program now in affect in Lake Apopka, using

contact herbicides to control hydrilla, in keeping with the management objectives aimed

at improving the sports fishery, may represent a more practical and viable alternative than

completely eliminating hydrilla.

There is controversy between aquatic weed specialists, that recommend not letting

hydrilla grow in any Florida lakes, and fishermen and UF biologists that say that a small

amount (<15% coverage (PVI)) of hydrilla should improve the largemouth bass fishery.









Perhaps allowing hydrilla to grow in limited areas in Lake Apopka should be considered

again, despite the debate.

A key lake management action should be to balance the needs of anglers with

other members of the community that enjoy looking at or boating in an open lake

(Canfield et al. 2000). If the entire lake were to be completely covered with aquatic

macrophytes, largemouth bass anglers would enjoy fishing there, but the general public

would likely perceive the profuse growth of aquatic macrophytes as an aquatic weed

problem. If lake managers allowed the lake to have about 15% coverage (PVI) of rooted

aquatic vegetation, they could make anglers happy by improving the sport fishing and

also keep other members of the community happy by keeping most of the lake open

(Canfield et al. 2000).

If the expansion of hydrilla is not to be allowed, then another alternative to

mitigate the loss of largemouth bass would be stocking. Management efforts have been

conducted at Lake Apopka for several decades to improve the environmental conditions

in the lake (Conrow et al. 1993, Hoge et al. 2003). In lieu of the recent improvements, it

is a good time to stock largemouth bass into Lake Apopka.

Previous stocking by the FFWCC in 1990, using small fry, did not result in

adequate survival to produce a fishery (Johnson and Crumpton 1998). Because that

stocking was not successful in producing a fishery, the FFWCC could use fingerlings or

advance fingerlings. The use of advanced fingerlings to stock Lake Talquin, Florida, has

been more successful than stocking projects at Lake Apopka, which used smaller fish

(Dr. Daniel E. Canfield, Jr., professor, UF, personal communication).






52


Stocking larger (> 24 cm) wild largemouth bass into Lake Griffin enhanced the

economic activity in the surrounding community (Canfield et al. 2005). If fingerlings or

advanced fingerlings were stocked into Lake Apopka, and fishermen caught them,

anglers would come back. It could improve the economic viability of the largemouth

bass fishery in Lake Apopka. Of course, it would be more viable to stock largemouth

bass into Lake Apopka once protected, vegetated areas were established. The additional

plants would also make it easier for anglers to locate the fish.
















LIST OF REFERENCES


Aggus, L. R. and G. V. Elliott. 1975. Effects of cover and food on year-class strength of
largemouth bass. P. 317-322. In R. H. Stroud and H. Clepper (eds.). Black bass
biology and management. Sport Fishing Institute, Wash., DC.

Andrus, C. 2000. Experiences from the field: alcove sampling on the Willamette River,
OR. P. 43-46. In S. M. Allen-Gil (ed.). New perspectives in electrofishing.
EPA/600/R-99/108. USEPA, Wash., DC.

Bachmann, R. W., B. L. Jones, D. D. Fox, M. V. Hoyer, L. A. Bull and D. E. Canfield, Jr.
1996. Relations between trophic state indicators and fish in Florida (U.S.A.) lakes.
Can. J. Aquat. Sci. 53:842-855.

Bachmann, R. W., M. V. Hoyer and D. E. Canfield, Jr. 1999. The restoration of Lake
Apopka in relation to alternative stable states. Hydrobiol. 394:219-232.

Bachmann, R. W., M. V. Hoyer and D. E. Canfield, Jr. 2000a. The potential for wave
disturbance in shallow Florida lakes. Lake and Reserv. Manage. 16(4):281-291.

Bachmann, R. W., M. V. Hoyer and D. E. Canfield, Jr. 2000b. Internal heterotrophy
following the switch from macrophytes to algae in Lake Apopka, Florida.
Hydrobiol. 418:217-227.

Bachmann, R. W., M. V. Hoyer and D. E. Canfield, Jr. 2001a. Evaluation of recent
limnological changes at Lake Apopka. Hydrobiol. 448:19-26.

Bachmann, R. W., M. V. Hoyer and D. E. Canfield, Jr. 2001b. Sediment removal by the
Lake Apopka marsh flow-way. Hydrobiol. 448:7-10.

Barko, J. W. and R. M. Smart. 1981. Comparative influences of light and temperature on
the growth and metabolism of selected submersed freshwater macrophytes. Ecol.
Monogr. 51(2):219-235.

Barko, J. W., D. G. Hardin and M. S. Matthews. 1982. Growth and morphology of
submersed freshwater macrophytes in relation to light and temperature. Can. J. Bot.
60:877-887.

Bayley, P. B. and D. J. Austen. 2002. Capture efficiency of a boat electrofisher. Trans.
Am. Fish. Soc. 131:435-451.









Bayley, S., V. D. Stotts, P. F. Springer and J. Stennis. 1978. Changes in submerged
aquatic macrophyte populations at the head of Chesapeake Bay, 1958-1975. Estuar.
1(3):171-182.

Beverton, R. J. H. and S. J. Holt. 1957. On the dynamics of exploited fish populations.
Fishery investigations series II. Marine Fisheries Great Britain, Ministry of Ag.,
Fish., and Food 19:1-533.

Bintz, J. C. and S. W. Nixon. 2001. Responses of eelgrass Zostera marina seedlings to
reduced light. Mar. Ecol. Prog. Ser. 223:133-141.

Blanch, S. J., G. G. Ganf and K. F. Walker. 1998. Growth and recruitment in Vallisneria
americana as related to average irradiance in the water column. Aquat. Bot.
61:181-205.

Canfield, D. E., Jr. and M. V. Hoyer. 1992. Aquatic macrophytes and their relationship to
the limnology of Florida lakes. SP 115. Institute of Food and Agricultural Science
(IFAS), UF, Gainesville, FL. 612 p.

Canfield, D. E., Jr., M. V. Hoyer and F. Bennett. 2005. Restoration of the economic
vitality of Lake Griffin's largemouth bass fishery. Final report. Submitted to: Lake
County Water Authority, Tavares, FL. Department of Fisheries and Aquatic
Sciences (FAS), IFAS, UF, Gainesville, FL. 103 p.

Canfield, D. E., Jr., R. W. Bachmann and M. V. Hoyer. 2000. A management alternative
for Lake Apopka. Lake and Reserv. Manage. 16(3):205-221.

Carter, V. and N. B. Rybicki. 1985. The effects of grazers and light penetration on the
survival of transplants of Vallisneria americana Michx. in the tidal Potomac River,
MD. Aquat. Bot. 23:197-213.

Carter, V. and N. B. Rybicki. 1990. Light attenuation and submersed macrophyte
distribution in the tidal Potomac River and Estuary. Estuar. 13(4):441-452.

Carter, V., J. E. Paschal, Jr. and N. Bartow. 1985. Distribution and abundance of
submersed aquatic vegetation in the tidal Potomac River and Estuary, Maryland
and Virginia, May 1978 to November 1981. A water quality study of the tidal
Potomac River and Estuary. Water supply paper 2234-A. U.S. Geological Survey
(USGS). 46 p.

Catling, P. M., K. W. Spicer, M. Biernacki and J. Lovett Doust. 1994. The biology of
Canadian weeds. 103. Vallisneria americana Michx. Can. J. Plant Sci. 74(4):883-
897.

Chambers, P. A. and J. Kalff. 1985. Depth distribution and biomass of submersed aquatic
macrophyte communities in relation to Secchi depth. Can. J. Fish. Aquat. Sci.
42:701-709.









Chestnut, T. L. and E. H. Barman, Jr. 1974. Aquatic vascular plants of Lake Apopka.
Florida Sci. 37(1):60-64.

Chew, R. L. 1974. Early life history of the Florida largemouth bass. Fishery bulletin no.
7. Florida Game and Fresh Water Fish Commission, Tallahassee, FL. 76 p.

Clugston, J. P. 1963. Lake Apopka, Florida, a changing lake and its vegetation. Quart. J.
Florida Acad. Sci. 26(2):168-174.

Conrow, R. and J. Peterson. 2000. A panel atlas of the major aquatic plants of Lake
Apopka, Florida using global positioning (GPS) and geographic information (GIS)
systems. Technical memorandum no. 37. SJRWMD, Palatka, FL. 69 p.

Conrow, R., W. Godwin, M. Coveney and L. E. Battoe. 1993. SWIM plan for Lake
Apopka. SJRWMD, Palatka, FL. 163 p.

Crowder, L. B. and W. E. Cooper. 1979. Structural complexity and fish-prey interactions
in ponds: a point of view. P. 1-10. In D. L. Johnson and R. A. Stein (eds.).
Response of fish to habitat structure in standing water. Spec. publ. 6. N. Central
Div. Am. Fish. Soc., Bethesda, MD.

Crumpton, J. E. and W. F. Godwin. 1997. Rough fish harvesting in Lake Apopka
summary report, 1993-97. Florida Game and Fresh Water Fish Commission.
Prepared for: Lake Apopka restoration project. Special publ. SJ97-SP23.
SJRWMD, Palatka, FL. 24 p.

Danek, L. J. and M. S. Tomlinson. 1989. Bathymetric analysis of Lake Apopka. Special
publ. SJ 89-SP6. SJRWMD, Palatka, FL. 35 p.

Davies, W. D., W. L. Shelton and S. P. Malvestuto. 1982. Prey-dependent recruitment of
largemouth bass: a conceptual model. Fish. 7(6):12-15.

Davis, J. H. 1946. The peat deposits of Florida, their occurrence, development and uses.
Florida Geological Survey, Tallahassee, FL. 247 p.

Dennison, W. C. 1987. Effects of light on seagrass photosynthesis, growth and depth
distribution. Aquat. Bot. 27:15-26.

Dequine, J. F. 1950. Results of rough fish control operations in Lake Apopka during
December 1949 and January 1950. Mimeographed report. Florida Game and Fresh
Water Fish Commission, Tallahassee, FL. 7 p.

Dequine, J. F. and C. E. Hall, Jr. 1951. A brief study of the commercial and sport
fisheries of Lake Apopka. Florida Game and Fresh Water Fish Commission,
Tallahassee, FL. 12 p.









Dibble, E. D. and K. J. Killgore. 1994. A habitat-based approach for studying fish-plant
interactions. Misc. paper A-94-2. U.S. Army Corps of Engineers, Waterways
Experiment Station, Vicksburg, MS. P. 32-40.

Dibble, E. D., K. J. Killgore and S. L. Harrel. 1996. Assessment offish-plant interactions.
Am. Fish. Soc. Sympos. 16:357-372.

Doyle, R. D. 2001. Effects of waves on the early growth of Vallisneria americana.
Freshwat. Biol. 46:389-397.

Doyle, R. D. and R. M. Smart. 2001. Impacts of water column turbidity on the survival
and growth of Vallisneria americana winterbuds and seedlings. Lake and Reserv.
Manage. 17(1):17-28.

Duarte, C. M. and J. Kalff. 1987. Latitudinal influences on the depths of maximum
colonization and maximum biomass of submerged angiosperms in lakes. Can. J.
Fish. Aquat. Sci. 44:1759-1764.

Durocher, P. P., W. C. Provine and J. E. Kraai. 1984. Relationship between abundance of
largemouth bass and submerged vegetation in Texas reservoirs. N. Am. J. Fish.
Manage. 4:84-88.

Goldsborough, W. J. and W. M. Kemp. 1988. Light responses of a submersed
macrophyte: implications for survival in turbid tidal waters. Ecol. 69(6):1775-1786.

Grimshaw, H. J., K. Havens, B. Sharfstein, A. Steinman, D. Anson, T. East, R. P. Maki,
A. Rodusky and K-R. Jin. 2002. The effects of shading on morphometric and
meristic characteristics of wild celery, Vallisneria americana Michx., transplants
from Lake Okeechobee, Florida. Arch. Hydrobiol. 155(1):65-81.

Gutreuter, S. J. and R. O. Anderson. 1985. Importance of body size to the recruitment
process in largemouth bass populations. Trans. Am. Fish. Soc. 114:317-327.

Hardin, S. and L. L. Connor. 1992. Variability of electrofishing crew efficiency, and
sampling requirements for estimating reliable catch rates. N. Am. J. Fish. Manage.
12:612-617.

Hoge, V. R., R. Conrow, D. L. Stites, M. F. Coveney, E. R. Marzolf, E. F. Lowe and L.
E. Battoe. 2003. SWIM plan for Lake Apopka, Florida. SJRWMD, Palatka, FL.
196 p.

Holcomb, D. E. 1977. Final report. D-J Project F-30. Upper Ocklawaha basin fisheries
investigations, 1973-1977. Florida Game and Fresh Water Fish Commission,
Tallahassee, Florida. 107 p.

Holcomb, D. E., W. Johnson, J. Jenkins, J. Bitter and L. Prevatt. 1975a. Oklawaha basin
fisheries investigation. Federal aid in fish restoration Dingell-Johnson project F-30-
2. Florida Game and Fresh Water Fish Commission, Tallahassee, FL.









Holcomb, D. E., W. Johnson, J. Jenkins, J. Bitter, L. Prevatt and P. Metzger. 1975b.
Study I: Upper Oklawaha basin fisheries investigations. Dingell-Johnson project F-
30-2. Second annual performance report Oklawaha basin fisheries investigations.
Florida Game and Fresh Water Fish Commission, Tallahassee, FL.

Hoyer, M. V. and D. E. Canfield, Jr. 1994. Handbook of common freshwater fish in
Florida lakes. SP 160. IF, UF, Gainesville, FL. 177 p.

Hoyer, M. V. and D. E. Canfield, Jr. 1996a. Largemouth bass abundance and aquatic
vegetation in Florida lakes: an empirical analysis. J. Aquat. Plant Manage. 34:23-
32.

Hoyer, M. V. and D. E. Canfield, Jr. 1996b. Lake size, aquatic macrophytes, and
largemouth bass abundance in Florida lakes: a reply. J. Aquat. Plant Manage.
34:48-50.

Hoyer, M. V., D. E. Canfield, Jr., C. A. Horsburgh and K. Brown. 1996. Florida
freshwater plants: a handbook of common aquatic plants in Florida lakes. SP 189.
IF, UF, Gainesville, FL. 260 p.

Hoyer, M. V., M. D. Netherland, M. S. Allen and D. E. Canfield, Jr. 2005. Hydrilla
management in Florida: a summary and discussion of issues identified by
professionals with future management recommendations. Final document. Hydrilla
issues workshop. Florida LAKEWATCH, FAS, IFAS, UF, Gainesville, FL. 68 p.

Hudon, C., S. Lalonde and P. Gagnon. 2000. Ranking the effects of site exposure, plant
growth form, water depth, and transparency on aquatic plant biomass. Can. J. Fish.
Aquat. Sci. 57(Suppl. 1):31-42.

Huffstutler, K. K., J. E. Burgess and B. B. Glenn. 1965. Biological, physical and
chemical study of Lake Apopka 1962-1964. Bureau of Sanitary Engineering,
Florida State Board of Health, Jacksonville, FL. 55 p.

Jaggers, B. V. 1994. Vallisneria americana: considerations for restoration in Florida.
Florida Game and Fresh Water Fish Commission, Eustis, FL. 33 p.

James, W. F. and J. W. Barko. 1994. Macrophyte influences on sediment resuspension
and export in a shallow impoundment. Lake and Reserv. Manage. 10(2):95-102.

Johnson, W. E. and J. E. Crumpton. 1998. Lake Apopka fish population assessment.
Final report for contract 97W121 for SJRWMD. Florida Game and Fresh Water
Fish Commission, Eustis, Fl. 39 p.

Kenworthy, W. J. and M. S. Fonseca. 1996. Light requirements of seagrasses Halodule
wrightii and Syringodiufiliforme derived from the relationship between diffuse
light attenuation maximum depth distribution. Estuar. 19(3):740-750.









Kerwin, J. A., R. E. Munro and W. W. A. Peterson. 1976. Distribution and abundance of
aquatic vegetation in the upper Chesapeake Bay, 1971-1974. P. 393-400. In J.
Davis (ed.). The effects of Tropical Storm Agnes on the Chesapeake Bay estuarine
system. Chesapeake Research Consortium, Inc., Baltimore, MD.

Kimber, A., C. E. Korschgen and A. G. van der Valk. 1995a. The distribution of
Vallisneria americana seeds and seedling light requirements in the upper
Mississippi River. Can. J. Bot. 73:1966-1973.

Kimber, A., J. L. Owens and W. G. Crumpton. 1995b. Light availability and growth of
wildcelery (Vallisneria americana) in upper Mississippi River backwaters.
Regulated Rivers: Res. and Manage. 11:167-174.

Kolz, A. L. 1989. A power transfer theory for electrofishing. P. 1-10. In Electrofishing, a
power related phenomenon. Fish and wildlife technical report 22. U.S. Fish and
Wildlife Service (FWS), U.S. Dept. Interior, Wash., DC.

Korschgen, C. E. and W. L. Green. 1988. American wild celery (Vallisneria americana):
ecological considerations for restoration. Fish and wildlife technical report 19.
FWS, U.S. Dept. Interior, Wash., DC. 24 p.

Korschgen, C. E., W. L. Green and K. P. Kenow. 1997. Effects ofirradiance on growth
and winter bud production by Vallisneria americana and consequences to its
abundance and distribution. Aquat. Bot. 58:1-9.

Kramer, R. H. and L. L. Smith, Jr. 1962. Formation of year classes in largemouth bass.
Trans. Am. Fish. Soc. 91:29-41.

Lake Apopka Restoration Council. 1986. Lake Apopka restoration progress report and
recommendations. W. S. Turnbull (Chairman). Submitted to the 1987 Florida
legislature. 71 p.

Latta, W. C. 1975. Dynamics of bass in large natural lakes. P. 175-182. In R. H. Stroud
and H. Clepper (eds.). Black bass biology and management. Sport Fishing Institute,
Wash., DC.

Loreny, R. C. and C. E. Herderndorf. 1982. Growth dynamics of Cladophora glomerata
in western Lake Erie in some environmental factors. J. Great lakes Res. 8(1):42-53.

Lowe, E. F., L. E. Battoe, D. L. Stites and M. F. Coveney. 1992. Particulate phosphorus
removal via wetland filtration: an examination of potential for hypertrophic lake
restoration. Environ. Manage. 16(1):67-74.

Lowe, E. F., L. E. Battoe, M. Coveney and D. Stites. 1999. Setting water quality goals for
restoration of Lake Apopka: inferring past conditions. Lake and Reserv. Manage.
15(2):103-120.









Lowe, E. F., L. E. Battoe, M. F. Coveney, C. L. Schelske, K. E. Havens, E. R. Marzolf
and K. R. Reddy. 2001. The restoration of Lake Apopka in relation to alternative
stable states: an alternative view to that of Bachmann et al. (1999). Hydrobiol.
448:11-18.

Maceina, M. J. and J. V. Shireman. 1980. The use of a recording fathometer for
determination of distribution and biomass of hydrilla. J. Aquat. Plant Manage.
18:34-39.

Meyer, B. S., F. H. Bell, L. C. Thompson and E. I. Clay. 1943. Effect of depth of
immersion on apparent photosynthesis in submersed vascular aquatics. Ecol.
24:393-399.

Middelboe, A. L. and S. Markager. 1997. Depth limits and minimum light requirements
of freshwater macrophytes. Freshwat. Biol. 37:553-568.

Moore, K. A., B. A. Anderson, D. J. Wilcox, R. J. Orth and M. Naylor. 2003. Changes in
seagrass distribution as evidence of historical water conditions. Gulf of Mexico Sci.
21(1):142-143.

Moxley, D. J. and F. H. Langford. 1982. Beneficial effects ofhydrilla on two eutrophic
lakes in central Florida. Proc. Ann. Conf. Southeast Assoc. Fish and Wildl.
Agencies. 36:280-286.

Moyer, E. J., M. W. Holon, J. J. Sweatman, R. S. Butler and V. P. Williams. 1995.
Fishery response to habitat restoration in Lake Tohopekaliga, Florida. N. Am. J.
Fish. Manage. 15:591-595.

National Oceanic and Atmospheric Administration (NOAA). 2005. National Hurricane
Center, National Weather Service, Miami, FL. Online:
http://www.newflorida.org/storm/history.html. Accessed August 2005.

Nichols, S. A. 1997. Seasonal and sampling variability in some Wisconsin lake plant
communities. J. Freshwat. Ecol. 12(2):173-182.

Nielsen, S. L., K. Sand-Jensen, J. Borum and O. Geetz-Hansen. 2002. Depth colonization
of eelgrass (Zostera marina) and macroalgae as determined by water transparency
in Danish coastal waters. Estuar. 25(5): 1025-1032.

Olson, M. H. 1996. Ontogenetic niche shifts in largemouth bass: variability and
consequences for first-year growth. Ecol. 77(1): 179-190.

Ott, L. R and M. Longnecker. 2001. An introduction to statistical methods and data
analysis. Fifth edition. Wadsworth Group, Pacific Grove, CA. 1152 p.

Porak, W., S. Crawford and R. Cailteux. 1999. Biology and management of the Florida
largemouth bass. Educational bulletin No. 3. Division of Fisheries, Florida Game
and Fresh Water Fish Commission, Tallahassee, FL. 18 p.









Reynolds, J. B. 1983. Electrofishing. P. 147-163. In L. A. Nielsen and D. L. Johnson
(eds.). Fisheries techniques. Am. Fish. Soc., Bethesda, MD.

Reynolds, J. B. 2000. Electrofishing theory. P. 3-24. In S. M. Allen-Gil (ed.). New
perspectives in electrofishing. EPA/600/R-99/108. USEPA, Wash., DC.

Rybicki, N. B. and V. Carter. 1986. Effect of sediment depth and sediment type on the
survival of Vallisneria americana Michx. grown from tubers. Aquat. Bot. 24:233-
240.

Rybicki, N. B. and V. Carter. 2002. Light and temperature effects on the growth of wild
celery and hydrilla. J. Aquat. Plant Manage. 40:92-99.

St. Johns River Water Management District (SJRWMD). 2005. Hydrologic data.
SJRWMD, Palatka, FL. Online:
http://arcimspub.sjrwmd.com/website/dahds/design/index.html. Accessed August
2005.

Sand-Jensen, K. and T. V. Madsen. 1991. Minimum light requirements of submerged
freshwater macrophytes in laboratory growth experiments. J. Ecol. 79:749-764.

Savino, J. F. and R. A. Stein. 1982. Predatory-prey interaction between largemouth bass
and bluegills as influenced by simulated, submersed vegetation. Trans. Am. Fish.
Soc. 11:255-266.

Scheffer, M., M. R. de Redelijkheid and F. Noppert. 1992. Distribution and dynamics of
submerged vegetation in a chain of shallow eutrophic lakes. Aquat. Bot. 42:199-
216.

Schelske, C. and P. Brezonik. 1992. Restoration case studies. Can Lake Apopka be
restored? P. 393-398. In Restoration of aquatic ecosystems: science, technology,
and public policy. Report of committee on restoration of aquatic ecosytems.
National Research Council. National Academy Press, Wash., DC.

Schelske, C. L. and W. F. Kenney. 2001. Model erroneously predicts failure for
restoration of Lake Apopka, a hypereutrophic, subtropical lake. Hydrobiol. 448:1-
5.

Schelske, C. L., M. F. Coveney, F. J. Aldridge, W. F. Kenney and J. E. Cable. 2000.
Wind or nutrients: historic development of hypereutrophy in Lake Apopka, Florida.
Limnol. and Lake Manage. 2000+. Arch. Hydrobiol. Spec. Issues Advanc. Limnol.
55:543-563.

Schneider, R. F. and J. A. Little. 1969. Characterization of bottom sediments and selected
nitrogen and phosphorus sources in Lake Apopka, Florida. Technical Programs,
Southeast Water Laboratory, Federal Water Pollut. Control Admin., U.S. Depart. of
the Interior, Athens, GA. 35 p.









Sheldon, R. B. and C. W. Boylen. 1977. Maximum depth inhabited by aquatic vascular
plants. Am. Midl. Nat. 97(1):248-254.

Shelton, W. L., W. D. Davies, T. A. King and T. J. Timmons. 1979. Variation in the
growth of the initial year class of largemouth bass in West Point Reservoir,
Alabama and Georgia. Trans. Am. Fish. Soc. 108:142-149.

Shofner, J. H. 1982. History of Apopka and northwest Orange County, Florida. Apopka
Historical Society. Rose Printing Co., Tallahassee, FL. 357 p.

Smart, R. M. 1992. Competition among introduced and native species. Proceedings,
twenty-seventh annual meeting APCRP. Bellevue, WA. Final report. Prepared for
U.S. Army Corps of Eng. Wash., DC. Pub. Environ. Lab., U.S. Army Eng.
Waterways Exp. Sta., Vicksburg, MS.

Spence, D. H. N. 1972. Light on freshwater macrophytes. Trans. Bot. Soc. Edinb.
41:491-505.

Strickland, J. D. H. 1958. Solar radiation penetrating the ocean. A review of
requirements, data and methods of measurement, with particular reference to
photosynthetic productivity. J. Fish. Res. Board Canada. 15:453-493.

Swingle, H. S. 1950. Relationships and dynamics of balanced and unbalanced fish
populations. Bull. 274. Ala. Polytech. Inst. Agric. Exp. Sta. 73 p.

Timmons, T. J., W. L. Shelton and W. D. Davies. 1980. Differential growth of
largemouth bass in West Point Reservoir, Alabama-Georgia. Trans. Am. Fish. Soc.
109:176-186.

Titus, J. E. and M. S. Adams. 1979. Coexistence and the comparative light relations of
the submersed macrophytes Myriophyllum spicatum L. and Vallisneria americana
Michx. Oecol. (Berl.) 40:273-286.

United States Environmental Protection Agency (USEPA). 1979. Final environmental
impact statement for Lake Apopka restoration project. Lake and Orange counties
Florida. EPA 904/9-79-43. USEPA. 443 p.

Wegener, W. L. and V. P. Williams. 1974. Fish population responses to improved lake
habitat utilizing an extreme drawdown. Proc. Ann. Conf. S. E. Assoc. Game and
Fish Comm. 28:144-161.

Valiela, I. 1995. Marine ecological processes. Second edition. Springer-Verlag, New
York, Inc., NY. 686 p.

Zimmerman, R. C., A. Cabello-Pasini and R. S. Alberte. 1994. Modeling daily
production of aquatic macrophytes from irradiance measurements: a comparative
analysis. Mar. Ecol. Prog. Ser. 114:185-196.















BIOGRAPHICAL SKETCH

Stephen J. Murphy earned an Associate of Arts degree at Valencia Community

College in Orlando, Florida, in 2001. He went on to earn a Bachelor of Science degree

with a major in wildlife, ecology, and conservation (WEC) at the UF, College of

Agricultural and Life Sciences (CALS) in August 2003. He also completed the CALS

upper division honors program in August 2003.




Full Text

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ASSESSMENT OF FISH AND PLANT COMMUNITIES IN LAKE APOPKA, FLORIDA By STEPHEN J. MURPHY A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2005

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Copyright 2005 By Stephen J. Murphy

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iii ACKNOWLEDGMENTS Appreciation is expressed to all those who assisted me w ith this research. David Watson and Dan Willis of Florida LAKEWATCH extended their expertise in electrofishing activities. Alexis Caffrey helped take light meter measurements and helped survey aquatic plants, along with Heather Hammers and Laura Stockman. Elizabeth Daneman and Erich Marzolf from the St. Johns River Water Management District (SJRWMD), William Johnson from th e Florida Fish and Wildlife Conservation Commission (FFWCC), and Mark Hoyer from the University of Florida provided previous data on the fish and plant communitie s. Karen Brown from the University of Florida (UF), Center for Aqua tic and Invasive Plants, assi sted me in locating journal articles for my aquatic plant literature re view. Dr. Roger Bachmann guided me in analyzing limnological data. Dr. Daniel E. Canfield, Jr. served as my committee chairman and advisor, and directed me to wards excellence and professionalism in the scientific field. Finally, Dr Charles Cichra and Dr. Kenneth Langeland served on my committee and helped oversee this research.

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iv TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iii LIST OF TABLES...............................................................................................................v LIST OF FIGURES...........................................................................................................vi ABSTRACT......................................................................................................................v ii INTRODUCTION...............................................................................................................1 MATERIALS AND METHODS.........................................................................................8 Fish........................................................................................................................... ....8 Aquatic Macrophytes..................................................................................................10 Statistical Analyses.....................................................................................................15 RESULTS AND DISCUSSION........................................................................................19 Fish........................................................................................................................... ..19 Aquatic Macrophytes..................................................................................................29 LAKE MANAGEMENT RECOMMENDATIONS.........................................................46 LIST OF REFERENCES...................................................................................................53 BIOGRAPHICAL SKETCH.............................................................................................62

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v LIST OF TABLES Table page 1 Electrofishing boat setup used by differe nt studies at Lake Apopka, Florida..........17 2 Electrofishing control box settings us ed by different studies at Lake Apopka, Florida......................................................................................................................17 3 Electrofishing methods used by differe nt studies at Lake Apopka, Florida............18 4 Common and scientific names of fish co llected by individual studies at Lake Apopka, Florida........................................................................................................36 5 Water chemistry parameters measured for Lake Apopka, Florida, in June – October 2004............................................................................................................37 6 Mean electrofishing catch per unit effort and standard error of fish number (number/hr) and weight (kg/h r) for Lake Apopka, Florida......................................37 7 Mean yearly and combined electrofishing catch per unit effort and standard error of fish number (number/hr) for La ke Apopka, Florida, by Johnson and Crumpton (1998)......................................................................................................38 8 Annual mean electrofishing catch per unit effort number (number/hr) of two size groups of largemouth bass, bluegill, a nd redear sunfish collected in Lake Apopka, Florida........................................................................................................39 9 Occurrence of plant spec ies in twenty evenly-spa ced transects around Lake Apopka, Florida, in 2004..........................................................................................39 10 Location, area (m2), and maximum depth (m) of eel-grass beds in Lake Apopka, Florida, in 2004........................................................................................................40

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vi LIST OF FIGURES Figure page 1 Lake Apopka and surrounding area...........................................................................7 2 Mean electrofishing catch per unit effo rt estimates of total fish abundance (number/hr) for Lake Apopka, Florida.....................................................................41 3 Mean electrofishing catch per unit effo rt estimates of total fish abundance (number/hr) for the combined data of di fferent studies for Lake Apopka, Florida..41 4 Individual fish species percent of to tal number collected by electrofishing for Lake Apopka, Florida, by Johnson and Crumpton (1998) for 1989 – 1993............42 5 Individual fish species percent of to tal number collected by electrofishing for Lake Apopka, Florida, in June – August 2004.........................................................42 6 Length frequency distribution of bluegi ll collected by electrofishing for Lake Apopka, Florida, in June – August 2004..................................................................43 7 Length frequency distribution of redear sunfish collected by electrofishing for Lake Apopka, Florida, in June – August 2004.........................................................43 8 Mean electrofishing catch per unit effort estimates of largemouth bass abundance (number/hr) for Lake Apopka, Florida...................................................44 9 Mean electrofishing catch per unit effort estimates of largemouth bass abundance (number/hr) for the data sets of combined years from different studies for Lake Apopka, Florida.............................................................................44 10 Length frequency distribution of largem outh bass collected by electrofishing for Lake Apopka, Florida, in June – August 2004.........................................................45 11 Electrofishing catch per unit effort of largemouth bass (kg/hr) versus total chlorophyll a (g/L) for 60 Florida lakes.................................................................45

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vii Abstract of Thesis Presen ted to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science ASSESSMENT OF FISH AND PLANT COMMUNITIES IN LAKE APOPKA, FLORIDA By Stephen J. Murphy December 2005 Chair: Daniel E. Canfield, Jr. Major Department: Fisherie s and Aquatic Sciences Since the 1960s, an enormous amount of time and resources has been expended by the State of Florida and other government entities trying to improve the water quality in Lake Apopka, a hypereutrophic lake in central Florida; however, the lake remains in a turbid algal state in the ea rly 2000s. The objective of th is study was to assess the effectiveness of the restoration efforts in returning Lake Apopka b ack to its historic primary use of recreational fishing for largemouth bass ( Micropterus salmoides floridanus ). The assessment was accomplished by surveying the fish populations and aquatic plant communities in the lake to determine if there has been an increase in the abundance of largemouth bass or an expa nsion in the area oc cupied by aquatic vegetation. Fish were sampled by electrofi shing on three occasions in June – August 2004. Submersed macrophyte beds, primarily eel-grass ( Vallisneria americana ), and floating-leaved and emergent plants we re sampled in October 2004. The mean largemouth bass catch rate in 2004 was 7 fish/h r. The combined catch rate from 1989 to

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viii 1993 was also 7 fish/hr, thus showing th at the largemouth bass population did not increase in relative abundance during the la st decade. The abundance of largemouth bass continues to be lower than expected for La ke ApopkaÂ’s trophic status in comparison to other Florida lakes. Submersed, floating-leav ed, and emergent plants covered less than 1% of the surface area of the lake in 2004, i ndicating that the rooted aquatic vegetation has not expanded in the last several decades. Eel-grass colonized a total lake bottom area of approximately 900 m2 in 2004 compared with an estimated 11,032 m2 in 1999. Eelgrass has drastically declined during the past five years since it was replanted around the shore in 1999. It now occupies only 8% of its former area that it occupied in 1999. The restoration efforts at Lake Apopka have not yet been successful in restoring the largemouth bass fishery or in expanding the area occupied by aquatic vegetation. Reducing the abundance of planktonic algae th rough nutrient management is the primary restoration strategy for agencies such as th e St. Johns River Water Management District (SJRWMD). Other factors besides light at tenuation by planktonic algae, however, are involved in limiting the abundance of largemouth bass and expansion of aquatic macrophytes. The depth and fluidity of sedi ments, and wind resuspension of sediments, are also major factors. It could be seve ral more decades before the largemouth bass fishery is improved while relying on the curr ent restoration strate gy unless alternative management strategies are also utilized. Three alternative management strategies or ideas that have been discussed are drawdown, artificial reefs or ba rriers, and stocking.

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1 INTRODUCTION Lake Apopka is the fourth largest lake in Florida with a surface area of 12,465 ha (Hoge et al. 2003). It is locat ed northwest of Orlando, Florida, in both Orange and Lake counties (Figure 1). It is shallow (1.6 m mean depth) and polymictic. It is hypereutrophic with high nutrient and chlo rophyll levels (100 g/L mean total phosphorus (TP) and 59 g/L mean chlorophyll a (chl a )), and low transparency (0.35 m mean Secchi depth (SD)) (Hoge et al. 2003). These limnological parameter values (TP, chl a and SD) are mean 2004 values obtained from the St. Johns River Water Management District (SJRWMD). The lake is nearly round exce pt that it is shaped like a funnel or gourd neck at the southern end of the lake (Figure 1). Vegetable farms (muck farms) were established on the north end of the lake after 1940 for World War II wartime food production. Prior to 1950, Lake Apopka contained clea r water, and dense growths of Illinois pondweed ( Potamogeton illinoensis ) and eel-grass ( Vallisneria americana ) down to depths of 2.4 m (Clugston 1963, Chestnut a nd Barman 1974). About 80% of the lake was inhabited by aquatic plants. Clugston (1963) reported that Illinois pondweed began at about 180 m from the shor eline and extended across the en tire length and breath of the lake except in deep-water areas ( 2.4 m). Water hyacinth ( Eichhornia crassipes ) grew profusely around the entire shoreline of th e lake (Clugston 1963). Boating around the lake was restricted to tra ils through submersed vegetation and to openings not covered by extensive mats of water hyacinth (Clugston 1963).

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2 Lake Apopka was nationally renowne d as a premier largemouth bass ( Micropterus salmoides floridanus ) fishing lake (Dequine 1950, Dequine and Hall 1951, Shofner 1982). Anglers came from throughout th e United States to fish for trophy-sized largemouth bass (Davis 1946, Dequine 1950, Clugston 1963, Chestnut and Barman 1974). By the early 1950s, there were an estim ated 13 fishing camps with a value to the local economy of over one million dollars annually (Dequine and Hall 1951, Shofner 1982). Lake Apopka was changed in the early tw entieth century by flood plain alteration, water level stabilization, and urban and agricu ltural runoff (Huffstutler et al. 1965). Also, in the 1940s, farms at the north end of th e lake expanded by draining marsh areas. Following the expansion of the farms, farmer s began to pump an increased amount of nutrient-rich water back into Lake Apopka (Clugston 1963). A hurricane in 1947 uprooted many of the macrophytes in the la ke according to Mr. John Dequine (retired biologist, Florida Game and Fresh Wate r Fish Commission, personal communication), Clugston (1963), Schneider and Little (1969), Lake Apopka Restora tion Council (1986), and Bachmann et al. (1999). Within se veral years, the remaining macrophytes disappeared in other parts of the lake as well, coinciding wi th a switch to a turbid algal state (Clugston 1963). There is controversy about the role of the hurricane in the loss of the macrophytes and about whether the switch from rooted macrophytes to algae was the result of natural causes or the result of the numerous human activities (Schelske and Brezonik 1992, Bachmann et al. 1999, Lowe et al. 1999, 2001, Canfield et al. 2000, Schelske et al. 2000, Schelske and Kenney 2001). Regardless of the mechanisms, sport

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3 fishing for largemouth bass declined in th e late 1950s and early 1960s (Clugston 1963, Huffstutler et al. 1965, Lake A popka Restoration Council 1986). According to Johnson and Crumpton ( 1998), the largemouth bass fishery and aquatic vegetation community have been func tionally non-existent at Lake Apopka since the 1960s. Dequine and Hall (1951) estimat ed that over 9,513 largemouth bass were harvested in January 1951 alone. Johnson a nd Crumpton (1998) stated that the combined harvest over the last two d ecades (from 1978 to 1998) probably would not equal that one monthÂ’s harvest. Aquatic vegetation in the 1980s and 1990s has only occupied a narrow belt around the shoreline of the lake, comprising less than 1% of the surface area of lake (Canfield and Hoyer 1992, Johnson and Crum pton 1998). Dominant emergent plant species were cattail ( Typha spp.) and woody wetland species (red maple ( Acer rubrum ) and Carolina willow ( Salix caroliniana )), which occupied 38% a nd 44% of the shoreline, respectively, in 1997 (Johnson and Crumpton 19 98). There were isolated stands of aquatic grasses (maidencane ( Panicum hemitomon ), torpedograss ( Panicum repens ), Egyptian paspalidium ( Paspalidium geminatum )), and soft-stem bulrush ( Scirpus validus ), which together occupied 8% of shoreline (Johnson and Crumpton 1998). The dominant floating-leaved plant species was water hyacinth in 1986, occurring in 27% of transects (Canfield and Hoye r 1992). The occurrence of floating-leaved or submersed plant species was not reported by Johnson a nd Crumpton (1998). The relative species richness of aquatic macrophytes (10 species) and fish (16 species) in 1986 was low in comparison with other Florida lakes (Canfield and Hoyer 1992).

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4 A thick layer of flocculent sediments ( 1.5 m mean thickness) covers 90% of the lake bottom in almost all areas of the lake (Schneider and Little 1969). There is a firm bottom in some parts of the west shore and in some parts of the shoreline in the gourd neck area. These unconsolidated sedi ments are often resuspended by the wind, contributing to the high turbidity, and do not allo w plants to anchor their roots (Carter et al. 1985, Doyle 2001, Doyle and Smart 2001) or largemouth bass to successfully nest (Porak et al. 1999). Point sources of nutrient loading from se wage and citrus processing plants were eliminated by the 1980s, and discharges from farming operations were reduced in 1992 (Johnson and Crumpton 1998, Bachmann et al. 1999, Canfield et al. 2000, Hoge et al. 2003). The majority of these farmlands we re purchased by the SJRWMD in the late 1990s. The SJRWMD continues to conduct mana gement efforts to restore Lake Apopka under the Lake Apopka Surface Water Improvement and Management (SWIM) program (Conrow et al. 1993, Hoge et al. 2003). The current restoration program stra tegy, headed by the SJRWMD, is based primarily on reducing external nutrient loading, focusing primarily on phosphorus (P) reductions (Hoge et al. 2003). The P criter ion proposed by the SJRWMD for the lake is 55 g/L (Hoge et al. 2003). Other projects of the current restoration program have included removing gizzard shad ( Dorosoma cepedianum ) from the lake and planting macrophytes around the shore in the 1990s. De spite the enormous amount of time and resources that have been expended trying to improve the water quality in Lake Apopka and to return the lake to its former clea r-water, macrophyte-dominated state, nationally

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5 renowned for its largemouth bass fishery, the lake remains in a turbid algal state (Bachmann et al. 1999). There is a lack of unanimity regardi ng the efficacy of restoration efforts (Bachmann et al. 1999, 2001a, b, Lowe et al. 1999, 2001, Canfield et al. 2000, Schelske et al. 2000, Schelske and Kenney 2001). Some au thors do not believe that the restoration program, based primarily on an external P reduction program, will be successful in improving the water clarity or in expanding th e aquatic vegetation needed as habitat for largemouth bass in the near-future (Bachmann et al. 1999, 2001a, b, Canfield et al. 2000). Alternative hypotheses regarding the limiting f actor responsible for causing the turbidity of the water, for example wind resuspen sion of sediments (Bachmann et al. 1999, 2000a, b), have been put forth but have not yet been acted upon. Recent management strategies have not included alternative methods and ideas such as drawdown or artificial barriers that could reduce the turbidity in the water from resuspended particles and poten tially improve the largemouth bass fishery. For example, a major drawdown could consolidate and comp act the sediments (Wegener and Williams 1974, Moyer et al. 1995) if the technical proble ms, such as the amount of water to be moved and the length of time that the lake woul d stay drained, could be resolved (United States Environmental Protection Agency (USEPA ) 1979). Also, placing artificial barriers around the perimeter of the lake could provide calm, protected waters and improve the habitat for largemouth bass in thos e areas (Canfield et al. 2000). No studies have been conducted to find out if the aquatic plants, which were planted by the SJRWMD in or before 1999, have expanded in area to determine if the restoration program has been successful in one of its primary objectives of restoring lake

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6 habitat (Hoge et al. 2003), a nd to determine if the money that has been expended has been well spent. For example, more th an $100,000,000 in Federal and State funds were used to purchase farms, with drainage to the lake, to take them out of production. A marsh flow-way was also constructed to re move phosphorus-rich particles from the lake water (Conrow et al. 1993, Hoge et al. 2003). A study was needed to assess the response of the fish and plant communities in Lake A popka to these restoration activities because of the controversy over the successf ulness of the restoration program. Previous studies to assess the fish an d plant communities in Lake Apopka were conducted by Canfield and Hoyer (1992) and Johnson and Crumpton (1998). The objective of this study was to evaluate the e ffectiveness of the restoration program in restoring the largemouth bass fishery and th e aquatic plant community. This objective was accomplished by sampling the littoral fish populations and the aquatic macrophyte community. The criteria, for determining if the restoration program was effective, was whether or not the largemouth bass population ha s increased in abundanc e (catch rate as number/hr or kg/hr) in the la st two decades, or the aquatic macrophyte community, used as habitat by largemouth bass, has expanded in area (m2 or ha) since 1999. To make this determination, the abundance and structure of the littoral fish populations and aquatic macrophyte community, surveyed by this study in 2004, were compared, and tested as appropriate, to those of previous studies.

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7 Lake County Orange County Lake ApopkaApopka-Beauclair Canal Gourd nec k Winter Garden Oakland Magnolia Park Monteverde Turnpike SR 50 Former farm lands0 1 2 Kilometers N S E W Ferndale Ocoee Apopka US 441 Figure 1. Lake Apopka and surrounding area (modeled using Hoge et al. 2003, page 14).

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8 MATERIALS AND METHODS Fish Fish were electrofished in near-shore areas of the main part of Lake Apopka, excluding the gourd neck area and the adjoining canals. Ten transects were sampled once monthly in June, July, and August 2004 us ing a Coffelt Mfg., Inc. control box. Ten additional transects were sampled in June us ing a Smith-Root, Inc. control box as part of a control box comparison study, thus totaling 40 transects. Transects were evenly spaced around the lake in all habitats. Each transect was 10 minutes in duration, with continuous current input. Methods were similar to t hose used by Canfield and Hoyer (1992), Hoyer (University of Florida (UF), unpublished data), and Johnson and Crumpton (1998). Fish were collected, identified to species, measured to the nearest mm total length (TL), and released back into the lake. Individual fish weights were calculated from measured lengths using total weight to length regression formulas developed for individual Florida freshwater fish species by Hoyer and Canfield (1994). The total number and weight of fish were calculated by transect and then averaged across the 40 transects to yield catch per uni t electrofishing effort (number or kg/hr of electrofishing) statistics. At each electrofishing trans ect, the depth and dominant vegetation, if present, were recorded. Dissolved oxygen (DO) concentration (mg/L), Secchi disc depth (SD) (m), specific conductance (S/cm at 25 C), and water temperature (C) were measured at four near-shore stations, when the electrof ishing was conducted (one station in each of

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9 the north, east, south, and west regions of the lake). Dissolved oxygen concentration, specific conductance, and water temperatur e were measured by using a Yellow Springs Instrument Company Model 85 Meter. Coffelt Mfg., Inc. control boxes were used in collecting fish in previous studies at Lake Apopka by Canfield and Hoyer (1992) and by Hoyer (UF, unpublished data). Coffelt Mfg., Inc. recently went out of business and the only company that now manufactures electrofishing control boxes is now Smith-Root, Inc. The Florida Fish and Wildlife Conservation Commission (FFWCC) replaced all of its Coffelt Mfg., Inc. control boxes with control boxes manufactured by Smith-Root, Inc. in the 1990s, but the UF, Department of Fisheries and Aquatic Sc iences (FAS) uses both brands of control boxes. Because the catch rate of this study (which used both brands of control boxes) was compared to previous studies by Canfield and Hoyer (1992), Hoyer (UF, unpublished data), and Johnson and Crumpton (1998) that did not all use the same brand of control box, it was important to conduct a comparison study to account for any possible differences that might be due to using different control boxes. A comparison study was conducted in June 2004 by using control boxes manufactured by Smith-Root, Inc. and Coffelt Mf g., Inc. to simultaneously collect fish in 10 paired transects in similar habitat. The data from paired transects were used to test for differences in catch rate between the two control boxe s using a paired t test. Each boat started from the middle of the habitat, 10 m apart, and work ed away from each other to the ends of the habitat. The two boats used in the comparison study were set up identically except for the control boxes. Bo th boats were 5 m in length, made of aluminum, powered by 50-hp Mercury moto rs, and equipped with 5000-watt Honda

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10 EG5000X generators (Table 1). Both boats had one boom with an attached 62-cm diameter ring, with six 1-cm diameter, 1.2m long, stainless steel cables in place, for transmitting electricity into the water. Bo th control boxes were set at 7-9 amps, 180-190 volts, 60-80 pulses per second, and (pulsed) al ternating current output (Table 2). All persons participating in the study had prior experience in electrofishing. One person, in each boat, dipped fish. Although the equipment and sampling design us ed in this study were similar to previous studies on Lake Apopka, there were some differences. Johnson and Crumpton (1998) was the only study that used two el ectric booms. A study was not conducted to determine if having two booms would result in collecting more fish than using only one boom. Additionally, no studies were found in the literature th at compared the efficiency of using two booms versus one boom. Johnson and Crumpton (1998) had the most samples (870 transects in 1989 – 1993, and 150 transects in 1996 – 1997) (Table 3). They collected fish in 5-min transects using random sampling in 1989 – 1993, and both random and selected sampling in 1996 – 1997. All the other studies collected fish in 10-min transects usi ng evenly distributed sampling. Hoyer (UF, unpublished data) samp led only the northern half of the lake, whereas, all of the other studi es sampled the entire lake. Aquatic Macrophytes Dominant plant species were recorded at each of the evenly spaced, electrofishing transects during each sampling occasion. Four fa thometer transects (north to south, west to east, northwest to southeast, and southw est to northeast) were run across the entire diameter (~17 km) of the lake in August 2004 to record the location and amount, if any, of submersed vegetation in Lake Apopka. The procedures for using a recording

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11 fathometer and determining quantitative ve getation parameters have been described previously (Maceina and Shireman 1980). The widths of floating-leaved and emergent plant zones (m) were estimated by eye at 30 transects evenly spaced around the lake in October 2004. Estimating fixed distances wa s practiced just prior to sampling and consistent methods were used to make and record estimations of distance. Dissolved oxygen concentration and SD were measured at four near-shore stations, on the date that vegetation was sampled (one station in each of the north, east, south, and west regions of the lake). The 16 largest beds of eel-grass, repo rted by the SJRWMD (Conrow and Peterson 2000), were sampled in October 2004. Ee l-grass was the only submersed macrophyte sampled in this study because it was the only submersed macrophyte reported to be abundant (~ 1 ha) in the lake besides hydrilla ( Hydrilla verticillata 0.5 ha) (Conrow and Peterson 2000). Hydrilla was not sampled during this study because contact herbicide has been applied regularly by the SJRWMD to keep it from expanding (Erich Marzolf, environmental scientist, SJRWMD, Palatka, FL, personal communication). The location and abundance of hydrilla also changes frequently. All sampled eel-grass beds were located on the west side of the lake, with a few exceptions. Only a few small beds were repor ted on the north, east, or south sides of the lake (Conrow and Peterson 2000). Seven additio nal sites were sampled in the north (3 sites), east (1 site), and south (3 sites) re gions of the lake, even though they were small (Conrow and Peterson 2000), so that the entire lake would be repres ented by the locations that were chosen. Sites were found using GPS coordinates obtained from the SJRWMD.

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12 At each site, the area (m2) of the plant bed was estimated by eye from the boat for all but the largest beds. Estimating fixed di stances was practiced just prior to sampling and consistent methods were used to make and record estimations of distance. Plant beds, over 100 m2 in area, were walked around while simultaneously measuring their area (m2) with a handheld GPS receiver. The percen t density (from 0 to 100% for sparse to dense aggregations) was estimated by eye. The type of soil (sand or some degree of silt/mud) was determined by pushing on the substrate with a rod. The maximum water depth (m) that the plant bed was growing in was determined by lowering a Secchi disk until it rested on the substrate and measuring th e vertical distance (m) from the substrate to the water surface with the attached cord. Light attenuation in Lake Apopka wa s measured (in quanta units) using a photometer (LI-COR model LI1400 data logger) attached to an underwater quantum sensor (LI-192SA) and a spherical quantum sensor (LI-193SA). Three samples, spaced 15 m apart, were taken at th e center of the lake on th ree sampling occasions (once monthly in June, August, and October 2004) for a total of nine samples. Irradiance measurements were taken at the center of th e lake because of depth limitations near shore. A sample consisted of taking a seri es of downwelling irradiation measurements every 0.2 m into the water column starting fr om the surface until either depth or light became limited (as seen by negative irradian ce measurements), whichever was reached first. Measurements were taken with th e spherical quantum sensor laying facing up on the deck to measure ambient atmospheric irradiance and with the underwater sensor attached to a graduated rod that was held straight out and away from the samplerÂ’s body on the sunny side of the boat w ith the rod aligned vertically.

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13 The maximum depth of colonization (MDC ) is the maximum depth at which an aquatic macrophyte species is capable of co lonizing. Mittelboe and Markager (1997) stated that the MDC was defined by the deep est growing plant observed. Since MDC is thought to be primarily limited by irradian ce (Chambers and Kal ff 1985, Carter et al. 1985), measurements of downwelling irradiance in the water column, and calculations of the percent of downwelling su rface irradiance at depth, can be used to determine the theoretical MDC (Korschgen et al. 1997). On e percent of downwe lling surface irradiance (Io) is generally taken as the theoretical MDC of aquatic macrophytes (Dennison 1987, Valiela 1995) because it is the compensa tion depth at which photosynthesis and plant respiration are equivalent (Korschgen et al. 1997). Aquatic macrophytes are not always able to colonize down to their theoretical MDC except under optimal conditions (Spence 1972, Barko and Smart 1981, Chambers and Kalff 1985, Scheffer et al. 1992, Hudon et al. 2000). The lower depth limit, with some exceptions, more commonly occurs at light levels be tween 5 and 10% Io (Sheldon and Boylen 1977, Barko et al. 1982, Chambers and Kalff 1985, Kimber et al. 1995a, b). Dennison (1987) stated that the maximum depth limit for freshwater macrophytes was roughly equivalent to the Secchi disc depth, wh ich is often taken as the 10% light level (Strickland 1958). The maximum depth of growth (MDG) is defined in this paper as the maximum depth corresponding to the minimum percent of Io at which an aquatic macrophyte species predominantly grows down to, as limited by light attenuation (Sheldon and Boylen 1977, Kenworthy and Fonseca 1996, Ni chols 1997, Moore et al. 2003). Other studies have more strictly defined the M DG as the maximum depth corresponding to the

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14 minimum percent of Io needed for there to be a specifi ed production (number or g) or elongation (cm) of leaf, meristem, or shoot or production (g) of biomass, within a specified period of time (days) (Barko and Smart 1981, Barko et al. 1982, Loreny and Herderndorf 1982, Dennison 1987, Duarte and Kalff 1987, Sand-Jensen and Madsen 1991, Korschgen et al. 1997, Blanch et al 1998, Bintz and Nixon 2001, Grimshaw et al. 2002, Nielsen et al. 2002). The theoretical M DG for eel-grass was es tablished in this study by referencing previous studies on the minimum percent of Io needed for eel-grass to grow. For example, the maximum depth corresponding to a minimum referenced percent of Io, needed for eel-grass to gr ow, was taken as the MDG. The data from the light meter measurements were used to determine the theoretical MDC and MDG of eel-grass in Lake Apopka. The theoretical MDC and MDG were chosen as 1% Io and 8% Io, respectively, because aut hors in the literature have reported that eel-grass and other aquati c vascular plants are capable of colonizing down to depths of 1% Io and that they grow down to about 8% Io (Sheldon and Boylen 1977, Barko et al. 1982, Carter and R ybicki 1985, 1990, Duarte and Kalff 1987, Goldsborough and Kemp 1988, Sand-Jensen and Madsen 1991, Zimmerman et al. 1994). For each sample, the ratio of dow nwelling irradiance at depth (Id) to Io, taken as a percent, was calculated using Microsoft Office Excel 2003 to determine theoretical MDC and MDG. For example, the ratio of Id to Io, taken as a percent, yields the percent downwelling irradiance at a given depth in the water column. Then, the water depth corresponding to 1% and 8% Io equals the theoretical MDC and MDG, respectively. The total area (m2) of eel-grass that was found in Lake Apopka during this study was subtracted from the total area re ported by the SJRWMD in 1999 (Conrow and

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15 Peterson 2000) to determine if eel-grass was expanding, remaining constant, or declining. The observed and theoretical MDC and MDG were compared to determine if the maximum depth at which eel-grass was found to be growing agrees with the theoretical depth to which it should be able to grow. The observed MDG used in my analysis was derived from the maximum depth (m) at which eel-grass was measured to be predominantly growing. Similarly, the observe d MDC used in my analysis was derived from the maximum depth at which eel-gra ss was found to be growing at the 23 sites sampled. The area of the lake, that was available for eel-grass to colonize and grow based on the observed MDC and MDG, was calculate d using a bathymetric map (Danek and Tomlinson 1989). This area was compared to the total area of eel-grass found to determine the percentage of available area that eel-grass inhabited under the current light regime. The percentage of the total lake area that eel-grass was theoretically able to colonize and grow, under the current light regime, was also calculated. Statistical Analyses The catch rates of total fish and largemout h bass of this study were compared to the catch rates of previous studies conducted in 1986 by Canfield and Hoyer (1992); in 1987 – 1996, excluding 1990, by Hoyer (UF, unpublished data); and in 1989 – 1993 and 1996 – 1997 (largemouth bass only) by Johnson and Crumpton (1998). T tests were used, where appropriate, to determine if ther e had been a statistical difference in the abundance of total fish or individual fish species in the near-shore region of Lake Apopka. Raw data were available only for Johnson and Crumpton (1998) for 1989 – 1993, and not for 1996 – 1997. Their report and ta bles were used to determine the catch rate of largemouth bass, bluegill ( Lepomis macrochirus ), and redear sunfish ( Lepomis

PAGE 24

16 microlophus ) for 1996 – 1997. Microsoft Office Excel 2003 was used to analyze all data (the fish and plant data collected in this study, as well as data collected by other individuals). The population of largemouth bass at Lake Apopka, from 1986 to 2004, was graphically compared to 60 other Florida la kes sampled by Canfield and Hoyer (1992), by plotting the mean catch per unit effort (CPU E) (kg/hr) of largemouth bass for all of the lakes against their corresponding mean chl a (g/L) value. Four se parately identified data points were given for the i ndividual studies that samp led Lake Apopka from 1986 to 2004. Chlorophyll data points, for the indi vidual studies conducted at Lake Apopka, were the mean yearly chlorophyll values, for the years in which Lake Apopka was sampled, obtained from the SJRWMD. Chlorophyll data points, for the 60 lakes sampled by Canfield and Hoyer (1992) were the mean chlorophyll values reported in Canfield and Hoyer (1992). Data were transformed to their logarithms (base 10) to reduce heterogeneity of variance. The resulting pl ot allows comparison of the mean CPUE of largemouth bass of all the la kes based on their mean chl a values. The efficiency of collecting total fi sh using control boxes manufactured by different companies, Smith-Root, Inc. versus Coffelt Mfg, Inc., was tested for significant differences using a paired t test. The efficiency of coll ecting two categories of fish was also tested using paired t tests. Centrarchids (warmouth ( Lepomis gulosus ), bluegill, redear sunfish, and largemouth bass) were lumped into one category. Other noncentrarchids (Florida gar ( Lepisosteus platyrhincus ), bowfin ( Amia calva ), gizzard shad, blue tilapia ( Tilapia aurea ), yellow bullhead ( Ameiurus natalis ), brown bullhead

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17 ( Ameiurus nebulosus ), and channel catfish ( Ictalurus punctatus )) were lumped into a second category. Table 1. Electrofishing boat setup used by different studies at Lake Apopka, Florida. Study Generator Model Number of Booms Number of Persons Dipping Fish This Study (2004) Honda EG5000X 1 1 Johnson & Crumpton (1998) Honda EG5000X 2 1 Hoyer (Unpublished data) Honda EG5000X 1 1 Canfield & Hoyer (1992) Honda EG5000X 1 1 Table 2. Electrofishing control box settings used by different studi es at Lake Apopka, Florida. Study Control Box Model Output Mode Output Amps Output Volts Pulse Width Frequency This Study (2004) Coffelt VVP-15 Smith-Root VI-A Pulsed AC Pulsed AC 7 – 9 6 – 8 180 177 50% 2 ms 80 – 100 — Johnson & Crumpton (1998) Smith-Root VI-A Pulsed AC or Pulsed DC 5 – 7 177 – 500 2 – 5 ms — Hoyer (Unpublished data) Coffelt VVP-15 Pulsed AC 7 – 9 180 50% 80 – 100 Canfield & Hoyer (1992) Coffelt VVP-15 Pulsed AC 7 – 9 180 50% 80 – 100

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18Table 3. Electrofishing methods used by di fferent studies at La ke Apopka, Florida. Study Month and Years Sampled Number of Samples (N) Elapsed Time of Each Transect With Continuous Current Sampling Method Region of Lake This Study (2004) Jun 2004 Jul 2004 – Aug 2004 20 20 10 10 Proportioned by habitat Evenly distributed Entire lakea Entire lakea Johnson & Crumpton (1998) Mar 1989 – Nov 1993b Nov 1996 – Sept 1997c 870 180 5 5 Random 75 random, 75 selected Entire lake Entire lake Hoyer (Unpublished data) Mar 1987 – Jan 1996d 62 10 Evenly distributed Northern half only Canfield and Hoyer (1992) Aug 1986 9 10 Evenly distributed Entire lakea aNot including the gourd neck area or canals. bTwenty-nine months were sampled bimonthly in the odd months of the year. cSix months were sampled bimonthly in the odd months of the year. dSampling was conducted only in January, February, or March.

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19 RESULTS AND DISCUSSION Fish Twenty species of fish were collected in 2004 (Table 4). Canfield and Hoyer (1992), Hoyer (UF, unpublished data), and Johnson and Crumpton (1998) collected 16, 22, and 26 species, respectively. These differences in species richness are within a range that would be expected from a stable fi sh community when temporal and personnel differences in sampling are accounted for (Reynolds 1983, Hardin and Conner 1992, Andrus 2000, Ott and Longnecker 2001, Bayley and Austen 2002). Since Johnson and Crumpton (1998) took th e most number of samples (870), bimonthly, over a five-year period, using na tural laws of probabilities (Ott and Longnecker 2001), it would be expected for them to encounter more rare species than the other studies that took less samples or took all of their samples in only one or a few months, or only in a certain season of the y ear. Also, since Canfie ld and Hoyer (1992) only sampled on one date, it is reasonable that they collected the smallest number of species. Differences in the manner in which personne l sample can result in changes in the number and type of fish collected (R eynolds 1983, Hardin and Conner 1992, Andrus 2000, Bayley and Austen 2002). Personnel, that are meticulous in collecting every fish regardless of size, are likely to collect a great er quantity of smaller, rare species. Also, misidentification can result in an incorrect number of fish species being recorded.

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20 There was no significant difference in the number of total fish, centrarchids, or non-centrarchids collected between Smith-Root, Inc. and Coffelt Mfg., Inc. control boxes (p > 0.05 for all three tests), although there were some interesting findings. When the Smith-Root, Inc. control box was used, slightly more fish (23) were collected overall for all 10 combined transects than when the Co ffelt Mfg., Inc. control box was used. There was higher variation in the to tal number of fish collected with the Coffelt Mfg., Inc. control box (standard error = 7.1/ hr) than with the Smith-Root, Inc. control box (standard error = 6.1/hr). Also, when the Coffelt Mf g., Inc. control box wa s used, proportionally more centrarchid fish were caught than non-centrarchids compared to the Smith-Root, Inc. control box. These results may apply only to conditi ons present at Lake Apopka during the time of sampling (Bayley and Austen 2002). For example, the high mean conductivity (453 S/cm at 25 C) in Lake Apopka at the tim e of sampling, decreased the efficiency of collecting fish, while using either brand of control box (Kolz 1989). Reynolds (2000) stated that conductivity was the single most important environmental factor in electrofishing. Temperature is also important. It affects the ability of the fish to float, respond, and escape (Reynolds 2000). Mean water chemistry parameters during sampling were 5.9 mg/L DO, 0.37 m SD, a nd 31.6 C water temperature (Table 5). The total catch rate in 2004 was 156 fish/h r. Mean catch for Canfield and Hoyer (1992), Hoyer (UF, unpublished data), and Johnson and Crumpton (1998) (1989 – 1993 data) were 203, 268, and 365 fish/hr, respectivel y (Figures 2 and 3). Comparison of the yearly mean total catch rate over time suggest s that the mean total abundance of fish has declined since 1993 in the near-s hore region in Lake Apopka (p 0.05).

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21 The total catch rate of this study was only tested for differences with Johnson and Crumpton (1998), for the data from 1989 – 1993, because the data of that time period were the most representative, of the different studies, of the fish populations in Lake Apopka, based on the fact that they took th e most samples (870 transects), bimonthly, over an extended period of time (5 years) (Materials and Me thods, Table 3). Canfield and Hoyer (1992) only sampled on one occasi on (9 transects). Hoyer (UF, unpublished data) only sampled the northern ha lf of the lake (62 transects). Johnson and Crumpton (1998) was the only st udy that used two electric booms. Using two booms could help explain why thei r mean total catch rate was higher than Canfield and Hoyer (1992) and Hoyer (UF, unpublished data) during the same, or close to the same, time period. If using two boo ms enabled Johnson and Crumpton (1998) to collect more total fish than they would have collected using just one it would result in a larger reported difference in the cat ch rate of total fish over time. Additionally, the mean total catch rate remained stable or increased from 1986 – 1993 (Figure 3). In 1993, the total catch rate seems to have declined dramatically. Johnson and Crumpton (1998) stated that th e abundance of open water fish species (gizzard shad, threadfin shad ( Dorosoma petenense ), blue tilapia, and black crappie ( Pomoxis nigromaculatus )) as well as centrarchids (blu egill, redear sunfish, and largemouth bass) all declined from 1989 – 1993 to 1996 – 1997. It was appropriate, therefore, to test for a decrease in the total cat ch rate from 1993 to 2004. Part of the reason for the decline in the to tal abundance of fish may be attributed to the extensive harvesting of gizzard shad. For example, Crumpton and Godwin (1997)

PAGE 30

22 reported that, from January 1993 through June 1997, commercial fishermen harvested over 5 million gizzard shad weighing about 2.3 million kg from Lake Apopka. Secondly, adverse environmental conditions present at the time of sampling could also have reduced the total catch rate in 2004. For example, Hurricane Charley passed over central Florida on 13 August (Nationa l Oceanic and Atmospheric Administration (NOAA) 2005), just five days prior to the da te that fish were sampled on 18 August. A widespread mud plume was observed in the center of the lake while sampling fish on that date. A widespread fish kill was also observe d across the entire north half of the lake. Additionally, the mean DO c oncentration (3.48 mg/L) for th e near-shore stations in August was low. Lastly, it is possible that the decrease in mean yearly chl a from about 97g/L in 1990 to 59 g/L in 2004 could have resulted in decreased productivity in the lake as well as a reduction in the abundan ce of open water fish species (Bachmann et al. 1996). These chl a values were based on unpublished da ta obtained from the SJRWMD. Because it was suspected that the adve rse environmental conditions in August 2004 affected the total catch rate, the 2004 tota l catch rate was divided by month. The mean total catch rates for June, July, and August were 149, 285, and 44 fish/hr, respectively. The mean total catch rate in August was much lower than the two previous months and contributed to the low total catch rate in 2004. Comparison of total catch rate among all the studies, by using the same months that were sampled in 2004, would have provided a direct comparison. Unfortunately, none of the previous studies sampled in the same months (June, July, and August) as this study in 200 4 (see Materials and Methods, Table 3).

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23 Comparison of the 2004 individual fish speci es percent of total, with Johnson and Crumpton (1998), for 1989 – 1993, suggests that ther e has been a decrease in percent of total fish for open water fish species (gizzard shad, threadfin shad, black crappie, blue tilapia, and brown bullhead) ove r time (Figures 4 and 5). These open water species composed 11% of the total fish number in 2004, a decrease from 56% of the total number in 1989 – 1993. These values represent a species composition change from open water species being most abundant in the near-sho re region in previous years (1989 – 1993) to centrarchids being dominant in 2004. A decr ease in gizzard shad and threadfin shad (from 34 to 5% of total fish numbers) contri buted the largest proportion of the change. No dramatic changes in the abundanc e of rare species were observed. Centrarchids (warmouth, bluegill, redear sunfish, and largemou th bass) comprised 78% of the fish collected in 2004, an incr ease from 29% of the fish in 1989 – 1993 (Figures 4 and 5). The most abundant spec ies in 2004 were bluegill and redear sunfish with catch rates of 86 and 16 fish/hr, respec tively (Table 6). The catch rates for these species in 1989 – 1993 were 73 and 18 fish/hr, respectively (Table 7). Comparison of the mean catch rate over time suggests that bluegill abundance is similar from previous years, even though there is a st atistical difference (p 0.05). This difference in the catch ra te of bluegill and redear sunfish over time is within a range expected from a stable fish populat ion, given the natural fluctuations in fish populations, and the temporal differences in sampling (Swingle 1950, Latta 1975, Ott and Longnecker 2001). Latta (1975) stated that the abundance of fish populations changes dynamically in response to changing envir onmental (e.g., temperature, wind, dissolved oxygen, competition, predation) and biological (e.g., reproduction, growth, and mortality)

PAGE 32

24 factors. Swingle (1950) stat ed that fish populations are regulated by the number of offspring in the present year, and the nu mber remaining in the population from the previous year. He also stated that fish populations dynamically change depending on the number and ratio of predator and forage fish present. Ott and Longnecker (2001) stated, that as time increases between sampling o ccasions, greater differences in abundance between samples can be expected. These change s in the abundance of bluegill and redear sunfish over time are not very big considering all of the possible stochastic environmental and biological changes over time, the amount of time that has passed between sampling occasions, and the natural variation in sampling. The catch rate of small (< 14 cm total leng th (TL)) bluegill and redear sunfish was 66 and 2.6 fish/hr, respectively, in 2004 (T able 8). The catch rate of large ( 14 cm TL) bluegill and redear sunfish was 20 and 14 fi sh/hr, respectively, in 2004. Bluegill and redear sunfish were dominated by small length classes in 2004, as in the past, based on summary data taken from Table 5 in Johnson and Crumpton (1998), and presented in this study (Table 8). Redear sunf ish reached slightly larger mean length than bluegill (Figures 6 and 7). Johnson and Crumpton ( 1998) reported that the annual mean catch rate of large ( 14 cm) bluegill and redear sunfish were lower in 1996 – 1997 than values from 1989 – 1993. Note that Johnson and Crumpton (1998) summary data was from 1989 – 1992 instead of for 1989 – 1993. The catch rate of bluegill and redear sunfish 14 cm seems to have rebounded in 2004 to be similar to values reported for 1989 – 1993 by Johnson and Crumpton (1998). The lake-wide largemouth bass catch rate in 2004 was 6.9 fish/hr. Canfield and Hoyer (1992), Hoyer (UF, unpublished data ), and Johnson and Crumpton (1998) (for

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25 1989 – 1993, and 1996 – 1997) collected 1.3, 0.8, 6.5, and 3.6 fish/hr, respectively (Figures 8 and 9). Comparison of the yearly mean largemout h bass catch rate over time shows that the mean catch rate of 6.9 fish/h r in 2004 was not statistic ally different from the combined mean catch rate of 6.5 fish/hr in 1989 – 1993 (p > 0.05), slightly more than one decade ago. This indicates that the la rgemouth bass population has not significantly increased in abundance over the last decade. The mean largemouth bass catch rate of th is study (6.9 fish/hr) was only tested for an increase in largemouth bass abundance w ith that of Johnson and Crumpton (1998) for 1989 – 1993 because mean catch rate of that study was the highest (6.5 fish/hr) of the previous studies (as well as the fact that thei r data were most representative of the fish populations in Lake Apopka, as explained earlie r). Testing for an increase in largemouth bass abundance with Johnson and Crumpton (1998) for 1989 – 1993, was more conclusive than testing for an increase with the other studies, which had lower mean catch rates. It should be noted, however, that if using two booms enabled Johnson and Crumpton (1998) to collect more largemouth ba ss than they would ha ve collected using just one boom, it would result in a smalle r reported difference in the catch rate of largemouth bass over time. Largemouth bass collected in 2004 ranged in size from 7.1 to 51.6 cm TL (Figure 10), and in calculated weight from 3.4 to 2096 g. There was a low catch rate of small (<24 cm) largemouth bass, as in previous years (T able 8). The fact that small fish (< 24 cm) are represented shows that repr oduction is occurring in Lake Apopka. Largemouth bass were absent from the 16 – 23.9 cm TL size group. This suggests that juveniles may be particularly vulnerable to predation and other sources of

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26 mortality at this size (Bever ton and Holt 1957). On a stat ewide basis, largemouth bass that average 24 cm TL are about 1 to 2 years old (Porak et al. 1999). The dominant size group in 2004 was 24 – 31.9 cm TL. If one-y ear-old fish are undergoing extremely high mortality, this size group woul d logically be a mixture of tw o-year-old and older fish. Largemouth bass that are recruite d into the larger size groups ( 24 cm) seem to be less susceptible to mortality as shown by the grea ter frequency of fish in those size groups. An alternative explanation for the absence of 16 – 23.9 cm fish is that fish in Lake Apopka have rapid growth (Dr. Charles Cich ra, professor, UF, pe rsonal communication). Sampling was conducted from June through August while largemouth bass in Apopka likely spawn from February through April. The small fish could thus be young-of-the year fish. Rapid growth could result in fi sh between one and two years old exceeding 24 cm TL by summer. Largemouth bass from Lake Apopka should thus be aged to determine whether the low abundance of 16 – 23.9 cm TL largemouth bass is due to high mortality or rapid growth. Largemouth bass are reproducing, growing, a nd recruiting to large size in Lake Apopka, but on a population basis, their abundance is low ( 7 fish/hr), especially when compared with other Florida lakes. Many Fl orida lakes have mean electrofishing catch rates of more than 20 largemouth bass/hr. For example, Lakes Okahumpka, Miona, Wales, Clear, Baldwin, and Susannah we re reported to have 26, 60, 92, 232, 42, and 129 fish/hr, respectively (Canfield and Hoyer 1992). Comparison of largemouth bass populati ons from Lake Apopka and 60 other Florida lakes, sampled by Canfield and H oyer (1992), shows that the abundance of largemouth bass at Lake Apopka in 2004 contin ues to be lower than expected for its

PAGE 35

27 trophic status as estimated by its chlorophy ll content (Figure 11). The relationship between largemouth bass and trophic status is positive suggesting that eutrophic and hypereutrophic Florida lakes will have a high abundance of largemouth bass (Bachmann et al. 1996). Lake Apopka is a hypereutrophic lake and in the absence of other limiting factors, it would be expected to have a high abundance of largemouth bass. But the results of this study as well as two out of three other previous studies on Lake Apopka indicate that the abundance of largemouth bass is low (F igure 11), suggesting that something is limiting their abundance. The am ount of quality habitat is most likely the limiting factor (Porak et al. 1999). The first year of life is critical to the su rvival of largemouth bass. The structure provided by aquatic vegetation, terrestrial brush, and rockpiles offers age-zero largemouth bass protection from predators (Aggus and Elliot 1975, Crowder and Cooper 1979, Savino and Stein 1982, Durocher et al. 1984, Dibble and Kilgor e 1994). Suitable prey such as zooplankton and small forage fish are more readily available in aquatic vegetation and other structur e than in open areas (Duroc her et al. 1984, Gutreuter and Anderson 1985, Dibble and Kilgore 1994). Availability of food of the proper type and size contribu tes to differential growth in young largemouth bass (Aggus and Elliot 197 5, Shelton et al. 1979, Timmons et al. 1980, Gutreuter and Anderson 1985, Olson 1996). Faster growing juveniles make the switch to piscivory earlier than slower growing fish (Gutreuter and Anderson 1985, Olson 1996). Rate of growth is one of the primary determinants of the recruitment of largemouth bass to stock size (Kramer and Smith 1962, Aggus and Elliot 1975, Olson 1996). A higher percentage of fast growing largemouth bass that reach a large size in

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28 their first winter are recruite d than slow growing fish (Kramer and Smith 1962, Davies et al. 1982, Gutreuter and Anderson 1985). Expanding cover in Lake Apopka would resu lt in a decrease in mortality of agezero largemouth bass due to decreased predation in their critical first year of life. Additionally, young-of-the-y ear largemouth bass would be ab le to obtain more of the proper type and size of food, thus enabling them to grow faster to maturity. As a result, a higher percentage of juvenile largemouth bass would likely be recruited to stock size in Lake Apopka. Submersed and emergent aquatic macrophytes provide additional benefits to both adult and young largemouth bass. They provide spawning substrate (Kramer and Smith 1962, Chew 1974) and protect spawning nests from wind and waves (Kramer and Smith 1962, Holcomb et al. 1975a, b). Aquatic macro phytes are an important component of the ecosystem of a lake (Durocher et al. 1984, Dibbl e et al 1996). Plants have the ability to affect water chemistry. Their abundance is inversely related with phytoplankton biomass as measured by chlorophyll, and is positively related to water clarity as measured by use of a Secchi disc (Canfield and Hoyer 1992). However, aquatic plants do not increase the lake-wide clarity of water nor decrease the phytoplankton biomass until there is 30 to 50% coverage (percent volume inhabited (P VI)) (Canfield and Hoyer 1992). A narrow belt of aquatic plants will not reduce lake-w ide phytoplankton biomass. A 15% coverage (PVI) could help largemouth bass populations, however, by providing critical habitat needed by age-0 largemouth bass during their first year of life (Canfield and Hoyer 1992).

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29 Aquatic plants could be part icularly helpful in solving problems associated with fluid sediments in Lake Apopka. They woul d help stabilize the bottom by anchoring the sediments (Carter and Rybicki 1985) and they would reduce turbidity from wind resuspension of the sediments (Canfield and Hoyer 1992, James and Barko 1994). Plants would additionally tend to reta rd large waves by baffling wa ve action and thus provide protection for less well-anchored species such as coontail ( Ceratophyllum demersum ) (Carter and Rybicki 1985) a nd reduce shoreline erosion (Canfield and Hoyer 1992). Previous studies have indicat ed that for some lakes, th e lack of aquatic vegetation can be detrimental to fish populations. For example, Canfield and Hoyer (1992) demonstrated in a 60-lake study of Florida lake s that there exists a potential for depressed fish populations at low levels of aquatic m acrophytes (< 15% coverage (PVI)). Porak et al. (1999) suggested that a lack of aquatic plants was detrim ental to the survival of young largemouth bass due to decrea sed shelter and food supply. In large, shallow Florida lakes withou t macrophytes, such as Lake Apopka, the shoreline habitat is the only refuge from pr edation for juvenile largemouth bass (Hoyer and Canfield (1996a, b). The limited shorel ine habitat in Lake Apopka may not be sufficient for adequate largemouth bass recruitm ent. The addition of about 15% coverage (PVI) of aquatic macrophytes or other stru cture would allow sufficient young-of-the-year largemouth bass to recruit into adulthood to allow Lake Apopka and other similar lakes to reach their carrying capacity (Hoyer and Canfield 1996a, b). Aquatic Macrophytes Lake Apopka continues to have a low abundance of aquatic macrophytes ( 0.9 percent area covered (PAC) and 0.4% PVI). The plants only occupied a narrow (mean = 19.4 m) belt around the shoreline in 2004, with a few exceptions. There were some

PAGE 38

30 isolated stands of soft-stem bulrush (8.5 ha) that existed around the perimeter and in the northern portion of the lake (Hog Island), as previously noted by Johnson and Crumpton (1998). Remnant stands of aquatic grass, pr imarily Egyptian paspalidium (1.5 ha), also existed in various places around the perimeter of the lake. Vegetated areas are import ant largemouth bass habita t. Johnson and Crumpton (1998) reported that soft-stem bulrush and aquatic grass (Egyptian paspalidium, maidencane, and torpedograss) sites contained the largest total mean biomass for all four principle sportfish species (largemouth bass, bluegill, redear sunfis h, and black crappie) in both 1989 – 1993 and 1996 – 1997 sampling periods for Lake Apopka. Total mean biomass for sportfish was lowest in open sites. The most commonly occurring plants in 2004 were cattail, duck potato ( Sagittaria lancifolia ), and pickerelweed ( Pontederia cordata ) (Table 9). No submersed vegetation existed in the open area of the lake outside of the narrow belt of emergent aquatic plants. Essentially, the rooted aquatic vegetation in Lake Apopka has not expanded in the last two decades and remains similar to what the lake had after the loss of its 80% coverage of aquatic plants in 1947 (Clugston 1963, Schneider and Little 1969, Holcomb 1977, Lake Apopka Restoration Counc il 1986, Johnson and Crumpton 1998). Eel-grass was the only submersed vascul ar aquatic macrophyte besides hydrilla that was observed in 2004. Eel-grass is a versatile submersed aquatic plant that is capable of surviving in a variety of growi ng conditions (Jaggers 1994) It can inhabit a variety of sediment types (sand, silty sand, or mud) (Korschgen and Green 1988, Catling et al. 1994). It is more shade adapted (Mey er et al. 1943) than se veral other submersed aquatic plants (e.g., Myriophyllum spp. and Potamogeton spp.) because of its

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31 physiological adaptability to low (1% Io) light regimes (Titus and Adams 1979, Carter and Rybicki 1985, Korschgen and Green 1988, Ca tling et al. 1994, Rybicki and Carter 2002). It is capable of surviving and even flourishing in eutrophic water (Catling et al. 1994, Jaggers 1994). It is also capable of making major comebacks after restoration (Carter and Rybicki 1990, Kimber et al. 1995a, b). Studies have reported, howeve r, that eel-grass, grown fr om tubers, did not survive in greater than 0.25 m of sediment (Car ter et al. 1985, Rybi cki and Carter 1986, Korschgen and Green 1988). Studies also f ound that there were significant population declines caused by excessive (numerically undefined) turbidity or highly variable turbidity (Korschgen and Green 1988, Jaggers 1994). Korschgen and Green (1988) noted that it was subject to uprooti ng by tropical storms. For exam ple, Tropical Storm Agnes, which struck the East Coast in 1972, was cited as a factor in the decr ease of eel-grass in different portions of the Chesapeake Bay (Kerwi n et al. 1976, Bayley et al. 1978). Carter et al. (1985) reported that stor m damage was also partially re sponsible for the decline of eel-grass in the Potomac River in the 1930s. They indicated that deposition of 0.15 – 0.25 m of sediments from storms were sufficien t to completely wipe out populations of eel-grass, naiad ( Najas gracillima and N. guadalupensis ), and common elodea ( Elodea canadensis ). Years or decades may be required fo r recovery after exceptionally severe storms (Carter et al. 1985). The growth of eel-grass in Lake Apopka has been a special concern to Florida agencies (Jaggers 1994). It is a valuable pl ant that is used as refuge and habitat for invertebrates and fish populations (Hoyer et al. 1996). Eel-grass was planted by the FFWCC to an unknown degree in the 1990s (W illiam Johnson, administrator, FFWCC,

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32 Eustis, FL, personal communication). It was also planted in plots around the shore of Lake Apopka by the SJRWMD during drought conditions in 1998 and 1999 (Conrow and Peterson 2000). Of the 23 eel-grass sites that were sampled, beds were present at 15 sites (Table 10). Twelve of the sites, wh ere eel-grass was present, were located on the west side of the lake; two closely spaced sites were located on the south side; and one site was located on the east side. No plants were found at se ven of the sites, and only a single plant was found at one site. All but two of the 15 beds were small (< 100 m2). There was one medium (279 m2) bed near Smith Island (on the west shoreline). There was another medium (536 m2) bed near Monteverde Boat Ramp (also on the west shoreline). No large (> 1000 m2) plant beds were found during this study. The density of the plant beds ranged from 1 to 100%. The average density of eelgrass was estimated to be 50%, at those site s where it was present. Hurricane Jeanne passed over central Florida on 25 Septembe r 2004 (NOAA 2005), one week before eelgrass was sampled on 1 October 2004. An attempt was made to find eel-grass uprooted by the recent hurricane, but only a couple of plants were observed to be uprooted. The total lake bottom colonized by eelgrass in 2004 was approximately 900 m2 (Table 10). The SJRWMD reported an area of 11,032 m2 in 1999 (Conrow and Peterson 2000). Therefore, the observed eel-grass ar ea in 2004 was only 8% of that reported by the SJRWMD. The drought in 1999 – 2000, followed by rising waters in 2000 should have created ideal growing conditions for the expansion of eel-grass. The natural drawdown would have oxidized and compacted the exposed sediments. Oxidation would have released nutrients from the soil, s timulating plants to regenerate and expand

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33 (Wegener and Williams 1974, Moyer et al. 1995) Compaction of the soil would have provided a firmer bottom for rooting and holding plants. However, this study shows that eel-grass drastically declined during the past five years at Lake Apopka. This suggests that there is a limiting factor that is prev enting eel-grass from su rviving and expanding. Studies in the upper Mississippi River and Chesapeake Bay (C arter and Rybicki 1990, Kimber et al. 1995a, b) reported that eel-grass only grew to 12 – 15% incident light (Io ) because of turbidity in the water colu mn caused by suspended sediments. Later, when the turbidity from suspended sediment s was reduced through restoration efforts, eel-grass recolonized those st udy sites, but only grew down to depths of 5 – 10% Io. The observed and theoretical MDC and M DG of eel-grass, in Lake Apopka in 2004, were compared to determine if eel-gra ss was growing to its potential depth, as referenced by the primary literature. The observed MDC and MDG of eel-grass in June – August 2004 were 1.3 and 0.8 m, respectively, at a mean lake surface elevation of 20.3 m (66.5 ft) National Geodetic Vertical Datu m 1929 (NGVD 29). Hydrologic data were obtained from the SJRWMD (2005). The th eoretical MDC and MDG were 1.3 and 1.0 m based on the mean depths corresponding to light meter measurements of 1 and 8% Io. Eel-grass, therefore, seems to be growing near its potential MDC and MDG because the observed values of MDC and MDG agree closely to the theoretical values. However, the four hurricanes (Charlie Frances, Ivan, and Jeanne, NOAA 2005), all of which occurred before my sampling, that passed over Florid a in the summer of 2004, dropped 0.4 m of total precip itation, and undoubtedly influenced the results. When the hurricanes are accounted for by cal culating the observed MDC and MDG at a lower lake level (20.0 m, NGVD 29), eel-grass would be predominantly growing at 12 –

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34 15% Io and reaching a maximum depth at 5% Io. These results i ndicate that other environmental factors are limiting the depth of growth of eel-grass other than light attenuation. The area of the lake that is available for eel-grass to colonize and grow at the observed MDC and MDG (at lake surface elev ation 20.3 m, NGVD 29) was calculated to be 3940 and 848 ha, respectively. As a percent, eel-grass is only inhabiting 0.002% of the 3940 ha available at MDC and 0.011% of the 848 ha available at MDG under the current light regime, strongly indicating that other factors are involved in limiting the growth and survival of eel-g rass besides light attenuation. The 3940 and 848 ha, at MDC and MDG, repres ents an estimated 32% of the lake available for eel-grass to colonize and 7% of the lake available to grow in under the current light regime. This indicates that there is enough irradiance in the water column for eel-grass to colonize in shallow water around the shorelin e of the lake but that the light conditions in the water column need to significantly improve be fore eel-grass can be expected to grow well enough to occupy a la rger proportion of the total lake area. There is a general belief that irradiance primarily controls the depth-distribution of aquatic macrophytes (Barko and Smart 1981, Chambers and Kal ff 1985, Carter and Rybicki 1990). Studies have recognized, however, that other environmental factors besides nutrient enrichment and phytoplankt on shading are also responsible for limiting aquatic macrophyte colonization. Chambers and Kalff (1985) stated th at wave action and substrate type also play a major role in determining the distribution and abundance of aquatic macrophytes. Spence (1972) indicat ed that turbulence and wave action influenced aquatic macrophyte co lonization. Carter et al. (1 985) reported that, other than

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35 phytoplankton, storm pressure, grazing pressure, substrate characterist ics, and suspended sediments are all factors that in different circumstances coul d be individually or jointly responsible for limiting the depth-distribution (or spatial extent) of aquatic macrophytes. Eel-grass in this study was only found at sites having firm sediments and not at any sites with sediments deeper than 0.25 m. These observati ons agree with studies that reported that eel-grass, grown from tubers, did not survive in gr eater than 0.25 m of sediment (Carter et al. 1985, Rybicki and Carter 1986, Korschgen and Green 1988). The depth of sediments (1.5 m mean thickness) covering 90% of Lake ApopkaÂ’s bottom (Schneider and Little 1969) is too thick to allow eel-grass to inhabit those areas. The depth and fluidity of sediments, and wind re suspension of sediments, are probably major factors that are limiting the growth and survival of eel-g rass in Lake Apopka. These hypotheses are supported by the fact that Lake Apopka is a large, shallow, and nearly round lake with a long fetch (Bachmann et al. 1999). Because of these combined attributes, the bottom sediments are often resu spended in the lake (Scheffer et al. 1992, Bachmann et al. 1999). Carter et al. (1985) stated that where fetches are long, eel-grass plants are easily uprooted from fine sediments.

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36 Table 4. Common and scientific names of fish collected by individu al studies at Lake Apopka, Florida. Common Name Scientific Name Canfield and Hoyer (1992) (for 1986) Hoyer (UF) (unpubl. data) (1987-1989) (1991-1996) Johnson and Crumpton (1998) (for 1989-1993) This Study (for 2004) Florida gar Lepisosteus platyrhincus x x x x Longnose gar Lepisosteus osseus x x Bowfin Amia calva x x Gizzard shad Dorosoma cepedianum x x x x Threadfin shad Dorosoma petenense x x x x Black crappie Pomoxis nigromaculatus x x x x Blue tilapia Tilapia aurea x x x Golden shiner Notemigonus crysoleucas x x x Lake chubsucker Erimyzon sucetta x Taillight shiner Notropis maculatus x x Yellow bullhead Ameiurus natalis x x x x Brown bullhead Ameiurus nebulosus x x x x Channel catfish Ictalurus punctatus x x x White catfish Ictalurus catus x x x Tadpole madtom Noturus gyrinus x x x Seminole killifish Fundulus seminolis x x x x Bluefin killifish Lucania goodei x Eastern mosquitofish Gambusia holbrooki x x x x Sailfin molly Poecilia latipinna x Pugnose minnow Opsopoeodus emiliae x Brook silverside Labidesthes sicculus x x Inland silverside Menidia beryllina x x Tidewater silverside Menidia peninsulae x x Everglades pygmy sunfish Elassoma evergladei x Warmouth Lepomis gulosus x x x Bluegill Lepomis macrochirus x x x x Redear sunfish Lepomis microlophus x x x x Spotted sunfish Lepomis punctatus x Largemouth bass Micropterus salmoides x x x x Sunshine bass Morone chrysops X M. saxatilis x x Atlantic needlefish Strongylura marina x x

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37 Table 5. Water chemistry parameters measur ed for Lake Apopka, Florida, in June – October 2004. Water Quality Parameter Location Number of Samples Average Range Dissolved oxygen (mg/L) Near shore stations 16 5.9 (0.8 – 11.9) Secchi depth (m) Near shore stations & center of the lake 18 0.37 (0.20 – 0.49) Specific conductance (S/cm at 25 C) Near shore stations 12 453 (403 – 506) Water temperature (C) Near shore stations 10 31.6 (29.5 – 33.7) Table 6. Mean electrofishing catch per unit effort and standard error of fish number (number/hr) and weight (kg/hr) for Lake Apopka, Florida. Forty 10-min transects were sampled in June – August 2004. Common Name Number (number/hr) Standard Error Calculated Weight (kg/hr) Standard Error Florida gar 7.41.285.6 0.99 Longnose gar 0.60.360.2 0.11 Bowfin 0.80.320.9 0.43 Gizzard shad 6.62.150.8 0.29 Threadfin shad 1.70.740.0 0.00 Black crappie 6.91.301.2 0.31 Blue tilapia 0.80.380.4 0.17 Yellow bullhead 0.20.150.0 0.03 Brown bullhead 1.70.610.6 0.22 Channel catfish 0.60.470.1 0.07 Tadpole madtom 0.50.330.0 0.00 Seminole killifish 2.70.860.0 0.01 Eastern mosquitofish 3.51.340.0 0.00 Brook silverside 0.20.150.0 0.00 Inland silverside 0.30.210.0 0.00 Warmouth 12.63.850.8 0.24 Bluegill 86.420.524.1 1.05 Redear sunfish 16.45.051.6 0.47 Largemouth bass 6.91.604.1 1.11 Atlantic needlefish 0.20.150.0 0.01 Total 156.5 20.3

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38 Table 7. Mean yearly and combined electrof ishing catch per unit effort and standard error of fish number (number/hr) fo r Lake Apopka, Florida, by Johnson and Crumpton (1998). Eight hundred seventy 5-min transects were sampled bimonthly from March 1989 to November 1993. Number (number/hr) Common Name 19891990199119921993 Combined 1989-1993 Standard Errora Florida gar 3.93.65.16.18.3 5.40.85 Longnose gar 0.30.51.70.71.1 0.90.24 Bowfin 0.80.70.60.70.8 0.70.04 Gizzard shad 101.871.859.343.442.5 63.810.96 Threadfin shad 49.447.1107.556.037.3 59.612.38 Black crappie 26.233.734.852.368.8 43.27.71 Blue tilapia 7.17.68.515.317.7 11.22.18 Golden shiner 9.27.97.15.26.5 7.20.67 Taillight shiner 2.66.84.66.58.2 5.70.98 Yellow bullhead 2.61.41.41.82.9 2.00.31 Brown bullhead 45.025.724.814.422.5 26.55.04 Channel catfish 0.10.00.00.00.0 0.00.0 White catfish 0.60.91.83.816.5 4.73.00 Tadpole madtom 0.00.00.00.10.0 0.00.01 Seminole killifish 3.67.412.810.89.3 8.81.57 Eastern mosquitofish 4.210.67.36.17.4 7.11.05 Sailfin molly 0.10.70.50.30.6 0.40.12 Pugnose minnow 0.00.00.10.00.0 0.00.01 Brook silverside 0.00.00.01.90.0 0.40.37 Inland silverside 12.315.715.96.13.5 10.72.53 Warmouth 5.66.04.39.511.7 7.41.37 Bluegill 62.067.355.397.683.2 73.17.67 Redear sunfish 11.118.115.321.124.6 18.12.33 Spotted sunfish 0.50.20.10.00.0 0.10.09 Largemouth bass 5.66.55.97.96.2 6.50.41 Atlantic needlefish 0.10.10.10.20.3 0.20.03 Total 356.0341.0375.0369.0381.0 364.07.17aThe combined catch per unit effort number (number/ hr) was averaged by month and then by year to obtain the standard error.

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39 Table 8. Annual mean electrofishing catch per unit effort number (number/hr) of two size groups of largemouth bass, bluegill, and redear sunfish collected in Lake Apopka, Florida, by Johnson and Crumpton (1998) for June – May of 1989 – 1990, 1990 – 1991, and 1991 – 1992, and November 1996 – September 1997 (bimonthly samples), and by this study for June – August 2004 (once monthly samples). Common Name 1989-1990a1990-1991a1991-1992a1996-1997 2004 Largemouth bass ( 24 cm) 4.84.86.02.4 6.0 Largemouth bass (< 24 cm) 2.41.21.21.2 0.9 Bluegill ( 14 cm) 22.818.020.415.6 20.0 Bluegill (< 14 cm) 40.854.066.031.2 66.5 Redear sunfish ( 14 cm) 9.69.69.61.2 13.8 Redear sunfish (< 14 cm) 4.86.012.0 3.6 2.6a Summary data from 1989 – 1992 and 1996 – 19 97 were taken from Johnson and Crumpton (1998), Table 5, which did not report the catch rate of size groups in 1993. Table 9. Occurrence of plant species in twenty evenly-spaced transects around Lake Apopka, Florida, in 2004. Common Name Scientific Name Percent of Transects Aquatic Plants Cattail Typha spp. 95 Duck potato Sagittaria lancifolia 65 Pickerelweed Pontederia cordata 45 Soft-stem bulrush Scirpus validus 30 Water pennywort Hydrocotyle umbellata 30 Egyptian paspalidium Paspalidium geminatum 25 Water primrose Ludwigia octovalvis 25 Eel-grass Vallisneria americana 20 Wild taro Colocasia esculenta 15 Torpedograss Panicum repens 10 Hydrilla Hydrilla verticillata 5 Terrestrial Brush Carolina willow Salix caroliniana 50 Elderberry Sambucus canadensis 15 Wax myrtle Myrica cerifera 15 Hardwood Mixture Red maple Acer rubrum 30 Loblolly-bay Gordonia lasianthus 15 Sweetbay Magnolia virginiana 15

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40 Table 10. Location, area (m2), and maximum depth (m) of eel-grass beds in Lake Apopka, Florida, in 2004. GPS Locations Area (m2) Reported by the SJRWMD in 1999 (unpublished dataa) Area (m2) Measured in 2004 Maximum Depth of Plant Bed (m) Twenty three sites where eel-grass beds were sampled on 1 October 2004 X:-81.66268 Y:28.59395 1465.0None sighted — X:-81.66999 Y:28.60700 1277.3(one plant) 1.0 0.9 X:-81.65463 Y:28.59138 885.3None sighted — X:-81.67006 Y:28.60724 517.9Includedb 0.9 X:-81.65359 Y:28.68176 510.9None sighted — X:-81.67829 Y:28.61896 494.4278.9 0.9 X:-81.67803 Y:28.61925 355.729.2 0.9 X:-81.60593 Y:28.56912 333.02.6 0.9 X:-81.67317 Y:28.61035 310.5536.0 1.4 X:-81.54957 Y:28.62397 308.08.3 0.5 X:-81.65332 Y:28.68184 281.9None sighted — X:-81.68426 Y:28.66171 240.8None sighted — X:-81.67196 Y:28.60970 237.4Includedb 1.4 X:-81.66989 Y:28.60720 201.8Includedb 0.9 X:-81.67787 Y:28.62014 199.51.8 0.9 X:-81.65359 Y:28.68210 174.0None sighted — X:-81.60584 Y:28.56924 165.2Includedb 0.9 X:-81.69429 Y:28.64223 93.5None sighted — X:-81.68031 Y:28.62056 55.510.5 0.9 X:-81.68025 Y:28.62054 54.5Includedb 0.9 X:-81.66973 Y:28.60674 41.6Includedb 0.9 X:-81.58700 Y:28.57731 27.0None sighted — X:-81.68030 Y:28.62049 12.121.0 0.9 Total 8242.7 889.3 Six sites where eel-grass beds were observed while electrofishing in June – August 2004c X:-81.64903 Y:28.58658 —1.8 0.9 X:-81.64948 Y:28.58717 —1.8 0.9 X:-81.64950 Y:28.58781 —1.8 0.9 X:-81.67127 Y:28.60920 —1.8 0.9 X:-81.67183 Y:28.60972 —1.8 0.9 X:-81.66442 Y:28.59677 —1.8 0.9 Total 10.8 aThe data shown here for 23 sampling sites are a subset of the unpublished data set obtained from the SJRWMD. The total area for all the eel-grass beds in the data set is 11032.1 m2, which includes only the area of the plant beds in the major part of the lake and not the area of those in the gourd neck area, Marsh Flow-Way, or canals. b The SJRWMD reported beds that were near each othe r as separate beds, identified with separate GPS coordinates. At some of the sites reported by the SJRWMD to have multiple beds, only one bed was found, or in some instances the boundry separating multiple beds was not distinguishable. In these instances, the total area (m2) of closely spaced bed locations was recorded only once at the GPS coordinates of one bed. The area (m2) of any nearby beds was annotated as included. cThe six eel-grass beds observed while electrofishing we re nearly identical in area and maximum depth.

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41 0 50 100 150 200 250 300 350 400 450 5001 9 86 1 9 87 1988 1989 1990 1991 199 2 199 3 199 4 1 99 5 1 99 6 1 99 7 1 99 8 1 9 99 2 0 00 2 0 01 2 0 02 2 0 03 2 0 04CPUE of Total Fish (number/hr) Figure 2. Mean electrofishing catch per unit effort estimates of total fish abundance (number/hr) for Lake Apopka, Florida, sampled by Canfield and Hoyer (1992) ( ), Hoyer (UF, unpublished data) ( ), Johnson and Crumpton (1998) ( ), and this study ( ). Data were not availabl e for Johnson and Crumpton (1998) for 1996 – 1997. 0 50 100 150 200 250 300 350 400 Canfield and Hoyer (1992) (for 1986) Hoyer (unpubl. data) (for 1987 1989, 19911996) Johnson and Crumpton (1998) (for 1989 1993) This Study (for 2004)CPUE of Total Fish (number/hr) Figure 3. Mean electrofishing catch per unit effort estimates of total fish abundance (number/hr) for the combined data of different studies for Lake Apopka, Florida.

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42 0 5 10 15 20 25Flori d a ga r Longnose gar B owfin G izzard s h ad Threa d fi n s ha d B lack cr ap pie B l ue tila pi a G ol de n s hi ner Taillight shiner Yel l ow bul l he ad Brown b ullhead Chann el ca t f i sh W hi t e c at f i sh Tad po le m a dtom Se m i nol e killifis h Ea s tern m osq ui tofi s h S ai l fin m ol l y Pugnose minnow Br oo k sil v ers i de In la nd s i l ve rs i de W armouth B luegill Redear sunfish Spot t ed sunf i s h Lar ge mo ut h bass At l antic nee d lefishCommon NamePercent of Total Number of Fish Figure 4. Individual fish speci es percent of total number collected by electrofishing for Lake Apopka, Florida, by Johnson and Crumpton (1998) for 1989 – 1993. 0 5 10 15 20 25Florida gar Lon gnose gar B ow fin Gizzard shad Thr ea dfin s had Bl ac k cr ap pi e B l u e t i l apia G ol den shiner Tai l l i ght s hi ner Yel l ow B ul l he ad B r own bu l l he ad Channel catfish White catfish T a dpol e madt o m Seminole k illifi s h Ea st e rn m osq ui t of i sh S ai l f i n molly Pug nos e m i nn ow Broo k silv er side I nl a nd silversideWar m ou t h Bl ue gi l l R ed ea r sunf i s h Spo tt e d s unfish Largem o uth bas s Atl a nt i c need l ef i shCommon NamePercent of Total Number of Fish55.2 Figure 5. Individual fish speci es percent of total number collected by electrofishing for Lake Apopka, Florida, in June – August 2004.

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43 0 50 100 150 200 250 300 0.0-3.94.0-7.98.0-11.912.0-15.916.0-19.920.0-23.924.0-27.9 Total Length (cm)Frequency Figure 6. Length frequency distribution of bl uegill collected by elec trofishing for Lake Apopka, Florida, in June – August 2004. 0 10 20 30 40 50 60 70 0.0-3.94.0-7.98.0-11.912.0-15.916.0-19.920.0-23.924.0-27.9 Total Length (cm)Frequency Figure 7. Length frequency distribution of re dear sunfish collected by electrofishing for Lake Apopka, Florida, in June – August 2004.

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44 0 1 2 3 4 5 6 7 8 9 101 9 8 6 1 9 8 7 1 9 8 8 1 9 8 9 1 9 9 0 1 9 9 1 1 9 9 2 1 9 9 3 1 9 9 4 1 9 9 5 1 9 9 6 1 9 9 7 1 9 9 8 1 9 9 9 2 0 0 0 2 0 0 1 2 0 0 2 2 0 0 3 2 0 0 4CPUE of Largemouth Bass (number/hr) Figure 8. Mean electrofishing catch per uni t effort estimates of largemouth bass abundance (number/hr) for Lake Apopka, Florida, sampled by Canfield and Hoyer (1992) ( ), Hoyer (UF, unpublished data) ( ), Johnson and Crumpton (1998) ( ), and this study ( ). 0 1 2 3 4 5 6 7 8 9 Canfield and Hoyer (1992) (for 1986) Hoyer (unpubl. data) (for 19871989, 19911996) Johnson and Crumpton (1998) (for 1989 1993) Johnson and Crumpton (1998) (for 1996-1997) This Study (for 2004)CPUE of Largemouth Bass (number/hr) Figure 9. Mean electrofishing catch per uni t effort estimates of largemouth bass abundance (number/hr) for the data sets of combined years from different studies for Lake Apopka, Florida.

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45 0 2 4 6 8 10 12 14 16 18 0.0-7.98.0-15.916.0-23.924.0-31.932.0-39.940.0-47.948.0-53.9 Total Length (cm)Frequency Figure 10. Length frequency di stribution of largemouth bass collected by electrofishing for Lake Apopka, Florida, in June – August 2004. 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 0.00.51.01.52.02.5 Log Chlorophyll a (ug/L)Log CPUE Largemouth Bass (kg/h Figure 11. Electrofishing catch per unit effort of largemouth bass (kg/hr) versus total chlorophyll a (g/L) for 60 Florida lakes sampled by Canfield and Hoyer (1992) and Lake Apopka, Florida, samp led by Canfield and Hoyer (1992) ( ), Hoyer (UF, unpublished data) ( ), Johnson and Crumpton (1998) ( ), and this study ( ). A regression line is included.

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46 LAKE MANAGEMENT RECOMMENDATIONS Restoration efforts have not yet been successful in in creasing the largemouth bass population or expanding the area occupied by aq uatic vegetation in Lake Apopka. It is up to lake managers to come up with ideas to improve the largemouth bass fishery so that anglers can enjoy recreationa l fishing in the lake. A drawdown was proposed by the USEPA as part of its environmental impact statement in 1978 as a way to improve the largemouth bass fishery (USEPA 1979). Do wndraw has been a successful tool by increasing the water clarity and littoral vege tation in several Florida lakes including Lakes Tohopekaliga, Trafford, Hancock, a nd Griffin (USEPA 1979). However, a drawdown was not recommended by the SJRWMD for Lake Apopka for several reasons including the high cost (of at least $20 million) and increased nutrient flow to downstream lakes (Lowe et al. 1992). A dditionally, there were concerns over the quantity of water to be pumped, the amount of unconsolidated muck, the type of vegetation that would grow, and the re strictive time sche dule (USEPA 1979). Conditions in Lake Apopka have changed since 1979. Over $100,000,000 in Federal and State funds was sp ent to buy out farms, to reduce or eliminate nutrient-rich pumpage back into the lake, and to constr uct a marsh flow-way, to remove phosphorusrich particles from the la ke water (Conrow et al. 1993, Hoge et al. 2003). Mean phosphorus levels dropped from over 200 g/L in 1979, to about 100 g/L, in 2004. The Lake County Water Authority also recently prop osed building an alum treatment plant for Lake Apopka that would help reduce phosphorus levels even more. In light of these

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47 improvements, it would be a good idea to r econsider drawdown. The concern over increased nutrient flow to downstream lakes is no longer as big of an issue in 2004, as it was in 1979, because nutrient levels are lower now, than they were before. Since a drawdown was not approved and may never be approved, the next step for lake managers is to look for other viable al ternative strategies that could potentially improve the largemouth bass fishery in Lake Apopka. Other alternat ive ideas have been proposed that could potentially improve the habitat for la rgemouth bass in Lake Apopka, but have not been acted upon by the state agencies For example, artifi cial reefs could be placed along the shoreline as habitat for larg emouth bass and other littoral fish (Canfield et al. 2000). Canfield et al (2000) also suggested allowing hydrilla, a fast-growing exotic submersed aquatic plant, to grow behind the protective barriers to provide habitat for largemouth bass. If at least 50% covera ge (PVI) of submerse d aquatic vegetation occurred, it would be enough for the water to start to clear in those local areas and provide additional benefits (Canfield and Hoyer 1992). Hydrilla is an exotic aquatic plant that has invaded many lakes. It will often outcompete native aquatic macrophyte species an d expand to fill in an entire water body, and interfere with navigation and other uses of a water body (Hoyer et al. 2005). Control of hydrilla across lakes has been unsuccessful (H oyer et al. 2005). It spreads from one water body to another when fragments and tubers left attached to vehicles, trailers, or propellers, are transported from one water body to another. It also spreads when fragments and tubers, from one water body, drif t into another attached water body. It costs a tremendous amount of money, to pur chase herbicides and equipment, and to provide manpower to control it. Allowing hydri lla to grow anywhere in Florida lakes,

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48 such as suggested by Canfield et al. (2000), is controversial. However, Lake Apopka historically had about 80% a quatic macrophyte coverage (PVI). So it should not be a big issue if hydrilla were to expand in to the open area of this lake. Recent studies have stated that in certa in situations, native aquatic macrophytes will grow in close association with hydrilla For example, Rybi cki and Carter (2002) found populations of eel-grass, Eurasian wa ter milfoil ( Myriophyllum spicatum ), and coontail growing within hydrilla and along the edges, in portions of the Potomac River recovering from poor water transparency and high turbidity. Smart (1992), in experimental plots, that were monitored for a duration of one year, showed that Illinois pondweed, eel-grass, and hydrilla, that were pl anted in randomly assigned plots, could grow together for one year, as long as Illinois pondweed and eel -grass were planted before or at the same time as hydrilla. Il linois pondweed and hydrilla grew in the canopy and eelgrass grew in the understory. Smart (1992) stated that eel-g rass is considered to be a later successional species than hydrilla. In the long r un, eel-grass should theoretically be able to recolonize areas that were formerly dominated by hydrilla. Th ere is evidence in Florida lakes that native aquatic macrophyte species recolonized areas that were dominated by hydrilla for several years. For example, Lake Okahumpka, Fl orida, was dominated by hydrilla for several years, in the late 1990s and early 2000s (Mark Hoyer, res earch manager, UF, personal communication). A regular maintenance c ontrol program, in the early 2000s, using contact herbicides, put hydr illa into submission. Native submersed aquatic macrophyte species (e.g., Illinois pondweed and eel-grass) recolonized areas pr eviously dominated by hydrilla.

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49 Hydrilla is already present in small qu antities in Lake Apopka. Erich Marzolf (environmental scientist, SJRWMD, Palatka, FL, personal communica tion) stated that contact herbicide is applied regularly by the SJRWMD to keep it from expanding. Eelgrass and hydrilla beds were observed near each other during this study at Lake Apopka in 2004. Eel-grass plants were also observed growing within hydrilla beds and along the edges. Evidence from Lake Okahumpka, Florida (a hypereutrophic lake similar to Lake Apopka), and from Lake Apopka itself, suggests that if hydrilla were allowed to grow in small quantities ( 15% PVI) around the periphery of Lake Apopka, to provide habitat for largemouth bass, that no more than the already existing maintenance control program using contact herbicides woul d be required to keep hydrilla in check, and that native submersed aquatic macrophyte species (e.g., Illinois pondweed and eel-grass) could coexist with hydrilla. Erich Marzolf also raised c oncerns about not being able to control hydrilla and it spreading to downstream lakes, if it were allowed to grow. Hydrilla is already in the lakes that are downstream of Lake Apopka. Maintenance contro l of hydrilla, with contact herbicides, is already needed as well, in those lakes. La kes Beauclair and Dora, the nearest downstream lakes from Lake Apopka, are separated from Lake Apopka by the Apopka-Beauclair Canal that is about 48 km long, and about 10 m average width. Should hydrilla be allowed to grow in limited areas in Lake Apopka, the likelihood of invasion by hydrilla, by fragment s and tubers drifting to those downstream lakes would be reduced to minimal risk because the Apopka-Beauclair Canal is a long and narrow canal. Additional expenditures might be needed to control hydrilla in Lake Apopka and

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50 in downstream lakes, if hydrilla were allowe d to grow in limited ar eas in Lake Apopka. It might be appropriate for lake managers to perform a cost assessment to balance the income from a largemouth bass fishery to the surrounding community against the additional expenditures need ed to control hydrilla. Hypereutrophic lakes function differently than other lakes. Authors have suggested in recent years that hydrilla can benefit hypereutrophic lakes such as Lake Apopka where both light attenuation and deep sediments prevent na tive vegetation from colonizing major parts of the lake (Moxl ey and Langford 1982, Canfield and Hoyer 1992, Porak et al. 1999, Hoyer et al. 2005) by providing habitat, food resources, and refugia for fish and wildlife (Aggus and Elliot 1975, Duro cher et al. 1984, Dibble and Kilgore 1994, Dibble et al. 1996, Porak et al 1999). Canfield et al. (2000) suggested that the combination of light attenuation and wind re suspension of sediments in Lake Apopka should prevent hydrilla from filling in the open area of the lake in the same way that native plants are now being prevented from co lonizing that area. In a hydrilla workshop (Hoyer et al. 2005), it was recommended for hype reutrophic lakes lik e Lake Apopka that a regular control program such as the progr am now in affect in Lake Apopka, using contact herbicides to control hydrilla, in k eeping with the management objectives aimed at improving the sports fishery, may represent a more practical and viab le alternative than completely eliminating hydrilla. There is controversy between aquatic w eed specialists, that recommend not letting hydrilla grow in any Florida lakes, and fisher men and UF biologists that say that a small amount ( 15% coverage (PVI)) of hydrilla should improve the largemouth bass fishery.

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51 Perhaps allowing hydrilla to grow in limited areas in Lake Apopka should be considered again, despite the debate. A key lake management action should be to balance the need s of anglers with other members of the community that enj oy looking at or boating in an open lake (Canfield et al. 2000). If the entire lake were to be completely covered with aquatic macrophytes, largemouth bass anglers would enjo y fishing there, but the general public would likely perceive the profuse growth of aquatic macrophytes as an aquatic weed problem. If lake managers allowed the lake to have about 15% cove rage (PVI) of rooted aquatic vegetation, they could make angler s happy by improving the sport fishing and also keep other members of the community happy by keeping most of the lake open (Canfield et al. 2000). If the expansion of hydrilla is not to be allowed, then another alternative to mitigate the loss of largemouth bass would be stocking. Management efforts have been conducted at Lake Apopka for several decades to improve the environmental conditions in the lake (Conrow et al. 1993, Hoge et al. 2003 ). In lieu of the recent improvements, it is a good time to stock largemouth bass into Lake Apopka. Previous stocking by the FFWCC in 1990, using small fry, did not result in adequate survival to produce a fisher y (Johnson and Crumpton 1998). Because that stocking was not successful in producing a fi shery, the FFWCC could use fingerlings or advance fingerlings. The use of advanced finge rlings to stock Lake Talquin, Florida, has been more successful than stocking projects at Lake Apopka, which used smaller fish (Dr. Daniel E. Canfield, Jr., profe ssor, UF, personal communication).

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52 Stocking larger ( 24 cm) wild largemouth bass into Lake Griffin enhanced the economic activity in the surrounding community (C anfield et al. 2005). If fingerlings or advanced fingerlings were stocked into Lake Apopka, and fishermen caught them, anglers would come back. It could improve the economic viability of the largemouth bass fishery in Lake Apopka. Of course, it would be more viable to stock largemouth bass into Lake Apopka once protected, vegetate d areas were establis hed. The additional plants would also make it easier for anglers to locate the fish.

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53 LIST OF REFERENCES Aggus, L. R. and G. V. Elliott. 1975. Effect s of cover and food on year-class strength of largemouth bass. P. 317-322. In R. H. Stroud and H. Cl epper (eds.). Black bass biology and management. Sport Fi shing Institute, Wash., DC. Andrus, C. 2000. Experiences from the field: alcove sampling on the Willamette River, OR. P. 43-46. In S. M. Allen-Gil (ed.). New pe rspectives in electrofishing. EPA/600/R-99/108. USEPA, Wash., DC. Bachmann, R. W., B. L. Jones, D. D. Fox, M. V. Hoyer, L. A. Bull and D. E. Canfield, Jr. 1996. Relations between trophic state indicators and fish in Florida (U.S.A.) lakes. Can. J. Aquat. Sci. 53:842-855. Bachmann, R. W., M. V. Hoyer and D. E. Canfield, Jr. 1999. The restoration of Lake Apopka in relation to alternative stable states. Hydrobiol. 394:219-232. Bachmann, R. W., M. V. Hoyer and D. E. Canfield, Jr. 2000a. The potential for wave disturbance in shallow Fl orida lakes. Lake and Reserv. Manage. 16(4):281-291. Bachmann, R. W., M. V. Hoyer and D. E. Canfield, Jr. 2000b. Internal heterotrophy following the switch from macrophytes to algae in Lake Apopka, Florida. Hydrobiol. 418:217-227. Bachmann, R. W., M. V. Hoyer and D. E. Canfield, Jr. 2001a. Evaluation of recent limnological changes at Lake Apopka. Hydrobiol. 448:19-26. Bachmann, R. W., M. V. Hoyer and D. E. Canfield, Jr. 2001b. Sediment removal by the Lake Apopka marsh flow-way. Hydrobiol. 448:7-10. Barko, J. W. and R. M. Smart. 1981. Compara tive influences of light and temperature on the growth and metabolism of selected submersed freshwater macrophytes. Ecol. Monogr. 51(2):219-235. Barko, J. W., D. G. Hardin and M. S. Matthews. 1982. Growth and morphology of submersed freshwater macrophytes in relation to light and temperat ure. Can. J. Bot. 60:877-887. Bayley, P. B. and D. J. Austen. 2002. Capture efficiency of a boat el ectrofisher. Trans. Am. Fish. Soc. 131:435-451.

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54 Bayley, S., V. D. Stotts, P. F. Springer and J. Stennis. 1978. Changes in submerged aquatic macrophyte populations at the h ead of Chesapeake Bay, 1958-1975. Estuar. 1(3):171-182. Beverton, R. J. H. and S. J. Holt. 1957. On the dynamics of expl oited fish populations. Fishery investigations series II. Marine Fisheries Great Britain, Ministry of Ag., Fish., and Food 19:1-533. Bintz, J. C. and S. W. Nixon. 2001. Responses of eelgrass Zostera marina seedlings to reduced light. Mar. Ecol Prog. Ser. 223:133-141. Blanch, S. J., G. G. Ganf and K. F. Walker. 1998. Growth and recruitment in Vallisneria americana as related to average irradiance in the water column. Aquat. Bot. 61:181-205. Canfield, D. E., Jr. and M. V. Hoyer. 1992. A quatic macrophytes and their relationship to the limnology of Florida lakes. SP115. In stitute of Food and Agricultural Science (IFAS), UF, Gainesville, FL. 612 p. Canfield, D. E., Jr., M. V. Hoyer and F. Bennett. 2005. Restoration of the economic vitality of Lake GriffinÂ’s largemouth bass fishery. Final report. Submitted to: Lake County Water Authority, Tavares, FL. Department of Fisheries and Aquatic Sciences (FAS), IFAS, UF, Gainesville, FL. 103 p. Canfield, D. E., Jr., R. W. Bachmann and M. V. Hoyer. 2000. A management alternative for Lake Apopka. Lake and Re serv. Manage. 16(3):205-221. Carter, V. and N. B. Rybicki. 1985. The eff ects of grazers and light penetration on the survival of transplants of Vallisneria americana Michx. in the tidal Potomac River, MD. Aquat. Bot. 23:197-213. Carter, V. and N. B. Rybicki. 1990. Li ght attenuation and submersed macrophyte distribution in the tidal Potomac Rive r and Estuary. Estuar. 13(4):441-452. Carter, V., J. E. Paschal, Jr. and N. Bartow. 1985. Distribution and abundance of submersed aquatic vegetation in the ti dal Potomac River and Estuary, Maryland and Virginia, May 1978 to November 1981. A water quality study of the tidal Potomac River and Estuary. Water supply paper 2234-A. U.S. Geological Survey (USGS). 46 p. Catling, P. M., K. W. Spicer, M. Biernack i and J. Lovett Doust. 1994. The biology of Canadian weeds. 103. Vallisneria americana Michx. Can. J. Plant Sci. 74(4):883897. Chambers, P. A. and J. Kalff. 1985. Depth di stribution and biomass of submersed aquatic macrophyte communities in relation to Secch i depth. Can. J. Fish. Aquat. Sci. 42:701-709.

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55 Chestnut, T. L. and E. H. Barman, Jr. 1974. Aquatic vascular plants of Lake Apopka. Florida Sci. 37(1):60-64. Chew, R. L. 1974. Early life history of the Fl orida largemouth bass. Fishery bulletin no. 7. Florida Game and Fresh Water Fi sh Commission, Tallahassee, FL. 76 p. Clugston, J. P. 1963. Lake Apopka, Florida, a ch anging lake and its ve getation. Quart. J. Florida Acad. Sci. 26(2):168-174. Conrow, R. and J. Peterson. 2000. A panel atla s of the major aquatic plants of Lake Apopka, Florida using global positioning (G PS) and geographic information (GIS) systems. Technical memorandum no. 37. SJRWMD, Palatka, FL. 69 p. Conrow, R., W. Godwin, M. Coveney and L. E. Battoe. 1993. SWIM plan for Lake Apopka. SJRWMD, Palatka, FL. 163 p. Crowder, L. B. and W. E. Cooper. 1979. Struct ural complexity and fish-prey interactions in ponds: a point of view. P. 1-10. In D. L. Johnson and R. A. Stein (eds.). Response of fish to habitat structure in standing water. Spec. publ. 6. N. Central Div. Am. Fish. Soc., Bethesda, MD. Crumpton, J. E. and W. F. Godwin. 1997. Rough fish harvesting in Lake Apopka summary report, 1993-97. Florida Game and Fresh Water Fish Commission. Prepared for: Lake Apopka restora tion project. Special publ. SJ97-SP23. SJRWMD, Palatka, FL. 24 p. Danek, L. J. and M. S. Tomlinson. 1989. Bat hymetric analysis of Lake Apopka. Special publ. SJ 89-SP6. SJRWMD, Palatka, FL. 35 p. Davies, W. D., W. L. Shelt on and S. P. Malvestuto. 1982. Pr ey-dependent recruitment of largemouth bass: a conceptual model. Fish. 7(6):12-15. Davis, J. H. 1946. The peat deposits of Florid a, their occurrence, development and uses. Florida Geological Survey, Tallahassee, FL. 247 p. Dennison, W. C. 1987. Effects of light on s eagrass photosynthesis, growth and depth distribution. Aquat. Bot. 27:15-26. Dequine, J. F. 1950. Results of rough fish control operations in Lake Apopka during December 1949 and January 1950. Mimeographe d report. Florida Game and Fresh Water Fish Commission, Tallahassee, FL. 7 p. Dequine, J. F. and C. E. Hall, Jr. 1951. A brief study of the commercial and sport fisheries of Lake Apopka. Florida Ga me and Fresh Water Fish Commission, Tallahassee, FL. 12 p.

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56 Dibble, E. D. and K. J. Killgore. 1994. A habitat-based approach for studying fish-plant interactions. Misc. paper A-94-2. U.S. Army Corps of Engineers, Waterways Experiment Station, Vicksburg, MS. P. 32-40. Dibble, E. D., K. J. Killgore and S. L. Harrel. 1996. Assessment of fish-plant interactions. Am. Fish. Soc. Sympos. 16:357-372. Doyle, R. D. 2001. Effects of waves on the early growth of Vallisneria americana Freshwat. Biol. 46:389-397. Doyle, R. D. and R. M. Smart. 2001. Impacts of water column turbid ity on the survival and growth of Vallisneria americana winterbuds and seedling s. Lake and Reserv. Manage. 17(1):17-28. Duarte, C. M. and J. Kalff. 1987. Latitudi nal influences on the depths of maximum colonization and maximum biomass of submerged angiosperms in lakes. Can. J. Fish. Aquat. Sci. 44:1759-1764. Durocher, P. P., W. C. Provine and J. E. Kraai. 1984. Relationship between abundance of largemouth bass and submerged vegetation in Texas reservoirs. N. Am. J. Fish. Manage. 4:84-88. Goldsborough, W. J. and W. M. Kem p. 1988. Light responses of a submersed macrophyte: implications for survival in turbid tidal wate rs. Ecol. 69(6):1775-1786. Grimshaw, H. J., K. Havens, B. Sharfstein, A. Steinman, D. Anson, T. East, R. P. Maki, A. Rodusky and K-R. Jin. 2002. The eff ects of shading on morphometric and meristic characteristics of wild celery, Vallisneria americana Michx., transplants from Lake Okeechobee, Florida. Arch. Hydrobiol. 155(1):65-81. Gutreuter, S. J. and R. O. Anderson. 1985. Importance of body size to the recruitment process in largemouth bass populations Trans. Am. Fish. Soc. 114:317-327. Hardin, S. and L. L. Connor. 1992. Variabilit y of electrofishing crew efficiency, and sampling requirements for estimating reliable catch rates. N. Am. J. Fish. Manage. 12:612-617. Hoge, V. R., R. Conrow, D. L. Stites, M. F. Coveney, E. R. Marzolf, E. F. Lowe and L. E. Battoe. 2003. SWIM plan for Lake Apopka, Florida. SJRWMD, Palatka, FL. 196 p. Holcomb, D. E. 1977. Final report. D-J Proj ect F-30. Upper Ocklawaha basin fisheries investigations, 1973-1977. Florida Game and Fresh Water Fish Commission, Tallahassee, Florida. 107 p. Holcomb, D. E., W. Johnson, J. Jenkins, J. Bitter and L. Prevatt. 1975a. Oklawaha basin fisheries investigation. Fede ral aid in fish restorati on Dingell-Johnson project F-302. Florida Game and Fresh Water Fish Commission, Tallahassee, FL.

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57 Holcomb, D. E., W. Johnson, J. Jenkins, J. Bitter, L. Prevatt and P. Metzger. 1975b. Study I: Upper Oklawaha basin fisheries i nvestigations. Dingell-Johnson project F30-2. Second annual performance report Okla waha basin fisherie s investigations. Florida Game and Fresh Water Fi sh Commission, Tallahassee, FL. Hoyer, M. V. and D. E. Canfield, Jr 1994. Handbook of common fr eshwater fish in Florida lakes. SP 160. IF, UF Gainesville, FL. 177 p. Hoyer, M. V. and D. E. Canfield, Jr 1996a. Largemouth bass abundance and aquatic vegetation in Florida lakes: an empirical analysis. J. Aquat. Plant Manage. 34:2332. Hoyer, M. V. and D. E. Canfield, Jr 1996b. Lake size, aquatic macrophytes, and largemouth bass abundance in Florida lake s: a reply. J. Aquat. Plant Manage. 34:48-50. Hoyer, M. V., D. E. Canfield, Jr., C. A. Horsburgh and K. Brown. 1996. Florida freshwater plants: a handbook of common a quatic plants in Florida lakes. SP 189. IF, UF, Gainesville, FL. 260 p. Hoyer, M. V., M. D. Netherland, M. S. A llen and D. E. Canfield, Jr. 2005. Hydrilla management in Florida: a summary a nd discussion of issues identified by professionals with future management recommendations. Final document. Hydrilla issues workshop. Florida LAKEWATCH, FAS, IFAS, UF, Gainesville, FL. 68 p. Hudon, C., S. Lalonde and P. Gagnon. 2000. Ranking the effects of site exposure, plant growth form, water depth, and transparency on aquatic plant biomass. Can. J. Fish. Aquat. Sci. 57(Suppl. 1):31-42. Huffstutler, K. K., J. E. Burgess and B. B. Glenn. 1965. Biological, physical and chemical study of Lake Apopka 1962-1964. Bureau of Sanitary Engineering, Florida State Board of Hea lth, Jacksonville, FL. 55 p. Jaggers, B. V. 1994. Vallisneria americana : considerations for re storation in Florida. Florida Game and Fresh Water Fi sh Commission, Eustis, FL. 33 p. James, W. F. and J. W. Barko. 1994. Macrophyt e influences on sediment resuspension and export in a shallow impoundment. La ke and Reserv. Manage. 10(2):95-102. Johnson, W. E. and J. E. Crumpton. 1998. Lake Apopka fish population assessment. Final report for contract 97W121 for SJRWMD. Florid a Game and Fresh Water Fish Commission, Eustis, Fl. 39 p. Kenworthy, W. J. and M. S. Fonseca. 1996. Light requirements of seagrasses Halodule wrightii and Syringodiu filiforme derived from the relationship between diffuse light attenuation maximum depth distribution. Estuar. 19(3):740-750.

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58 Kerwin, J. A., R. E. Munro and W. W. A. Peterson. 1976. Distribution and abundance of aquatic vegetation in the uppe r Chesapeake Bay, 1971-1974. P. 393-400. In J. Davis (ed.). The effects of Tropical Storm Agnes on the Chesapeake Bay estuarine system. Chesapeake Research Consortium, Inc., Baltimore, MD. Kimber, A., C. E. Korschgen and A. G. van der Valk. 1995a. The distribution of Vallisneria americana seeds and seedling light requirements in the upper Mississippi River. Ca n. J. Bot. 73:1966-1973. Kimber, A., J. L. Owens and W. G. Crumpt on. 1995b. Light availability and growth of wildcelery ( Vallisneria americana ) in upper Mississippi River backwaters. Regulated Rivers: Res. and Manage. 11:167-174. Kolz, A. L. 1989. A power transfer th eory for electrofishing. P. 1-10. In Electrofishing, a power related phenomenon. Fish and wildlif e technical report 22. U.S. Fish and Wildlife Service (FWS), U.S. Dept. Interior, Wash., DC. Korschgen, C. E. and W. L. Green. 1988. American wild celery ( Vallisneria americana ): ecological considerations for restorati on. Fish and wildlife technical report 19. FWS, U.S. Dept. Interior, Wash., DC. 24 p. Korschgen, C. E., W. L. Green and K. P. Kenow. 1997. Effects of irradiance on growth and winter bud production by Vallisneria americana and consequences to its abundance and distribution. Aquat. Bot. 58:1-9. Kramer, R. H. and L. L. Smith, Jr. 1962. Form ation of year classes in largemouth bass. Trans. Am. Fish. Soc. 91:29-41. Lake Apopka Restoration Council. 1986. Lake Apopka restoration progress report and recommendations. W. S. Turnbull (Chairman). Submitted to the 1987 Florida legislature. 71 p. Latta, W. C. 1975. Dynamics of bass in large natural lakes. P. 175-182. In R. H. Stroud and H. Clepper (eds.). Black bass biology a nd management. Sport Fishing Institute, Wash., DC. Loreny, R. C. and C. E. Herderndorf. 1982. Growth dynamics of Cladophora glomerata in western Lake Erie in some environmenta l factors. J. Great lakes Res. 8(1):42-53. Lowe, E. F., L. E. Battoe, D. L. Stites and M. F. Coveney. 1992. Particulate phosphorus removal via wetland filtration: an examina tion of potential for hypertrophic lake restoration. Environ. Manage. 16(1):67-74. Lowe, E. F., L. E. Battoe, M. Coveney and D. Stites. 1999. Setting water quality goals for restoration of Lake Apopka : inferring past conditions. Lake and Reserv. Manage. 15(2):103-120.

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59 Lowe, E. F., L. E. Battoe, M. F. Coveney, C. L. Schelske, K. E. Havens, E. R. Marzolf and K. R. Reddy. 2001. The restoration of Lake Apopka in relation to alternative stable states: an alternative view to that of Bachmann et al. (1999). Hydrobiol. 448:11-18. Maceina, M. J. and J. V. Shireman. 1980. The use of a recording fathometer for determination of distribution and biomass of hydrilla. J. Aquat. Plant Manage. 18:34-39. Meyer, B. S., F. H. Bell, L. C. Thompson and E. I. Clay. 1943. Effect of depth of immersion on apparent photosynthesis in submersed vascular aquatics. Ecol. 24:393-399. Middelboe, A. L. and S. Markager. 1997. De pth limits and minimum light requirements of freshwater macrophytes. Freshwat. Biol. 37:553-568. Moore, K. A., B. A. Anderson, D. J. Wilcox, R. J. Orth and M. Naylor. 2003. Changes in seagrass distribution as evidence of historic al water conditions. Gulf of Mexico Sci. 21(1):142-143. Moxley, D. J. and F. H. Langford. 1982. Benefi cial effects of hydrilla on two eutrophic lakes in central Florida. Proc. Ann. C onf. Southeast Assoc. Fish and Wildl. Agencies. 36:280-286. Moyer, E. J., M. W. Holon, J. J. Sweatman, R. S. Butler and V. P. Williams. 1995. Fishery response to habitat restoration in Lake Tohopekaliga, Florida. N. Am. J. Fish. Manage. 15:591-595. National Oceanic and Atmospheric Admi nistration (NOAA). 2005. National Hurricane Center, National Weather Service, Miami, FL. Online: http://www.newflorida.o rg/storm/history.html Accessed August 2005. Nichols, S. A. 1997. Seasonal and sampling va riability in some Wisconsin lake plant communities. J. Freshwat. Ecol. 12(2):173-182. Nielsen, S. L., K. Sand-Jensen, J. Borum and O. Geetz-Hansen. 2002. Depth colonization of eelgrass ( Zostera marina ) and macroalgae as determined by water transparency in Danish coastal waters. Estuar. 25(5): 1025-1032. Olson, M. H. 1996. Ontogenetic niche shifts in largemouth bass: variability and consequences for first-year growth. Ecol. 77(1):179-190. Ott, L. R and M. Longnecker. 2001. An intr oduction to statistical methods and data analysis. Fifth edition. Wadswo rth Group, Pacific Grove, CA. 1152 p. Porak, W., S. Crawford and R. Cailteux. 1999. Biology and management of the Florida largemouth bass. Educational bulletin No. 3. Division of Fisheries, Florida Game and Fresh Water Fish Commission, Tallahassee, FL. 18 p.

PAGE 68

60 Reynolds, J. B. 1983. Electrofishing. P. 147-163. In L. A. Nielsen and D. L. Johnson (eds.). Fisheries techniques. Am. Fish. Soc., Bethesda, MD. Reynolds, J. B. 2000. Electrofishing theory. P. 3-24. In S. M. Allen-Gil (ed.). New perspectives in electrofishing. EPA/600/R-99/108. USEPA, Wash., DC. Rybicki, N. B. and V. Carter. 1986. Effect of sediment depth and sediment type on the survival of Vallisneria americana Michx. grown from tubers. Aquat. Bot. 24:233240. Rybicki, N. B. and V. Carter. 2002. Light and temperature effects on the growth of wild celery and hydrilla. J. A quat. Plant Manage. 40:92-99. St. Johns River Water Management Dist rict (SJRWMD). 20 05. Hydrologic data. SJRWMD, Palatka, FL. Online: http://arcimspub.sjrwmd.com/we bsite/dahds/design/index.html Accessed August 2005. Sand-Jensen, K. and T. V. Madsen. 1991. Mi nimum light requirements of submerged freshwater macrophytes in laboratory gr owth experiments. J. Ecol. 79:749-764. Savino, J. F. and R. A. Stein. 1982. Predator y-prey interaction between largemouth bass and bluegills as influenced by simulate d, submersed vegetation. Trans. Am. Fish. Soc. 11:255-266. Scheffer, M., M. R. de Redelijkheid and F. Noppert. 1992. Distribu tion and dynamics of submerged vegetation in a chain of sha llow eutrophic lakes. Aquat. Bot. 42:199216. Schelske, C. and P. Brezonik. 1992. Restora tion case studies. Can Lake Apopka be restored? P. 393-398. In Restoration of aquatic ecos ystems: science, technology, and public policy. Report of committee on restoration of aquatic ecosytems. National Research Council. Nati onal Academy Press, Wash., DC. Schelske, C. L. and W. F. Kenney. 2001. M odel erroneously predicts failure for restoration of Lake Apopka, a hypereutr ophic, subtropical lake. Hydrobiol. 448:15. Schelske, C. L., M. F. Coveney, F. J. Al dridge, W. F. Kenney and J. E. Cable. 2000. Wind or nutrients: historic development of hypereutrophy in La ke Apopka, Florida. Limnol. and Lake Manage. 2000+. Arch. H ydrobiol. Spec. Issues Advanc. Limnol. 55:543-563. Schneider, R. F. and J. A. Little. 1969. Charact erization of bottom sediments and selected nitrogen and phosphorus sources in Lake Apopka, Florida. Technical Programs, Southeast Water Laboratory, Federal Water Pollut. Control Admin., U.S. Depart. of the Interior, Athens, GA. 35 p.

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61 Sheldon, R. B. and C. W. Boylen. 1977. Maxi mum depth inhabited by aquatic vascular plants. Am. Midl. Nat. 97(1):248-254. Shelton, W. L., W. D. Davies, T. A. Ki ng and T. J. Timmons. 1979. Variation in the growth of the initial year class of largemouth bass in West Point Reservoir, Alabama and Georgia. Trans. Am. Fish. Soc. 108:142-149. Shofner, J. H. 1982. History of Apopka and northwest Orange County, Florida. Apopka Historical Society. Rose Prin ting Co., Tallahassee, FL. 357 p. Smart, R. M. 1992. Competition among introduced and native species. Proceedings, twenty-seventh annual meeting APCRP. Be llevue, WA. Final report. Prepared for U.S. Army Corps of Eng. Wash., DC Pub. Environ. Lab., U.S. Army Eng. Waterways Exp. Sta., Vicksburg, MS. Spence, D. H. N. 1972. Light on freshwater macrophytes. Trans. Bot. Soc. Edinb. 41:491-505. Strickland, J. D. H. 1958. Solar radiati on penetrating the ocean. A review of requirements, data and methods of measur ement, with particular reference to photosynthetic productivity. J. Fi sh. Res. Board Canada. 15:453-493. Swingle, H. S. 1950. Relationships and dyna mics of balanced and unbalanced fish populations. Bull. 274. Ala. Polytec h. Inst. Agric. Exp. Sta. 73 p. Timmons, T. J., W. L. Shelton and W. D. Davies. 1980. Differ ential growth of largemouth bass in West Point Reservoir, Alabama-Georgia. Trans. Am. Fish. Soc. 109:176-186. Titus, J. E. and M. S. Adams. 1979. Coexiste nce and the comparativ e light relations of the submersed macrophytes Myriophyllum spicatum L. and Vallisneria americana Michx. Oecol. (Berl.) 40:273-286. United States Environmental Protection Ag ency (USEPA). 1979. Final environmental impact statement for Lake Apopka restor ation project. Lake and Orange counties Florida. EPA 904/9-79-43. USEPA. 443 p. Wegener, W. L. and V. P. Williams. 1974. Fi sh population responses to improved lake habitat utilizing an extreme drawdown. Pr oc. Ann. Conf. S. E. Assoc. Game and Fish Comm. 28:144-161. Valiela, I. 1995. Marine ecological processe s. Second edition. Springer-Verlag, New York, Inc., NY. 686 p. Zimmerman, R. C., A. Cabello-Pasini a nd R. S. Alberte. 1994. Modeling daily production of aquatic macrophytes from irra diance measurements: a comparative analysis. Mar. Ecol. Prog. Ser. 114:185-196.

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62 BIOGRAPHICAL SKETCH Stephen J. Murphy earned an Associate of Arts degree at Valencia Community College in Orlando, Florida, in 2001. He went on to earn a Bachelor of Science degree with a major in wildlife, ecology, and c onservation (WEC) at the UF, College of Agricultural and Life Sciences (CALS) in August 2003. He also completed the CALS upper division honors program in August 2003.