Citation
Effects of Stocking Wild-Adult Largemouth Bass on the Fishery at Lake Griffin, Florida

Material Information

Title:
Effects of Stocking Wild-Adult Largemouth Bass on the Fishery at Lake Griffin, Florida
Creator:
Pecora, Darren
Place of Publication:
[Gainesville, Fla.]
Publisher:
University of Florida
Publication Date:
Language:
english
Physical Description:
1 online resource (74 p.)

Thesis/Dissertation Information

Degree:
Master's ( M.S.)
Degree Grantor:
University of Florida
Degree Disciplines:
Fisheries and Aquatic Sciences
Forest Resources and Conservation
Committee Chair:
Canfield, Daniel E.
Committee Members:
Cichra, Charles E.
Estes, James R.
Graduation Date:
8/8/2009

Subjects

Subjects / Keywords:
Bodies of water ( jstor )
Canals ( jstor )
Chlorophylls ( jstor )
Fish ( jstor )
Fisheries ( jstor )
Fishers ( jstor )
Freshwater bass ( jstor )
Lakes ( jstor )
Mortality ( jstor )
Wildlife population estimation ( jstor )
Forest Resources and Conservation -- Dissertations, Academic -- UF
bass, largemouth, stocking
City of Eustis ( local )
Genre:
Electronic Thesis or Dissertation
born-digital ( sobekcm )
Fisheries and Aquatic Sciences thesis, M.S.

Notes

Abstract:
Lake Griffin was stocked with approximately 14,000 wild-adult largemouth bass from 2005 to 2007 to stimulate economic activity related to the fishery. An electrofishing survey was initiated at Lake Griffin in 2007 to determine the status of the stocked fish population 3 years after stocking. The mean dispersal distance from stocking sites for 122 caught stocked largemouth bass was 2.9 km, with the maximum-recorded distance being 9.2 km. Mean CPUE (fish/hour) of native largemouth bass between canal and main lake areas were not significantly different, indicating stocked and wild fish were mixing evenly. Mortality estimates for stocking years 2006 (Z= 1.087) and 2007 (Z=1.295) are similar to the 2007 native largemouth bass estimates (Z= 1.054). There was no change in native largemouth bass condition post stocking. The stocked largemouth bass in May 2007 contributed 13% to total electrofishing largemouth bass catch, with a CPUE of 0.09 (fish/minute) immediately after the last stocking in 2007. Two years later, in March 2009, the total electrofishing catch of stocked largemouth bass was 3%, with a 0.03 (fish/minute) CPUE. Water level and macrophyte abundances were the primary environmental factors influencing largemouth bass abundance, but management actions focusing on these factors have been rejected by the public, and climatic conditions may prevent enhanced lake fluctuation. To enhance the largemouth bass fishery at Lake Griffin, construction of artificial habitat is recommended for the main lake along with continued stocking of wild adult largemouth bass. Stocking wild-adult largemouth bass captured from non-fished waters is a cost-effective fisheries management tool, supported by anglers, and the weight of scientific evidence suggests only positive effects. ( en )
General Note:
In the series University of Florida Digital Collections.
General Note:
Includes vita.
Bibliography:
Includes bibliographical references.
Source of Description:
Description based on online resource; title from PDF title page.
Source of Description:
This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Thesis:
Thesis (M.S.)--University of Florida, 2009.
Local:
Adviser: Canfield, Daniel E.
Electronic Access:
RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2010-08-31
Statement of Responsibility:
by Darren Pecora.

Record Information

Source Institution:
UFRGP
Rights Management:
Copyright Pecora, Darren. Permission granted to the University of Florida to digitize, archive and distribute 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:
8/31/2010
Resource Identifier:
489119667 ( OCLC )
Classification:
LD1780 2009 ( lcc )

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are biologically productive lakes (eutrophic to hypereutrophic) and Lake Griffin is one of

FFWCC's fish management lakes (Administrative code Rule 68A-20.004). Approximately 3,804

ha constitute the main lake and are used for open water recreational activities (SJRWMD 2003),

with the remaining area (2,876 ha) made up of primarily swamp and wetlands which were

historically dominated by sawgrass (Cladium jamaicense), but were drained and diked off from

1955 to 1990 for muck farming (Marburger et al. 2002). There are approximately 40 canals (24+

kilometers in length) around Lake Griffin which were dredged prior to 1960 to provide

landowners access to the lake, and these canals were maintenance-dredged between 2005 and

2007 (Figure 2-2).

Lake Griffin is one of nine water bodies in the Harris Chain of Lakes (also known as

Ocklawaha Chain of Lakes). Lake Griffin serves as the headwaters of the Ocklawaha River, a

major tributary of the St. Johns River. Lake Griffin receives water, which passes through a dam

on Haines Creek primarily from the eight upstream lakes, while a dam downstream on the

Ocklawaha River (Moss Bluff) regulates water levels in Lake Griffin according to the U.S. Army

Corps of Engineers regulation schedule (Schluter and Godwin 2003).

Water Levels

The mean water level for Lake Griffin since 1946 was 58.65 ft, with a recorded minimum

level of 56.63 ft and a maximum level of 60.14 ft (SJRWMD; Table 2-1, Figure 2-3). The mean

annual change in water level for the period of record was 1.84 ft, with a recorded annual

minimum change of 0.91 ft and an annual maximum change of 7.14 ft (Table 2-1, Figure 2-3).

On average, the water levels were much higher in Lake Griffin before 1960 with a peak at 60.14

feet after Hurricane Donna. This overall trend in decreasing water level since 1960 is due to lack

of rainfall explained by the Atlantic Multidecadal Oscillation (Kelly and Gore 2008). Major

yearly changes in water level occurred in 1974 and 1984. In 1974, the Moss Bluff dam on the













12%

10%

8%

6%

4%

2%

0%


1980


1985


1990


1995


2000


2 I )


2010


Year


Figure 2-9. Percent area coverage of hydrilla for Lake Griffin, Florida (data obtained from
FLDEP).


0000
(A A0


o00 CO C0
0 -- COO


\o ^o
k0 ',0
o 0-


YeaO rO O 1 0 I ',O C

Year


0- 0
00
1,) W


ItQ I"-
00
00


i Li h
000
000
ON --0 0C


Figure 2-10. Annual mean largemouth bass electrofishing catch per unit effort (CPUE) for a
variety of sizes of largemouth bass in Lake Griffin, Florida (data obtained from
FFWCC).


CPUE LMB < 200 nll TL
---- CPUE LMB > 2001111 nTL
--- CPUELMB 200-299nuiiTL
---- CPUELMB > 300nun TL
---)--- CPUELMB > 360nmun TL
-*- CPUEAll Sizes

I 7-- W I T










4.5-


O3.5
U

o 3-
'r--
0)
0
2.5-


2-
-1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0
LoglO CPUELMB >200mmTL
Figure 4-15. Relationship between annual largemouth bass creel catch, estimated by roving creel
survey and electrofishing CPUE (fish/minute) of largemouth bass (> 200 mm TL),
with a linear line fit to the data (R2=0.000013), for Lake Griffin, Florida (data
obtained from FFWCC).


90000
80000
70000
60000
50000
40000
30000
20000
10000
0


Ole


1965 1970 1975 1980 1985 1990 1995 2000 2005

Year


Figure 4-16. Angler effort (hours) for largemouth bass, estimated by roving creel survey for
Lake Griffin, Florida (data obtained from FFWCC).









outlet of Lake Griffin broke causing a large (4.2 ft) fluctuation in water level (Figure 2-3). The

next major event in 1984 (7.1 ft) was an experimental drawdown and subsequent refill by

FFWCC to improve the fishery. The least amount of yearly fluctuation occurred between 1995

and 2002 (Table 2-1, Figure 2-3). From 1995 through 2002, Florida was under statewide

drought conditions (Veredi et al. 2006).

Water Quality

In many Florida lakes, cultural eutrophication has been a major concern over the past 30

years, with many efforts aimed at reducing nutrient inputs (Terrell et al. 2000). Until recently,

Lake Griffin was considered one of the most polluted lakes in Florida (SJRWMD 2003). Over

the past 50 years, farming activities, water-level stabilization, and residential development

around the lake have caused significant degradation in water quality and clarity (Schluter and

Godwin 2003). Large nutrient inputs from adjoining agricultural operations have been targeted

as the primary cause of dense algal blooms which have purportedly increased deposition of soft

organic sediments to the benthic substrate (Schluter and Godwin 2003). Lake Griffin is the

subject of major environmental restoration. Some restoration efforts on Lake Griffin include:

farm land acquisition, lake level fluctuation, removal of gizzard shad, and a marsh filtration

system (SJRWMD 2003). All of these activities except lake level fluctuation are aimed at

reducing nutrient loading to and nutrient concentration in the system, particularly phosphorus,

while lake level fluctuations are intended to improve the vegetated habitat of the lake.

Consequently, Lake Griffin has been the subject of many environmental studies and a long-term

record exists for many physical, chemical and biological attributes.

Total phosphorus concentrations, ranging from 47 [g/L to 181 [g/L, exhibited a

downward trend froml973 to 2007 (Figure 2-4), but the long-term phosphorus mean was 100

[g/L (Table 2-1). The highest levels of total phosphorus generally corresponded with low water









Ricker, W. E. 1975. Computation and interpretation of biological statistics offish populations.
Department of the Environment, Fisheries and Marine Science, Bulletin 191, Ottawa,
Canada.

Schluter, C. A., and W. F. Godwin. 2003. Lake Griffin Fish Habitat Suitability Study. Available:
http://proceedings.esri.com/library/userconf/proc03/p0792.pdf (March 2008).

Shafer, M. D., R. E. Dickinson, J. P. Heaney, and W. C. Huber. 1986. Gazetteer of Florida
Lakes. Publication No. 96. Florida Water Resources Research Center. University of
Florida. Gainesville, Florida.

Smith, B. W., and W. C. Reeves. 1986. Stocking warmwater species to restore or enhance
fisheries. Pages 17-29 in R. H. Stroud, editor. Fish culture in fisheries management.
American Fisheries Society, Fish Culture Section. Bethesda, Maryland.

(SJRWMD) St. Johns River Water Management District. 2003. Lake Griffin : Fast Facts.
Available: www.sjrwmd.com/publications/pdfs/fs lgriffin.pdf (February 2008).

Strange, R. J., C. D. Berry, and C. B. Schreak. 1975. Aquatic plant control and reservoir
fisheries. Pages 513-525 in H. Clepper, editor. Black bass biology and Management. Sport
Fishing Institute, Washington, D. C.

Terrell, J. B., D. L. Watson, M. V. Hoyer, M. S. Allen, and D. E. Canfield, Jr. 2000. Temporal
water chemistry trends (1967-1997) for a population of Florida water bodies. Lake and
Reservoir Management 16:177-194.

U.S. Department of Interior, Fish and Wildlife Service and U.S. Department of Commerce,
Census Bureau. 2006. National survey of fishing, hunting, and wildlife-associated
recreation.

Verdi, R. J., Tomlinson, S. A., and R. L. Marella. 2006. The drought of 1998-2002: impacts on
Florida's hydrology and landscape. U.S. Geological Survey Circular 1295.Tallahasse,
Florida

Wicker, A. M., and W. E. Johnson. 1987. Relationships among fat content, condition factor, and
first-year survival of Florida largemouth bass. Transactions of the American Fisheries
Society 116:264-271.

Wilson, J., C. W. Osenberg, C. M. St. Mary, C. A. Watson, and W. J. Lindberg. 2001. Artificial
reefs, the attraction-production issue, and density dependence in marine ornamental fishes.
Aquarium Science and Conservation 3:95-105.

Zimmerman, R. C., A. Cabello-Pasini, and R. S. Alberte. 1994. Modeling daily production of
aquatic macrophytes from irradiance measurements: a comparative analysis. Marine
Ecological Progressive Series 114:185-196.









ACKNOWLEDGMENTS

I thank my graduate advisor, Dr. Dan Canfield Jr., without whom none of this would have

been possible. I also thank my committee members, Dr. Charles Cichra and Jim Estes for their

guidance and advice. I thank Mark Hoyer for his guidance and assistance and Florida

LAKEWATCH staff and graduate students for their field and logistical help, particularly Jesse

Stephens, Bubba Thomas, Dana Bigham, Jenney Lazzarino, and Kurt Larson. I thank Sherry

Giardina for helping me with forms and meeting deadlines. I thank the following individuals for

help on this project Dan Gwinn, Mike Allen, Lauren Marcinkiewicz, Towns Burgess, Jared

Flowers, Bill Pine, Matt Catalano, John Benton, and Bill Johnson. I thank my friends and family

who have kept encouraging me through this endeavor. Finally, I thank God!



















I I 1I 1 1


* Native Fish
m Stocked Fish


I I I I


* 0 'ui 0 iu 0 'i 0 i i 0 i L 0 Li
0 I'- Lk e 00
o * I I I I I I I
c)- J1A A (A L A C --C ( I
000000000000
Total Length (nmm) Main Lake June 2008


__ItiitIIIILI


m Native Fish
m Stocked Fish


'- U- U-) 13k

oo0


I I

0 LA


10 A 0 01

SC C0000
0000


Total Length (mun) Canals June 2008


Figure 4-5. Continued.


Illlle II










0.4-

0.2-
E -
0-
8 -
) -0.2-
'r- -
0)
0 -0.4-

-0.6-

n Q-


1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5 2.6
LoglO Chlorophyll (pg/L)


Figure 4-11. Relationship between LoglO Secchi (m) and LoglO Chlorophyll (tg/L) with a
linear line fit to the data (R2=0.31), for Lake Griffin, Florida, for data collected from
1969 to 2007 (data obtained from FFWCC, SJRWMD, and Florida LAKEWATCH).




+ CIdorophyll --CPUE LMB > 200 1mm TL


350
300
250
200
150
100
50
0


1

0.8

S0.6

S0.4

0.2 -

0


cc cc00000 0 0 0 0 0
0 0 c 00000c D O DO O 0 0 0

Year

Figure 4-12. Annual mean chlorophyll concentration and electrofishing catch-per-unit-effort
(CPUE) of largemouth bass (> 200 mm TL), for Lake Griffin, Florida (data obtained
from FFWCC, Florida LAKEWATCH, and SJRWMD).


- .. ,


-.











25000

n 20000
S2 -- Creel Harvest
15000 -Creel Catch

S10000

5000


1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Year


Figure 2-11. Estimated annual angler catch and harvest from Lake Griffin, Florida from 1966 to
2006 (data obtained from FFWCC).









so that long-term data sets remain comparable with future creel information. Perhaps, what

would be the best approach now would be the implementation of three or four creel surveys that

include the adjoining waters like canals as well as the main lake to determine the impact on

effort and harvest estimates. This will add costs to the creel survey, but it is clear that the costs

will be justified if it helps biologists make better decisions for the resource.

The next phase of restoration at Lake Griffin according to personnel from the St. Johns

River Water Management District is reestablishment of spawning and nursery habitat for

desirable fish (i.e., largemouth bass) species (Schluter and Godwin 2003). The District's

program includes the reconnection of the former adjoining farmlands once wetlands are re-

established. The estimated time for complete ecosystem restoration for Lake Griffin, however, is

60 years (HCLRC 2008) because SJRWMD is focusing on nutrient removal. Reconnection of

adjoining marshes that were once used for farming, will provide additional spawning habitat,

nursery habitat, and fishing areas

If Lake Griffin were solely a "Fish Management" lake and the only consideration for

managers was optimization of largemouth bass catch and harvest, a major water level fluctuation

would be the first choice to stimulate the largemouth bass population in Lake Griffin. Regularly-

scheduled lowering of water levels followed by refill is the least expensive and best approach.

This was demonstrated by FFWCC with its 1984 experimental drawdown (Figure 4-7).

However, Lake Griffin is a multipurpose recreational lake and there are other considerations

such as access issues and growth of the non-native aquatic plants like hydrilla and its effects on

non-angling recreation.

While there are a myriad of public concerns, major reductions in Lake Griffin's water level

have not been accepted by the public since the 1980s. Recently, the canals around the lake have









complexity is an important habitat feature for young-of-the-year and sub-adult largemouth bass

survival (Hoyer and Canfield 1996) by providing reduced predation (Strange et al. 1975) and

increased prey (Crowder and Copper 1982). When stocking non-adult largemouth bass into

waters with no cover or structure, stocked largemouth bass mortality up to 90% can be expected

(Miranda and Hubbard 1994). Although it is now generally accepted that larger-sized stocked

largemouth bass exhibit higher survival than smaller fish (Heidinger and Brooks 2002),

aquaculture production of advanced fingerlings and adult fish in hatcheries remains difficult and

expensive.

Advanced fingerling largemouth bass (65 to 90 mm total length [TL]) are now produced at

the Richloam State Fish Hatchery by FFWCC, but successful stocking has only been

documented in one Florida lake (Mesing 2008), despite attempts to stock advanced sizes of

largemouth bass into Florida lakes (Porak et al. 2002). Lorenzen (1996) found lower mortality

for stocked fish that were raised in aquaculture systems where the fish fed on natural foods and

were raised in earthen ponds. Lorenzen's (1996) findings led Florida LAKEWATCH to

conclude in 2003 that stocking adult-sized fish from non-aquacultured (i.e., wild fish) private

natural waters should aid in reducing stocking mortality, and enhance long-term survival of

stocked fish in a large lake system where numerous predators such as birds and other fish species

exist. In many northern states, stocking hatchery-raised adult trout is a common management

practice for a variety of recreational fisheries, especially "put and take" fisheries (Miko et al.

1995). Survival of hatchery reared trout is expected to be low and harvest of these fish is

encouraged. The only comparable practice for warm water fish is the collection of fish from

drained water bodies and their relocation to other water bodies (e.g., Carlander 1954). In the

1950s, fish rescue programs were conducted frequently in the upper Mississippi River drainage









CHAPTER 6
CONCLUSION

The stocking of wild-adult largemouth bass resulted in an estimated 10 to 15%

contribution to the abundance in CPUE of largemouth bass in electrofishing catches in May and

June 2007. If it were possible to double or triple this stocking rate, there might be an even

greater effect on abundance of largemouth bass in the system. My results confirm that stocked

largemouth bass are indeed moving outside of the creel area where they were stocked and into

canals. FFWCC did not sample canals in their creel survey, primarily because they were

following their long-term creel protocol. Canals are clearly utilized by fishermen according to

Larson's (2009) report and my electrofishing efforts, but largemouth bass abundance was similar

in the canals and the main lake.

Florida LAKEWATCH stocked Lake Griffin at -1 fish per hectare. I also believe that an

adult largemouth bass stocking project like this one will have a more profound effect on a

smaller system if stocked at a higher rate. In 2008, nearby Lake Dora was stocked by Florida

LAKEWATCH with -4000 largemouth bass greater than 200 mm TL. Post-stocking

electrofishing revealed -20% contribution to the greater than 200 mm TL population of

largemouth bass. Lake Dora is nearly half the size (1810 ha) of Lake Griffin and does not have

nearly the same amount of canals for stocked fish to disperse into. Stocking adult fish at higher

rates or into smaller lakes should be done with caution as the fisheries biologist must make

certain there is an adequate forage base. However, in hypereutrophic lakes like Lake Griffin this

should not be an issue.

Based on my evaluations and those of Larson (2009), the weight of evidence supports the

stocking of wild-adult largemouth bass using the Florida LAKEWATCH protocol. Large

numbers (4000 plus fish per year) of wild-adult bass were procured for three years from private









lake; rather based on Larson' s (2009) angler survey it might be more reasonable to think the

anglers are preferentially targeting canals. Therefore, the disproportionate numbers of the tag

returns from the canals must have been the result of angler behavior. The canals offer habitat

where the anglers can catch fish and some anglers may be targeting canals for reasons such as,

the canals are more accessible to back-yard anglers and safer to fish in boats due to less wind and

wave action. The canals are also shaded by trees growing on the banks, making a cooler fishing

experience during warm periods.

Mortality

Besides having largemouth bass moving to adjoining waters or completely outside the

Lake Griffin system, a great reduction in the number of stocked largemouth bass caught over

time could be the result of higher mortality rates. The monthly Lake Griffin electrofishing data

and calculated mortality estimates from catch curves were used to compare this study's estimates

of mortality to FFWCC's mortality estimates for native Lake Griffin largemouth bass. Mortality

and survival estimates of stocked fish are similar to native fish (Table 4-3).

Mortality estimates for the individual stocking years, tag year 2006 cohort (Z= 1.087) and

2007 cohort (Z=1.295), were similar to the 2007 native largemouth bass estimate (Z= 1.054).

These estimates were made from data collected many months after stocking had occurred. These

estimates provide evidence that FFWCC's reported low catch of stocked fish may have been due

to selective die-offs resulting from transportation (approximately 2-3 hours) and stocking stress

(Table 4-3). The collection of wild-adult largemouth bass from distant non-fished waters may

have been a contributing factor effecting stocked fish mortality. Stocked fish were transported

during the cooler months, which was a viable stocking technique employed by Florida

LAKEWATCH to reduce mortality.









group (Chapter 373.467 F.S. and the Lake County Water Authority, a special taxing district for

the management of Lake County's lakes). These groups, after hearing the pros and cons of

stocking fingerling, advanced fingerling, and adult largemouth bass, authorized a

research/demonstration stocking project by Florida LAKEWATCH in an attempt to enhance the

fishery quickly (within 3 years) by increasing the abundance of catchable-size fish. The

LAKEWATCH approach was to stock Lake Griffin with large numbers (4,000 plus fish/year) of

wild-adult (> 200 mm total length (TL); average size stocked 305 mm TL) largemouth bass

taken from private waters (Larson 2009).

Supplemental stocking of hatchery-produced largemouth bass is a common management

practice by fish management agencies throughout the United States; Forty-one states have

stocked hatchery-raised fry, fingerling, advanced-fingerling, or adult largemouth bass (Smith and

Reeves 1986). Limited literature exists on the success of stocking programs for hatchery-raised

sub-adult and adult largemouth bass into large systems (Porak 1994, Buynak et al. 1999). Porak

et al. (2002), however, suggested stocking advanced fingerling largemouth bass could provide a

potential approach to circumvent a largemouth bass recruitment bottleneck caused by the loss of

aquatic macrophytes, and increase recruitment of largemouth bass to age one in nutrient-enriched

Florida lakes. This suggestion is based in part on research conducted by Wicker and Johnson

(1987), who found that high rates of mortality occur when age-0 largemouth bass shift to

piscivory in a hypereutrophic Florida lake.

Use of advanced sizes of hatchery produced largemouth bass was also supported by

research on a wide range of Florida lakes indicating that poor recruitment in lakes may be related

to decreased shoreline habitat to lake surface area ratio (Hoyer and Canfield 1996); hence, the

importance of macrophytes is increased for large lakes. Aquatic macrophyte structural









Table 2-1. Water level and water quality parameters (mean and ranges) for Lake Griffin,
Florida.
Yearly


Total
Phosphorous
([tg/L)


Secchi (cm)
37


Chlorophyll
([g/L)


Minimum 56.63 0.91 2243 47
Maximum 60.14 7.14 5630 181
Note: Data obtained from FFWCC, Florida LAKEWATCH, and SJRWMD


Parameters
Mean


Mean
Water
Level (ft)
58.65


Change
in Water
Level
(ft)
1.84


Total
Nitrogen
(34g/L)
3140


27
316













A




* Native Fish
* Stocked Fish


'"'
00


jD CD -D CD iD D\ C\


0000000


Total Length (mmn) Main Lake May 2007


B





SNative Fish
* Stocked Fish


A C
O 0
C oC
O


-P -P iA "Al O\ C\
C) C: CD

C) CD CD
C: C: C) C CD CI
0 ^l 0rm 0 cn


00 0 000


Total Length (nmn) Canals June 2007


Figure 4-5. The number and size of native and stocked largemouth bass captured via
electrofishing in the canals and main lake of Lake Griffin, Florida. A) Main Lake
May 2007. B) Canals June 2007. C) Main Lake June 2008. D) Canals June 2008. E)
Main Lake March 2009. F) Canals March 2009.


450
400
350
300
250
200
150
100
50
0


r16 L









EFFECTS OF STOCKING WILD-ADULT LARGEMOUTH BASS ON THE FISHERY AT
LAKE GRIFFIN, FLORIDA




















By

DARREN JOHN PECORA


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

2009









help determine if stocked wild-adult fish die from transportation stress or how many adjoining

waters could be influenced through a single-lake stocking program. In this project, dispersal

information obtained through fishery-independent sampling (electrofishing) also assisted with

determining if stocked fish were preferentially using adjoining canals rather than the main lake at

Lake Griffin.

The percent contribution of stocked fish to electrofishing catches was determined along

with what percent of stocked largemouth bass remained in Lake Griffin after a two-year period

of no stocking. The mortality of stocked largemouth bass was determined through information

obtained from the electrofishing catches. The estimated mortality rate was compared to native

largemouth bass mortality in Lake Griffin to determine if stocked fish mortality is greater.

A change in condition factor for native Lake Griffin largemouth bass after the stocking was

investigated to insure there was an adequate forage base. Stocking adult-wild fish could be

detrimental to Lake Griffins' largemouth bass population if the existing largemouth bass

population is near carrying capacity.

Trends in historical water quality and habitat abundance, especially total phosphorus

([g/L), total nitrogen ([g/L), chlorophyll ([g/L), Secchi depth (cm), mean water level (ft), yearly

change in water level (ft), and whole-lake aquatic macrophyte percent aerial coverage were

specifically investigated to determine if there are patterns between these environmental variables

and Lake Griffin's largemouth bass population size as assessed by historical electrofishing

(CPUE) and roving creel surveys. If patterns exist, workable guidelines for the future

management of largemouth bass in Lake Griffin could be formulated.

The determination of persistence, mortality, and percent contribution of stocked adult-sized

largemouth bass in to the Lake Griffin population of largemouth bass provided information so


































To my mother, father, and sisters for their unconditional love and support









CHAPTER 3
METHODS

A total of 13,933 largemouth bass greater than 200 mm TL were stocked into Lake Griffin

during the winter months (December to April) between 2004 and 2007 (4,234 fish stocked in

2005, 5033 fish in 2006, and 4,666 fish in 2007) by Florida LAKEWATCH (Larson 2009). All

stocked largemouth bass received a left-pelvic fin clip and fish greater than 275 mm TL (N =

10,538) were dorsally implanted with orange Hallprint PDA plastic-tipped dart tags. Dart tags

had individual identification numbers; therefore, each tagged fish could be individually identified

upon capture. Florida LAKEWATCH stocked largemouth bass into the main area of Lake

Griffin, not into canals or adjoining waters. Larson (2009) provides a full description of the

Florida LAKEWATCH largemouth bass stocking program.

Introduced-fish and native largemouth bass were collected by electrofishing in Lake

Griffin's near-shore waters and adjoining canals to evaluate dispersal of stocked largemouth bass

from their introduction locations (50 plus sites) in the main area of Lake Griffin (FFWCC's creel

zone), percent contribution of stocked bass, and the mortality of stocked fish. An electrofishing

protocol, similar to that used by FFWCC and Florida LAKEWATCH (Larson 2009), was used

during this study. An electrofishing boat equipped with a 5-kw generator (Honda EG5000) and a

Smithroot model VI-A pulsator was used to collect largemouth bass. The electrofishing crew

consisted of two people; one individual netted fish from the bow and placed fish into a live well,

while the other person operated the boat and the pulsator. Between April 2007 and March 2009

(23 sampling days), 364 ten-minute electrofishing transects were sampled (Table 3-1).

Lake Griffin's shoreline vegetation (versus open-water sites) was targeted during

electrofishing of the main-lake to enhance the probability of largemouth bass capture. Transects

were placed evenly around Lake Griffin's shoreline and a GPS unit recorded start and end-points










12

io
10


6
q,
0
4

2
C.


, I- I- I- ,-, '-- ,, ,, ,, I, '- ' t c) I' 13 1" 13 1" 1 > I'
---1 ---1 ----1 oo oo o o o oo o-o o-o o o .o 'o o -o -o o o 0 o o o o o o o o o
VI C\ -10 6 o 0 f \ --OI cQ Co o V I 00 '^ C> I V -.. II cOcO C-)Q(AL4 hQ 10--0' O0
Year

Figure 4-6. The annual change in water level and estimated percent area coverage of hydrilla in
Lake Griffin, Florida (data obtained from SJRWMD and FLDEP).


W W W W W >1. 10 I'D 11 0 t t 1 0 11.0 t0 C:> C:> C^J) C:> CD CD C:
o i-^ >o C C4 ---) 0 CoO : ")W 4> h 1- --]\ .) 00 "o C i- t-- w -t'L --,I 0 o 100 o o


Year

Figure 4-7. Yearly change in water level, percent area coverage of hydrilla, and electrofishing
catch-per-unit-effort (CPUE) of largemouth bass (<200 mm TL and > 200 mm TL)
for Lake Griffin, Florida (data obtained from SJRWMD, FLDEP and FFWCC).


-- Anmnual Change in Water
Level

t I -*- Hydrilla




~c-(-
t '" 'i/' 1',




^- ^ / -^ -* ^ --* H -- *4 ^^. 's .y t *^^


12

10

C^ 8

6

O, 4



0
r o









CPUE was calculated by dividing the total number offish captured for an individual transect by

the total minutes of electrofishing (fish per minute). Sampling transects during each month were

grouped together to provide a mean monthly CPUE estimate. Canals and main lake were

separated to evaluate the difference in percent contribution between canals and the main lake.

The April and May 2007 main-lake transects were combined to provide a single 2007 "May"

main-lake CPUE estimate. The "May" estimate was compared to the June 2007 canal CPUE

estimate.

To obtain lake-wide percent contribution of stocked fish and their CPUE for each month,

the total number of stocked largemouth bass as well as all largemouth bass caught for each main

lake and canal transect were combined and then divided by either the total number of largemouth

bass caught (% contribution) or the total number of minutes electrofished (CPUE). The April,

May, and June 2007 main lake and canal transects were combined to calculate "May" mean

percent contribution and CPUE estimate.

To determine if stocked largemouth bass are exhibiting the same mortality rates as native

Lake Griffin largemouth bass, two separate CPUE data groupings (2006 tags only and 2007 tags

only) were plotted in Microsoft Excel. Mortality estimates for the stocked largemouth bass were

calculated from catch curves (Ricker 1975). Tagged (fish with fin clips only were not included)

largemouth bass CPUE for 2006 and 2007 stocking years were calculated separately. To

calculate individual stocking year mortalities, 2006 and 2007 canal and main lake CPUEs

(tagged fish/minute) were again combined for each monthly sampling event. To calculate

individual stocking years 2006 and 2007 CPUE (tagged fish/minute), April, May, and June

(2007) were combined to obtain the "May" CPUE estimate. Electrofishing data from April 2006

was obtained (Mark Hoyer, personal communication, Florida LAKEWATCH) and used to




































2009 Darren John Pecora









the Ocklawaha River, and other backwaters, where the majority (65%) of Florida

LAKEWATCH-stocked fish were caught according to angler tag call-in reports (Larson 2009).

Largemouth bass must move at some point in their lives to use available resources

throughout a water body/reservoir (Copeland and Noble 1994). Heidinger and Brooks (2002)

stated that because stocked largemouth bass are relocated fish, they initially do not have a home

range and exhibit more movement than native largemouth bass. Dequine and Hall (1950) found

that stocked largemouth bass move variable distances (0 to 9.6 km, with one fish moving 15.3

km) from where they were released. While the movement pattern of stocked Florida

LAKEWATCH fish was unknown to Larson (2009), it was clear, from tag returns that stocked

fish were moving outside the main area of Lake Griffin. This movement of largemouth bass

raised the issue of how long stocked wild-adult largemouth bass would persist in Lake Griffin

and how long anglers could expect to catch these fish given the many environmental factors that

could also affect largemouth bass survival.

To address some of the biological issues surrounding Florida LAKEWATCH's wild-adult

largemouth bass stocking program, this project had four primary objectives:

1) Determine the dispersal distance of stocked wild-adult largemouth bass,

2) Determine the persistence, mortality, and percent contribution over time of the
LAKEWATCH stocked largemouth bass,

3) Determine if the stocked largemouth bass were exhibiting greater abundance in canals over
the main lake or were being displaced into canal areas,

4) Determine what environmental factors influence largemouth bass abundance and the
largemouth bass fishery in Lake Griffin.

The dispersal of stocked largemouth bass was investigated because it provided insight into

fish movement that could influence management decisions such as the number of stocking sites

needed for a given water body. More importantly, dispersal information provided evidence to









that managers can make judgments about whether stocking these fish is an effective tool. It also

provided information about how often stocking might be needed to meet a particular

management goal. Additionally, information about the dispersal of stocked fish, and a

determination of whether stocked fish preferentially chose un-surveyed canals was important to

explain the patterns of persistence that might be observed. The influence of environmental

factors affecting largemouth bass abundance and the fishery was investigated so that the use of

the stock enhancement project could be described in a broader management context.









of each electrofishing transect. All largemouth bass that were caught in each sampling transect

were measured for total length in millimeters (mm). Largemouth bass were then examined for

pelvic fin clips and/or an orange Hallprint dart tag. Tag numbers and fin clips were recorded and

the fish were returned to the lake after processing.

Data Analysis: Dispersal of individual tagged fish was determined using a GPS to

determine release coordinates and electrofishing recapture coordinates, which were plotted using

ArcView GIS (HCL Technologies Ltd., New Delhi India). Electrofishing GPS recapture

coordinate data were also obtained from FFWCC (personal communication, John Benton, Eustis

Laboratory). Once points were loaded for an individual tagged fish, the ArcView measuring

tool was used to estimate dispersal distance. Measurements were made between the stocking

point and the closest start or end point in the electofishing transects using straight lines staying in

the bounds of Lake Griffin waters and around land features in ArcView. Minimum, maximum,

and mean distance stocked largemouth bass dispersed from release site were calculated.

To determine if wild largemouth bass electrofishing CPUE (largemouth bass per hour of

electrofishing) were different between canal and main lake habitats, the mean electrofishing

CPUE, fish per hour, was calculated for each transect in canals and the main body. Once the

means were calculated for both data sets, the data were transformed [LoglO (catch+1)] to

normalize the distribution. The transformed mean CPUE for canals and main lake were then

compared using a t-Test: Two-Sample Assuming Unequal Variances. Microsoft Excel was used

for this analysis and the alpha level of rejection was set at 0.05.

The percent contribution and persistence of stocked fish was calculated simply by the ratio

of marked (tagged and clipped) largemouth bass to all largemouth bass captured during

electrofishing for each sampling period. To obtain catch per unit effort for largemouth bass,









call-in survey reported 326 largemouth bass catch locations of which 84 (26%) were from the

main part of Lake Griffin (creel zone) and 212 (65%) were reported from non-stocked adjacent

waters (e.g., connected canals and marshes). The other 30 caught largemouth bass (9%) were

reported from other non-stocked waters (e.g., Lake Eustis). The greater number of largemouth

bass caught in the canals (Larson 2009) raised the question of whether the stocked fish were

preferentially selecting the adjoining waters or were being displaced into canals due to lack of

available habitat in the main lake.

Mesing and Wicker (1986) found several fish migrated up to 3 km from their home ranges

during the spawning season to wave-protected sites within canals. Lake Griffin has many wave-

protected canals and stocked fish were present in these areas during the spawning season.

Differences in the mean CPUE of all largemouth bass captured in the main lake versus the canals

were examined to assess if stocked fish were preferentially selecting the canals or being

displaced from the main lake. It did not appear that stocked largemouth bass had any greater

preference for canals than wild fish. The ratio of the numbers of stocked fish in the canals

collected by electrofishing to wild fish was similar to that found in the lake over the study period

(Table 4-1, Table 4-2).

When comparing the native largemouth bass electrofishing catch, the mean CPUE for

canals was 41fish/hour, with a minimum of 0 fish/hour and a maximum of 114 fish/hour. The

mean CPUE for the main lake was 44 fish/hour, with a minimum of 0 fish/hour and a maximum

of 138 fish/hour. The results from the t-test comparing the mean CPUE (logl0 ([catch +1)]

transformed) between canal and main lake areas found that the mean CPUEs were not

significantly different (t= -1.049, df=150, P two tail = 0.296). This finding strongly suggests that

the fish were not preferentially seeking the canals nor were they being displaced from the main










-- Yearly Water Level Change


60.50
60.00
59.50
59.00
58.50
58.00
57.50
57.00
56.50
56.00
1945 1955 1965 1975 1985 1995 2005
Year


Figure 2-3. Annual mean water level and yearly change in water level
Lake Griffin, Florida (data obtained from SJRWMD).


200
180
160
140
120
100
80
60
40
20
0


from 1946 to 2007, for


-, I


1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Year

Figure 2-4. Annual mean total phosphorus (tg/L) for Lake Griffin, Florida (data obtained from
FFWCC, SJRWMD, and Florida LAKEWATCH).


- Mean W'ater Level









There was no relationship between angler catch and electrofishing CPUE (R2=0.000013, P

> 0.05, N= 1) of largemouth bass (Figure 4-15). The primary reason for decreased angler catch

of largemouth bass in 2004 to 2006 (3 lowest years ever measured) was a decrease in angler

effort (Figure 4-16). Unfortunately, anglers were not surveyed for long periods of time at Lake

Griffin by FFWCC's roving creel survey, because of lack of angler effort. Angler effort was

highest from 1987-1990 (Figure 4-16) when large year classes were produced in prior years

when the lake had 20% coverage of aquatic plants (i.e., 1984 to 1986). These year classes

eventually produced trophy fish. In the late 1990s, the lake started getting bad press due to

environmental problems (dead floating alligators, toxic algae, low lake levels) and the negative

image probably drove anglers and other recreational users away from Lake Griffin (HCLRC

2002).

When creel surveys resumed in 2004, few anglers were using the Lake Griffin resource

(Figure 4-16). In 2005, Lake Griffin received its first stocking of adult-sized largemouth bass.

Over the next two years, there was a slight increase in angling effort (724 hours 2003, 2649

hours 2004, 4034 hours 2005, and 6443 hours 2006; Figure 4-16). Angler effort in the 2006 creel

survey, however, was still low compared to historical levels. Largemouth bass angler catch per

effort initially increased greatly in 2004 and has not decreased from historical levels (Figure 4-

17).

The electrofishing CPUE of largemouth bass (> 200 mm TL) appears to be back to

previously measured levels (Figure 4-12), but creel catch and effort are down (Figure 2-11, 4-

16), which suggest that the fishery is partially psychologically driven rather than biologically

driven and/or the bad press the lake received in the late 1990s is taking longer than the fish

population to recover. Based on electrofishing CPUE, the fish should be there. Larson's (2009)












-.3 + 2008


S2.5 0 2004

I-
S1.5- o Linear (2008)
S1 y = 3.2186x- 5.4127
0.5 -- Linear (2004)
0 y= 3.329x- 5.7039

2 2.5 3

LoglO Total Length (gm)


Figure 4-3. The loglO total length verses loglO weight of native largemouth bass pre (2004) and
post (2008) stocking in Lake Griffin, Florida (data obtained from FFWCC).


- Linear (2008)

_-- Linear (2004)


LoglO Total Length (gm)


Figure 4-4. The loglO total length verses loglO weight linear regression line comparison of
native largemouth bass pre (2004) and post (2008) stocking in Lake Griffin, Florida
(data obtained from FFWCC).












m u- .

d-0.2- *
N -0.4-

S-0.6-
LI.
0 -0.8-
o
0
0 *
-J .2-

-1.4- I I I I I-
-0.8 -0.6 -0.4 -0.2 0 .1 .2 .3 .4 .5
Log10 Secchi Depth (m)
Figure 4-13. Relationship between LoglO CPUE (fish per minute) for all sizes of largemouth
bass captured by electrofishing and Secchi depth (m) with a linear line fit to the data
(R2=0.43), for Lake Griffin, Florida, for data collected from 1969 to 2007 (data
obtained from FFWCC, SJRWMD, and Florida LAKEWATCH).




-*- Chlorophyll -*-Average Water Level


350
300
250
200
150
100
50
0 -
1965


60.50
60.00
59.50
59.00
58.50
58.00
57.50
57.00
56.50
56.00


1975 1985 1995 2005


Year


Figure 4-14. Annual mean chlorophyll concentration and annual mean water level for Lake
Griffin Florida (data obtained from FFWCC, Florida LAKEWATCH, and
SJRWVMD).









2.6-
2.5-
22.4-
g2.3-
=2.2-
2.1-
o 2-
1.9-
-
0
o 1.8-
1.7-
1.6-
1.5-
1.4-


1.7 1.8


1.9 2 2.1 2.2 2.3


Log 10 Total Phosphorus(pg/L)

Figure 4-9. Relationship between loglO chlorophyll (tg/L) and loglO total phosphorus (tg/L)
with a linear line fit to the data (R2=0.16), for Lake Griffin, Florida, for data collected
from 1974 to 2007 (data obtained from FFWCC, SJRWMD, and Florida
LAKEWATCH).


3.3 3.4 3.5 3.6 3.7 3.8
LoglO Total Nitrogen (pg/L)
Figure 4-10. Relationship between loglO chlorophyll (gg/L) and loglO total nitrogen (gg/L)
with a linear line fit to the data (R2=0.66), for Lake Griffin, Florida, for data collected
from 1969 to 2007 (data obtained from FFWCC, SJRWMD, and Florida
LAKEWATCH).



























1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Year

Figure 2-7. Annual mean Secchi depth (cm) for Lake Griffin, Florida (data obtained from
FFWCC, SJRWMD, and Florida LAKEWATCH).


600

S50%

o 40%

o 30%

0 20%
0)
> 10%

0%


I i i N


1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Year

Figure 2-8. Aquatic macrophyte areal coverage estimated by aerial photographs, for Lake
Griffin, Florida (data obtained from FFWCC).









artificial habitat is recommended for the main lake along with continued stocking of wild adult

largemouth bass. Stocking wild-adult largemouth bass captured from non-fished waters is a

cost-effective fisheries management tool, supported by anglers, and the weight of scientific

evidence suggests only positive effects.









study estimated the economic impact generated by stocking to be ranging into the millions of

dollars. During this time period, the lake was getting good press, which most likely had an effect

on angler effort. One of the major objectives of Larson's study was to stimulate angler interest

in the lake. Stocking large fish in public view should have an effect on effort. A primary goal of

fish and wildlife management agencies is to increase angler effort on water bodies because this

increases license sales and economic activity associated with the fishery.










6000 --- --- Total Nitrogen 350

5000 ---Total Phosphonrs -300
SChllorophyll 250
4000
,- 200
3000 -
S.- 150

----2000-------- o
0 0
1000 0 0 00

0 .. 0

S---1 ---1 00 C00 I I 0 0
'tN C0 0- 0I < i O 1'C
Year


Figure 4-8. Total nitrogen (gg/L), total phosphorus (gg/L), and chlorophyll concentration (gg/L)
trends for Lake Griffin, Florida (data obtained from FFWCC, Florida
LAKEWATCH, and SJRWMD).









non-fished waters and there are many others sources of wild adult largemouth bass in Florida.

Stocking these fish into a large hypereutrophic lake resulted in a significant increase of fish,

although, we don't know if it is an addition or replacement. Stocked largemouth bass dispersed

over distances ranging up to 9 km and fish did not seem to suffer abnormal mortality rates

compared to the native fish due to stocking stress. Stocked fish are still present in the Lake

Griffin fishery two years after the last stocking event and the mortality rate was similar to the

native fish in the lake. The stocking event did not cause a change in fish condition indicating

that there is plenty of forage available. Stocked largemouth bass were not being displaced into

canals and seem to be mixing evenly throughout the population in the main lake, strongly

suggesting better habitat is needed in the main lake to attract fish and anglers.

Overall, there have been no measurable negative effects of stocking and given the "weight

of evidence argument", fish management agencies should consider the stocking of wild-adult

largemouth bass as a viable fishery management tool. When assessing complex environmental

issues such as those at Lake Griffin, it is difficult to prove anything with 100% certainty or

establish strong environmental/biological relationships. Consequently, fisheries management is

art and science; for many issues such as supplemental fish stocking, the scientific community

shall remain divided, with some individuals being strong advocates for stocking and some being

just as strong detractors (Mesing et al. 2008). Such controversy will probably continue to exist

after decades of debate because the criteria for success are ever changing.









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

EFFECTS OF STOCKING WILD-ADULT LARGEMOUTH BASS ON THE FISHERY AT
LAKE GRIFFIN, FLORIDA

By

Darren John Pecora

August 2009

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

Lake Griffin was stocked with approximately 14,000 wild-adult largemouth bass from

2005 to 2007 to stimulate economic activity related to the fishery. An electrofishing survey was

initiated at Lake Griffin in 2007 to determine the status of the stocked fish population 3 years

after stocking. The mean dispersal distance from stocking sites for 122 caught stocked

largemouth bass was 2.9 km, with the maximum-recorded distance being 9.2 km. Mean CPUE

(fish/hour) of native largemouth bass between canal and main lake areas were not significantly

different, indicating stocked and wild fish were mixing evenly. Mortality estimates for stocking

years 2006 (Z= 1.087) and 2007 (Z=1.295) are similar to the 2007 native largemouth bass

estimates (Z= 1.054). There was no change in native largemouth bass condition post stocking.

The stocked largemouth bass in May 2007 contributed 13% to total electrofishing largemouth

bass catch, with a CPUE of 0.09 (fish/minute) immediately after the last stocking in 2007. Two

years later, in March 2009, the total electrofishing catch of stocked largemouth bass was 3%,

with a 0.03 (fish/minute) CPUE. Water level and macrophyte abundances were the primary

environmental factors influencing largemouth bass abundance, but management actions focusing

on these factors have been rejected by the public, and climatic conditions may prevent enhanced

lake fluctuation. To enhance the largemouth bass fishery at Lake Griffin, construction of









CHAPTER 5
FISHERY MANAGEMENT IMPLICATIONS

When Lake Griffin was sampled immediately following the last stocking in 2007, stocked

fish represented 10 to 15% of the catch. The percent contribution information demonstrates that

the stocking program impacted the largemouth bass population in Lake Griffin. Larson (2009)

also estimated that the stocking program enhanced revenues (ranging from $324,000 to 2.7

million dollars) to the local communities. Thus, stocking of wild-adult bass, with its apparent

positive cost:benefit ratio, was recommended by Larson (2009) as a viable fish management tool

for Lake Griffin.

An angler creel survey is perhaps the most important fisheries management survey to

evaluate fisheries, because it provides information on what the anglers are experiencing.

Interpretation of results, however, must be placed in context before statements are made

regarding the success or failure of a management action. The situation at Lake Griffin is a prime

example. The 2006 FFWCC creel survey did not provide evidence for the success of the Florida

LAKEWATCH wild-adult largemouth bass stocking program. The creel survey was conducted

in the open lake and failed to consider the myriad of canals and adjoining waters where anglers

could and did catch fish.

As stated over 20 years ago by Mesing and Wicker (1986), creel surveys on large Florida

lakes should include canal areas connected to the lake if realistic harvest figures are to be

obtained during the spawning season. When considering the catch information from canals

collected by Larson (2009), an argument for the cost-effectiveness of the stocking program can

be advanced. However, at Lake Griffin, it is now clear that the presence of canals influenced

angler catch and harvest estimates, thus future angler surveys at Lake Griffin should include

adjoining waters like canals. The challenge is maintaining the past survey protocol sufficiently









LIST OF TABLES


Table page

2-1 Water level and water quality parameters (mean and ranges) for Lake Griffin,
F lorida ...................................... ........... ........ ... ....... 24

3-1 The date and number of electrofishing transects sampled in main lake areas and canal
areas of Lake Griffin, Florida from April 23, 2007 to March 13, 2009. ........................ 37

4-1 Electrofishing sampling results for canals; total catch of largemouth bass greater than
200 mm TL, stocked largemouth bass catch (marked), stocked fish per minute
(CPUE), and percent of stocked fish to total catch (% total catch) for Lake Griffin,
F lorida ...................................... ........... ........ ... ....... 49

4-2 Electrofishing sampling results for main lake total catch of largemouth bass greater
than 200 mm TL, stocked largemouth bass catch (marked), stocked fish per minute
(CPUE), and percent of stocked fish to total catch (% total catch) for Lake Griffin,
F lorida ...................................... ........... ........ ... ....... 49

4-3 A comparison of mortality estimates Z-Annual (instantaneous mortality rate), S-
Annual (annual survival), and A-Annual (annual total mortality) of stocked
largemouth bass and native largemouth bass from Lake Griffin, Florida..........................49

4-4 Electrofishing sampling combined results for main lake and canal; total catch of
largemouth bass greater than 200 mm TL, stocked largemouth bass catch (marked),
stocked fish per minute (CPUE), and percent of stocked fish to total catch (% total
catch) for Lake Griffin, Florida....................... ..................................... 50









Table 4-1. Electrofishing sampling results for canals; total catch oflargemouth bass greater than
200 mm TL, stocked largemouth bass catch (marked), stocked fish per minute
(CPUE), and percent of stocked fish to total catch (% total catch) for Lake Griffin,
Florida.
Electrofishing Sampling For Canals
Date Total Catch Marked CPUE % Total Catch
Jun-07 262 39 0.10 15
Nov-07 50 2 0.02 4
Feb-08 94 5 0.04 5
Mar-08 103 7 0.04 7
Jun-08 109 9 0.05 8
Mar-09 134 6 0.03 4


Table 4-2. Electrofishing sampling results for main lake total catch of largemouth bass greater
than 200 mm TL, stocked largemouth bass catch (marked), stocked fish per minute
(CPUE), and percent of stocked fish to total catch (% total catch) for Lake Griffin,
Florida.
Electrofishing Sampling For Main Lake
Date Total Catch Marked CPUE % Total Catch
May-07 964 123 0.09 13
Nov-07 191 11 0.04 6
Feb-08 176 8 0.04 5
Mar-08 154 8 0.04 5
Jun-08 174 5 0.02 3
Mar-09 116 2 0.01 2


Table 4-3. A comparison of mortality estimates Z-Annual (instantaneous mortality rate), S-
Annual (annual survival), and A-Annual (annual total mortality) of stocked
largemouth bass and native largemouth bass from Lake Griffin, Florida.
Lake Griffin Largemouth Bass Mortality Parameter Estimates
Parameter 2007 Tags Only 2006 Tags Only Native Fish 2007 Catch Curve


Z-Annual
A-Annua
S-Annual


1.295 1.087 1.054
1 0.726 0.663 0.652
0.274 0.337 0.348









CHAPTER 2
STUDY SITE DESCRIPTION AND LAKE GRIFFIN'S ENVIRONMENTAL HISTORY

Introduction

Lake Griffin is a large (6,680 ha) hypereutrophic (mean chlorophyll 99 [g/L; Table 2-1)

freshwater lake in central Florida (Figure 2-1) (Canfield 1981). The lake has been studied by

numerous organizations since the 1940s and this study used a great deal of the historical

environmental information understand the environmental factors influencing Lake Griffin's

largemouth bass population. Water level information from 1946 to 2007 was obtained from St.

Johns River Water Management District (SJRWMD). Water quality data including chlorophyll,

total nitrogen, and total phosphorus concentrations as well as Secchi depth (1969 to 1978 and

1981 to 1994) were primarily obtained from FFWCC (personal communication Bill Johnson,

Eustis Laboratory), but information was also obtained from the files of Florida LAKEWATCH

(1979 to 1980; downloaded from wateratlas.org) and SJRWMD (1995 to 2007; personal

communication Brian Sparks, Palatka office). Total aquatic macrophyte coverage (percent lake

surface area), as estimated by aerial photography since 1947, was obtained from the files of

FFWCC (personal communication Bill Johnson, Eustis Laboratory). The Florida Department of

Environmental Protection (FLDEP) provided estimates of the percent area coverage of hydrilla

(personal communication Rob Kipker, Tallahassee office). Largemouth bass population

abundance data, including electrofishing catch-per-unit-effort (CPUE) and roving creel data

(harvest, catch, effort), were obtained from FFWCC (personal communication Bill Johnson,

Eustis Laboratory).

Geography

Lake Griffin is located primarily in Lake County, Florida, (Shafer et al. 1986) (Figure 2-1)

in Florida's Central Valley physiographic region (Canfield 1981). Lakes in the Central Valley

















I~i4LL~l


I I II I I I


I I I


* Native Fish
m Stocked Fish


0 -
o I I I I I I I
c)- J1A A (A L A C --C ( I
000000000000
Total Length (mmu) Main Lake March 2009


4ELLEII.


LArO
00


I0 L

Li 0
_r_ _r


LA 0 0LA
I l
000
O Us ,


m Native Fish
m Stocked Fish


Total Length (nun) Canals March 2009


Figure 4-5. Continued.









CHAPTER 1
INTRODUCTION

Largemouth bass (Micropterus salmoides) is one of the most sought after sportfish in the

United States (U. S. Department of the Interior 2006). Florida largemouth bass (M.s.floridanus)

is an economically important game fish, contributing 632 million dollars per year to Florida's

economy (U. S. Department of the Interior 2006). Lake Griffin, a 6,680-ha hypereutrophic lake

in Central Florida, supported a recreational fishery valued at 2.3 million dollars annually in the

late 1980s (Milon and Welsh 1989). However, the value of the sport fishery had declined by

90% by the late 1990s, which was directly linked to the decline of the largemouth bass fishery

(Benton 2000). According to Larson (2009), the stocking of wild-adult largemouth bass into

Lake Griffin by the University of Florida's Florida LAKEWATCH program after 2004 was

responsible for an economic improvement of up to 2.7 million dollars per year. The reported

economic enhancement by stocking wild-adult largemouth bass, however, has been questioned.

Fish sampling revealed that only up to 10% of the Lake Griffin largemouth bass population

consisted of the Florida LAKEWATCH-stocked largemouth bass soon after stocking. This lead

to the questioning of the effectiveness of the enhancement by Florida Fish and Wildlife

Conservation Commission (FFWCC) biologists working on Lake Griffin (HCLRC 2007) and

University of Florida faculty (Dr. Mike Allen, personal communication, University of Florida).

The low catch rate of stocked fish may have been the result of not stocking enough fish, fish

moving out of the lake, or an excessive fish mortality rate from handling stress or a lack of

adequate forage.

The sport fish population and fishery of Lake Griffin were at a historical low point in 1999

(Benton 2000). As a result, interest in stocking the lake with largemouth bass became a priority

for the Harris Chain of Lakes Restoration Council, a legislatively-appointed citizen's advisory













6000

5000

4000

3000

2000

1000


0 I I I I I
1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Year

Figure 2-5. Annual mean total nitrogen ([g/L) for Lake Griffin Florida (data obtained from
FFWCC, SJRWMD, and Florida LAKEWATCH).


350
S300
250
200

o 150
100
-C
00
g 50
5 0
1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Year

Figure 2-6. Annual mean chlorophyll concentrations (gg/L) for Lake Griffin, Florida (data
obtained from FFWCC, SJRWMD, and Florida LAKEWATCH).









received maintenance dredging. This dredging was promoted: to increase boaters' access and

allow for enhanced lake level fluctuation (i.e., 1-3 feet) (HCLRC 2007). The increased water

level, of Lake Griffin after the 2004 hurricane season, coincided with a positive response in the

CPUE of largemouth bass, reaching historical high levels (Figure 4-7). Major drawdowns (i.e., 3

feet or more) don't provide boaters access, but enhanced fluctuation is not as disruptive.

Therefore, regularly-scheduled enhanced fluctuations (reduce water levels to the outer edge of

the emergent macrophytes), such as the one in 2002-2003, would provide fish managers with

their best opportunity to maintain a reasonable largemouth bass population, if public support for

a major lowering of water levels cannot be garnered.

A potential problem, for even well-managed enhanced water level fluctuations, is that

major droughts have struck Florida in recent years. Florida's water managers, therefore, tend to

be conservative even with enhanced fluctuation so as not to garner public opposition when

drought conditions occur. The water managers rely on weather modeling for precipitation

predictions, thus even well-planned enhanced fluctuations could be precluded for extended

periods of time, especially if sufficient water cannot be stored in the upstream lakes. Another

major drawback of water level fluctuation in the eyes of the public and some environmental

agencies is the potential growth of hydrilla. Unless the prevailing attitudes towards hydrilla

change (Hoyer et al. 2005), hydrilla at Lake Griffin will have to be managed, which can be

expensive.

Like the canals, the presence of reconnected marshes may not substantially increase angler

effort within Lake Griffin proper. In examining trends in largemouth bass CPUE for fish >200

mm TL (Figure 4-7), the evidence is pretty strong that harvestable-size largemouth bass should

be sufficiently abundant in the main stem of Lake Griffin to support fishing, but angler effort










Table 3-1. The date and number of electrofishing transects sampled in main lake areas and canal
areas of Lake Griffin, Florida from April 23, 2007 to March 13, 2009.
10-Minute Electrofishing Transects on Lake Griffin
Date Main Lake Transects Canal Transects
04/23/2007 17 0
05/15/2007 16 0
05/17/2007 16 0
05/22/2007 16 0
05/23/2007 16 0
05/24/2007 16 0
05/29/2007 16 0
05/30/2007 10 0
05/31/2007 16 0
06/05/2007 0 17
06/06/2007 0 13
06/07/2007 0 9
11/05/2007 15 5
11/06/2007 14 5
02/19/2008 9 8
02/20/2008 12 4
03/12/2008 8 9
03/13/2008 10 7
06/24/2008 14 2
06/25/2008 8 8
06/26/2008 8 8
03/12/2009 8 8
03/13/2009 6 10









basin where adult fish were relocated from lands flooded by the river to nearby lakes and

reservoirs. For a while, the fish rescue programs were an important fisheries management tool.

Consequently, collection and stocking of wild-adult largemouth bass from non-fished private

Florida waters could also become a useful fisheries management tool in Florida.

As with any tool, its cost-benefit must be considered. There are dollar costs and biological

costs, especially if the management tool has a negative impact (e.g., reduced fish condition factor

resulting from over stocking) on the fisheries. A review of the literature finds stocking programs

often report mixed results because of different agency objectives (Hoffman and Bettoli 2005).

More importantly, the positive impacts of largemouth bass stocking programs on fisheries are

often underestimated (Copeland and Noble 1994) because there are no established guidelines to

measure the success of supplemental stocking (Heidinger and Brooks 2002). Biologists use a

number of different criteria to evaluate stocking programs, including: stocked fish harvested,

percent of stocked fish in a year class, and cost:benefit ratios (Heidinger and Brooks 2002).

Cost-benefit ratios are typically calculated from creel surveys that evaluate the catch of stocked

fish by anglers.

Florida LAKEWATCH is the only organization to stock wild-adult largemouth bass on

such a massive scale in Florida (Florida LAKEWATCH 2007). Larson (2009) studied the

associated economic activity at Lake Griffin for Florida LAKEWATCH following the stocking

of wild-adult largemouth bass and concluded the approach was cost-effective based on the

estimated revenue generated and the stimulation of angler interest. However, the survival of

stocked fish and their contribution to the fishery has been questioned as a result of findings from

a FFWCC creel survey of Lake Griffin in 2006, two years after the initial stocking. This creel

survey, however, only covered the main stem of Lake Griffin, not its adjoining canals, marshes,









LIST OF REFERENCES


Bachmann, R. W., M. V. Hoyer, and D. E. Canfield, Jr. 1999. The restoration of Lake Apopka in
relation to alternative stable states. Hydrobiologia 394:219-232.

Bachmann, R. W., M. V. Hoyer, and D. E. Canfield, Jr. 2000. The potential for wave disturbance
in shallow Florida lakes. Lake and Reservoir Management 16:281-291.

Benton, J. W. 2000. Central Florida Fisheries Development: Lake Griffin Fisheries
Improvement. Annual Report for 1999-2000. Florida Game and Freshwater Fish
Commission. Tallahassee, FL. P. 10-31.

Buynak, G. L., B. Mitchell, D. Michaelson, and K. Frey. 1999. Stocking subadult largemouth
bass to meet angler expectations at Carr Creek Lake, Kentucky. North American Journal of
Fisheries Management 19:1017-1027.

Canfield, Jr., D.E. 1981. Chemical and trophic state characteristics of Florida lakes in relation to
regional geology. Florida Agricultural Experimental Station Journal Series 3513.

Canfield, Jr., D.E. 1983. Prediction of chlorophyll a concentrations in Florida lakes: the
importance of phosphorus and nitrogen. Water Recourses Bulletin 19:255-62.

Canfield, Jr, D.E., and L. M. Hodgson. 1981. Prediction of Secchi disc depths in Florida lakes;
Impact of algal biomass and organic color. Florida Agricultural Experimental Station
Journal Series 3255.

Carlander, H.B. 1954. A history of fish and fishing in the Upper Mississippi River. Upper
Mississippi River Conservation Committee, Rock Island, Illinois.

Cole, G.A. 1983. Textbook of Limnology, 3rd Edition. C.V. Mosby Company. St. Louis,
Missouri.

Copeland, J. R., and R. L. Noble. 1994. Movements by young-of-year and yearling largemouth
bass and their implications for supplemental stocking. North American Journal of
Fisheries Management 14:199-124.

Crowder, L. B., and W. E. Cooper. 1979. Structural complexity and fish-prey interactions
in ponds: A point of view. Pages 2-10 in, Johnson, D. L., and R. A Stein, editors.
Response of fish to habitat structure in standing water. North Central Division, American
Fisheries Society, Spec. Publication No. 6.

Demers, E., R. S. McKinley, A. H. Weatherley, and D. J. McQueen. 1996. Activity patterns of
largemouth and smallmouth bass determined with electromyogram biotelemetry.
Transactions of the American Fisheries Society 125:434-439.

Dequine, J. F., and C. E. Hall, Jr. 1950. Results of some tagging studies of the Florida
largemouth bass, Micropterous salmoidesfloridanus. Transactions of the American
Fisheries Society 79:155-166.









































Figure 2-1. Map of Lake Griffin, Lake County, Florida.









economic stimulus (ranging from $324,000 up to $2.7 million per year). Also, fisheries

managers must understand that the ability of largemouth bass to move distances on the

magnitude of kilometers may result in non-stocked adjoining waters being stocked, thus diluting

the impact of stocking on the receiving water. Depending on lake size, stocking at multiple sites

quickly disperse fish throughout the system.









TABLE OF CONTENTS



A C K N O W L E D G M E N T S ......... ............... ...................................................................................... 4

LIST O F TA B LE S ....... .. ............. ..... ................................ ... ......... ....... 6

L IST O F FIG U R E S ..................................................... .............................. 7

A B STR A CT ...................... ...................... .......... ................ 10

CHAPTER

1 IN T R O D U C T IO N ............................................................................................ ..................... 12

2 STUDY SITE DESCRIPTION AND LAKE GRIFFIN'S ENVIRONMENTAL
HISTORY ...... ............................................ ................... .19

Introduction ........................................ ..................... 19
G eo g ra p h y ................... ................... ...................1.........9
W after L ev e ls ............................................................................................ 2 0
W after Quality ..................................... ............. ............... 21
A quatic M acrophytes ...................................................... 22
Largem outh B ass Population....................................................................................................... 23
L arg em ou th B ass F ish ery ............................................................................................... 2 3

3 M ETH OD S ........................................ ..................... 32

4 RESULTS AND DISCUSSION ........... .............................38

Introduction ........................................ ..................... 38
F ish D isp ersal ................... ..............................................3 8
M mortality .. ................................................... 4 1
P ersisten c e ................................ ................................................................................................... 4 2
Lake Griffin Fish Condition ......................................... ........................ 42
Native Verses Stocked Largemouth Bass Length-Frequency ...............................................43
Environment Factors and Largemouth Bass..................... ..... ..................... 43

5 FISHERY MANAGEMENT IMPLICATIONS ................................... 63

6 C O N C L U S IO N ...............................................................................................................6 8

LIST OF REFEREN CE S ......... .............................................................................. ............... 70

B IO G R A PH IC A L SK E T C H ....................................................... .............................................. 74









different. However, the 2008 values and most of the measured weights in 2008 were greater than

those recorded in 2004 (Figure 4-4). This finding demonstrated no negative change in the

weight-length relationship after stocking, suggesting there was plenty of forage in Lake Griffin.

Native Verses Stocked Largemouth Bass Length-Frequency

Stocking adult largemouth bass could potentially alter the length frequency of largemouth

bass in Lake Griffin. The length frequency of native verses stocked largemouth bass caught by

use of electrofishing on three different sampling events spaced roughly one year apart ((Figure 4-

5 (A-F)) are all different, but stocked fish do contribute weakly to the length frequency. The

length frequency distribution between fish caught in canals and the main lake also appear to be

different ((Figure 4-5 (A-F)). Examining the largemouth bass cohort trends reveal a large size

class (301-350 mm TL and 351-400 mm TL) that shows up in the May 2007 catch, and moves

through larger size classes over the next two years ((Figure 4-5 (A)). In the main lake sample

from March 2009, a large size class (151-200 mm TL), presumably young-of-the-year, enters the

catch ((Figure 4-5 (E)). This size class of young-of-the-year was the largest sampled during this

project, which indicates that recruitment of largemouth bass was occurring naturally.

Recruitment of fish from spawning in Lake Griffin therefore probably diminished persistence

and percent contribution estimates and potentially inflated the mortality estimates. Biologists,

however, should expect such changes when stocking any lake where a resident population

already exists.

Environment Factors and Largemouth Bass

Lake Griffin's largemouth bass fishery and population has gone through many changes. In

Florida, lake level fluctuation has often been considered as a dominant factor influencing fish

populations (Moyer et al. 1995). Historically, Lake Griffin and the Harris Chain of Lakes

fluctuated more than the current regulation schedule permits (Figure 2-3). Water level









4-16 Angler effort (hours) for largemouth bass, estimated by roving creel survey for Lake
Griffin, Florida (data obtained from FFWCC). ......................................................... 61

4-17 Historical angler effort (hours) and catch per effort (fish per hour) for largemouth
bass, based on roving creel survey data (data obtained from FFWCC). ........................ 62









indicate that the non-native hydrilla (Hydrilla verticillata) peaked in abundance (11% areal

coverage) in 1987 following the 1984 experimental drawdown (Figure 2-9). By 2001, hydrilla

coverage was reduced to 0.009% and overall aquatic plant coverage was reduced to <2% by

2006 (Figure 2-9). Lake Griffin has changed from a macrophyte dominated system to an open-

water algal system since the 1960s with many of the water quality changes reflecting

expectations with the establishment of the new alternative state (Bachmann et al. 1999).

Largemouth Bass Population

Largemouth bass electrofishing CPUE were depressed during the late 1990s and early

2000s (Figure 2-10). Young of the year (<200 mm) largemouth bass electrofishing CPUE was

the highest ever recorded following the1984 drawdown (Figure 2-10). This largel984 year class

can be seen in the fishery for years following the 1984 drawdown with historic high catches of

harvestable sized fish (>360 mm, Figure 2-10).

Largemouth Bass Fishery

Roving creel surveys were first conducted by FFWCC starting in 1966. Estimates of catch

and release of largemouth bass were not made during the early years of the creel survey. An

estimated 23,722 largemouth bass were harvested during the first year (1968) the survey was

conducted, which was the highest harvest on record (Figure 2-11). Catch (catch and release) of

largemouth bass, first estimated in 1978, reached a high point of 20,000 fish in 1987 and a low of

121 fish in 2003 (Figure 2-11). Catch and harvest of largemouth bass have declined since 1971

except following the experimental drawdown in 1984.









Persistence

Another important question related to the Florida LAKEWATCH stocking program was

the persistence of the stocked fish; this will provide some assessment of how long anglers could

expect to catch stocked fish. In this study, the last fish stocking occurred in March 2007. In

May and June 2007, the highest percent (13% main lake, 15% canals) of stocked fish was

captured and CPUE was the highest measured (0.09 fish/minute in main lake, 0.10 fish/minute in

canals; Table 4-1, Table 4-2). Combining the main lake and canal areas for a total contribution

percentage and CPUE also yielded the highest catch estimates in May (13% and 0.09 fish/minute

CPUE; Table 4-4). Two years after the last stocking event (March 2009), electrofishing

demonstrated that stocked largemouth bass were still present in the population (2% and 0.01

fish/minute CPUE in main lake; 4% and 0.03 fish/minute CPUE in canals; Table 4-1, Table 4-2).

When the two regions of Lake Griffin are considered a single unit, the estimate was 3% and 0.03

fish/minute CPUE (Table 4-4).

There were no rewards for the largemouth bass that Florida LAKEWATCH stocked and no

tag call-in advertisements. Stocked largemouth bass with tags are still being reported in the

fishery by anglers (2009, four stocked fish reported) (Larson 2009). Recruitment of largemouth

bass into the fishery may also contribute to reduced stocked fish catches.

Lake Griffin Fish Condition

Overstocking a lake with too many top predators can adversely affect the predator prey

"balance" and affect the weight of individual fish because of a lack of forage (Noble 1981). The

length-weight relationship for native largemouth bass in 2004 (pre-stocking) was compared to

the 2008 (post stocking) relationship in Lake Griffin to determine if the condition of resident

bass was reduced (Figure 4-3). An ANOCOVA analysis indicated the slopes (Pr > F = 0.0274, >

a=0.05) and intercepts (Pr > F = 0.018, < a=0.05) of the regression lines were significantly









aquatic macrophyte percent aerial coverage) and largemouth bass abundance estimates

(electrofishing CPUE and roving creel catch) were investigated using correlation analysis. JMP

version 5.01 software (SAS Institute 1989) was used for all statistical analyses. Data were

transformed (Log 10) and the alpha level of rejection was set at 0.05.








Lake Griffin
Canal Dredging


SCompleted
Under Piog'ess


Figure 2-2. Map of Lake Griffin canals which were dredged from 2005 to 2007.


ILCWAI









nutrient concentrations, particularly nitrogen and phosphorus, in Florida's lakes (Canfield 1983);

Lake Griffin shows this trend (Figure 4-8).

Chlorophyll concentrations in Lake Griffin were significantly related to total phosphorus,

but the relationship was weak (R2=0.16; P < 0.05, N=31) (Figure 4-9). On the other hand,

chlorophyll concentrations had a strong relationship (R2=0.66; P< 0.001, N=34) with total

nitrogen, which suggests that Lake Griffin is nitrogen limited (Figure 4-10).

Chlorophyll concentrations in Lake Griffin had a significant relationship (R2=0.31, P<

0.001; N=34) with water clarity as measured with a Secchi disc (Figure 4-11). Electrofishing

catchability decreases with high chlorophyll concentrations due to reduced water clarity because

it is harder to see stunned fish (Reynolds 1996, Mclnerny and Cross 2000). In the sampling

events between 1997 through 2002, electrofishing largemouth bass CPUE was at an all time low

compared to before and after that time period (Figure 4-12). During these times, high

chlorophyll and low water clarity may well have contributed to the lower electrofishing

catchability as Secchi depth and CPUE (LMB all sizes) exhibited a significant (R2 = 0.43; p <

0.05, N=21) positive relationship (Figure 4-13).

Elevated chlorophyll concentrations at Lake Griffin were associated with low water

conditions (Figure 4-14). Areas of Lake Griffin that were targeted for electrofishing were

typically emergent vegetation in most years. These plants may not have always been accessible

to electrofishing due to low water; therefore, water level in combination with chlorophyll at Lake

Griffin may also have had a role in this decrease in CPUE due to electrofishing catchability. The

fish may have moved to open water during the drought and were not as vulnerable to the

electrofishing gear.









CHAPTER 4
RESULTS AND DISCUSSION

Introduction

Florida LAKEWATCH stocked Lake Griffin with 13,933 wild-adult largemouth bass that

were placed into the main lake from 2005 to 2007. FFWCC surveyed anglers using Lake Griffin

proper in 2006 and showed only a limited catch of stocked fish. Florida LAKEWATCH also

found the percent of the largemouth bass population caught by use of electrofishing did not

increase above 15% despite stocking 4000 plus fish per year. These findings raised the single

most important question related to all stocking programs and that is: What happened to the

stocked fish?

Fish Dispersal

Largemouth bass are known to individually exhibit different movement patterns with some

individuals being transient while others occupy discrete home ranges (Demers et al. 1996).

Larson (2009) reported the majority (65%) of Florida LAKEWATCH-stocked fish were caught

by anglers fishing adjoining canals, marshes, and the Ocklawaha River. These angler reports

indicated the stocked largemouth bass were moving great distances from their stocking sites.

Dispersal movements of the individual stocked adult largemouth bass (N=122 fish), as assessed

by this study's electrofishing efforts were highly variable (Figure 4-1). Stocked fish dispersed

variable distances in relation to time from stocking release (Figure 4-2). A few (-16%) fish did

not leave the immediate stocking area, but the vast majority (84%) of largemouth bass traveled

over 0.5 km (Figure 4-1). The mean dispersal distance for the caught stocked fish was 2.9 km,

with minimum and maximum recorded distances of 0 and 9.2 km.

The great distance moved by the stocked largemouth bass in Lake Griffin was not a major

surprise because of the results of earlier works by Dequine and Hall (1950) and Mesing and









calculate individual stocking year 2006 mortality estimate. Data were transformed using natural

logarithms and then plotted, and CPUE was regressed against time for the sampling period. The

slope of this line is represents the instantaneous monthly mortality rate. The monthly rate was

multiplied by 12 (12 months in a year) to get an annual estimate of mortality (Z). This total

annual mortality rate (Z) was then used to calculate annual survival (S= e -Z) and annual total

mortality (A= 1-e -Z), according to Ricker (1975). The mortality calculations were then

compared to an estimate provided by FFWCC for Lake Griffin's native largemouth bass for 2007

(John Benton, personal communication, Eustis Laboratory).

To determine if there was a change in native Lake Griffin largemouth bass condition

(plumpness) after stocking, weight/length data sets, for native largemouth bass provided by

FFWCC (personal communication, John Benton, Eustis Laboratory) for 2004 (pre stocking) and

2008 (post stocking), were compared. Transformed (LoglO) weights of fish greater than 150

mm TL were regressed against transformed (LoglO) lengths for each year (2004 N= 353, 2008

N= 345) in Microsoft excel. A linear regression line was fit to each year's data and an analysis

of covariance (ANOCOVA) was completed using SAS (proc GLM; SAS Institute 2008) to test

for differences in intercepts and slopes of the regression, where the alpha level of rejection was

set at 0.05. The ANOCOVA model used to test equality of slopes was:

Log 10 WEIGHT = Log 10 TOTAL LENGTH + YEAR + Log 10 TOTAL LENGTH*

YEAR

and the ANOCOVA model used to test for differences in intercepts was:

Log 10 WEIGHT = Log 10 TOTAL LENGTH + YEAR

Patterns between available environmental parameters (i.e., total phosphorus, total nitrogen,

chlorophyll, Secchi depth, mean water level, yearly change in water level, and whole-lake









remains low (Figure 4-17). This suggests that there is an angler perception problem and work

needs to be directed towards massive habitat work that will induce anglers to fish Lake Griffin

proper.

Submerged aquatic macrophytes would be the preferred habitat for many fish biologists,

but there are many reasons why submerged plants will not become established in Lake Griffin in

a timely manner. One potential approach to attract/produce fish would then be the establishment

of large numbers/areas of artificial fish attractors, especially the creation of hard-rock bottom

with limestone as done by FFWCC at Lake Eustis off the public fishing pier. Plastic crates filled

with lime rock could be anchored in group configurations or reefs into areas of the lake to

provide fish refuge. A reef ball structure could also be used at a greater expense as a fish

attractor. Another option (even more expensive) is to remediate and or dredge the remaining

canals, which exist around the lake to provide additional fish habitat. Largemouth bass use

canals for spawning and as nursery habitat. Additional canals could also be dredged on some of

the conservation land around the lake and be protected from fishing. These artificial structures

will attract anglers as well as fish. The largemouth bass fishery at Lake Griffin is primarily a

catch and release fishery (90% of anglers; Larson 2009), so the establishment of artificial

attractors will not adversely affect the fish population. The production/attraction issue (a

concerned raised by ecologists; Wilson 2001) that is associated with artificial habitat, therefore,

is not a major concern at Lake Griffin.

Stocking additional wild-adult largemouth bass is recommended to occur simultaneously

with the habitat improvement and expansion projects because the stocked fish will at least

provide anglers with a positive outlook on the Lake Griffin fishery. It is also clear from Larson's

(2009) work that the cost of stocking (< $150,000 per year) is far less than the potential









LIST OF FIGURES


Figure pe

2-1 M ap of Lake Griffin, Lake County, Florida. ............................................ ............... 25

2-2 Map of Lake Griffin canals which were dredged from 2005 to 2007. ............................26

2-3 Annual mean water level and yearly change in water level from 1946 to 2007, for
Lake Griffin, Florida (data obtained from SJRWMD). ..............................................27

2-4 Annual mean total phosphorus (tg/L) for Lake Griffin, Florida (data obtained from
FFWCC, SJRWMD, and Florida LAKEWATCH). ....................................... ...............27

2-5 Annual mean total nitrogen (tg/L) for Lake Griffin Florida (data obtained from
FFWCC, SJRWMD, and Florida LAKEWATCH). ................................ ................ 28

2-6 Annual mean chlorophyll concentrations (tg/L) for Lake Griffin, Florida (data
obtained from FFWCC, SJRWMD, and Florida LAKEWATCH)................ ........ 28

2-7 Annual mean Secchi depth (cm) for Lake Griffin, Florida (data obtained from
FFWCC, SJRWMD, and Florida LAKEWATCH). ....................................... ...............29

2-8 Aquatic macrophyte areal coverage estimated by aerial photographs, for Lake
Griffin, Florida (data obtained from FFW CC). ............... ........................... .............. 29

2-9 Percent area coverage of hydrilla for Lake Griffin, Florida (data obtained from
FLDEP). ..................................... ........ 30

2-10 Annual mean largemouth bass electrofishing catch per unit effort (CPUE) for a
variety of sizes of largemouth bass in Lake Griffin, Florida (data obtained from
F F W C C ) ................... ................... ................... .................................... .. 3 0

2-11 Estimated annual angler catch and harvest from Lake Griffin, Florida from 1966 to
2006 (data obtained from FFW CC). .............. .. ............................... ............. 31

4-1 The percent of largemouth bass and corresponding distances dispersed from stocking
points to electrofishing recapture points in Lake Griffin, Florida. .....................................51

4-2 The dispersal distance from stocking release point verses the number of days post
stocking for electrofished recaptured largemouth bass in Lake Griffin, Florida ..............51

4-3 The loglO total length verses loglO weight of native largemouth bass pre (2004) and
post (2008) stocking in Lake Griffin, Florida (data obtained from FFWCC) .................. 52

4-4 The loglO total length verses loglO weight linear regression line comparison of
native largemouth bass pre (2004) and post (2008) stocking in Lake Griffin, Florida
(data obtained from FFW CC)..... ................................................. ....... ............... 52









fluctuation (i.e., drawdown) has therefore been used to enhance fisheries in Florida lakes (Nagid

et al. 2003).

FFWCC initiated a major drawdown of water at Lake Griffin in 1984. Following 1984,

record angler catches oflargemouth bass were measured (Figure 2-11). Electrofishing CPUE

(Figure 2-10) also reached record levels. An examination of available data for Lake Griffin

found that mean water level and electrofishing CPUE (largemouth bass (LMB) all sizes) were

significantly related (p < 0.05), but the relationship was weak (R2 = 0.31; N=21).

Based on statistically significant relationships and experience in the field, it is easy to see

why a fish and wildlife agency like FFWCC would recommend an experimental drawdown; but

in a multi-use lake like Lake Griffin attention must be paid to the concerns of the public (Hoyer

and Canfield 1994). Following the 1984 drawdown, the growth of aquatic plants was a

beneficial habitat improvement, but these plants became a weed problem for the public because

of their interference with navigation. When tested, the percent area coverage of hydrilla and

estimated angler catch at Lake Griffin also had a significant relationship (R2 = 0.32; p < 0.05,

N=12) as was the significant relationship between total percent aerial coverage of vegetation and

angler harvest (R2 = 0.27; p < 0.05, N=29). These significant relationships, however, are weak

suggesting the total amount of plants needed in Lake Griffin may not be as great as produced

during the 1984 drawdown to maintain a good fishery, and there may be other factors controlling

fish abundance.

How many aquatic plants are needed in an individual water body has been debated for

many years. Durocher et al. (1984) determined that any reduction of submerged vegetation

below 20% would result in a reduced largemouth bass standing crop in Texas reservoirs. Hoyer

and Canfield (1996) reported that there was no correlation between aquatic macrophyte









BIOGRAPHICAL SKETCH

Darren John Pecora was born in 1979, to John S. and Jolanta A. Pecora. He grew up in

Unionville, Connecticut, on a small lake, where he spent his childhood swimming, fishing, and

exploring. As he matured, his curiosity of the outdoors led him to become an avid outdoorsman,

hunting, fishing and camping around New England. He graduated from Avon Old Farms Prep

School in 1997 with an interest in ecology. Darren earned his B. S. in environmental science in

2001, majoring in both wildlife biology and fisheries science at Unity College in Maine. After

graduation, Darren worked around the country for a variety of fish and wildlife agencies. First,

he worked for the Maine Atlantic Salmon Commission, where he worked on the restoration of

endangered Atlantic salmon. Next, he worked for U. S. Geological Survey's Pacific Islands

Ecosystem Research Center, Hawaii Volcanoes National Park, Hawaii on an endangered bird

restoration project. Then, he worked for the Connecticut Department of Environmental

Protection Fisheries Division on fisheries management projects and later, was employed by the

U. S. Geological Survey's Columbia River Research Laboratory Cook, Washington, where he

conducted research on the efficacy of alternative technology fish screens. Next, he worked for

U.S. Fish and Wildlife Service in the Fairbanks, Alaska office on a project that was focused on

estimating the abundance of migrating Yukon River fall chum salmon for in-season management

of the subsistence fishery. Finally, he made his way down to the University of Florida in 2006,

where he started off as a technician for Dr. Bill Pine working on the Apalachicola River and in

Sarasota Bay. In the fall of 2006, Darrenjoined Dr. Daniel E. Canfield, Jr.'s lab, where he

worked on the Lake Griffin largemouth bass stocking project. In August 2007, Darren began his

master's research at the University of Florida, Department of Fisheries and Aquatic Sciences.

Darren completed his master's research in 2009.









abundance (percent area coverage and percent volume infestation) and largemouth bass standing

crop in small (<300 ha) Florida lakes. However, they concluded plants are more important in

larger lakes like Lake Griffin. Following the 1984 drawdown, Lake Griffin's aquatic plant

community increased from 1% to 20% coverage (Figure 2-8). Hydrilla, a non-native major

invasive species in Florida lakes, was the dominant (11%) plant after the 7-foot change in water

level (Figure 4-6). Aquatic plants and other associated problems with drawdowns caused public

uproar at Lake Griffin among the non-angling public due to issues such as boating access,

hydrilla coverage, floating plant islands, and lack of access; all resulted in public opposition to

future drawdowns (HCLRC 2007). Therefore, the question that must be asked is what else could

be done for a multi-use lake if public support for a massive drawdown cannot be garnered.

It seems based on the historical record and as measured after the 2003 water level rise

(Figure 2-3), that an enhanced water level fluctuation of one meter would stimulate enough

aquatic plant growth (1-3 %) to cause an increase in largemouth bass recruitment (Figure 4-6;

Figure 4-7). This enhanced water level fluctuation would become even more important once the

adjoining marshes are reconnected to the main lake because high water level caused by the

Atlantic Multidecadal Oscillation may be a primary environmental factor driving the fishery at

Lake Griffin.

If efforts are to be continued to reestablish aquatic plants in Lake Griffin through planting

(HCOLRC 2006), it must be recognized that such efforts will be limited by algal biomass

(chlorophyll) in the water column (Figure 4-8). Elevated chlorophyll concentrations affect light

attenuation to the bottom sediments (Cole 1994), and because aquatic macrophytes require light

to grow, light availability is one of the most important factors regulating the distribution of

aquatic macrophytes (Zimmermann et al. 1994). Chlorophyll concentrations are controlled by









Table 4-4. Electrofishing sampling combined results for main lake and canal; total catch of
largemouth bass greater than 200 mm TL, stocked largemouth bass catch (marked),
stocked fish per minute (CPUE), and percent of stocked fish to total catch (% total
catch) for Lake Griffin, Florida.
Electrofishing Sampling For Main Lake and Canals
Date Total Catch # Transects Marked CPUE % Total Catch
May-07 1226 178 162 0.09 13
Nov-07 241 39 13 0.03 5
Feb-08 270 33 13 0.04 5
Mar-08 257 34 15 0.04 6
Jun-08 283 48 14 0.03 5
Mar-09 250 32 8 0.03 3









McInerny M. C, and T. K. Cross. 2000. Effects of sampling time, intraspecific density, and
environmental variables on electrofishing catch per effort of largemouth bass in Minnesota
lakes. North American Journal of Fisheries Management 20:328-336.

Mesing, C. L., and A. M. Wicker. 1986. Home range, spawning migrations, and homing of
radio-tagged Florida largemouth bass in two central Florida lakes. Transactions of the
American Fisheries Society 115:286-295.

Mesing, C. L., R. L. Cailteux, A. P. Strickland, E. A. Long, and M. W. Rogers. 2008. Stocking
of advanced-fingerling largemouth bass to supplement year-classes in Lake Talquin,
Florida. North American Journal of Fisheries Management 28:1762-1774.

Miko, D.A., H. L. Schramm, Jr., S. D. Arey, J. A. Dennis, and N. E. Mathews. 1995.
Determination of stocking densities for satisfactory put-and-take rainbow trout fisheries.
North American Journal of Fisheries Management 15:823-829.

Milon, J. W., and R. Welsh. 1989. An economic analysis of sport fishing and the effects of
hydrilla management in Lake County, Florida. Economic Report 118, Food and Resource
Economics Department. University of Florida. Gainesville, Florida.

Miranda, L. E., and W. D. Hubbard. 1994. Winter survival of age-0 largemouth bass relative to
size, predators, and shelter. North American Journal of Fisheries Management 14:790-796.

Moyer, E. J, M. W. Hulon, J. J Sweatman, R. S. Butler, and V. P. Williams. 1995. Fishery
responses to habitat restoration in Lake Tohopekaliga, Florida. North American Journal of
Fisheries Management 15:591-595.

Nagid, E. J., M. S. Duncan, and T. M. Tuten. 2003. Largemouth bass age distribution on
Rodman Reservoir following an extreme drawdown. Florida Fish and Wildlife
Conservation Commission. Completion Report, Lower Ocklawaha Basin Fisheries
Investigations. Gainesville, Florida.

Noble, R. L. 1981. Management of forage fishes in impoundments of the southern United States.
Transactions of the American Fisheries Society 110:738-750.

Porak, W. F. 1994. Largemouth bass investigations: research and management of trophy
largemouth bass. Florida Fish and Wildlife Conservation Commission. Project F-24. Study
XVI.

Porak, W.F., W.E. Johnson, S. Crawford, D.J. Renfro, T.R. Schoeb, R.B. Stout, R. A. Krause,
and R.A. DeMauro. 2002 Factors affecting survival of largemouth bass raised on artificial
diets and stocked into Florida lakes. Pages 649-666 in D.P. Philippi and M.S. Ridgeway,
editors. Black bass: ecology, conservation, and management. American Fisheries Society,
Symposium 31, Bethesda, Maryland.

Reynolds, J.B. 1996. Electrofishing. Pages 221-253 in B. R. Murphy, and D. W. Willis, editors.
Fisheries techniques, 2nd edition. American Fisheries Society, Bethesda, Maryland.









Wicker (1986). Dequine and Hall (1950) conducted a largemouth bass (95 marked fish)

migration study at Lake Griffin and found that fish (14 largemouth bass had complete movement

data) moved variable distances (0 to 9.6 km, with one fish moving 15.3 km) from where they

were released. Mesing and Wicker (1986) conducted a largemouth bass telemetry study on

nearby Lake Eustis and Lake Yale and found maximum home range dimensions ranged from

0.05 km to 2.4 km, where the home range dimensions were based on 2,047 radio locations with

22 adult fish. In that study, they also demonstrated that largemouth bass could move large

distances or not move at all.

The measured dispersal distances during this study provided evidence that part of the

reason why FFWCC reported limited catch of stocked fish in the main area of Lake Griffin was

because the fish moved. Lake Griffin is an open system allowing stocked fish to move into

adjoining canals, marshes, and the Ocklawaha River. Anglers caught stocked fish below the dam

at Moss Bluff, indicating there is an unknown rate of downstream escapement.

Anglers also moved largemouth bass from Lake Griffin. Tournament anglers who traveled

from other lakes (via Haines Creek or Ocklawaha River) removed largemouth bass caught in

Lake Griffin when they brought them to weigh-ins areas such as Lake Harris (personal

communication, numerous anglers). While most largemouth bass anglers practiced catch and

release, some anglers reported transporting large (>2.3 kg) stocked largemouth bass in their live

wells to stock them into other water bodies. Clearly there is some unknown quantity of stocked

and native largemouth bass leaving Lake Griffin due to angler activities.

Following FFWCC's 2006 creel-survey, Florida LAKEWATCH's focus became the

disparity in the number of largemouth bass caught in the main area of Lake Griffin and the

number of fish caught in adjoining waters, especially in Larson's (2009) study where angler tag









4-5 The number and size of native and stocked largemouth bass captured via
electrofishing in the canals and main lake of Lake Griffin, Florida. A) Main Lake
May 2007. B) Canals June 2007. C) Main Lake June 2008. D) Canals June 2008.
E) M ain Lake M arch 2009. F) Canals M arch 2009....................................... ...... ........ 53

4-6 The annual change in water level and estimated percent area coverage ofhydrilla in
Lake Griffin, Florida (data obtained from SJRWMD and FLDEP). .................................. 56

4-7 Yearly change in water level, percent area coverage ofhydrilla, and electrofishing
catch-per-unit-effort (CPUE) of largemouth bass (<200 mm TL and > 200 mm TL)
for Lake Griffin, Florida (data obtained from SJRWMD, FLDEP and FFWCC). ............56

4-8 Total nitrogen ([g/L), total phosphorus ([g/L), and chlorophyll concentration ([g/L)
trends for Lake Griffin, Florida (data obtained from FFWCC, Florida
LA K EW A T CH and SJR W M D ). .......................................................................................... 57

4-9 Relationship between loglO chlorophyll ([g/L) and loglO total phosphorus ([g/L)
with a linear line fit to the data (R2=0.16), for Lake Griffin, Florida, for data
collected from 1974 to 2007 (data obtained from FFWCC, SJRWMD, and Florida
L A K E W A T C H ). .................................................................................................................... 5 8

4-10 Relationship between loglO chlorophyll ([g/L) and loglO total nitrogen ([g/L) with
a linear line fit to the data (R2=0.66), for Lake Griffin, Florida, for data collected
from 1969 to 2007 (data obtained from FFWCC, SJRWMD, and Florida
L A K E W A T C H ). .................................................................................................................... 5 8

4-11 Relationship between LoglO Secchi (m) and LoglO Chlorophyll ([g/L) with a linear
line fit to the data (R2=0.31), for Lake Griffin, Florida, for data collected from 1969
to 2007 (data obtained from FFWCC, SJRWMD, and Florida LAKEWATCH).............59

4-12 Annual mean chlorophyll concentration and electrofishing catch-per-unit-effort
(CPUE) of largemouth bass (> 200 mm TL), for Lake Griffin, Florida (data obtained
from FFWCC, Florida LAKEWATCH, and SJRWMD). .................................................. 59

4-13 Relationship between LoglO CPUE (fish per minute) for all sizes of largemouth bass
captured by electrofishing and Secchi depth (m) with a linear line fit to the data
(R2=0.43), for Lake Griffin, Florida, for data collected from 1969 to 2007 (data
obtained from FFWCC, SJRWMD, and Florida LAKEWATCH) .................................. 60

4-14 Annual mean chlorophyll concentration and annual mean water level for Lake
Griffin Florida (data obtained from FFWCC, Florida LAKEWATCH, and
S JR W M D ) .............................................................................................................................. 6 0

4-15 Relationship between annual largemouth bass creel catch, estimated by roving creel
survey and electrofishing CPUE (fish/minute) of largemouth bass (> 200 mm TL),
with a linear line fit to the data (R2=0.000013), for Lake Griffin, Florida (data
ob tain ed from F F W C C ). .................................................. ................................................ 6 1











18
16
14
12
10
8-


4
2
0


ON ON O
ON ONON
br N b
t1
o o0
o o0
o 'r0
t1


0 0 '/I 0 'I 0 'I 0 0 'I I 0
S T r nn 0000000000' r--- 0 00 01


Meters From Release Point

Figure 4-1. The percent of largemouth bass and corresponding distances dispersed from stocking
points to electrofishing recapture points in Lake Griffin, Florida.


10000
9000 *
8000 -
7000
6000 *
5000 .
4000 *
3000
2000 .-- *
1000
0


-.-1 -4
Nmuber of Days Post Stocking Release


Figure 4-2. The dispersal distance from stocking release point verses the number of days post
stocking for electrofished recaptured largemouth bass in Lake Griffin, Florida.









90000 ---Effort 1.2
80000
70000 CPE
( 60000 0.8
o 50000 \,0.6
0.6
40000

20000 *' 0
10000
0 I 0
1965 1970 1975 1980 1985 1990 1995 2000 2005
Year

Figure 4-17. Historical angler effort (hours) and catch per effort (fish per hour) for largemouth
bass, based on roving creel survey data (data obtained from FFWCC).









level years, suggesting wind-induced resuspension when water depth is low (Bachmann et. al.

2000) and the hydraulic flushing rate of the lake may be important factors influencing in-lake

water chemistry.

Total nitrogen concentrations, unlike phosphorus concentrations, increased over time

(Figure 2-5). Total nitrogen averaged 3140 [g/L, and ranged from 2240 [g/L to 5630 [g/L

(Table 2-1). The measured concentrations reflect the nutrient enriched status of Lake Griffin,

and like phosphorus, maximum total nitrogen concentrations were typically higher during low

water level years (especially the drought period from 1995 to 2002).

Like total nitrogen, chlorophyll concentrations in Lake Griffin increased between 1995 and

2000 (Figure 2-6). For the period of record, chlorophyll concentrations averaged 99 [g/L and

ranged from 27 [g/L to 316 [g/L (Table 2-1). Also like total phosphorus and total nitrogen, the

maximum chlorophyll values corresponded with low water levels and drought conditions from

1995 to 2002. Water clarity, as measured by use of a Secchi disc declined from 1995 to 2002

(Figure 2-7) as expected since chlorophyll concentrations influence water clarity in Florida lakes

(Canfield and Hodgson 1981). Over the historical record, Secchi disc readings averaged 37 cm,

ranging from 6 cm to 76 cm (Table 2-1). The lowest water clarity was measured during the 1995

to 2002 drought period when total phosphorus, total nitrogen, and chlorophyll concentrations

were the greatest. Water transparency has remained less than 30 cm in Lake Griffin since 1995

(Figure 2-7).

Aquatic Macrophytes

Nearly half of Lake Griffin was covered by aquatic macrophytes (estimated by aerial

photograph analysis, Bill Johnson FFWCC), particularly spatterdock (Nuphar luteum) (Figure 2-

8). Boat trails were cut into the dense aquatic vegetation, primarily on the north end of the lake,

to allow boaters access. Aquatic plant surveys conducted between 1983 and 2006 by FLDEP









Durocher, P. P., W.C. Provine, and J.E. Kraai. 1984. Relationship between abundance of
largemouth bass and submersed vegetation in Texas reservoirs. North American Journal of
Fisheries Management 4:84-88.

Florida LAKEWATCH. 2007. Restoration of the Economic Vitality of Lake Griffin's
Largemouth Bass Fishery: A Research/Demonstration Project / Phase III. Final Report.
Department of Fisheries and Aquatic Sciences. Institute of Food and Agricultural Sciences,
University of Florida, Gainesville, Florida.

(HCLRC) Harris Chain of Lakes Restoration Council. 2002, 2006, 2007, 2008. Reports to the
Legislature. Tallahassee, Florida.

Heidinger, R. C., and R. C. Brooks. 2002. Relative contribution of stocked minnow-fed and
pellet-fed advanced fingerling largemouth bass to year-classes in Crab Orchard Lake,
Illinois. Pages 703-714 in D.P. Philippi and M.S. Ridgeway, editors. Black bass: ecology,
conservation, and management. American Fisheries Society, Symposium 31, Bethesda
Maryland.

Hoffman, K.J., and P. W. Bettoli. 2005. Growth, dispersal, mortality, and contribution of
largemouth bass stocked into Chickamauga Lake, Tennessee. North American Journal of
Fisheries Management 25:1518-1527.

Hoyer, M. V. and D. E. Canfield, Jr. 1994. Bird abundance and species richness on Florida lakes:
influence of trophic status, lake morphology, and aquatic macrophytes. Hydrobiologia
297/280:107-119.

Hoyer, M. V., and D.E. Canfield, Jr. 1996. Largemouth bass abundance and aquatic vegetation in
Florida lakes: an empirical analysis. Journal of Aquatic Plant Management 34:23-32.

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. Proceeding of a Special Symposium. Florida
LAKEWATCH, Department of Fisheries and Aquatic Sciences, University of Florida,
Institute of Food and Agricultural Sciences. Gainesville, Florida.

Kelly, M.H., and J.A. Gore. 2008. Florida river flow patterns and the Atlantic multidecadal
oscillation. River Research and Applications. 24: 598-616.

Larson, K.W. 2009. Stocking wild-adult largemouth bass Micropterus salmoidesfloridanus to
improve fishing and associated economic activity at Lake Griffin, Florida. Masters thesis.
University of Florida. Gainesville, Florida.

Lorenzen, K. 1996. The relationship between body weight and natural mortality in fish: a
comparison of natural ecosystems and aquaculture. Journal of Fish Biology 49:627-647.

Marburger, J. E., W. E. Johnson, T. S. Gross, D. R., and Di. J. Douglas. 2002. Residual
organochlorine pesticides in soils and fish from wetland restoration areas in central
Florida, USA. Wetlands 22:705-711.




Full Text

PAGE 1

1 EFFECTS OF STOCKING WILD -ADULT LARGEMOUTH BASS ON THE FISHERY AT LAKE GRIFFIN, FLORIDA By DARREN JOHN PECORA A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENT S FOR TH E DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2009

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2 2009 Darren John Pecora

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3 To my mother, father, and sisters for their unconditional love and support

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4 ACKNOWLEDGMENTS I thank my gradua te advisor, Dr. Dan Canfield Jr., without whom none of this would have been possible. I also thank my committee members, Dr. Charles Cichra and Jim Estes for their guidance and advice. I thank Mark Hoyer for his guidance and assistance and Florida LAKEWA TCH staff and graduate students for their field and logistical help particularly Jesse Stephens, Bubba Thomas, Dana Bigham, Jenney Lazzarino and Kurt Larson. I thank Sherry Giardina for helping me with forms and meeting deadlines. I thank the following individuals for help on this project Dan Gwinn, Mike Allen, Lauren Marcinkiewicz, Towns Burgess, Jared Flowers, Bill Pine, Matt Catalano, John Benton, and Bill Johnson. I thank my friends and family who have kept encouraging me through this endeavor. F inally, I thank God!

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS .................................................................................................................... 4 LIST OF TABLES ................................................................................................................................ 6 LIST OF FIGU RES .............................................................................................................................. 7 ABSTRACT ........................................................................................................................................ 10 CHAPTER 1 INTRODUCTION ....................................................................................................................... 12 2 STUDY SITE DESCRIPTION AND LAKE GRIFFINS ENVIRONMENTAL HISTORY .................................................................................................................................... 19 Introduction ................................................................................................................................. 19 Geography .................................................................................................................................... 19 Water Levels ................................................................................................................................ 20 Water Quality .............................................................................................................................. 21 Aquatic Macrophytes .................................................................................................................. 22 Largemouth Bass Population ...................................................................................................... 23 Largemouth Bass Fishery ........................................................................................................... 23 3 METHODS .................................................................................................................................. 32 4 RESULTS AND DISCUSSION ................................................................................................ 38 Introduction ................................................................................................................................. 38 Fish Dispersal .............................................................................................................................. 38 Mortality ...................................................................................................................................... 41 Persistence ................................................................................................................................... 42 Lake Griffin Fish Condition ....................................................................................................... 42 Native Verses Stocked Largemouth Bass Length Frequency .................................................. 43 Environment Factors and Largemouth Bass .............................................................................. 43 5 FISHERY MANAGEMENT I MPLICATIONS ....................................................................... 63 6 CONCLUSION ........................................................................................................................... 68 LIST OF REFERENCES ................................................................................................................... 70 BIOGRAPHICA L SKETCH ............................................................................................................. 74

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6 LIST OF TABLES Table page 2 1 Water level and water quality parameters (mean and ranges) for Lake Griffin, Florida. .................................................................................................................................... 24 3 1 The date and number of electrofishing transects sampled in main lake areas and canal a reas of Lake Griffin, Florida from April 23, 2007 to March 13, 2009. ............................ 37 4 1 Electrofishing sampling results for canals; total catch of largemouth bass greater than 200 mm TL, stocked largemout h bass catch (marked), stocked fish per minute (CPUE), and percent of stocked fish to total catch (% total catch) for Lake Griffin, Florida. .................................................................................................................................... 49 4 2 Electrofishing sampling results for main lak e total catch of largemouth bass greater than 200 mm TL, stocked largemouth bass catch (marked), stocked fish per minute (CPUE), and percent of stocked fish to total catch (% total catch) for Lake Griffin, Florida. .................................................................................................................................... 49 4 3 A comparison of mortality estimates Z -Annual (instantaneous mortality rate), S Annual (annual survival), and A -Annual (annual total mortality) of stocked largemouth bass and native largemouth bass from Lake Griffin, Florida. ......................... 49 4 4 Electrofishing sampling combined results for main lake and canal; total catch of largemouth bass greater than 200 mm TL, stocked largemouth bass catch (marked), stocked fish per minute (CPUE), and percent of stocked fish to total catch (% total catch) for Lake Griffin, Florida. ............................................................................................ 50

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7 LIST OF FIGURES Figure page 2 1 Map of Lake Griffin, Lake County, Florida. ........................................................................ 25 2 2 Map of Lake Griffin canals which were dredged from 2005 to 2007. ............................... 26 2 3 Annual mean water level and yearly change in water level from 1946 to 2007, for Lake Griffin, Florida (data obtained from SJRWMD). ....................................................... 27 2 4 Annual mean total phosphorus (g/L) for Lake Griffin, Florida (data obtained from FFWCC, SJRWMD, and Florida LAKEWATCH). ............................................................ 27 2 5 Annual mean total nitrogen (g/L) for Lake Griffin Florida (data obtained from FFWCC, SJRWMD, and Florida LAKEWATCH). ............................................................ 28 2 6 Annual mean chlorophyll concentrations (g/L) for Lake Griffin, Florida (data obtained from FFWCC, SJRWMD, and Florida LAKEWATCH). .................................... 28 2 7 Annual mean Secchi depth (cm) for Lake Griffin, Florida (data obtained from FFWCC, SJRWMD, and Florida LAKEWATCH). ............................................................ 29 2 8 Aquatic macrophyte areal coverage estimated by aerial photographs, for Lake Griffin, Flori da (data obtained from FFWCC). .................................................................... 29 2 9 Percent area coverage of hydrilla for Lake Griffin, Florida (data obtained from FL DEP). .................................................................................................................................. 30 2 10 Annual mean largemouth bass electrofishing catch per unit effort (CPUE) for a variety of sizes of largemout h bass in Lake Griffin, Florida (data obtained from FFWCC). ................................................................................................................................. 30 2 11 Estimated annual angler catch and harvest from Lake Griffin, Florida from 1966 to 2006 (data obtained from FFWCC). ..................................................................................... 31 4 1 The percent of largemouth bass and corre sponding distances dispersed from stocking points to electrofishing recapture points in Lake Griffin, Florida. ..................................... 51 4 2 Th e dispersal distance from stocking release point verses the number of days post stocking for electrofished recaptured largemouth bass in Lake Griffin, Florida. .............. 51 4 3 The log10 total length verses log10 weight of native largemouth bass pre (2004) and post (2008) stocking in Lake Griffin, Florida (data obtained from FFWCC). ................... 52 4 4 The log10 total length verses log10 weight linear regression line comparison of native largemouth bass pre (2004) and post (2008) stocking in Lake Griffin, Florida (data obtained from FFWCC). ............................................................................................... 52

PAGE 8

8 4 5 The number and size of native and stocked largemouth bass captured via electrofishin g in the canals and main lake of Lake Griffin, Florida. A) Main Lake May 2007. B) Canals June 2007. C) Main Lake June 2008. D) Canals June 2008. E) Main Lake March 2009. F) Canals March 2009. ........................................................... 53 4 6 The annual change in water level and estimated percent area coverage of hydrilla in Lake Griffin, Florida (data obtained from SJRWMD and FLDEP). .................................. 56 4 7 Yearly change in water level, percent area coverage of hydrilla, and electrofishing catch -per unit -effort (CPUE) of largemouth bass (<200 mm T L and > 200 mm TL) for Lake Griffin, Florida (data obtained from SJRWMD, FLDEP and FFWCC). ............ 56 4 8 Total nitrogen (g/L), total phosphorus (g/L), and chlorophyll concentration (g/L) trends for Lake Griffin, Florida (data obtained from FFWCC, Florida LAKEWATCH, and SJRWMD). .......................................................................................... 57 4 9 Relationship between log10 chlorophyll (g/L) and log10 total phosphorus (g/L) with a linear line fit to the data (R2=0.16), for Lake Griffin, Florida, for data collected from 1974 to 2007 (d ata obtained from FFWCC, SJRWMD, and Florida LAKEWATCH). .................................................................................................................... 58 4 10 Relationship between log10 chlorophyll (g/L) and log10 total nitrogen (g/L) with a linear line fit to the data (R2=0.66), for Lake Griffin, Florida, for data collected from 1969 to 2007 (data obtained from FFWCC, SJRWMD, and Florida LAKEWATCH). .................................................................................................................... 58 4 11 Relationship between Log10 Secchi (m) and Log10 Chlorophyll (g/L) with a linear line fit to the data (R2=0.31), for Lake Griffin, Florida, for data collected from 1969 to 2007 (data obtained from FFWCC, SJRWMD, and Florida LAKEWATCH). ............. 59 4 12 Annual mean chlorophyll concentration and electrofishing catch-per unit effort (CPUE) of largemouth bass (> 200 mm TL), for Lake Griffin, Florida (data obtained from FFWCC, Florida LAKEWATCH, and SJRWMD). ................................................... 59 4 13 Relationship between Log10 CPUE (fish per minute) for all sizes of largemouth bass captured by electrofishing and Secchi depth (m) with a linear line fit to the da ta (R2=0.43), for Lake Griffin, Florida, for data collected from 1969 to 2007 (data obtained from FFWCC, SJRWMD, and Florida LAKEWATCH). .................................... 60 4 14 Annual mean chlorophyll concentration and annual mean water level for Lake Griffin Florida (data obtained from FFWCC, Florida LAKEWATCH, and SJRWMD). ............................................................................................................................. 60 4 15 Relationship between annual largemouth bass creel catch, estimated by roving creel survey and electrofishing CPUE (fish/minute) of largemouth bass (> 200 mm TL), with a linear line fit to the d ata (R2=0.000013), for Lake Griffin, Florida (data obtained from FFWCC). ........................................................................................................ 6 1

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9 4 16 Angler effort (hours) for largemouth bass, estimated by roving creel survey for Lake Griffin, Florida (data obtained from FFWCC). .................................................................... 61 4 17 Historical angler effort (hours) and catch per effort (fish per hour) for largemouth bass, based on roving creel survey data (data obtained from FFWCC). ............................ 62

PAGE 10

10 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 EFFECTS OF STOCKING WILD -ADULT LARGEMOUTH BASS ON THE FISHERY AT LAKE GRIFFIN, FLORIDA By Darren John Pecora August 2009 Chair: Daniel E. Canfield, Jr. Major: Fisheries and Aquatic Science Lake Griffin was stocked with appr oximately 14,000 wildadult largemouth bass from 2005 to 2007 to stimulate economic activity related to the fishery. An electrofishing survey was initiated at Lake Griffin in 2007 to determine the status of the stocked fish population 3 years after stocki ng. The mean dispersal distance from stocking sites for 122 caught stocked largemouth bass was 2.9 km with the maximum recorded distance being 9.2 km. Mean CPUE (fish/hour) of native largemouth bass between canal and main lake areas were not significantly different, indicating stocked and wild fish were mixing evenly. Mortality estimates for stocking years 2006 (Z= 1.087) and 2007 (Z=1.295) are similar to the 2007 native largemo uth bass estimates ( Z= 1.0 54). There w as no change in native largemouth bass condition post stocking. The stocked largemouth bass in May 2007 contributed 13% to total electrofishing largemouth bass catch with a CPUE of 0.09 (fish/minute) immediately after the last stocking in 2007. Two years later in March 2009, the total electrofishing catch of stocked largemouth bass was 3%, with a 0.03 (fish/minute) CPUE. Water level and macrophyte abundances were the primary environmental factors influencing largemouth bass abundance, but management actions focus ing on these factors have been rejected by the public and climatic conditions may prevent enhanced lake fluctuation To enhance the largemouth bass fishery at Lake Griffin, construction of

PAGE 11

11 artific ial habitat is recommended for the main lake along with continued stocking of wild adult largemouth bass. Stocking wildadult largemouth bass captured from non-fished waters is a cost -effective fisheries management tool, supported by anglers, and the weight of scientific evidence suggests only positive effects.

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12 CHAPTER 1 INTRODUCTION Largemouth bass ( Micropterus salmoid es ) is one of the most sought after sportfish in the United States (U. S. Department of the Interior 2006). Florida largemouth bass ( M.s.floridanus ) is an economically important game fish, contributing 632 million dollars per year to Floridas economy (U. S. Department of the Interior 2006). Lake Griffin, a 6,680ha hypereutrophic lake in Central Florida supported a recreational fishery valued at 2.3 million dollars annually in the late 1980s (Milon and Welsh 1989). However, the value of the sport fishery had declined by 90% by the late 1990s, which was directly linked to the decline of the largemouth bass fishery (Benton 2000). According to Larson (2009), the stocking of wildadult largemouth bass into Lake Griffin by the University of Floridas Florida LAKEWATCH program after 2004 was responsible for an economic improvement of up to 2.7 million dollars per year. The reporte d economic enhancement by stocking wildadult largemouth bass, however, has been questioned F ish sampling revealed that only up to 10% of the Lake Griffin largemouth bass population consisted of the Florida LAKEWATCH -stocked largemouth bass soon after stocking This lead to the questioning of the effectiveness of the enhancement by Florida Fish and Wildlife Conservation Commission (FFWCC) biologists working on Lake Griffin (HCLRC 2007) and University of Florida faculty (Dr. Mike Allen, personal communic ation University of Florida ). The low catch rate of stocked fish may have been the result of not stocking enough fish, fish moving out of the lake, or an excessive fish mortality rate from handling stress or a lack of adequate forage. The sport fish popu lation and fishery of Lake Griffin w ere at a historical low point in 1999 (Benton 2000). As a result, interest in stocking the lake with largemouth bass became a priority for the Harris Chain of Lakes Restoration Council, a legislatively appointed citi zens advisory

PAGE 13

13 group (Chapter 373.467 F.S. and the Lake County Water Authority, a special taxing district for the management of Lake Countys lakes ). These groups, after hearing the pros and cons of stocking fingerling, advanced fingerling, and adult largemouth bass, authorized a research/demonstration stocking project by Florida LAKEWATCH in an attempt to enhance the fishery quickly (within 3 years) by increasing the abundance of catchable -size fish. The LAKEWATCH approach was to stock Lake Griffin with large numbers (4,000 plus fish/year) of wild adult (> 200 mm total length ( TL ); average size stocked 305 mm TL) largemouth bass taken from private waters (Larson 2009). Supplemental stocking of hatcheryproduced largemouth bass is a common management prac tice by fish management agencies throughout the United States ; Forty one states have stocked hatchery raised fry, fingerling, advanced-fingerling, or adult largemouth bass (Smith and Reeves 1986). Limited literature exists on the success of stocking progr ams for hatchery raised sub adult and adult largemouth bass into large systems (Porak 1994, Buynak et al. 1999). Porak et al. (2002), however, suggested stocking advanced fingerling largemouth bass could provide a potential approach to circumvent a largem outh bass recruitment bottleneck caused by the loss of aquatic macrophytes, and increase recruitment of largemouth bass to age one in nutrient -enriched Florida lakes. This suggestion is based in part on research conducted by Wicker and Johnson (1987), who found that high rates of mortality occur when age0 largemouth bass shift to piscivory in a hypereutrophic Florida lake. Use of advanced sizes of hatchery produced largemouth bass was also supported by research on a wide range of Florida lakes indicatin g that poor recruitment in lakes may be related to decreased shoreline habitat to lake surface area ratio (Hoyer and Canfield 1996) ; hence, the importance of macrophytes is increased for large lakes. Aquatic macrophyte structural

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14 complexity is an important habitat feature for young -of the year and subadult largemouth bass survival (Hoyer and Canfield 1996) by providing reduced predation (Strange et al. 1975) and increased prey (Crowder and Copper 1982). When stocking nonadult largemouth bass into waters with no cover or structure, stocked largemouth bass mortality up to 90% can be expected (Miranda and Hubbard 1994). Although it is now generally accepted that larger -sized stocked largemouth bass exhibit higher survival than smaller fish (Heidinger and B rooks 2002), aquaculture production of advanced fingerlings and adult fish in hatcheries r emains difficult and expensive. Advanced fingerling largemouth bass (65 to 90 mm total length [TL]) are now produced at the Richloam State Fish Hatchery by FFWCC, but successful stocking has only been documented in one Florida lake (Me sing 2008), despite attempts to stock advanced sizes of largemouth bass into Florida lakes (Porak et al. 2002). Lorenzen (1996) found lower mortality for stocked fish that we re raised in aquaculture systems where the fish f ed on natural foods and we re raised in earthen ponds. Lorenzens (1996) findings led Florida LAKEWATCH to conclude in 2003 that stocking adult -sized fish from non aquacultured (i.e., wild fish) private natu ral waters should aid in reducing stocking mortality, and enhance long term survival of stocked fish in a large lake system where numerous predators such as birds and other fish species exist. In many northern states, stocking hatchery-raised adult t rout is a common management practice for a variety of recreational fisheries, especially put and take fisheries (Miko et al. 1995). Survival of hatchery reared trout is expected to be low and harvest of these fish is encouraged. The only comparable pra ctice for warm water fish is the collection of fish from drained water bodies and their relocation to other water bodies (e.g., Carlander 1954). In the 1950s, fish rescue programs were conducted frequently in the upper Mississippi River drainage

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15 basin whe re adult fish were relocated from lands flooded by the river to nearby lakes and reservoirs. For a while, the fish rescue programs were an important fisheries management tool. Consequently, collection and stocking of wildadult largemouth bass from non -fished private Florida waters could also become a useful fisheries management tool in Florida. As with any tool, its cost -benefit must be considered. There are dollar costs and biological costs, especially if the management tool has a negative impact (e.g. reduced fish condition factor resulting from over stocking) on the fisheries. A review of the literature finds stocking programs often report mixed results because of different agency objectives (Hoffman and Bettoli 2005). More importantly, the positiv e impacts of largemouth bass stocking programs on fisheries are often underestimated (Copeland and Noble 1994) because there are no established guidelines to measure the success of supplemental stocking (Heidinger and Brooks 2002). Biologists use a number of different criteria to evaluate stocking programs, including : stocked fish harvested, percent of stocked fish in a year class, and cost:benefit ratios (Heidinger and Brooks 2002). Cost -benefit ratios are typically calculated from creel surveys that ev aluate the catch of stocked fish by anglers. Florida LAKEWATCH is the only organization to stock wild adult largemouth bass on such a massive scale in Florida (Florida LAKEWATCH 200 7 ). Larson (2009) studied the associated economic activity at Lake Griffin for Florida LAKEWATCH following the stocking of wild adult largemouth bass and concluded the approach was cost -effective based on the estimated revenue generated and the stimulation of angler interest. However, the survival of stocked fish and their con tribution to the fishery has been questioned as a result of findings from a FFWCC creel survey of Lake Griffin in 2006, two years after the initial stocking This creel survey, however, only covered the main stem of Lake Griffin, not its adjoining canals, marshes,

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16 the Ocklawaha River, and other backwaters, where the majority (65%) of Florida LAKEWATCH -stocked fish were caught according to angler tag call in reports (Larson 2009). Largemouth bass must move at some point in their lives to use availa ble resources throughout a water body/reservoir (Copeland and Noble 1994). Heidinger and Brooks (2002) stated that because stocked largemouth bass are relocated fish, they initially do not have a home range and exhibit more movement than native largemouth bass. Dequine and Hall (1950) found that stocked largemouth bass move variable distances (0 to 9.6 km with one fish moving 15.3 km) from where they were released. While the movement pattern of stocked Florida LAKEWATCH fish was unknown to Larson (2009), it was clear, from tag returns that stocked fish were moving outside the main area of Lake Griffin. This movement of largemouth bass raised the issue of how long stocked wildadult largemouth bass would persist in Lake Griffin and how long anglers could expect to catch these fish given the many environmental factors that could also affect largemouth bass survival. To address some of the biological issues surrounding Florida LAKEWATCHs wild adult largemouth bass stocking program, this project had four primary objectives: 1 ) Determine the dispersal distance of stocked wild adult largemouth bass, 2 ) Determine the persistence, mortality, and percent contribution over time of the LAKEWATCH stocked largemouth bass, 3 ) Determine if the stocked largemouth b ass were exhibiting greater abundance in canals over the main lake or were being displaced into canal areas, 4 ) Determine what environmental factors influence largemouth bass abundance and the largemouth bass fishery in Lake Griffin. The dispersal of stocked largemouth bass was investigated because it provided insight into fish movement that could influence management decisions such as the number of stocking sites needed for a given water body. More importantly, dispersal information provided evidence to

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17 hel p determine if stocked wildadult fish die from transportation stress or how many adjoining waters could be influenced through a single -lake stocking program. In this project, dispersal information obtained through fishery-independent sampling (electrof ishing) also assisted with determining if stocked fish were preferentially using adjoining canals rather than the main lake at Lake Griffin. The percent contribution of stocked fish to electrofishing catches was determined along with what percent of stocke d largemouth bass remained in Lake Griffin after a two -year period of no stocking. The mortality of stocked largemouth bass was determined through information obtained from the electrofishing catches. The estimated mortality rate was compared to native l argemouth bass mortality in Lake Griffin to determine if stocked fish mortality is greater. A change in condition factor for native Lake Griffin largemouth bass after the stocking was investigated to insure there was an adequate forage base. Stocking adul t -wild fish could be detrimental to Lake Griffins largemouth bass population if the existing largemouth bass population is near carrying capacity. Trends in historical water quality and habitat abundance, especially total phosphorus (g/L), total nitroge n ( g/L), chlorophyll ( g/L), Secchi depth (cm) mean water level (ft), yearly change in water level (ft), and whole lake aquatic macrophyte percent aerial coverage were specifically investigated to determine if there are patterns between these envi ronmental variables and Lake Griffins largemouth bass population size as assessed by historical electrofishing (CPUE) and roving creel surveys. If patterns exist, workable guidelines for the future management of largemouth bass in Lake Griffin could be formulated. The determination of persistence, mortality and percent contribution of stocked adult -sized largemouth bass in to the Lake Griffin population of largemouth bass provided information so

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18 that managers can make judgments about whether stocking these fish is an effective tool. It also provide d information about how often stocking might be needed to meet a particular management goal. Additionally, information about the dispersal of stocked fish, and a determination of whether s tocked fish preferentially chose un -surveyed canals was important to explain the patterns of persistence that might be observed. The influence of environmental factors affecting largemouth bass abundance and the fishery was investigated so that t he use of the stock enhancement project could be described in a broade r management context.

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19 CHAPTER 2 STUDY SITE DESCRIPTION AND LAKE GRIFFINS ENVIRONMENTAL HISTORY Introduction Lake Griffin is a large (6,680 ha) hypereutrophic (mean chlorophyll 99 g/L; Table 2 1) freshwater lake in central Florida (Figure 2 1) (Canfield 1981). The lake has been studied by numerous organizations since the 1940s and this study used a great deal of the historical environmental information understand the environmental factors influencing Lake Griffins largemouth bass population. Water level information from 1946 to 2007 was obtained from St. Johns River Water Management District (SJRWMD). Water quality data including chlorophyll, total nitrogen, and tot al phosphorus concentrations as well as Secchi depth (1969 to 1978 and 1981 to 1994) were primarily obtained from FFWCC (personal communication Bill Johnson, Eustis Laboratory), but information was also obtained from the files of Florida LAKEWATCH (1979 to 1980; downloaded from wateratlas.org) and SJRWMD (1995 to 2007; personal communication Brian Sparks Palatka office ). Total aquatic macrophyte coverage (percent lake surface area) as estimated by aerial photography since 1947 was obtained from the file s of FFWCC (personal communication Bill Johnson, Eustis Laboratory). The Florida Department of Environmental Protection (FLDE P) provided estimates of the percent area coverage of hydrilla (personal communi cation Rob Kipker Tallahassee office ). Largemout h bass population abundance data including electrofishing catch -per unit -effort (CPUE) and roving creel data (harvest, catch, effort), were obtained from FFWCC (personal communication Bill Johnson, Eustis Laboratory). Geography Lake Griffin is located pri marily in Lake County, Florida (Shafer et al. 1986) (Figure 21) in Floridas Central Valley physiographic region (Canfield 1981). Lakes in the Central Valley

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20 are biologically productive lakes (eutrophic to hypereutrophic) and Lake Griffin is one of FFWC Cs fish management lakes (Administrative code Rule 68A 20.004). Approximately 3,804 ha constitute the main lake and are used for open water recreational activities (SJRWMD 2003), with the remaining area (2,876 ha) made up of primarily swamp and wetlands w hich were hist orically dominated by sawgrass (Cla dium jamaicense ), but were drained and diked off from 1955 to 1990 for muck farming (Marburger et al. 2002). There are approximately 40 canals (24+ k ilometers in length) around Lake Grif fin which were dredged prior to 1960 to provide landowners access to the lake and these canal s were maintenance -dredged between 2005 and 2007 (Figure 2 2). Lake Griffin is one of nine water bodies in the Harris Chain of Lakes (also known as Ocklawaha Chai n of Lakes). Lake Griffin serves as the headwaters of the Ocklawaha River, a major tributary of the St. Johns River. Lake Griffin receives water which passes through a dam on Haines Creek primarily from the eight upstream lakes, while a dam downstream o n the Ocklawaha River (Moss Bluff) regulates water levels in Lake Griffin according to the U.S. Army Corps of Engineers regulation schedule (Schluter and Godwin 2003). Water Levels The mean water level for Lake Griffin since 1946 was 58.65 ft, with a recorded minimum level of 56.63 ft and a maximum level of 60.14 ft ( SJRWMD; Table 2 1, Figure 2 3). The mean annual change in water level for the period of record was 1.84 ft, with a recorded annual minimum change of 0.91 ft and an annual maximum change of 7.1 4 ft (Table 2 1, Figure 23). On average, the water levels were much higher in Lake Griffin before 1960 with a peak at 60.14 feet after Hurricane Donna. This overall trend in decreasing water level since 1960 is due to lack of rainfall explained by the A tlantic Multidecadal Oscillation (Kelly and Gore 2008). Major yearly changes in water level occurred in 1974 and 1984. In 19 74, the Moss Bluff dam on the

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21 outlet of Lake Griffin broke causing a large (4.2 ft) fluctuation in water level (Figure 2 3). The ne xt major event in 1984 (7.1 ft) was an experimental drawdown and subsequent refill by FFWCC to improve the fishery. The least amount of yearly fluctuation occurred between 1995 and 2002 (Table 2 1, Figure 2 3). From 1995 through 2002, Florida was under s tatewide drought conditions (Veredi et al. 2006). Water Quality In many Florida lakes, cultural eutrophication has been a major concern over the past 30 years, with many efforts aimed at reducing nutrient inputs ( Terrel l et al. 2000). Until recen tly, Lake Griffin was considered one of the most polluted lakes in Florida (SJRWMD 2003). Over the past 50 years, farming activities, water level stabilization, and residential development around the lake have caused significant degradation in water quali ty and clarity (Schluter and G odwin 2003). Large nutrient inputs from adjoining agricultural operations have been targeted as the primary cause of dense algal blooms which have purportedly increased deposition of soft organic sediments to the benthic substrate (Schluter and G odwin 2003). Lake Griffin is the subject of major environmental restoration. Some restoration efforts on Lake Griff i n include : farm land acquisition, lake level fluctuation, removal of gizzard shad, and a marsh filtration system (SJ RWMD 2003). All of these activities except lake level fluctuation are aimed at reducing nutrient loading to and nutrient concentration in the system, particularly phosphorus while lake level fluctuations are intended to improve the vegetated habitat of t he lake. Consequently, Lake Griffin has been the subject of many environmental studies and a longterm record exists for many physical, chemical and biological attributes. Total phosphorus concentrations, ranging from 47 g/L to 181 g/L, exhibited a down ward trend from1973 to 2007 (Figure 2 4), but the longterm phospho rus mean was 100 g/L (Table 2 1 ). The highest levels of total phosphorus generally corresponded with low water

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22 level years, suggesting wind induced resuspension when water depth is low (Bachmann et. al. 2000) and the hydraulic flushing rate of the lake may be important factors influe ncing inlake water chemistry. Total nitrogen concentrations, unlike phosphorus concentrations, increased over time (Figure 2 5) Total nitrogen averaged 3140 g/L, and ranged from 2240 g/L to 5630 g/L (Table 2 1). The measured concentrations reflect the nutrient enriched status of Lake Griffin, and like phosphorus, maximum total nitrogen concentrations were typically higher during low water level years (esp ec ially the drought period from 1995 to 2002). Like total nitrogen, chlorophyll concentrations in Lake Griffin increased between 1995 and 2000 (Figure 2 6). For the period of record, chloroph yll concentrations averaged 99 g/L and ranged from 27 g/L to 3 16 g/L (Table 2 1). Also like total phosphorus and total nitrogen, the maximum chlorophyll values corresponded with low water levels and drought conditions from 1995 to 2002. W ater clarity, as measured by use of a Secchi disc declined from 1995 to 2002 (Figure 2 7) as expected since chlorophyll concentrations influence water clarity in Florida lakes (Canfield and Hodgson 1981) Over the historical record Secchi disc readings averaged 37 cm, ranging from 6 cm to 76 cm (Table 21). The lowest water clar ity was measured during the 1995 to 2002 drought period when total phosphorus, total nitrogen and chlorophyll concentrations were the greatest. Water transparency has remained less than 30 cm in Lake Griffin since 1995 (Figure 2 7). Aquatic Macrophytes N early half of Lake Griffin was covered by aquatic macrophytes (estimated by aerial photograph analysis, Bill Johnson FFWCC) particularly spatter dock ( Nuphar lute u m ) (Figur e 2 8) Boat trails were cut into the dense aquatic vegetation primarily on the north end of the lake to allow boaters access. Aquatic plant surveys conducted between 1983 and 2006 by FLDEP

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23 indicate that the non -native hydrilla ( Hydrilla verticillata ) peaked in abundance (11% areal coverage) in 1987 following the 1984 experimental dra wdown (Figure 29). By 2001, hydrilla coverage was reduced to 0.009% and overall aquatic plant coverage was reduced to <2% by 2006 (Figure 2 9). Lake Griffin has changed from a macrophyte dominated system to an openwater algal system since the 1960s with many of the water quality ch anges reflecting expectations with the establishment of the new alternative state (Bachmann et al. 1999). Largemouth Bass Population Larg emouth bass electrofishing CPUE were depressed during the late 1990s and early 2000s (Fig ure 2 10). Young of the year (<200 mm ) largemouth bass electrofishing CPUE was the highest ever recorded following the1984 drawdown (Figure 2 10) This large1984 year class can be seen in the fishery for years following the 1984 drawdown with historic high catches of harvestable sized fish (>360 mm, Figure 2 10). Largemouth Bass Fishery Roving creel surveys were first conducted by FFWCC starting in 1966. Estimates of catch and release of largemouth bass were not made during the early years of the c reel survey. An estimated 23,722 largemouth bass were harvested during the first year (1968) the survey was conducted which was the highest harvest on record (Figure 2 11). Catch (catch and release) of largemouth bass, first estimated in 1978 reached a high point of 20,000 fish in 1987 and a low of 121 fish in 2003 (Figure 2 11). Catch and harvest of largemouth bass have declined since 1971 except following the experimental drawdown in 1984.

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24 Table 2 1 Water level and water quality parameters (mean and ra nges) for Lake Griffin, Florida Parameters Mean Water Level (ft) Yearly Change in Water Level (ft) Total Nitrogen (g/L ) Total Phosphorous (g/L ) Secchi (cm) Chlorophyll (g/L ) Mean 58.65 1.84 3140 100 37 99 Minimum 56.63 0.91 2243 47 6 27 Maximum 60.14 7.14 5630 181 76 316 Note: Data obtained from FFWCC, Florida LAKEWATCH, and SJRWMD.

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25 Figure 2 1 Map of Lake Griffin, Lake County, Florida

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26 Figure 2 2 Map of Lake Griffin ca n als which were dredged from 2005 to 2007.

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27 Figure 2 3 Annual mean water level and yearly change in water level f rom 1946 to 2007, for Lake Griffin, Florida ( data obtained from SJRWMD). Figure 2 4 Annual mean total phos phorus ( g/L) for Lake Griffin, Florida (data obtained from FFWCC, SJRWMD, and Florida LAKEWATCH).

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28 Figure 2 5 Annual mean total nitrogen (g/L) for Lake Griffin Florida ( data obtained from FFWCC, SJRWMD, and Florida LAKEWATCH). Figure 2 6 Annual mean chlorophyll concentrations (g/L) for Lake Griffin, Florida ( data obtained from FFWCC SJRWMD, and Florida LAKEWATCH).

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29 Figure 2 7 Annual mean Secchi depth (cm) for Lake Griffin, Florida ( data obtained from FFWCC, SJRWMD, and Florida LAKEWATCH) Figure 2 8 Aquatic macrophyte areal coverage estimated by aerial photographs, for Lake Griffin, Florida ( data obtained from FFWCC).

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30 Figure 2 9 Percent area coverage of hydri lla for Lake Griffin, Florida ( data obtained from FLDEP). Figure 2 10. Annual mean largemouth bass electrofishing catch per unit effort (CPUE) for a variety of sizes of largemouth bass in Lake Griffin, Florida ( data obtaine d from FFWCC).

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31 Figure 2 11. Estimated annual angler catch and harvest from Lake Griffin, Florida from 1966 to 2006 ( data obtained from FFWCC).

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32 CHAPTER 3 METHODS A total of 13,933 largemouth bass greater than 200 mm TL were stocked into Lake Griffin during the winter months (December to April) between 2004 and 2007 (4,234 fish stocked in 2005, 5033 fish in 2006, and 4,666 fish in 2007) by Florida LAKEWATCH (Larson 2009). All stocked largemouth bass received a left pelvic fin clip and fish greater than 275 mm TL (N = 10,538) were dorsally implanted with orange Hallprint PDA plastic tipped dart tags. Dart tags had individual identification numbers; therefore each tagged fish could be individually identified upon capture. Flo rida LAKEWATCH stocked largemouth bass into the main area of Lake Griffin, not into canals or adjoining waters. Larson (2009) provides a full description of the Florida LAKEWATCH largemouth bass stocking program. Introduced -fish and native largemouth bass were collected by electrofishing in Lake Griffins near -shore waters and adjoining canals to evaluate dispersal of stocked largemouth bass from their introduction locations (50 plus sites) in the main area of Lake Griffin (FFWCCs creel zone), percent con tribution of stocked bass, and the mortality of stocked fish. An electrofishing protocol similar to that used by FFWCC and Florida LAKEWATCH (Larson 2009) was used during this study. An electrofishing boat equipped with a 5 kw generator (Honda EG5000) and a Smithroot model VI A pulsator was used to collect largemouth bass. The electrofishing crew consisted of two people; one individual netted fish from the bow and placed fish into a live well while the other person operated the boat and the pulsator. Between April 2007 and March 2009 (23 sampling days), 364 ten-minute electrofishing transects were sampled (Table 3 1). Lake Griffins shoreline vegetation (versus open-water sites) was targeted during electrofishing of the main -lake to enhance the proba bility of largemouth bass capture. Transects were placed evenly around Lake Griffins shoreline and a GPS unit recorded start and end points

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33 of each electrofishing transect. All largemouth bass that were caught in each sampling transect were measured for total length in millimeters (mm) Largemouth bass were then examined for pelvic fin clips and/or an orange Hallprint dart tag. Tag numbers and fin clips were recorded and the f ish were returned to the lake after processing. Data Analysis : Dispersal of individual tagged fish was determined using a GPS to determine release coordinates and electrofishing recapture coordinates which were plotted using ArcView GIS (HCL Technologies Ltd., New Delhi India). Electrof ishing GPS recapture coordinate data were also obtained from FFWCC (personal communication, John Benton, Eustis Laboratory). Once points were loaded for an individual tagged fish, the ArcView measuring tool was used to estimate dispersal distance. Measurements were made between the stocking poin t and the closest start or end point in the electofishing transects using straight lines staying in the bounds of Lake Griffin waters and around land features in ArcView. M inimum, maximum, and mean distance stocked largemouth bass dispersed from release site were calculated To determine if wild largemouth bass electrofishing CPUE (largemouth bass per hour of electrofishing) were different between canal and main lake habitats, the mean electrofishing CPUE, fish per hour, was calculated for each transect i n canals and the main body. Once the means were calculated for both data sets, the data were transformed [Log10 (catch+1)] to normalize the distribution. The transformed mean CPUE for canals and main lake were then compared using a t Test: Two Sample Ass uming Unequal Variances. Microsoft Excel was used for this analysis and t he alpha level of rejection was set at 0.05 The percent contribution and persistence of stocked fish was calculated simply by the ratio of marked (tagged and clipped) largemouth bas s to all largemouth bass captured during electrofishing for each sampling period. To obtain catch per unit effort for largemouth bass

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34 CPUE was calculated by dividing the total number of fish captured for an individual transect by the total minutes of ele ctrofishing (fish per minute) Sampling transects during each month were grouped together to provide a mean monthly CPUE estimate. Canals and main lake were separated to evaluate the difference in percent contribution between canals and the main lake. The April and May 2007 main-lake transects were combined to provide a single 2007 May main lake CPUE estimate. The May estimate was compared to the June 2007 canal CPUE estimate. To obtain lake -wide percent contribution of stocked fish and the ir CPUE for each month, the total number of stocked largemouth bass as well as all largemouth bass caught for each main lake and canal transect were combined and then divided by either the total number of largemouth bass caught (% contribution) or the tota l number of minutes electrofished (CPUE). The April, May and June 2007 main lake and canal transects were combined to calculate May mean percent contribution and CPUE estimate. To determine if stocked largemouth bass are exhibiting the same mortality r ates as native Lake Griffin largemouth bass, two separate CPUE data groupings (2006 tags only and 2007 tags only) were plotted in Microsoft Excel. M ortality estimates for the stocked largem outh bass were calculated from catch curves (Ricker 1975) Tagged (fish with fin clips only were not included) largemouth bass CPUE for 2006 and 2007 stocking years were calculated separately. To calculate individual stocking year mortalities, 2006 and 2007 canal and main lake CPUEs (tagged fish/minute) were again combined for each monthly sampling event. To calculate individual stocking years 2006 and 2007 CPUE (tagged fish/minute), April, May, and June (2007) were combined to obtain the May CPUE estimate. E lectrofishing data from April 2006 was obtained (Mark Hoyer, personal communication Florida LAKEWATCH ) and used to

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35 calculate individual stocking year 2006 mortality estimate Data were transformed using natural logarithms and then plotted, and CPUE was regressed against time for the sampling period. The slope of this line is represents the instantaneous monthly mortality rate. The monthly rate was multiplied by 12 (12 months in a year) to get an annual estimate of mortality (Z). This total annual mortality rate (Z) was then used to calcu late annual survival (S= e Z) and annual total mortality (A= 1 e Z), according to Ricker (1975). The mortality calculations were then compared to an estimate provided by F FWCC for Lake Griffins native largemouth bass for 2007 (John Benton, personal communicat ion Eustis Laboratory ). To determine if there was a change in native Lake Griffin largemouth bass condition (plumpness) after stocking, weight/length data sets for native largemouth bass provided by FFWCC (personal communication, John Benton, Eustis Labo ratory) for 2004 (pre stocking) and 2008 (post stocking) were compared. Transformed (Log10) weights of fish greater than 150 mm TL were regressed against transformed (Log10) lengths for each year (2004 N= 353, 2008 N= 345) in Microsoft excel. A linear r egression line was fit to each years data and an analysis of covariance (ANOCOVA) was completed using SAS (proc GLM; SAS Institute 2008) to test for differences in intercepts and slopes of the regression, where t he alpha level of rejection was set at 0.05. The ANOCOVA model used to test equality of slopes was: Log 10 WEIGHT = Log 10 TOTAL LENGTH + YEAR + Log 10 TOTAL LENGTH* YEAR and the ANOCOVA model used to test for differences in intercepts was: Log 10 WEIGHT = Log 10 TOTAL LENGTH + YEAR Patterns betw een available environmental parameters (i.e., total phosphorus, total nitrogen, chlorophyll, Secchi depth, mean water level, yearly change in water level, and wholelake

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36 aquatic macrophyte percent aerial coverage) and largemouth bass abundance estimates (e lectrofishing CPUE and roving creel catch) were investigated using correlation analysis. JMP version 5.01 software (SAS Institute 1989) was used for all statistical analyses. Data were transformed (Log 10) and t he alpha level of rejection was set at 0.05.

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37 Table 3 1 The date and number of electrofishing transects sampled in main lake areas and canal areas o f Lake Griffin, Florida from April 23, 2007 to March 13, 2009. 10 Minute Electrofishing Transects on Lake Griffin Date Main Lake Transects Canal Transects 04/23/2007 17 0 05/15/2007 16 0 05/17/2007 16 0 05/22/2007 16 0 05/23/2007 16 0 05/24/2007 16 0 05/29/2007 16 0 05/30/2007 10 0 05/31/2007 16 0 06/ 0 5/2007 0 17 06/ 0 6/2007 0 13 06/ 0 7/2007 0 9 11/ 0 5/2007 15 5 11/ 0 6/2007 14 5 02/19/2008 9 8 02/20/2008 12 4 03/12/2008 8 9 03/13/2008 10 7 06/24/2008 14 2 06/25/2008 8 8 06/26/2008 8 8 03/12/2009 8 8 03/13/2009 6 10

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38 CHAPTER 4 RESULTS AND DISCUSSION Introduction Florida LAKEWATCH stocked Lake Griffin w ith 13,933 wild adult largemouth bass that were placed into the main lake from 2005 to 2007. FFWCC surveyed anglers using Lake Griffin proper in 2006 and showed only a limited catch of stocked fish. Florida LAKEWATCH also found the percent of the largemo uth bass population caught by use of electrofishing did not increase above 15% despite stocking 4000 plus fish per year. These findings raised the single most important question related to all stocking programs and that is: What happened to the stocke d fish? Fish Dispersal Largemouth bass are known to individually exhibit different movement patterns with some individuals being transient while others occupy discrete home ranges (Demers et al. 1996). Larson (2009) reported the majority (65%) of Florida LAKEWATCH -stocked fish were caught by anglers fishing adjoining canals, marshes, and the Ocklawaha River. These angler reports indicated the stocked largemouth bass were moving great distances from their stocking sites. Dispersal movements of the individ ual stocked adult largemouth bass (N=122 fish), as assessed by this studys electrofishing efforts were highly variable ( Figure 4 1). Stocked fish dispersed variable distances in relation to time from stocking release (Figure 4 2). A few (~ 1 6%) fish did not leave the immediate stocking area, but the vast majority ( 8 4%) of largemouth bass traveled over 0.5 km (Figure 4 1). The mean dispersal distance for the caught stocked fish was 2.9 km, with minimum and maximum recorded distances of 0 and 9.2 km. Th e great distance moved by the stocked largemouth bass in Lake Griffin was not a major surprise because of the results of earlier works by Dequine and Hall (1950) and Mesing and

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39 Wicker (1986). Dequine and Hall (1950) conducted a largemouth bass (95 marked fish) migration study at Lake Griffin and found that fish (14 largemouth bass had complete movement data) moved variable distances (0 to 9.6 km with one fish moving 15.3 km) from where they were released. Mesing and Wicker (1986) conducted a largemouth bass telemetry study on nearby Lake Eustis and Lake Yale and found maximum home range dimensions ranged from 0.05 km to 2.4 km where t he home range dimensions were based on 2,047 radio locations with 22 adult fish. In that study, they also demonstrated t hat largemouth bass could move large distances or not move at all The measured dispersal distances during this study provided evidence that part of the reason why FFWCC reported limited catch of stocked fish in the main area of Lake Griffin was because th e fish moved. Lake Griffin is an open system allowing stocked fish to move into adjoining canals, marshes, and the Ocklawaha River. Anglers caught stocked fish below the dam at Moss Bluff, indicating there is an unknown rate of downstream escapem ent. Anglers also moved largemouth bass from Lake Griffin. Tournament anglers who traveled from other lakes (via Haines Creek or Ocklawaha River) removed largemouth bass caught in Lake Griffin when they brought them to weigh ins areas such as Lake Harris (personal communication, numerous anglers). While most largemouth bass anglers practiced catch and release, some anglers reported transporting large (>2.3 kg) stocked largemouth bass in their live wells to stock them into other water bodies. Clearly ther e is some unknown quantity of stocked and native largemouth bass leaving Lake Griffin due to angler activities. Following FFWCCs 2006 creel -survey, Florida LAKEWATCHs focus became the disparity in the number of largemouth bass caught in the main area of Lake Griffin and the number of fish caught in adjoining waters, especially in Larsons (2009) study where angler tag

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40 call in survey reported 326 largemouth bass catch locations of which 84 (26%) were from the main part of Lake Griffin (creel zone) and 212 (65%) were reported from non-stocked adjacent waters (e.g. connected canals and marshes). The other 30 caught largemouth bass (9%) were reported from other non -stocked waters (e.g. Lake Eustis). The greater number of largemouth bass caught in the can als (Larson 2009) raise d the question of whether the stocked fish we re preferentially selecting the adjoining waters or were being displaced into canal s due to lack of available habitat in the main lake. Mesing and Wicker (1986) found several fish mig rated up to 3 km from their home ranges during the spawning season to wave -protected sites within canals. Lake Griffin has many wave protected canals and stocked fish were present in these areas during the spawning season. Differences in the mean CPUE of all largemouth bass captured in the main lake versus the canals were examined to assess if stocked fish were preferentially selecting the canals or being displaced from the main lake. It did not appear that stocked largemouth bass had any greater preferen ce for canals than wild fish. The ratio of the numbers of stocked fish in the canals collected by electrofishing to wild fish was similar to that found in the lake over the study period (Table 4 1, Table 4 2 ). When comparing the native largemouth bass ele ctrofishing catch, t he mean CPUE for canals was 41fish/hour, with a minimum of 0 fish/hour and a maximum of 114 fish/hour. The mean CPUE for the main lake was 44 fish/hour, with a minimum of 0 fish/hour and a maximum of 138 fish/hour. The results from the t test comparing the mean CPUE (log10 ( [catch +1)] transformed) between canal and main lake areas found that the mean CPUEs were not significantly different (t= 1.049, df=150, P two tail = 0.296). This finding strongly suggests that the fish were not preferentially seeking the canals nor were they being displaced from the main

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41 lake; rather based on Larsons (2009) angler survey it might be more reasonable to think the anglers are preferentially targeting canals. Therefore, the disproportionate numbers of the tag returns from the canals must have been the result of angler behavior The canals offer habitat where the anglers can catch fish and some anglers may be targeting canals for reasons such as the canals are more accessible to back -yard anglers a nd safer to fish in boats due to less wind and wave action. The canals are also shaded by trees growing on the banks, making a cooler fishing experience during warm periods. Mortality Besides having largemouth bass moving to adjoining waters or completely outside the Lake Griffin system, a great reduction in the number of stocked largemouth bass caught over time could be the result of higher mortality rates The monthly Lake Griffin electrofishing data and calculated mortality estimates from catch curve s were used to compare this studys estimates of mortality to FFWCCs mortality estimates for native Lake Griffin largemouth bass. Mortality and survival estimates of stocked fish are s imilar to native fish (Table 4 3 ). Mortality estimates for the indivi dual stocking years, tag year 2006 cohort (Z= 1.087) and 2007 cohort (Z=1.295), were similar to the 2007 native large mouth bass estimate ( Z= 1.054). These estimates were made from data collected many months after stocking had occurred. These estimates pro vide evidence that FFWCCs report ed low catch of stocked fish may have been due to selective die -offs resulting from transportation (approximately 2 3 hours ) and stocking stress (Table 4 3 ). The collection of wildadult largemouth bass from distant non -fi sh ed waters may have been a contributing factor effecting stocked fish mortality. Stocked fish were transported during the cooler months, which was a viable stocking technique employed by Florida LAKEWATCH to reduce mortality.

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42 Persistence Another importan t question related to the Florida LAKEWATCH stocking program was the persistence of the stocked fish ; this will provide some assessment of how long angl ers could expect to catch stocked fish. In this study, the last fish stocking occurred in March 2007. In May and June 2007, the highest percent (13% main lake, 15% canals) of stocked fish was captured and CPUE was the highest measured (0.09 fish/minute in main lake, 0.10 fish/minut e in canals ; Table 4 1 Table 4 2 ). Combining the main lake and canal areas for a total contribution percentage and CPUE also yielded the highest catch estimates in May (13% and 0.09 fish/minute CPUE ; T able 4 4 ). Two years after the last stocking event (March 2009), electrofishing demonstrated that stocked largemouth bass were still present in the population (2% and 0.01 fish/minute CPUE in main lake; 4% and 0.03 fish/minute CPUE in canals ; Table 4 1, Table 4 2 ). When the two regions of Lake Griffin are considered a single unit, the estimate was 3% and 0.03 fish/minute CPUE (Table 4 4 ). There were no rewards for the largemouth bass that Florida LAKEWATCH stocked and no tag call -in advertisements. Stocked largemouth bass with tags are still being reported in the fishery by anglers (2009, four stocked fish reported) (Larson 2009) Recruitment of largemouth bass into the fishery may also contribute to reduced stocked fish catches. Lake Griffin Fish Condition Overstocking a lake with too many top predators can adversely affect the predator prey balance and affect the weight of individual fish because of a lack of forage (Noble 1981). The length -weight relationship for native largemouth bass in 2004 (pre -stocking) was compared to the 2008 (post stocking) relationship in Lake Griffin to determine if the condition of resident bass was reduced (Figure 4 3 ). An ANOCOVA analysis indicated the slopes ( Pr > F = 0.0274, > ) and intercepts s were significantly

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43 different. However, the 2008 values and most of the measured weights in 2008 were greater than those recorded in 2004 (Figure 4 4 ). This finding demonstrated no negative change in the weight length relationship after stocking, suggesting there was plenty of forage in Lake Griffin. Native Verses Stocked Largemouth Bass Length-Frequency Sto cking adult largemouth bass could potential ly alter the length frequency of l argemouth ba ss in Lake Griffin. T he length frequency of native verses stocked largemouth bass caught by use of electrofishing on three different sampling events spaced roughly one year apart ((Figure 4 5 (A -F) ) are all different, but stocked fish do contribute weakly to the length frequency. The length frequency distribution between fish caught in canals and the main lake a lso appear to be different ((Figure 4 5 (A -F)) Examining the largemouth bass cohort trends reveal a large size class (301350 mm TL and 351400 mm TL) that shows up in the May 2007 catch, and moves through larger siz e classes over the ne xt two years ((Figure 4 5 (A)) In the main lake sample from March 2009, a large size class (151200 mm TL) presumably young -of the -year, enters the catch ((Figure 4 5 (E)) This size class of young-of the year was the largest sampled during this proj ect, which indicate s that recruitment of largemouth bass was occurring naturally. Recruitment of fish from spawning in Lake Griffin therefore probably diminished persistence and percent contribution estimates and potentially inflated the mortality estima tes Biologists, however, should expect such changes when stocking any lake where a resi dent population already exists. Environment Factors and Largemouth Bass Lake Griffins largemouth bass fishery and population has gone through many changes. In Florida, lake level fluctuation has often been considered as a dominant factor influencing fish populations (Moyer et al. 1995). Historically Lake Griffin and the Harris Chain of Lakes fluctuated more than the current regulation schedule permits ( Figure 2 3). Water level

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44 fluctuation (i.e., drawdown) has therefore been used to enhance fisheries in Florida lakes (Nagid et al. 2003). FFWCC initiated a major drawdown of water at Lake Griffin in 1984. Following 1984, record angler catches of largemout h bass were measured (Figure 2 11). Electrofishing CPUE (Figure 2 10) also reached record levels. An e xamination of available data for Lake Griffin found that mean water level and electrofishing CPUE ( largemouth bass ( LMB ) all sizes) were signif icant ly related ( p < 0.05), but the relationship was weak (R2 = 0.31; N=21 ). Based on statistically significant relationships and experience in the field, it is easy to see why a fish and wildlife agency like FFWCC would recommen d an experimental drawdown; but in a multi use lake like Lake Griffin attention must be paid to the concerns of the public ( Hoyer and Canfield 1994). Following the 1984 drawdown, the growth of aquatic plants was a beneficial habitat improvement, but th ese plants became a weed problem for the public because of their interference with navigation. When tested, the percent area coverage of hydrilla and estimated angler catch at Lake Griffin also had a significant relationship (R2 = 0.32; p < 0.05, N=1 2 ) as was the significant relationship between total percent aerial coverage of vegetation and angler harvest (R2 = 0.27; p < 0.05, N=29 ). These s ignificant relationships, however, are weak suggesting the total amount of plants needed in Lake Griffin may not be as great as produced during the 1984 drawdown to maintain a good fishery, and there may be other factors controlling fish abundance How many aquatic plants are needed in an individual water body has been debated for many years. Durocher et al. (1984) determined that any reduction of submerged vegetation below 20% would result in a reduced largemouth bass standing crop in Texas reservoirs Hoyer and Canfield (1996) reported that there was no correlation between aquatic macrophyte

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45 abundance (percent area coverage and percent volume infestation) and largemouth bass standing crop in small (<300 ha) Florida lakes However they concluded plants are more important in larger lakes like Lake Griffin Following the 1984 drawdown, Lake Griffins aquatic plant co mmunity increased from 1% to 20% coverage (Figure 2 8). Hydrilla, a non -native major invasive species in Florida lakes, was the dominant (11%) plant after the 7 -foot change in water level (Figure 4 6 ). Aquatic plants and other associated problems with d rawdowns caused public uproar at Lake Griffin among the nonangling public due to issues such as boating access, hydrilla coverage, floating plant islands, and lack of access ; all resulted in public oppos ition to future draw downs (HCLRC 2007). The refore, the question that must be asked is what else could be done for a multi use lake if public support for a massive drawdown cannot be garnered. It seems based on the historical record and as measured after the 2003 water level rise (Figure 2 3) that an enhance d water level fluctuation of one meter would stimulate enough aquatic plant growth (1 3%) to cause an increase in largemou th bass recruitment (Figure 4 6 ; Figure 4 7 ). This enhanced water level fluctuation would become even more i mportant once the adjoining marshes are reconnected to the main lake because high water level caused by the Atlantic Multidecadal Oscillation may be a primary environmental factor driving the fishery at Lake Griffin. If efforts are to be continued to reest ablish aquatic plants in Lake Griffin through planting (HCOLRC 2006), it must be recognized that such efforts will be limited by algal biomass (chlorophyll) in the water column (Figure 4 8 ). Elevated chlorophyll concentrations affect light attenua tion to the bottom sediments (Cole 1994), and because aquatic macrophytes require light to grow, light availability is one of the most important factors regulating the distribution of aquatic macrophytes (Zimmermann et al. 1994). Chlorophyll concentratio n s are controlled by

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46 nutrient concentrations, particularly nitrogen and phosphorus, in Floridas lakes (Canfield 1983) ; L ake Griffin shows this trend (Figure 4 8 ). Chlorophyll concentrations in Lake Griffin were significant ly related to tota l phosphorus but the relationship was weak (R2=0.16; P < 0.05, N=31 ) (Figure 4 9 ). On the other hand c hlorophyll concentrations had a strong relationship (R2=0.66; P< 0.001, N=34 ) w ith total nitrogen, which sugges ts that Lake Griffin is nitrogen limited (Figure 4 10). Chlorophyll concentrations in Lake Griffin had a significant relationship (R2=0.31, P< 0.001; N=34 ) with water clarity as measured with a Secchi disc (Figure 4 1 1 ). Electrofishing catchabi lity decreases with high chlorophyll concentrations due to reduced water clarity because it is harder to see stunned fish (Reynolds 1996, Mclnerny and Cross 2000). In the sampling events between 1997 through 2002, electrofishing largemouth bass CPUE was a t an all time low compared to before and aft er that time period (Figure 4 1 2 ). During these times high chlorophyll and low water clarity may well have contributed to the lower electrofishing catchability as Secchi depth and CPUE (LMB all sizes) exhibite d a significant (R2 = 0.43; p < 0.0 5 N=21 ) positive relationship (Figure 4 13) Elevated chlorophyll concentrations at Lake Griffin w ere associated with low water conditions (Figure 4 1 4 ). Areas of Lake Griffin that were targeted for electrofishi ng were typically emergent vegetation in most years. These plants may not have always been accessible to electrofishing due to low water ; therefore, water level in combination with chlorophyll at Lake Griffin may also have had a role in this decrease in C PUE due to electrofishing catchability. The fish may have moved to open water during the drought and were not as vulnerable to the electrofishing gear.

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47 There was no relationship between angler catch and electrofishing CPUE (R2=0.000013, P > 0.05, N=11 ) of largemouth bass (Figure 4 15). The primary reason for decreased angler catch of largemouth bass in 2004 to 2006 (3 lowest years ever measured ) was a decrease in angler effort (Figure 4 1 6 ). Unfortunately, anglers were not surveyed for l on g periods of time at Lake Griffin by FFWCCs roving creel survey, because of lack of angler effort. Angler effort was highest from 19871990 (Figure 4 1 6 ) when large year classes were produced in prior years when the lake had 20 % coverage of aquatic plants (i.e. 1984 to 1986) These year classes eventually produced trophy fish. In the late 1990s, the lake started getting bad press due to environmental problems (dead floating alligators, toxic algae, low lake levels) and t he n egative image probably drove anglers and other recreational users away from Lake Griffin (HCLRC 2002). When creel surveys resumed in 2004, few anglers were using the La ke Griffin resource (Figure 4 1 6 ). In 2005, Lake Griffin received its first stocking of adult -sized largemouth bass. Over the next two years, there was a slight increase in angling effort (724 hours 2003, 2649 hours 2004, 4034 hours 2005, and 6443 hours 2006; Figure 4 1 6 ). Angler effort in the 2006 creel survey, however, was still low com pared to historical levels. Largemouth bass angler catch per effort initially increased greatly in 2004 and has not decreased fro m historical levels (Figure 4 1 7 ). The electrofishing CPUE of largemouth bass (> 200 mm TL ) appears to be back to previously measured levels (Figure 4 1 2 ), b ut creel catch and effort are down (Figure 2 11, 4 1 6 ), which suggest that the fis hery is partially psychologically driven rather than biologically driven and/or the bad press the lake received in the late 1990s is taking longer than the fish population to recover. Based on electrofishing CPUE, the fish should be there. Larsons (2009)

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48 study estimated the economic impact generated by stocking to be ranging into the millions of dollars. During this time period, the lake was getting good press which most likely had an effect on angler effort. One of the major objectives of Larsons study was to stimulate angler interest in the lake. Stocking large fish in public view should have an effect on effort. A primary goal of fish and wildlife management agencies is to increase angler effort on water bodies because this increases license sale s and economic activity associated with the fishery.

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49 Table 4 1 Electrofi shing sa mpling results for canal s ; total catch of largemouth bass greater than 200 mm TL, stocked largemouth bass catch ( marked ), stocked fish per minute (CPUE), and percent of stocked fish to total catch (% total catch) for Lake Griffin, Flor ida. Electrofi shing Sampling For Canals Date Total Ca tch Marked CPUE % Total Catch Jun 07 262 39 0.10 15 Nov 07 50 2 0.02 4 Feb 08 94 5 0.04 5 Mar 08 103 7 0.04 7 Jun 08 109 9 0.05 8 Mar 09 134 6 0.03 4 Table 4 2 Elec trofishing sampling results for main lake total catch of largemouth bass greater than 200 mm TL stocked largemouth bass catch (marked), stocked fish per minute (CPUE), and percent of stocked fish to total catch (% total catch) for Lake Griffi n, Florida. Electrofishing Sampling For Main Lake Date Total Ca tch Marked CPUE % T otal Catch May 07 964 123 0.09 13 Nov 07 191 11 0.04 6 Feb 08 176 8 0.04 5 Mar 08 154 8 0.04 5 Jun 08 174 5 0.02 3 Mar 09 116 2 0.01 2 Table 4 3 A comparison of mortality estimates Z -Annual (instantaneous mortality rate) S Annual (annual survival) and A -Annual ( annual total mortality ) of stocked largemouth ba ss and native largemouth bass from Lake Griffin, Florida. Lake Griffin Largemo uth Bass Mortality Parameter Estimates Parameter 2007 Tags Only 2006 Tags Only Native Fish 2007 Catch Curve Z Annual 1.295 1.087 1.054 A Annual 0.726 0.663 0.652 S Annual 0.274 0.337 0.348

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5 0 Table 4 4 Electrofishing sampling c ombined results for main lake and canal; total catch of largemouth bass greater than 200 mm TL stocked largemouth bass catch (marked), stocked fish per minute (CPUE), and percent of stocked fish to total catch (% total catch) for Lake Griffin, Florida. Electrofishing Sampling For Main Lake and Canals Date Total Ca tch # Transects Marked CPUE % Total Catch May 07 1226 178 162 0.09 13 Nov 07 241 39 13 0.03 5 Feb 08 270 33 13 0.04 5 Mar 08 257 34 15 0.04 6 Jun 08 283 48 14 0.03 5 Mar 09 250 32 8 0.03 3

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51 Figure 4 1 The percent of largemouth bass and corresponding distances dispersed from stocking points to electrofishing recapture points in Lake Griffin, Florida. Figure 4 2 The dispersal distance from stocking release point verses the number of days post stocking for electrofished recaptured largemouth bass in Lake Griffin, Florida.

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52 Figure 4 3 The log10 total length verses log10 weight of native largemouth bass pre (2004) and post (2008) stocking in Lake Griffin, Florida (data obtained from FFWCC) Figure 4 4 The log10 total length verses log10 weight linear regression line comparison of native largemouth bass pre (2004) and post (2008) stocking in Lake Griffin, Florida (data obt ained from FFWCC)

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53 Figure 4 5 The number and size of native and stocked largemouth bass captured via electrofishing in the canals and main lake of Lake Griffin, Florida. A) Main Lake May 2007. B) Canals Jun e 2007. C) Mai n Lake June 2008. D) Canals June 2008. E) Main Lake March 2009. F) Canals March 2009. A B

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54 Figure 4 5 Continued. C D

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55 Figure 4 5 Continued. E F

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56 Figure 4 6 The annual change in water level and estimated percent area coverage of hydrilla in Lake Griffin, Florida ( data obtained from SJRWMD and FLDEP). Figure 4 7 Yearly change in water level, percent area coverage o f hydrilla, and electrofishing catch -per unit -effort (CPUE) of largemouth bass (< 200 mm TL and > 200 mm TL) for Lake Griffin, Florida ( data obtained from SJRWMD, FLDEP and FFWCC).

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57 Figure 4 8 Total nitrogen (g/L), t otal phosphorus (g/L) and chlorophyll concentration (g/L) trends for Lake Griffin, Florida (data obtain ed from FF WCC, Florida LAKEWATCH and SJRWMD ).

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58 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5 2.6Log10 Chlorophyll (g/L) 1.7 1.8 1.9 2 2.1 2.2 2.3 Log10 Total Phosphorus (g/L) Figure 4 9 Relations hip between log10 chlorophyll ( g/L) and log10 total phosphorus ( g/L) with a linear line fit to the data (R2=0.16), for La ke Griffin, Florida for data collected from 1974 to 2007 (data obtained from FFWCC, SJRWMD, and Florida LAKEWATCH) 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5 2.6Log10 Chlorophyll (g/L) 3.3 3.4 3.5 3.6 3.7 3.8 Log10 Total Nitrogen (g/L) Figure 4 10. Relations hip between log10 chlorophyll (g/L) and log10 total nitrogen ( g/L) with a linear line fit to the data (R2=0.6 6), for Lake Griffin, Florida for data collected from 1969 to 2007 (data obtained from FFWCC, SJRWMD, and Florida LAKEWATC H)

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59 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 Log10 Secchi (m) 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5 2.6 Log10 Chlorophyll (g/L) Figure 4 1 1 Relations hip between Log10 Secchi (m) and Log10 Chlorophyll (g/L) with a linear line fit to the data (R2=0.31), for Lake G riffin, Florida for data collected from 1969 to 2007 (data obtained from FFWCC, SJRWMD, a nd Florida LAKEWATC H) Figure 4 1 2 Annual mean chlorophyll concentration and electrofishing catch per unit -effort (CPUE) of largemouth bass (> 200 mm TL), fo r Lake Griffin, Florida ( data obtained from FFWCC, Florida LAKEWATCH, and SJRW MD).

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60 -1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2Log10 CPUE All Sizes LMB -0.8 -0.6 -0.4 -0.2 0 .1 .2 .3 .4 .5 Log10 Secchi Depth (m) Figure 4 13. Relations hip between Log10 CPUE (fish per minute) for all sizes of largemouth bass captured by electrofishing and Secchi depth (m) with a linear line fit to the data (R2=0.43), for Lake G riffin, Florida for data collected from 1969 to 2007 (data obtained from FFWCC, SJRWMD, and Florida LAKEWATC H) Figure 4 1 4 Annual mean chlorophyll concentration and annual mean water level for Lake Griffin Florida ( data obtained from FFWCC, Flo rida LAKEWATCH, and SJRWMD).

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61 2 2.5 3 3.5 4 4.5Log10 Creel Catch -1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 Log10 CPUE LMB > 200 mm TL Figure 4 1 5 Relationship between a nnual largemouth bass creel catch estimated by roving creel survey and electrofishing CPUE ( fish /minute) of largemouth bass (> 200 mm TL), with a linear line fit to the data (R2=0.000013), fo r Lake Griffin, Florida ( data obtained from FFWCC) Figure 4 1 6 Angler effort (hours) for largemouth bass, estimated by roving creel survey for Lake Griffin Florida ( data obtained from FFWCC).

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62 Figure 4 1 7 His torical angler effort ( hours) and catch per effort (fish per hour) for largemouth bass based on roving creel survey data ( data obtained from FFWCC).

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63 CHAPTER 5 FISHERY MANAGEMENT IMPLICATIONS When Lake Griffin was sampled immediately followi ng the last stocking in 2007, stocked fish represented 10 to 15 % of the catch. The percent contribution information demonstrates that the stocking program impacted the largemouth bass population in Lake Griffin. Larson (200 9) also estimated that the stocking program enhanced revenues (ranging from $324,000 to 2.7 million dollars) to the local communities. Thus, stocking of wild adult bass, with its apparent positive cost:benefit ratio, was recommended by Larson (2009) as a viable fish management tool for Lake Griffin. An angler creel survey is perhaps the most important fisheries management survey to evaluate fisheries, because it provides information on what the anglers are experiencing. Interpretation of results, h owever, must be placed in context before statements are made regarding the success or failure of a management action. The situation at Lake Griffin is a prime example. The 2006 F FWCC creel survey did not provide evidence for the success of the Florida LAK EWATCH wild adult largemouth bass stocking program. The creel survey was conducted in the open lake and failed to consider the myriad of canals and adjoining waters where anglers could and did catch fish. As stated over 20 years ago by Mesing and Wicker ( 1986), creel surveys on large Florida lakes should include canal areas connected to the lake if realistic harvest figures are to be obtained during the spawning season. When considering the catch information from canals collected by Larson (2009), an argument for the cost effectiveness of the stocking program can be advanced. However, at Lake Griffin, it is now clear that the presence of canals influenced angler catch and harvest estimates, thus future angler surveys at Lake Griffin shoul d include adjoining waters like canals. The challenge is maintaining the past survey protocol sufficiently

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64 so that long term data sets remain comparable with future creel information. Perhaps, what would be the best approach now would be the implementat ion of three or four creel surveys that include the adjoining waters like canals as well as the main lake to determine the impact on effort and harvest estimates. This will add costs to the creel survey, but it is clear that the costs will be justified if it helps biologists make better decisions for the resource. The next phase of restoration at Lake Griffin according to personnel from the St. Johns River Water Management District is reestablishment of spawning and nursery habitat for desirable fish (i.e. largemouth bass) species (Schluter and Godwin 2003). The Districts program includes the reconnection of the former adjoining farmlands once wetlands are re established. The estimated time for complete ecosystem restoration for Lake Griffin, however, i s 60 years (HC L RC 2008) because SJRWMD is focusing on nutrient removal. Reconnection of adjoining marshes that were once used for farming, will provide additional spawning habitat, nursery habitat, and fishing areas If Lake Griffin were solely a Fish Ma nagement lake and the only consideration for managers was optimization of largemouth bass catch and harvest, a major water level fluctuation would be the first choice to stimulate the largemouth bass population in Lake Griffin. Regularly scheduled loweri ng of water levels followed by refill is the least expensive and best approach This was demonstrated by FFWCC with its 1984 experimental drawdown (Figure 4 7 ). However, Lake Griffin is a multipurpose recreational lake and there are other considerations such as access issues and growth of the non -native aquatic plants like hydrilla and its effects on non angling recreation. While there are a myriad of public concerns, major reductions in Lake Griffins water level have not been accepted by the public sinc e the 1980s. Recently, the canals around the lake have

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65 received maintenance dredging. This dredging was promoted: to increase boaters access and allow for enhanced lake level fluctuation ( i.e., 1 3 feet) (HCLRC 2007). The increased water level of Lake Griffin after the 2004 hurricane season coincided with a positive response in the CPUE of largemouth bass, reaching historical high levels (Figure 4 7 ). Major draw downs (i.e., 3 feet or more ) dont provide boaters access, but enhanced fluctuation is not as disrupti ve Therefore, regularly -scheduled enhanced fluctuations (reduce water levels to the outer edge of the emergent macrophytes), such as the one in 20022003, would provide fish managers with their best opportunity to maintain a reasonable largemouth bass population, if public su pport for a major lowering of water levels cannot be garnered. A potential problem, for even well -managed enhanced water level fluctuations, is that major droughts have struck Florida in recent years. Floridas water managers, therefore, tend to be conser vative even with enhanced fluctuation so as not to garner public opposition when drought conditions occur The water managers rely on weather modeling for precipitation predictions, thus even well -planned enhanced fluctuations could be precluded for exten ded periods of time, especially if sufficient water cannot be stored in the upstream lakes. Another major drawback of water level fluctuation in the eyes of the public and some environmental agencies is the potential growth of hydrilla. Unless the prevai ling attitudes towards hydrilla change (Hoyer et al. 2005), hydrilla at Lake Griffin will have to be managed, which can be expensive. Like the canals, the presence of reconnected marshes may not substantially increase angler effort within Lake Griffin pr oper. In examining trends in largemouth bass CPUE for fish >200 mm TL (Figure 4 7 ), the evidence is pretty strong that harvestable -size largemouth bass should be sufficiently abundant in the main stem of Lake Griffin to support fishing, but angler effort

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66 remains low (Figure 4 1 7). This suggests that there is an angler perception problem and work needs to be directed towards massive habitat work that will induce anglers to fish Lake Griffin proper. Submerged aquatic macrophytes would be the preferred habit at for many fish biologists, but there are many reasons why submerged plants will not be come established in Lake Griffin in a timely manner. One potential approach to attract /produce fish would then be the establishment of large numbers/a reas of a rtificial fish attractors, especially the creation of hard rock bottom with limestone as done by FFWCC at Lake Eustis off the public fishing pier. Plastic crates filled with lime rock could be anchored in group configurations or reefs into areas of the la ke to provide fish refuge. A reef ball structure could also be used at a greater expense as a fish attractor Another option (even more expensive) is to remediate and or dredge the remaining canals, which exist around the lake to provide additional fish habitat. Largemouth bass use canals for spawning and as nursery habitat. Additional canals could also be dredged on some of the conservation land around the lake and be protected from fishing. These artificial structures will attract anglers as well a s fish. The largemouth bass fishery at Lake Griffin is primarily a catch and release fishery (90% of anglers; Larson 2009), so the establishment of artificial attractors will not adversely affect the fish population. The production/attraction issue (a con cerned raised by ecologists; Wilson 2001) that is associated with artificial habitat, therefore, is not a major concern at Lake Griffin. Stocking additional wild adult largemouth bass is recommended to occur simultaneously with the habitat improvem ent and expansion projects because the stocked fish will at least provide anglers with a positive outlook on the Lake Griffin fishery. It is also clear from Larsons (2009) work that the cost of stocking (< $150,000 per year) is far less than the potentia l

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67 economic stimulus ( ranging from $324,000 up to $2.7 million per year). Also, fisheries managers must understand that the ability of largemouth bass to move distances on the magnitude of kilometers may result in non-stocked adjoining waters being stocked, thus diluting the im pact of stocking on the receiving water. Depending on lake size, stocking at multiple sites quickly disperse fish throughout the system.

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68 CHAPTER 6 CONCLUSION The stocking of wildadult largemouth bass resulted in an estimated 10 to 15% contribution t o the abundance in CPUE of largemouth bass in electrofishing catches in May and June 2007. If it were possible to double or triple this stocking rate, there might be an even greater effect on abundance of largemouth bass in the system. My results confirm that stocked largemouth bass are indeed moving outside of the creel area where they were stocked and into canals. FFWCC did not sample canals in their creel survey, primarily because they were following their longterm creel protocol. Canals are clearly utilized by fishermen according to Larsons (2009) report and my electrofishing efforts, but largemouth bass abundance was similar in the canals and the main lake. Florida LAKEWATCH stocked Lake Griffin at ~1 fish per hectare. I also believe that an adult largemouth bass stocking project like this one will have a more profound effect on a smaller system if stocked at a higher rate. In 2008, nearby Lake Dora was stocked by Florida LAKEWATCH with ~4000 largemouth bass greater than 200 mm TL. P ost -stocking electrofishing revealed ~20% contribution to the greater than 200 mm TL population of largemouth bass. Lake Dora is nearly half the size (1810 ha) of Lake Griffin and does not have nearly the same amount of canals for stocked fish to disperse into. Stocking adult fish at higher rates or in to smaller lakes should be done with caution as the fisheries biologist must make certain there is an adequate forage base. However, in hypereutrophic lakes like Lake Griffin this should not be an issue. Based on my evaluations and those of Larson (2009), the weight of evidence supports the stocking of wildadult largemouth bass using the Florida LAKEWATCH protocol. Large numbers (4000 plus fish per year) of wildadult bass were procured for three years f rom private

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69 non -fished waters and there are many others sources of wild adult largemouth bass in Florida. Stocking these fish into a large hypereutrophic lake resulted in a significant increase of fish although, we dont know if it is an addition or repl acement. Stocked largemouth bass dispersed over distances ranging up to 9 km and fish did not seem to suffer abnormal mortality rates compared to the native fish due to stocking stress. Stocked fish are still present in the Lake Griffin fishery two years after the last stocking event and t he mortality rate was similar to the native fish in the lake. The stocking event did not cause a change in fish condition indicating that there is plenty of forage available Stocked largemouth bass were not being disp laced into canals and seem to be mixing evenly throughout the population in the main lake strongly suggesting better habitat is needed in the main lake to attract fish and anglers. Overall, there have been no measurable negative effects of stocking and given the weight of evidence argument, fish management agencies should consider the stocking of wild adult largemouth bass as a viable fishery management tool. When assessing complex environmental issues such as those at Lake Griffin, it is difficult to prove anything with 100% certainty or establish strong environmental/biological relationships. Consequently, fisheries management is art and science ; f or many issues such as supplemental fish stocking, the scientific community shall remain divided, with s ome individuals being strong advocates for stocking and some being just as strong detractors ( Mesing et al. 2008). Such controversy will probably continue to exist after decades of debate because the criteria for success are ever changing.

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70 LIST OF REF ERENCES Bachmann, R. W., M. V. Hoyer, and D. E. Canfield, Jr. 1999. The restoration of Lake Apopka in relation to alternative stable states. Hydrobiologia 394:219232. Bachmann, R. W., M. V. Hoyer, and D. E. Canfield, Jr. 2000. The potential for wave disturbance in shallow Florida lakes. Lake and Reservoir Management 16: 281291. Benton, J. W. 2000. Central Florida Fisheries Development: Lake Griffin Fisheries Improvement. Annual Report for 19992000. Florida Game and Freshwater Fish Commission. Tallahassee FL. P.10 31. Buynak, G. L., B. Mitchell, D. Michaelson, and K. Frey. 1999. Stocking subadult largemouth bass to meet angler expectations at Carr Creek Lake, Kentucky. North American Journal of Fisheries Management 19:10171027. Canfi eld, Jr., D.E. 1981. Chemical and trophic state characteristics of Florida lakes in relation to regional geology. Florida Agricultural Experimental Station Journal Series 3513. Canfield, Jr., D.E. 1983. Prediction of chlorophyll a concentrations in Florida lakes: the importance of phosphorus and nitrogen. Water Recourses Bulletin 19:25562. Canfield, Jr, D.E. and L. M. Hodgson. 1981. Prediction of Secchi disc depths in Florida lakes; Impact of a lgal b iomass and o rganic c olor. Florida Agricultural Exper imental Station Journal Series 3255. Carlander, H.B. 1954. A history of fish and fishing in the Upper Mississippi River. Upper Mississippi River Conservation Committee, Rock Island, Illinois. Cole, G.A. 1983. Textbook of Limnology, 3rd Edition. C.V. Mosby Company. St. Louis, Missouri. Copeland, J. R., and R. L. Noble. 1994. Movements by youngof -year and yearling largemouth bass and their implications for supplemental stocking. North American Journal of Fisheries Management 14:199124. Crowder, L. B., and W. E. Cooper. 1979. Structural complexity and fishprey interactions in ponds: A point of view. Pages 2 10 in Johnson, D. L., and R. A Stein editors Response of fish to habitat structure in standing water. North Central Division Ame rican Fisheries Society Spec. Publication No. 6. Demers, E., R. S. McKinley, A. H. Weatherley and D. J. McQueen. 1996. Activity patterns of largemouth and smallmouth bass determined with electromyogram biotelemetry. Transactions of the American Fisheries Society 125:434439. Dequine, J. F., and C. E. Hall, Jr. 1950. Results of some tagging studies of the Florida largemouth bass, Micropterous salmoides floridanus Transactions of the American Fisheries Society 79:155166.

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71 Durocher, P. P., W.C. Provine, a nd J.E. Kraai. 1984. Relationship between abundance of l argemouth bass and submersed vegetation in Texas reservoirs. North American Journal of Fisheries Management 4:8488. Florida LAKEWATCH. 2007. Restoration of the Economic Vitality of Lake Griffins La rgemouth Bass Fishery: A Research/Demonstration Project / Phase III. Final Report. Department of Fisheries and Aquatic Sciences. Institute of Food and Agricultural Sciences University of Florida Gainesville, Fl orida (HCLRC) Harris Chain of Lakes Resto ration Council. 2002, 2006, 2007, 2008. Reports to the Legislature. Tallahassee, Florida. Heidinger, R. C., and R. C. Brooks. 2002. Relative contribution of stocked minnow -fed and pellet -fed advanced fingerling largemouth bass to year -classes in Crab Orchard Lake, Illinois. Pages 703714 in D.P. Philippi and M.S. Ridgeway editors. Black bass: ecology, conservation, and management. American Fisheries Society, Symposium 31, Bethesda Maryland. Hoffman, K.J., and P. W. Bettoli. 2005. Growth, d ispersal, m ortality, and c ontribution of l argemouth b ass s tocked into Chickamauga Lake, Tennessee. North American Journal of Fisheries Management 25:15181527. Hoyer, M. V. and D. E. Canfield, J r. 1994. Bird abundance and species richness on Florida lakes: influence of trophic status, lake morphology, and aq u atic macrophytes Hydrobiologia 297/280:107119. Hoyer, M. V., and D.E. Canfield, Jr. 1996. Largemouth bass abunda nce and aquatic vegetation in Florida lakes: an empirical analysis. Journal of Aquatic Plant Management 34:23 32. 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 id entified by professionals with future management recommendations. Proceeding of a Special Symposium. Florida LAKEWATCH, Department of Fisheries and Aquatic Sciences, University of Florida Institute of Food and Agricultural Sciences. Gainesville Florida Kelly, M.H. and J.A. Gore. 2008. Florida river flow patterns and the Atla ntic multidecadal oscillation. River Research and Applications. 24: 598616. Larson, K.W. 2009. Stocking wildadult largemouth bass Micropterus salmoides floridanus to improve fishing and associated economic activity at Lake Griffin, Florida. Masters t hesis. University of Florida. Gainesville, Florida. Lorenzen, K. 1996. The relationship between body weight and natural mortality in fish: a comparison of natural ecosystems and aquaculture. Journal of Fish Biol ogy 49:627647. Marburger, J. E., W. E. Johns on, T. S. Gross, D. R. and Di. J. Douglas. 2002. Residual organochlorine pesticides in soils and fish fro m wetland restoration areas in central Florida, USA. Wetlands 22:705 711.

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72 McInerny M. C, and T. K. Cross. 2000. Effects of sampling time, intraspe cific density, and environmental variables on electrofishing catch per effort of largemouth bass in Minnesota lakes. North American Journal of Fisheries Management 20:328 336. Mesing, C. L., and A. M. Wicker. 1986. Home range, s pawning migrations, and homi ng of radio -tagged Florida largemouth bass in two central Flor ida lakes. Transactions of the American Fisheries Society 115:286295. Mesing, C. L., R. L. Cailteux, A. P. Strickland, E. A. Long, and M. W. Rogers. 2008. Stocking of a dvanced -f ingerling l a rgemouth b ass to s upplement y ear -c lasses in Lake Talquin, Florida. North American J ournal of Fisheries Management 28:17621774. Miko, D.A., H. L. Schramm, Jr ., S. D. Arey, J. A. De nnis, and N. E. Mathews. 1995. Determination of stocking densities for satisfact ory put and take rainbow trout fisheries. North American Journal of Fisheries Management 15: 823829. Milon, J. W. and R. Welsh. 1989. An economic analysis of sport fishing and the effects of hydrilla management in Lake County, Florida. Economi c Report 118, Food and Resource Economics Department. University of Florida. Gainesville, Florida. Miranda, L. E., and W. D. Hubbard. 1994. Winter sur vival of age 0 largemouth bass relative to size, predators, and shelter. North American Journal of Fisheri es Management 14:790796. Moyer, E. J, M. W. Hulon, J. J Sweatman, R. S. But ler, and V. P. Williams. 1995. Fishery responses to h abitat r estoration in Lak e Tohopekaliga, Florida. North American Journal of Fisheries Management 15:591 595. Nagid, E. J., M S. Duncan, and T. M. Tuten. 2003. La rgemouth b ass a ge d istribution on Rodman Reservoir following an e xtreme d rawd own. Florida Fish and Wildlife Conservation Commission. Completion Report, Lower Ocklawaha Basin Fisheries Investigations. Gainesville Florida. Noble, R. L. 1981. Management of forage fishes in i mpoundments of the s outhern U nited States Transactions of the American Fisheries Societ y 110: 738750. Porak, W. F. 1994. Largemouth b ass i nvestigations: r esearch and m anagement of t rophy l argemouth b ass. Florida Fish and Wil dlife Conservation Commission. Project F 24. Study XVI. Porak, W.F., W.E. Johnson, S. Crawford, D.J. Renfro, T.R. Schoeb, R.B. Stout, R. A. Krause and R.A. DeMauro. 2 002 Factors affecting surv ival of largemouth bass raised on artificial diets and stocked into Florida lake s. Pages 649666 in D.P. Philippi and M.S. Ridgeway editors. Black ba ss: ecology, conservation, and management. American Fisheries Society, Symposium 31, Bethesda Maryland. Reynolds, J.B. 1996. Ele ctrofishing. Pages 221253 in B. R Murphy, and D. W. Willis editors. Fisheries techniques, 2nd edition. America n Fisheries Society, Bethesda, Maryland.

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73 Ricker, W. E. 1975. Computation and interpretation of biological statistics of fish populations. Depa rtment of the Environment, Fisheries and Marine Science, Bulletin 191, Ottawa, Canada. Schluter, C. A. and W. F. Godwin. 2003. Lake Griffin F ish Habitat Suitability Study. Available: http://proceedings.esri.com/library/use rconf/proc03/p0792.pdf. (March 2008). Shafer, M. D., R. E. Dickinson, J. P. Heaney, and W. C. Huber. 1986. Gazetteer of Florida Lakes. Publication No. 96. Florida Water Resources Research Center. University of Florida. Gainesville, Florida. Smith, B. W., and W. C. Reeves. 1986. Stocking warmwater species to restore or enhance fisheries. Pages 17 29 in R. H. Stroud, edi tor. Fish culture in fisheries m anagement. American Fisheries Society, Fish Culture S ection Bethesda, Maryland. (SJRWMD) St. Johns River Water Management District. 20 03. Lake Griffin : Fast Facts. Available: www.sjrwmd.com/publications/pdfs/fs_lgriffin .pdf. (February 2008). Strange, R. J., C. D. Berry, and C. B. Schreak. 1975. Aquat ic plant control and reservoir fisheries. Pages 513525 in H. Clepper, editor. Black b ass b iology and Management. Sport Fishing Institute, Washington, D. C. Terrell, J. B., D. L. Watson, M. V. Hoyer, M. S. Allen and D. E. Canfield Jr. 2000. Temporal water chemistry trends (19671997) for a population of Florida water bodies. Lake and Reservoir Management 16:177 194. U.S. Department of Interior, Fish and Wildlife Service an d U.S. Department of Commerce, Census Bureau. 2006. National s urvey of fishing, hunting, and wildlife associated recreation. Verdi, R. J., Tomlinson, S. A., and R. L. Marella 2 006. The drought of 19982002: impacts on Floridas hydrology and landscape. U .S. Geological Survey Circular 1295. Tallahasse, Florida Wicker, A. M. and W. E. Johnson. 1987. Relationships among f at c ontent, c ondition f actor, and f irst y ea r survival of Florida largemouth bass. Transactions of the American Fisheries Society 116: 264271. Wilson, J., C. W. Osenberg, C. M. St. Mary, C. A. Wa tson and W. J. Lindberg. 2001. Artificial reefs, the attraction -production issue, an d density dependence in marine ornamental fishes. Aquarium Science and Conservation 3:95105. Zimmerman, R. C., A Cabello -Pasini and R. S. Alberte. 1 994. Modeling daily production of aquatic macrophytes from irradiance measurements: a compar ative analysis. Marine Ecological Progressive Series 114:185196.

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74 BIOGRAPHICAL SKETCH Darren John Pecora was born in 1979, to John S. and Jolanta A. Pecora He grew up in Unionville, Connecticut on a small lake where he spent his childhood swimming, fishing and exploring. As he matured his curiosity of the outdoors led him to become an avid outdoorsman, hunt ing fish ing and camp ing around New England. He graduated from Avon Old Farms Prep School in 1997 with an interest in ecology. Darren earned his B. S. in e nvironmental s cience in 2001, majoring in both w ildlife b iology and fisheries s cience at Unity Colle ge in Maine. After graduation, Darren worked around the country for a variety of fish and wildlife agencies First he worked for the Maine Atlantic Salmon Commission where he worked on the restoration of endangered Atlantic salmon. Next, he worked for U. S. Geological Surveys Pacific Islands Ecosystem Research Center, Hawaii Volcanoes National Park, Hawaii on an endangered bird restoration project Then he worked for the Connecticut Department of Environmental Protection Fisheries Division on fisher ies management projects and later was employed by the U. S. Geological Surveys Columbia River Research Laboratory Cook, Washington, where he conduct ed research on the efficacy of alternative tech nology fish screens N ext he worked for U.S. Fish and Wil dlife Service in the Fairbanks Alaska office on a project that was focused on estimating the abundance of migrating Yukon River fall chum salmon for in-season management of the subsistence fishery Finally he made his way down to the University of Flori da in 2006, where he started off as a technician for Dr. Bill Pine working on the Apalachicola River and in Sarasota Bay. In the fall of 2006, Darren joined Dr. Daniel E. Canfield, Jr s lab where he worked on the Lake Griffin largemouth bass stocking pr oject. In August 2007, Darren began his m aster s research at the University of Florida, Department of Fisheries and Aquatic Sciences. Darren completed his m aster s research in 2009.