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EVALUATION OF LARGEMOUTH BASS EXPLOITATION AND POTENTIAL
HARVEST RESTRICTIONS AT RODMAN RESERVOIR, FLORIDA
By
KRISTIN RENE HENRY
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
2003
Copyright 2002
by
Kristin Rene Henry
To my parents Robert and Jacquieline Henry, thank you for all your love and support.
ACKNOWLEDGMENTS
My gratitude and appreciation go out to Dr. Mike Allen for serving as my advisor,
mentor, and committee chair; Dr. Daniel Canfield Jr., James Estes, Dr. Ramon Littell,
and Dr. Debra Murie for serving as members of my committee; and Robert Hujik and
Eric Nagid for dealing with the publicity associated with the study, processing all of the
tag returns, and providing advice and assistance throughout the study.
I thank the following people who made significant contributions to the field portion
of the study: J.Berg, T. Bonvechio, R. Burs, P. Cooney, T. Curtis, K. Dockendorf, M.
Duncan, S. Gardieff, J. Greenawalt, J. Hale, B. Hujik, G. Kaufman, S. Keller, E. Naged,
S. Naged, W. Porak, M. Randall, J. Rowe, B. Sergent, W. Tate, K. Tugend, P. Wheeler,
and G. Yeargin.
Finally, I thank everyone who provided advice and comments throughout the study;
their help has been greatly appreciated.
Funding for this study was provided by the Florida Fish and Wildlife Conservation
Commission.
TABLE OF CONTENTS
page
A C K N O W L E D G M E N T S ................................................................................................. iv
LIST OF TABLES ....................................................... .. ......... .............. vii
LIST OF FIGURES .............. .......................... ............ ........... .......... viii
ABSTRACT .............. .......................................... ix
INTRODUCTION .............. ................................... ..............
M E T H O D S .......................................................................... . 5
S tu d y S ite ....................................................................... 5
T ag g in g S tu dy ..................................................................... 5
A ge-and-G row th .................................................................................................. ....... 8
Analysis .............. ................... 8
Tagging Study ..................................... .............................. 8
A g e-an d-G row th ....................................................................... 13
R regulation Sim ulations ....................................................................... 15
R E S U L T S ................................................................................1 8
T aging Study .............................................................................................. ........ 18
A ge-and-G row th ..................................... .......................... 22
R regulation Sim ulations ....................................................................... 23
D IS C U S S IO N ....................................................................................................... 3 5
F U R T H E R ST U D Y ................................................................... ................................4 3
APPENDIX
A REW A R D SIG N -1 ............................................................................................... .......46
B T A G -R E TU R N IN V O IC E ....................................................................................... 47
C R E W A R D SIG N -2 ................................................................48
L IST O F R E FE R E N C E S .............................................................................. 49
v
B IO G R A PH IC A L SK E T C H ...................................................................... ..................53
LIST OF TABLES
Table p
1. Estimated catch of 2,638 largemouth bass tagged and released at Rodman Reservoir,
F lo rid a ...................................... ................................ ................ 3 0
2. Tag loss rates for single-tagged (p) and double-tagged (p2) largemouth bass at
R odm an R reservoir ...................... .. ........................... .. ...... .... ........... 32
3. Quarterly catch rates of tagged fish caught from Rodman Reservoir during the
first 3 quarters of 2001 and 2002 .... ...................... ...............33
LIST OF FIGURES
Figure page
1. Rodman Reservoir located in Putnam and Marion Counties, Florida..........................25
2. Von Bertalanffy growth models fit to mean-length-at-age values for male (triangles)
and female (squares) largemouth bass collected from Rodman Reservoir in
Janu ary 2002 ........................................................................26
3. Weighted catch curve based on number-at-age data for all fish collected during
electrofishing transects conducted at Rodman Reservoir in January 2002............27
4. E stim ated annual harvest of all fi sh ..................................................................... ... 28
5. Estim ated annual catch of all fish ................................................... ..................29
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
EVALUATION OF LARGEMOUTH BASS EXPLOITATION AND POTENTIAL
HARVEST RESTRICTIONS AT RODMAN RESERVOIR, FLORIDA
By
Kristin Rene Henry
May 2003
Chair: Dr. Micheal S. Allen
Major Department: Fisheries and Aquatic Sciences
Rodman Reservoir is considered a premier largemouth bass fishery in Florida, but
the large-fish (> 510-mm TL) potential of the reservoir could potentially be enhanced
with a harvest restriction. I conducted a variable reward tagging study to estimate
exploitation of largemouth bass at Rodman Reservoir. A total of 2,650 largemouth bass
> 345-mm TL were tagged from 2000-2002 using Hallprint dart-style tags. Monetary
rewards for tag returns ranged from $5-$100. Total mortality of largemouth bass was
estimated from a catch curve and gender-specific growth rates were determined from
annuli on sagittal otoliths. An age-structured model was used to simulate the response of
the fishery to various harvest restrictions. Tag returns showed that 42% of the
largemouth bass at Rodman Reservoir were caught in 2001; 11% of the population was
harvested, whereas 31% of the population was caught and released. Total annual
mortality was estimated at 49% and natural mortality at 38%. Length-specific
exploitation rates increased with fish size, indicating a preference among anglers for
harvesting large fish. Simulations showed that harvest of memorable-sized fish was
highest under a 510-mm minimum length limit. Overall total catch (fish > 254-mm TL)
and total catch of memorable-sized fish (> 510-mm TL) under the 510-mm minimum
length limit were second only to a catch and release regulation. Therefore, a 510-mm
minimum length limit would maximize angler catch rates but also allow anglers to
harvest large (> 510-mm TL) fish.
INTRODUCTION
Largemouth bass Micropterus salmoides support some of the most important
freshwater fisheries in the United States. The U.S. Fish and Wildlife Service estimates
that approximately 11.3 million American anglers pursue black bass (U.S. Department of
the Interior 2002). Freshwater fishing expenditures in Florida totaled an estimated $720
million in 1996, with 663,000 anglers targeting black bass. This is more than twice the
number of anglers that target any other freshwater sportfish in Florida (U.S. Department
of the Interior 1998).
Use of harvest restrictions has become an important part of maintaining and
improving largemouth bass fisheries. Harvest restrictions typically include length limits,
slot limits, and bag limits. Objectives of harvest restrictions are to manipulate predator-
prey relationships, increase growth rates of abundant but stunted individuals, increase
population size, increase the number of large fish, and/or increase angler catch rates
(Noble and Jones 1993).
Wilde (1997) compiled data from 49 minimum length-limit evaluations and 42 slot-
limit evaluations for largemouth bass at 88 lakes across the United States. He identified
trends in the response of largemouth bass populations to minimum length and slot limits.
Wilde (1997) found that minimum length limits increased catch rates of largemouth bass,
whereas slot limits (305-381 mm TL) increased the relative abundance of quality and
preferred-size largemouth bass. No evidence indicated that minimum length limits
increased the proportion of large fish or that slot limits increased angler catch rates
(Wilde 1997). A length-limit evaluation at Lake Harris, Florida, found a 40% increase in
angler catch rate two years after implementation (Benton and Douglas 1994). This
increase concurred with the length limit trends described by Wilde (1997).
Managers and research scientists have used computer models to predict the impact
of regulations on a fishery (Orth 1979; Zagar and Orth 1986; Beamesderfer and North
1995; Allen et al. 2002). Zagar and Orth (1986) modeled the effects of minimum length
and slot limits on a hypothetical largemouth bass fishery to identify optimal regulations.
They recommended a 356-mm minimum length limit to managers interested in
maximizing biomass harvested or a 305-406 mm slot limit for creating trophy bass
fisheries (Zagar and Orth 1986).
Models have been used to assess largemouth bass population responses to length
limits on national and regional levels. Beamesderfer and North (1995) characterized
largemouth bass populations within the Untied States by productivity level (i.e., low,
average, or high growth and natural mortality rates) and simulated the effects of length
limits at each productivity level. Beamsderfer and North (1995) found that population
responses to length limits (e.g., changes in yield, harvest, and biomass) were strongly
influenced by the productivity level of the population and that managers' options increase
with population productivity. Allen et al. (2002) assessed the potential benefits of
harvest restrictions based on growth and total mortality of 32 largemouth bass
populations in Florida waters. They indicated that length limits would improve yield and
total catch if growth was at least average and natural mortality was not substantially
higher than exploitation; they also found that high length limits reduced harvest
regardless of growth rate but improved angler catch rates.
Rodman Reservoir is a popular largemouth bass fishery with a reputation for
producing trophy fish. According to the Florida Fish and Wildlife Conservation
Commission (FFWCC) "Big Catch" program, a largemouth bass must be 3.6-kg or 610-
mm TL to qualify for trophy status. During the spring of 2000 two largemouth bass were
caught from the reservoir weighing 7.7-kg and 6.8-kg (Dan Canfield, Florida Lakewatch,
personal communication). The state record is currently held at 7.8-kg (FFWCC); thus
Rodman Reservoir has the ability to produce trophy bass.
The largemouth bass population at Rodman Reservoir, Florida has historically been
managed under statewide regulations. Regulations during standard operating conditions
(5.49-m above mean sea level) restrict angler harvest with a five fish bag limit and 356-
mm length limit, and allow only one fish in the bag limit to exceed 550-mm TL.
Additional regulations have been applied to the reservoir during periods of drawdown.
Regulations for the 2001/2002 drawdown (3.35-m above mean sea level) maintained the
five fish bag limit while increasing the length limit to 610-mm TL. Length limit
exemptions, however, have been granted to tournament anglers by the FFWCC at all
operating levels of the reservoir.
Anglers have expressed a desire for managers to further improve the largemouth
bass fishery at Rodman Reservoir. In response, I evaluated the potential for harvest
restrictions to enhance the largemouth bass fishery at Rodman Reservoir by identifying
regulations that would increase angler catch rates and/or increase the occurrence of large
fish (> 510-mm TL) in the creel. The objectives of this study were to (1) estimate angler
exploitation of largemouth bass using a reward-based tagging study; (2) estimate total
annual mortality using catch curve analysis; (3) estimate age and growth using otoliths;
4
and (4) employ computer models, based on these estimates of exploitation, total annual
mortality, and age and growth, to identify harvest restrictions that would increase overall
total catch (fish > 254-mm TL), total catch of large fish (> 510-mm TL), and harvest of
large fish at Rodman Reservoir.
METHODS
Study Site
Rodman Reservoir is a 3,700-ha eutrophic system located in Putnam and Marion
Counties, Florida. A relict of the Cross Florida Barge Canal project, Rodman Reservoir
encompasses a 26-km flooded section of the Ocklawaha River stretching from the Eureka
dam to the Senator George Kirkpatrick dam. Three distinct areas characterize the
reservoir. Upstream the reservoir consists of floodplain forest and riverine habitat. A
transition zone consisting of flats, stumps, and a submerged river channel follows leading
into the main pool of the reservoir (Canfield et al. 1993). The reservoir has a mean depth
of 2.11-m (Canfield et al. 1993). Six boat launches provide access to the reservoir.
Under normal operating conditions Rodman Reservoir is maintained at 5.49-m
above mean sea level (msl). The reservoir is drawn down at three to five year intervals to
control aquatic macrophytes. During drawdown periods the reservoir is reduced to 3.35-
m above msl, decreasing the flooded area by approximately 2,000 hectares (R. Hujik,
FFWCC, personal communication). The most recent drawdown event began December
1, 2001 and lasted until April 1, 2002. During this time a 610-mm minimum length limit
was placed on the largemouth bass fishery. This temporary regulation was intended to
prevent excessive harvest of largemouth bass during the drawdown.
Tagging Study
I divided the reservoir into four areas (Figure 1) and tagged an approximately equal
number of fish in each area. Area one included water north of the barge canal, west of
the state route 19 bridge, and east of the Kenwood entrance. Area two included all water
south of the barge canal and east of the Kenwood entrance. Area three included water
between the Kenwood entrance and the power lines at Orange Springs and Area four
include all water between the power lines and the entrance to Paynes Landing (Figure 1).
No fish were tagged upstream of Paynes Landing.
Fish were collected for tagging with a boat electrofisher and from angler
tournaments. Largemouth bass were captured using a 4.88-mjon boat outfitted for
electrofishing with a Coffelt VVP-15 electrofisher, as well as a Smith-Root SR-18H
electrofishing boat outfitted with a 9.0 GPP electrofisher. Both systems output DC
current at five to seven amps. All largemouth bass 345-mm TL and greater were
measured to the nearest millimeter total length (TL), tagged, and released into
approximately the same area from which they were captured. Tournament-caught fish >
345-mm TL were measured to the nearest millimeter, tagged, and released into the barge
canal between Areas 1, 2, and 3 (Figure 1). I assumed, based on previous age-and-
growth data for largemouth bass at Rodman Reservoir (Allen et al. 2002), that all tagged
fish 345-355 mm TL would recruit to the fishery (> 356-mm TL) within four months of
tagging.
Largemouth bass were tagged with 103-mm long plastic Hallprint dart tags with a
barb (18-mm long) and orange streamer (85-mm long). The monetary reward value,
return address, and a tag specific identification number were printed on the streamer of
each tag. Tags were injected into the body of the fish below the spiny dorsal fin rays
using a hollow stainless steel needle. When injected the barb of the tag hooked behind a
pterygiophore and the streamer extended in a posterior direction at a 45-degree angle to
the body.
Largemouth bass were tagged during two tagging periods to allow estimates of
exploitation in 2001 and 2002. The length of each tagging period was dictated by the
amount of time it took to tag approximately 1,300 fish. Tagging period one lasted from
November 2000 to March 2001 and tagging period two lasted from December 2001 to
January 2002. Fish were tagged with either one tag (single-tagged) or two tags (double-
tagged) during both tagging periods. Double-tagged fish were later used to estimate tag
loss rates. Single-tagged fish had a monetary reward value of either $5 or $50 and
double-tagged fish had a monetary reward value of $10 (2-$5 reward tags), $55 (1-$5 and
1-$50 reward tag), or $100 (2-$50 reward tags). Double-tagged fish worth $100 were
only released during tagging period-2. The variable-rewards offered for tag returns were
later used to estimate the reporting rate of tags. No tournament fish were double tagged,
due to a desire to minimize the handling time of these fish. Tag returns from double-
tagged fish were considered as a single return.
Press releases to local newspapers and reward signs were used to inform the public
about the study. Reward signs (Appendix 1) were posted at fishing access points around
the reservoir and at local bait and tackle shops. Mailer envelopes with tag-return forms
were available at local bait and tackle shops and were provided to anglers upon request.
Tag-return forms requested the angler name, address, social security number (required to
receive reward), date and location fish was caught, approximate length, fate of the fish
(i.e., harvested or released), and if the fish was caught during a tournament (Appendix 2).
Age-and-Growth
Age and growth of largemouth bass at Rodman Reservoir were estimated using fish
collected with electrofishing in January 2002. All largemouth bass collected during 20-
minute electrofishing transects were measured to the nearest millimeter total length. Five
fish per centimeter group up to 39-cm TL and all fish > 40-cm TL, excluding fish > 5.9-
kg, were collected and returned to the laboratory where weight and gender were
determined, and otoliths were removed.
Sagittal otoliths were removed from sub-sampled fish and read in whole-view
under a dissecting microscope by three independent readers. Otoliths that were 3-years
or older and otoliths with reader discrepancies when examined in whole-view were
sectioned (Hoyer et al. 1985). Two to four 0.50-mm sections were cut from the focus of
each otolith using a South Bay Technology low speed diamond wheel saw (model 650).
Sections from each fish were mounted on a half-frosted slide using Thermo Shandon
synthetic mount. Sectioned otoliths were read under a compound microscope by a
minimum of two independent readers. Sectioned otoliths with reader discrepancies were
re-read by the original readers as well as one additional reader. If the discrepancy
remained, the otolith was discarded. Crawford et al. (1989) found the formation of annuli
to occur as early as April for largemouth bass in Florida lakes, therefore because fish
were collected for age-and-growth in January I assumed a January birth date and assigned
each fish an age one year greater than the number of rings observed on the otolith.
Analysis
Tagging Study
Tag returns were adjusted for tag loss, tagging-related mortality, and non-reporting,
prior to estimating total annual catch and angler exploitation. Tag returns and
electrofishing recaptures of double-tagged fish were used to estimate tag loss. Anglers
that returned single tags from double-tagged fish were contacted by phone to verify that
only one tag was present at the time of capture. The time between tagging and recapture
was recorded for all double-tagged fish. I assumed that tag retention was linearly related
to time-at-large and developed two models, as per Miranda et al. (1997), to estimate the
logistic probability of tag loss (logit(/)) based on the period (P) in which the fish were
tagged:
logit(l) = a + b(time) (1)
where a is the intercept estimate, bl is the parameter estimate, and time is the number of
days between tagging and recapture. Tag returns from double-tagged fish were assigned
a dummy variable of 1 to indicate a single tag loss or 2 to indicate no tag loss. The
dummy variables and associated estimates of time at large (time) for tag returns from
double-tagged fish tagged in each period (P) were then used in Procedure LOGISTIC
(SAS 1996) to calculate estimates of a and bl for each tagging period. Once the
parameter estimates were obtained for equation 1, I estimated the logistic probability of
tag loss (logit(/)) for each tagging period and year based on the average time fish from a
given tagging period (P) were at large in year (y). These logistic probabilities were then
used in the following equation to calculate the probability of a single tag loss (p) for fish
tagged in period P and recaptured during year y (Miranda et al. 1997):
elogit(/)
P ( logit(1)) (2)
I assumed that all tag loss events were independent and subsequently estimated the
probability of a fish losing two tags as the square of the probability of a single tag loss
(p2). Estimates ofp and p2 were then subtracted from 1 to predict tag retention rates for
single-tagged fish (l-p) and double-tagged fish (1-p2). The total number of single-tagged
(Nsingle) and double-tagged (Ndouble) fish from each tagging period and year were then
adjusted based on their respective retention rates.
Tag-related mortality was estimated based on the results of a cage study, which
was conducted within the reservoir. A 2-m x 1-m x 1-m cage with 10-cm plastic bar
mesh was used to hold 3 to 16 fish per cage trial. Six to nine cage trials were conducted
per tagging period with each trial lasting a minimum of 40-hours. All cage trials were
conducted in Area 3 (Figure 1) of the reservoir. At the end of each trial fish were
checked for survival and released. Trials were conducted using fish captured via
electrofishing (trials = 11) as well as those collected at tournaments (trials = 4). The total
number of tagged fish were separated by capture method and tagging period, adjusted for
the appropriate tag-related mortality rate, and recombined.
Reporting rates of high-dollar reward tags in 2001 were estimated based on a
linear-logistic model created by Nichols et al. (1991):
S= e( 0.0045+0.0283(H))/(1 e (-0.0045+0.0283(H))) (3)
where H is the dollar value of a fish tagged with a high-dollar reward (i.e., $50, $55, or
$100) and XH is the reporting rate of tags from high-reward fish. This model was
originally created to estimate the reporting rate of duck bands based on the monetary
reward value of the band. Because the model was created in 1988, the reward values (H)
were converted from 2001 standards to the 1988 monetary equivalents based on the
Consumer Price Index (Nichols et al. 1991). The 1988 monetary equivalents used in
equation 3 were $33.40, $36.71, and $66.80 for $50, $55, and $100 rewards, respectively
(U.S. Department of Labor 2002). Reporting rate estimates calculated from equation 3
were most precise at high-reward values (Nichols et al. 1991). Therefore, I used equation
3 to estimate reporting rates of high-reward fish then calculated the reporting rate of low-
reward tags based on the assumption that all tagged fish had an equal probability of
recapture regardless of reward-value (equations 4 & 5).
I estimated the total number of H reward fish caught (CH) from the reservoir in
2001 using the following equation:
CH = R (4)
where RH is the number of tags returned in 2001 from fish tagged with a high-reward.
Equation 4 was repeated for all values of H. I then estimated the number of low-reward
fish caught (CL) from the reservoir in 2001 using the following ratio:
C C
50 L (5)
=- (5)
T0 TL
where L is the dollar value of a fish tagged with a low-reward (i.e., $5, $10), C50 is the
estimated number of $50-reward fish caught from the reservoir, and T50 and TL are the
original number of fish tagged with a $50-reward and a low-reward (L) respectively,
adjusted for the appropriate rates of tag loss (p, p2) and tagging mortality. Equation 5
was repeated for all values ofL. I then substituted RL (the number of tag returns from
low-reward value fish) and CL into equation 4 to estimate a reporting rate for low-reward
fish (4L) in 2001. This process was repeated for all low-reward values (i.e., $5 and $10).
Reporting rate estimates for all reward values were varied by + 50% to simulate possible
error associated with the reporting rate estimates.
Total annual catch (TAC) and total quarterly catch (TQC) of largemouth bass in
2001 were calculated as follows:
( C20ool0 + C.,2001)
STAC2001 (6)
SL,q,2001S + H,q,2001
q q,2o (zL, TH.,P ) ( L,,,2001 + ( H,,2001)
where 2001 denotes the year in which the fish were caught, P1 denotes the period in
which the fish were tagged (i.e., P1 = period 1), q represents the quarter in which the fish
were caught (i.e., qi = January 1st to March 31st, q2 = April 1st to June 30th, etc.), and i
represents all quarters previous to q within 2001.
Due to time constraints, I was unable to obtain a full year of tag return data for
2002 and therefore unable to estimate reward-specific reporting rates for 2002. However,
assuming that reporting rates did not vary significantly between years, I was able to use
the 2001 reporting rate estimates to calculate an estimate of the total number of
largemouth bass per reward value caught (CH,q,2002, CL,q,2002) from the reservoir in the first
three quarters of 2002 (equation 4). Quarterly estimates of CH and CL were then used to
estimate TQC of largemouth bass in 2002.
q2002Z CL q2002 C Hq,2002
.... (8)
H q)2 L H ) ( CL ,2002 +I CH,,,200)- x
P
X = v(Z TLP, + Z TH P, ) ( CL,2001 + Z CH,2001) (9)
where 2002 denotes the year in which fish were caught, i represents all quarters previous
to q within 2002, and X is a correction term that accounts for the reduced number of
season-1 fish present in the population at the start of 2002 due to natural mortality (v)
(see below) and tag removal in the previous year. Equation 9 assumes that all tags were
removed from fish caught by an angler in 2001, regardless of fate. Angler harvest of
tagged fish during the last month of the fourth quarter of 2001 and the entire first quarter
of 2002 was limited by the temporary 610-mm minimum length limit placed on the
largemouth bass fishery during the 2001/2002 reservoir drawdown.
Total harvest of largemouth bass per reward value (HL, HH) was estimated by
adjusting the number of fish reported by anglers as harvested for non-reporting. Tag
returns from fish with an unknown fate were divided proportionally among the known
fate groups prior to reporting rate adjustments. Estimates of HL and HH were used in
equation 6 in place of CL and CH to estimate total annual exploitation (u) (Ricker 1975) of
largemouth bass in 2001. The total annual exploitation rate was then subtracted from the
total annual catch rate to estimate the total annual catch and release rate for the reservoir.
Age-and-Growth
Data from the timed electrofishing transects was used to estimate total annual
mortality and gender-specific growth rates. I created a gender-specific age length key
from the subsampled largemouth bass collected during January 2002. Age-1 largemouth
bass of unknown gender were randomly assigned a gender based on the assumption that
sexually dimorphic growth rates are not evident in largemouth bass until age-2 (Schramm
and Smith 1987). I used a gender-specific age length key to assign a gender and age to
each individual in the whole sample (all fish captured during timed electrofishing
transects, January 2002). Gender-specific age frequencies were calculated and a catch
curve was fit for each gender. Age-1 fish were not included in the catch curve because
these fish had not fully recruited to the gear (Bayley and Austen 2002). Due to a low
sample size of older fish (< 5 fish per age-class over the age of 6) weighted catch curves
were fit to age-frequency plots. The instantaneous rate of total mortality (Z) was
estimated from the slope of the catch curve for each gender (Ricker 1975). I used the
following equations to estimate total annual mortality (A) and the annual rate of natural
mortality (v) for each gender (Ricker 1975):
A= 1- e- (10)
v =A-u (11)
I used the following equations to estimate mean-length-at-age (MLA) and variance
(02) for each gender (DeVries and Frie 1996):
MLA x (12)
2 ((ZJ)(Zfx2) (fX)2)
2f (13)
( ( ) [ ( -Z ) 1 ] ) ( 1 )
where x is a given centimeter group andf is the number of gender i fish of a given age in
centimeter group x. I used the von Bertalanffy growth model (Ricker 1975) to describe
gender-specific growth rates:
MLA = L(- e-k(age- to) (14)
Parameter estimates (Lo, k, to) were obtained for equation 14 using Procedure
NLIN (SAS 1996) and were based on previously calculated estimates of mean-length-at-
age (equations 12 & 13). The growth models were used to estimate mean total-length-at-
age (TLA) for each gender. Weight-length equations were created for male and female
largemouth bass at Rodman Reservoir based on the subsample of fish collected in 2002
(Ricker 1975):
W=aLb (15)
where W is the weight of the fish, L is the length of the fish, a is the intercept, b is the
shape parameter. Parameters were estimated from the loge transformed model:
log(W)= loga b log(L) (16)
Regulation Simulations
I used the Inland Fisheries Regulation Simulator (IFREGS) model described by
Allen and Miranda (1998) to simulate the response of the fishery to four minimum length
limits; 254-mm TL, 356-mm TL, 457-mm TL, and 510-mm TL, three slot limits; 381-
510-mm TL, 381-559-mm TL, and 381-610-mm TL, a maximum length limit; 457-mm
TL, and a complete catch and release regulation. The model required estimates of
gender-specific total length-at-age, gender and age specific rates of exploitation and
natural mortality, and parameter estimates from gender-specific weight-length equations
to forecast the annual age-structure of the population under a given harvest restriction.
Gender-specific estimates of mean TL-at-age were obtained from the von Bertalanffy
growth models (equation 14). Estimates of TL-at-age were used to describe annual
incremental growth. Within year growth was assumed to be linear. Gender and age
specific exploitation rates were obtained by calculating length specific exploitation rates
for quality (300-379 mm TL), preferred (380-509 mm TL), and memorable (510+ mm
TL) size fish (Anderson and Neumann 1996) and assigning these exploitation rates to
each gender based on mean total-length-at-age (equation 14). Gender and age specific
natural mortality rates were obtained by subtracting the gender and age specific
exploitation rates from total annual mortality (equation 11) and the parameter estimates
for the gender-specific weight-length equations were obtained from equation 15.
Gender and age specific exploitation rates were used to estimate total harvest (fish
> 254-mm TL) and harvest of quality, preferred, and memorable size fish. Gender and
age specific natural mortality estimates were combined with exploitation estimates to
describe total annual mortality and to predict the number of fish in the population each
year. The parameter estimates from the gender-specific weight-length equations were
used to transform fish lengths to fish weights in order to predict the annual biomass of the
population.
The model simulated length limits by protecting fish from harvest if they were
below a minimum length limit or within a slot limit. The model assumed that all fish >
254-mm TL were susceptible to harvest if they were not protected by a regulation. I ran
each simulation for 50-years with 1000 fish recruiting to age-1 (500-males, 500-females).
I used the predicted number of quality, preferred, and memorable size fish harvested as
well as the predicted total number of fish harvested from the 50th simulation year to
compare the effectiveness of each regulation for maximizing harvest. Estimates of
overall total catch (all fish > 254-mm TL) and total catch of quality, preferred, and
memorable size fish were calculated based on the age structure predicted for the 50th
simulation year under a given harvest restriction. Gender and age specific total catch
rates applied to the age structures were obtained by calculating length-specific
exploitation rates for quality, preferred, and memorable size fish and assigning these
catch rates to each gender based on mean TL-at-age. The predicted age structure for the
50th simulation year under each harvest restriction was then multiplied by the appropriate
total catch rates to obtain estimates of overall total catch and total catch of quality,
preferred, and memorable size fish.
In order to account for potential error associated with my reporting rates, all
simulations were repeated using gender-specific exploitation and natural mortality rates
associated with 50% variability in reporting rate. Previous studies that used multiple
methods (e.g., postcard surrogates, phone interviews, creel surveys, or surreptitiously
implanted tags) to estimate reporting rates have shown reporting rate variability to range
from 11% to 52% (Larson et al. 1991; Maceina et al. 1998; Miranda et al. 2002).
Therefore, simulations that used mortality estimates associated with + 50% variation in
reporting rate accounted for potential high variability in my reporting rate estimates.
Simulation results were compared to identify inconsistencies that would result from
incorrectly estimating the reporting rate of tags.
RESULTS
Tagging Study
Tagging-period one ran from November 28, 2000 to March 31, 2001, 50 sampling
trips were made to the reservoir during this time. Forty-four trips were dedicated to
electrofishing and the remaining 6 trips were spent tagging fish collected at tournaments.
A total of 1,368 largemouth bass were tagged during tagging period-1, 1,014 of these fish
were collected by electrofishing, and 354 fish were collected at tournaments. Tagging
period two ran from November 10, 2001 to January 9, 2002, 15 sampling trips were made
to the reservoir during this time. Fourteen of these trips were spent electrofishing and the
remaining trip was spent tagging fish at a tournament. A total of 1,270 largemouth bass
were tagged during period-2, 1,258 of these fish were collected by electrofishing and the
remaining 12 were collected at a tournament. Electrofishing catch rates were higher in
tagging period-2 this was likely due to the reservoir drawdown.
A summary of the number of fish tagged per period and reward value is presented
in Table 1. About half of the fish were tagged with $5 reward tags in both tagging
periods. A low number (n = 6) of $55 reward fish were released during period-1. A total
of 406 and 486 largemouth bass were double-tagged (reward value = $10, $55, $100)
during periods 1 & 2, respectively (Table 1).
Annual tag loss rates for single and double tagged fish are presented in Table 2.
Fish tagged in period-1 were at large an average of 87 days (range = 1 to 337 days)
before recapture in 2001 and 421 days (range = 329 to 528 days) before recapture in
2002. Fish tagged in period-2 were at large and average of 66 days (range = 0 to 250
days) before recapture in 2002 (Table 2). Based on the period tagged and the average
time at large, tag loss ranged from 4% to 26% for single-tagged fish and from 0.2% to
6.6% for double-tagged fish (Table 2). Tag loss was positively related to time at large.
Cage trials were conducted during both tagging periods, 9 trials (6 electrofishing
trials, 3 tournament trials) were conducted in 2001 and 6 in 2002 (5 electrofishing trials,
1 tournament trial). On average 10 fish (range = 3 to 16) were caged per trial and each
trial lasted an average of 50 hours (range = 43 to 79). A total of 145 fish were caged over
the course of the study, all of which survived, resulting in a tag related mortality rate of
0%. Therefore, the original number of fish (N) tagged in each period did not have to be
adjusted for tagging mortality. An estimated 1,314 tagged fish from period-1 remained in
the reservoir after tag loss in 2001 and about 1,246 tagged fish from period-2 remained
after tag loss in 2002. Period-1 fish present in the reservoir in 2002 were adjusted for tag
loss (p = 0.2576, p2 = 0.0663) based on an average of 421 days at large. They were also
adjusted for natural mortality v = 0.38 (described below) and angler removal of tags (n =
546) in 2001. Based on these adjustments I estimated that 382 largemouth bass tagged in
period-1 were present in the reservoir in 2002 (Table 1).
Tag returns were collected from January 1, 2001 to September 30, 2002. Tags
from 260 fish were returned in 2001 and tags from 231 fish were returned in the first
three quarters of 2002. During 2001, the percent return of tags ranged from 16% ($5
reward) to 33% ($55 reward) (Table 1). Estimated reporting rates were positively
correlated with monetary reward values and ranged from 39% ($5 reward) to 87% ($100
reward) (Table 1).
During 2001, 67 tagged fish were reported by anglers as harvested and 180 tagged
fish were reported as released. During the first three quarters of 2002, 24 tagged fish
were reported by anglers as harvested and 203 were reported as released. Thirteen fish
had an unknown fate in 2001 and 4 fish had an unknown fate in 2002. These fish were
divided among the known-fate categories (i.e., kept or released) based on the proportion
of fish in each reward category that were reported as kept or released. Total annual catch,
annual exploitation, and annual catch and release rates for largemouth bass in 2001 were
0.42, 0.11, and 0.31, respectively. Thus, about 26% (i.e., 0.11 / 0.42 = 0.26) of the
largemouth bass caught from the reservoir in 2001 were harvested and about 74% were
released. Tag returns from 2002 showed that the total catch, exploitation, and catch and
release rates for the first three quarters of 2002 were 0.30, 0.03, and 0.27, respectively,
indicating that about 90% of the fish caught in the first three quarters of 2002 were
released.
Length-specific estimates of exploitation, total catch, and natural mortality were
calculated for 2001 based on three length categories; quality (356-379-mm TL), preferred
(380-509-mm TL), and memorable (> 510-mm TL). Annual exploitation rates of quality,
preferred, and memorable fish were 0.08, 0.12, and 0.20, total annual catch rates were
0.38, 0.42, and 0.40, and natural mortality rates were 0.41, 0.37, and 0.29, respectively.
Anglers harvested 22%, 28%, and 50% of all the quality, preferred, and memorable size
fish, respectively, that were caught in 2001. Regulations during the first year of the
tagging study (2001) prevented anglers from harvesting fish < 356-mm TL, because these
fish were protected from harvest (u = 0) estimates of exploitation, total annual catch, and
natural mortality used in the simulation models for fish 254-355-mm TL were therefore
based on the calculated exploitation (u = 0.08), total annual catch (TC = 0.38), and
natural mortality (v = 0.41) rates associated with quality sized fish.
Altering reporting rate estimates by + 50% to account for possible variability
associated with the reporting rate estimates affected the estimates total annual catch,
exploitation, and natural mortality. Increasing reporting rate estimates by 50% resulted in
lower estimates of total annual catch and exploitation and a higher estimate of natural
mortality, reducing reporting rates by 50% had opposite effects. Increasing reporting
rates by 50% resulted in total annual catch rates of 0.26, 0.28, and 0.28, annual
exploitation rates of 0.06, 0.08, and 0.14, and natural mortality rates of 0.43, 0.41, and
0.35 for quality, preferred, and memorable size fish, respectively. Decreasing reporting
rates by 50% resulted in total annual catch rates of 0.76, 0.83, and 0.82, annual
exploitation rates of 0.17, 0.23, and 0.41, and natural mortality rates of 0.32, 0.26, and
0.08 for quality, preferred, and memorable size fish, respectively.
Quarterly tag returns were used to estimate total quarterly catch of largemouth bass
in all quarters of 2001 and in the first three quarters in 2002. TQC rates ranged from 3%
(Quarter-3, 2002) to 22% (Quarter-2, 2001) (Table 3). TQC rates in the first (TQC =
16%) and second (TQC = 22%)) quarters of 2001 were higher than TQC rates in the third
(TQC = 7%)) and fourth (TQC = 3%)) quarters of 2001, indicating a decline in catch
after June 30, 2001. The TQC rate of largemouth bass in the first quarter of 2001 (16%)
was less than the TQC rate in the first quarter of 2002 (20%) (Table 3). Additionally,
TQC rates in the second (22%) and third (7%) quarters of 2001 were higher than TQC
rates in the second (10%) and third (3%) quarter of 2002 (Table 3).
This chapter discusses what a style is, how it is applied, and how it should be used
to create your thesis or dissertation.
Age-and-Growth
Seventeen 20-minute electrofishing transects and one 10-minute electrofishing
transect were conducted from January 7, 2002 to January 9, 2002. A total of 1,239
largemouth bass were collected and measured (whole-sample). Three hundred and
twenty two largemouth bass (sub-sample) collected during sampling efforts, ranging from
80-603 mm TL, were returned to the laboratory to be measured, weighed, and gender and
age determined. Female largemouth bass in the whole sample did not exceed 600-mm
TL, whereas males did not exceed 530-mm TL. Female largemouth bass reached a mean
length of 587 20-mm TL by age-10, whereas male largemouth bass reached a mean
length of 435 6-mm TL by age-10 (Figure 2).
Gender specific values of number-at-age were used for catch curve analysis. Age
classes 7, 9, and 10 were underrepresented (< 5 fish) for both, male and female
largemouth bass. No eight year-old fish were collected. Gender specific rates of total
annual mortality calculated from the slopes of the catch curves were 0.46 and 0.51 for
male and female largemouth bass, respectively. Analysis of covariance showed that there
were no significant differences between the slopes (p = 0.6473) or y-intercepts (p =
0.8200) of the gender-specific catch curves, indicating that total annual mortality was not
significantly different between genders. Thus, gender-specific number-at-age values
were pooled and catch curve analysis was repeated for the pooled sample (Figure 3).
Total annual mortality for all fish was 0.49. Length-specific estimates of natural
mortality mentioned above were calculated based on length-specific exploitation rates
and the pooled estimate of total annual mortality (equation 11). Lengths and weights
pertaining to the sub-sampled fish were used to create the following gender-specific
weight-length equations for male (equation 20) and female (equation 21) largemouth
bass, respectively:
W = (4.42 x 106)L3207 (20)
W = (4.66 x 106)L3196 (21)
Regulation Simulations
Results of the simulations are summarized in Figures 4 and 5. Total annual harvest
of largemouth bass > 254-mm TL and total harvest of quality-sized fish were greatest
under a 254-mm minimum length limit (Figure 4A & 4B). Total harvest of preferred-
sized fish was greatest under a 356-mm minimum length limit (Figure 4C) and total
harvest of memorable-sized fish was greatest under a 510-mm minimum length limit
(Figure 4D). Overall total catch and total catch of preferred and memorable sized fish
were greatest under a catch and release regulation (Figure 5A, 5C, and 5D). The 510-mm
minimum length limit resulted in the second highest overall total catch and total catch of
preferred and memorable sized fish (Figure 5A, 5C, and 5D). The 457-mm minimum
length limit, the 510-mm minimum length limit, and the catch and released regulation all
maximized the total catch of quality-sized fish (Figure 5B).
Assuming anglers would not harvest fish < 254-mm TL, simulating the effects of a
254-mm minimum length limit on the fishery was essentially equivalent to simulating no
length limit. Using this regulation as a benchmark to identify the success of alternate
harvest restrictions revealed that the catch and release regulation, the 510-mm minimum
length limit, and the 457-mm minimum length limit were the top three regulations for
maximizing the overall total catch of largemouth bass as well as the total catch of quality,
preferred, and memorable size fish. The catch and release regulation yielded the highest
increase in total catch, increasing the overall total catch by 32% and increasing the total
catch of quality, preferred, and memorable sized fish by 8%, 54%, and 103%,
respectively compared to no length limit. The 510-mm minimum length limit was the
next most effective regulation for maximizing total catch, increasing the overall total
catch by 18% and increasing total catch of quality, preferred, and memorable sized fish
by 8%, 46%, and 100%, respectively. The 457-mm minimum length limit followed with
a 17% increase in the overall total catch and an 8%, 41%, and 77% percent increase in
the total catch of quality, preferred, and memorable size fish, respectively.
Simulations based on exploitation and natural mortality rates associated with +
50% error in reporting rate showed similar trends with regards to overall total harvest,
total harvest of preferred and memorable sized fish, overall total catch, and total catch of
quality, preferred, and memorable sized fish. However, simulation results associated
with a 50% increase in reporting rate estimates showed that several regulations (254-mm
minimum length limit, 457-mm maximum length limit, 381-510 mm slot limit, 381-559
mm slot, and 381-610 mm slot) would maximize total harvest of quality-sized fish.
SR 19
Kenwood
Orange 'q~I-
Tournament
Release
Area
i" i hidingg
4 0 4 8 Kilometers
r I
Figure 1. Rodman Reservoir located in Putnam and Marion Counties, Florida. Areas 1-4 represent designated capture and release
areas for the tagging study.
70
60
- 50
E
40
S30
MLAFemales =68.3(1- e0.2102(age+ 0.0035))
MLAMales = 46.0(1- e-0.3525(age 01374))
0 1 2 3 4 5 6 7 8 9 10
Age
Figure 2. Von Bertalanffy growth models fit to mean-length-at-age values for male
(triangles) and female (squares) largemouth bass collected from Rodman
Reservoir in January 2002.
y = -0.68(x) + 7.45
Z = -0.68
A = 0.49
2000 1998
1996
Year Class
1994 1992 1990
Figure 3. Weighted catch curve based on number-at-age data for all fish collected
during electrofishing transects conducted at Rodman Reservoir in January
2002. Total annual mortality of largemouth bass was 49%. A weighted
catch curve was fit to the data because the 1992 to 1995 year-classes were
underrepresented (< 5 fish).
All Fish
1000-
100-
10-
1 -
2002
Total Harvest
254MIN 356MIN 457MIN 510MIN 457MAX
381-510 381-559 381-610
Slot Slot Slot
Quality
254MIN 356MIN 457MIN 510MIN 457MAX 381-510
Slot
381-559 381-610
Slot Slot
Preferred
254MIN 356MIN 457MIN
510MIN 457MAX 381-510 381-559 381-610
Slot Slot Slot
Memorable
254MIN 356MIN 457MIN
H-
510MIN 457MAX 381-510 381-559 381-610
Slot Slot Slot
Regulation
Figure 4. Estimated annual harvest of all fish > 254-mm (A) and quality (300-379-
mm) (B), preferred (380-509-mm) (C), and memorable (> 510-mm) (D)
sized fish based on 50-year simulations run in IFREGS. All estimates are
based on 1,000 fish recruiting to age-1.
60
40
20 -
0
4 '
-n I --
40 -
30 -
20
10
0
C 40
30 -
20 -
10 -
0
15 -
10
5
0
n
Tn
F-I
r
11
Total Catch
F1 n n-
254 MIN 356 MIN 457 MIN 510 MIN 457 381-510 381-559 381-610 Catch &
MAX Slot Slot Slot Release
Quality
254 MIN 356 MIN 457 MIN 510 MIN 457 381-510 381-559 381-610 Catch &
MAX Slot Slot Slot Release
Preferred
254MIN 356MIN 457MIN 510MIN
457 381-510 381-559 381-610 Catch &
MAX Slot Slot Slot Release
Memorable
F n]H F]F
254MIN 356MIN 457MIN 510MIN 457MAX 381-510
Slot
381-559 381-610 Catch &
Slot Slot Release
Regulation
Figure 5. Estimated annual catch of all fish > 254-mm (A) and quality (300-379-mm)
(B), preferred (380-509-mm) (C), and memorable (> 510-mm) (D) sized
fish based on 50-year simulations run in IFREGS. All estimates are based
on 1,000 fish recruiting to age-1.
400 -
350
300 -
250
130
120
140
120
100
80
Table 1. Estimated catch of 2,638 largemouth bass tagged and released at Rodman Reservoir, Florida. The adjusted numbers of
tagged fish were corrected for tag loss (p &p2) and tagging mortality (0%). Period-1 adjusted tagged fish in 2002 were also
corrected for natural mortality and angler removal of tags during 2001. Tag returns were adjusted for non-reporting to obtain
estimated catch.
Tagging Recapture Adjusted Number Percent Reporting Estimated
Period Year Value Tagged Tag Loss Tagged Returned Returned Rate Catch
(P) (y) ($) (N) (p, p2) (T) (R) (%) (W) (C)
1 2001 5 739 0.0557 698 113 16 0.3893 290
1 2001 10* 400 0.0031 399 82 21 0.4944 166
1 2001 50 223 0.0557 210 63 30 0.7192 88
1 2001 55* 6 0.0031 6 2 33 0.7379 3
Total: 1,368 1,313 260 20% 547
Percent: 42%
1 2002 5 739 0.2576 188 23 12 0.3893 59
1 2002 10* 400 0.0663 135 23 17 0.4944 46
1 2002 50 223 0.2576 57 18 32 0.7192 25
1 2002 55* 6 0.0663 2 0 0 0.7379 0
Total: 1,368 382 64 130
Percent: 34%
Table 1. Continued
Tagging Recapture
Period Year
2002
2002
2002
2002
2002
Value
($)
5
10*
50
55*
100*
Total:
Percent:
Adjusted
Tagged Tag Loss Tagged
(N) (p. v2) (T)
686
400
104
50
30
1,270
0.0438
0.0019
0.0438
0.0019
0.0019
Percent Reporting Estimated
Returned Returned Rate Catch
(%)
656
399
99
50
30
1,234
0.3893
0.4944
0.7192
0.7379
0.8650
195
101
32
14
9
351
28%
* Indicates that the fish were tagged with two tags (double-tagged).
\ j \_I j \ j \ j yl j \ j \ j \ j \ j \ j
Table 2. Tag loss rates for single-tagged (p) and double-tagged (p2) largemouth bass
at Rodman Reservoir. Tag loss was estimated based on electrofishing and
angler recaptures of double-tagged fish. Proc LOGISTIC (SAS 1996) was
used to obtain intercept (a) and parameter (p) estimates for tag loss models:
logit(l) = a+b (time).
Tagging Recapture
Period Year
Parameter Average
Intercept Estimate Time
(bl)
(tii)
Tag Loss
Single Tag Double Tag
(p) (p2)
1 2001 -3.2904 0.0053 86.93 0.0557 0.0031
1 2002 -3.2904 0.0053 421.09 0.2576 0.0663
2 2002 -3.7512 0.0101 66.08 0.0438 0.0019
Table 3. Quarterly catch rates of tagged fish caught from Rodman Reservoir during
the first 3 quarters of 2001 and 2002. Adjusted tagged fish were corrected
for tag loss (p & p), tagging mortality (0%), and angler removal of tags (C).
Fish tagged in period-1 and recaptured in 2002 were adjusted for natural
mortality (v = 38%).
catches (C).
Recapture
Year
(y)
2001
2001
2001
2001
Value
($)
5
10
50
55
Returns were adjusted for non-reporting to estimate
Adjusted
Tagged
(T)
698
399
210
6
Number
Returned
(R)
Percent
Returned
(%)
Estimated
Catch
(C)
Percent
Caught
(%)
15
16
20
23
1,313 104
16%
2001
2001
2001
2001
590
336
168
5
1,099
11%
22%
2001
2001
2001
2001
Quarter
(q)
Total
Percent
2
2
2
2
Total
Percent
3
3
3
3
Total
Percent
Table 3. Continued
Recapture
Quarter Year
(a) (v)
Adjusted Number Percent Estimated Percent
Value Tagged Returned Returned Catch Caught
($) (T) (R) (%) (C) (%)
2002
2002
2002
2002
2002
5 844 67
10 534 49
50 156 23
55 52 5
100 30 7
1,616 151
5 672 27
10 435 18
50 124 15
55 45 5
100 22 0
1,298 65
5 603 5
10 399 6
50 103 3
55 38 0
100 22 1
1,165 15
Total
Percent
2002
2002
2002
2002
2002
Total
Percent
20%
2002
2002
2002
2002
2002
3
3
3
3
Total
Percent
10%
DISCUSSION
The optimal harvest restriction for the reservoir should provide the best
combination of overall total catch and total catch of large fish, while catering to angler
preferences. The top three regulations for improving overall total catch and total catch of
memorable-sized fish were (1) the catch and release regulation, (2) the 510-mm
minimum length limit, and (3) the 457-mm minimum length limit. In 2001, anglers
harvested memorable-sized largemouth bass at a much higher rate than smaller fish, thus
eliminating harvest with a catch and release regulation may interfere with preferences of
some angler groups. A catch and release regulation would also prevent tournaments from
taking place at the reservoir because tournament exemptions are prohibited under a catch
and release regulation (FFWCC). During the 2001 fiscal-year, the FFWCC granted
tournament exemptions at Rodman Reservoir to 37 tournament groups which involved
1,018 tournament anglers (W. Chamberlain, FFWCC, unpublished data). Eliminating the
ability to hold future tournaments by instating a catch and release regulation, would
therefore conflict with a substantial number of tournament anglers. Due to the potential
conflicts with angler groups, managers should consider alternatives to the catch and
release regulation.
The 510-mm minimum length limit and the 457-mm minimum length limit were
the next best regulations for maximizing overall total catch and the total catch of
memorable-sized fish. In addition, the 510-mm and 457-mm minimum length limits
were the most effective regulations for maximizing harvest of memorable-sized fish.
Both regulations had a similar effect on the total catch of largemouth bass, however the
total harvest of memorable-sized fish under the 510-mm minimum length limit was 22%
(range: 20% to 50%) higher than total harvest of memorable-sized fish under the 457-mm
minimum length limit. Therefore, the 510-mm minimum length limit would at least be
equivalent to if not better than the 457-mm minimum length limit. I suggest that
managers should consider implementing a 510-mm minimum length limit at Rodman
Reservoir. However, should managers have difficulty instating the 510-mm minimum
length limit because the regulation has not been previously approved for use by the
FFWCC, the 457-mm minimum length limit would serve as a suitable alternative. This
length limit has been previously used by the FFWCC to regulate largemouth bass
fisheries within Florida, and it is the next most effective regulation for maximizing
overall total catch and total catch and harvest of memorable-sized fish.
Estimates of annual exploitation used in the simulation models were based on 2001
tag returns and ranged from 8% (quality fish) to 20% (memorable fish). A review of
mortality rates associated with 30 largemouth bass populations in the United States
showed annual exploitation rates to range from 9-72% (average u = 36%) (Allen et al.
1998). Based on these findings the exploitation rates of largemouth bass at Rodman
Reservoir appear to be low compared to historical data in the United States. Despite the
low rates of exploitation, exploitation rates were positively related to fish length,
indicating a preference among angler to harvest large fish.
The total annual mortality rate used in the simulations was 49%. Allen et al. (1998)
reviewed mortality estimates for 30 largemouth bass populations in the United States and
found total annual mortality rates to range from 24-92% (average A = 64%). Allen et al.
(2002) calculated a 51% average total annual mortality rate for largemouth bass in 45
Florida water bodies. The total annual mortality rate of largemouth bass at Rodman
Reservoir was slightly lower than the national average but similar to the average total
annual mortality of largemouth bass in Florida waters.
Gender-specific mean total-length-at-age estimates used in the simulations
predicted that male largemouth bass would not exceed a mean total length of 443-mm,
thus precluding males from contributing to the memorable-size portion of the population.
Only one male largemouth bass was collected in excess of 510-mm TL during age-and-
growth sampling, therefore males did not contribute greatly to the memorable-size
portion of the population. Regulations that restrict harvest offish < 510-mm TL will
therefore focus the majority of the harvest on the female portion of the population.
Managers should be aware that focusing the majority of harvest on one gender could
eventually skew the sex ratio of the population.
Female largemouth bass at Rodman Reservoir reached memorable size between
ages 6 and 7 and reached an average weight of 2.2-kg by age-11. A previous study by
Allen et al. (2002) examined gender-specific growth rates for 35 largemouth bass
populations in Florida lakes and found that female largemouth bass with average growth
reached memorable size between ages 6 and 7. Therefore, female growth rates at
Rodman Reservoir were about average in comparison to other Florida water bodies.
According to the FFWCC 'Big Catch' program a largemouth bass must be > 610-mm TL
or > 3.6-kg to be considered a trophy catch. Average growth rates at Rodman Reservoir
do not produce trophy fish, thus memorable-sized fish were used as a gauge to measure
each regulation's effectiveness at increasing the number of large fish (> 510-mm TL)
within the reservoir.
Results of the tagging study showed that tag retention rates declined with
increasing time at large. Retention rates ranged from 96% (66 days at large) to 74% (421
days at large), based on the average number of days fish were at large. Renfro et al.
(1995) found 100% tag retention in largemouth bass that were tagged and held in
hatchery ponds for 3-months, and 98% average retention (range: 93% to 100%) for
largemouth bass that were tagged and held in sample ponds for 15-months, using the
same tags used in this study. Renfro et al. (1995) did not find retention rates to decrease
with increasing time at large. Retention rates calculated in this study were lower than
those calculated by Renfro et al. (1995). The individual error associated with fish tagging
was compounded by the high number of individuals (N = 25) that participated in tagging
efforts and may have contributed to the high level of tag loss observed in this study.
Additionally, anglers may have intentionally or inadvertently misreported the presence of
two tags in follow-up phone interviews. Conversations with anglers revealed a common
belief that both tags should not be removed from double-tagged fish. Some anglers
believed that it was wrong to remove both tags, while others believed they were
contributing to the success of the study by not removing all tags. In either case,
misreporting a tag loss from a double-tagged fish would have inflated my estimate of tag
loss. In response to this apparent confusion among anglers, signs were posted at boat
ramps in January 2002, indicating that all tags should be removed from double-tagged
fish (Appendix 3). Tag retention rates may have been more comparable to those found
by Renfro et al. (1995) had the angling community clearly understood how to treat
double-tagged fish.
Cage trials conducted during the fall and winter showed a 100% survival rate for
tagged fish. This survival rate was comparable to the survival rates calculated in
previous tagging studies (Tranquilli and Childers 1982; Renfro et al. 1995). Renfro et al.
(1995) showed that over the course of a three-month pond study mortality rates of fish
tagged with Halprint dart-style tags did not differ significantly from mortality rates of
untagged fish. Tranquilli and Childers (1982) also showed 100% survival rate for tagged
fish in a 191-day pond experiment.
Tag returns may have suffered from a lack of independence. Pollock et al. (2001)
suggested that anglers may have a tendency to collect low-reward tags until they gather
enough tags to make them worth mailing. Anglers participating in this study commonly
returned several tags at once indicating a possible lack of independence. The tag return
envelopes used in this study may have also contributed to the lack of independence in tag
returns. Tag return envelopes were not postage-paid therefore the cost and effort
associated with mailing a single tag may have outweighed the reward, possibly leading
anglers to accumulate tags until they had collected enough reward money to justify
mailing in the tags. This possible lack of independence in tag returns may have inflated
my reporting rate estimates.
The exploitation rate of largemouth bass calculated for the first three quarters of
2002 was low (u2002 = 3%) in comparison to the 2001 annual exploitation rate (u2001 =
11%). Although the 2002 exploitation rate will increase as tags are returned from fish
caught in the fourth quarter of 2002, I do not expect the exploitation rate to increase
dramatically nor do I expect it to match or exceed the 2001 annual exploitation rate. The
low exploitation rate in 2002 was probably due to (1) the 610-mm minimum length limit
implemented during the 2001-2002 reservoir drawdown and (2) a possible decline in the
return rate of tags from 2001 to 2002. The temporary 610-mm minimum length limit
placed on the largemouth bass fishery during the drawdown period coincided with the
first quarter of 2002 and protected the majority of the fish caught during that quarter from
harvest. Because 66% of all the fish caught in the first three quarters of 2002 were
caught during the first quarter of the year, the temporary length limit contributed to the
lower exploitation rate in 2002. In addition, using 2001 reporting rate estimates to
estimate total catch in 2002 may not have been appropriate since reporting rates have
been shown to decline from the first year of the study to subsequent years (Dequine and
Hall 1949; Moody 1960). If reporting rates declined from the first to second year of my
study, the use of first year reporting rates would result in underestimates of exploitation
and total catch in 2002. Reward-specific reporting rates were not calculated for 2002
because a complete year of tag return data was not available. Although 2002 reporting
rates were not available, comparing the percent return of tags in the second (11%) and
third (3%) quarters of 2001 to the second (5%) and third (1%) quarters of 2002 revealed a
decline in the return rate of tags (Table 3). However, the percent return of tags in the first
quarter of the year increased from 2001 (8%) to 2002 (9%) (Table 3). This increase may
be an indication that tag return rates did not decline with increasing study length.
Nevertheless, it is more likely that a decline in reporting rates occurred and was masked
by an increase in angler catch rates associate with the reservoir drawdown. Therefore,
angler catch rates calculated for the first three quarters of 2002 were probably
underestimated, leading to an underestimate of exploitation and total catch for 2002.
Harvest restrictions are often more effective at altering the age structure of
populations that have additive mortality rates as opposed to compensatory (Allen et al.
1998). Changing exploitation rates in populations with additive mortality has a direct
effect on total annual mortality. However, changing exploitation rates in populations
with compensatory mortality may not effectively reduce total annual mortality. Growth
and natural mortality of a population may also dictate the effectiveness of a regulation.
Beamesderfer and North (1995) found that angler catch rates and the occurrence of large
fish were likely to increase when harvest restrictions were applied to average (average
growth, average v) or productive (fast growth, low v) populations. Conversely, they
found that limiting exploitation of unproductive populations (slow growth, high v) may
not be beneficial because many fish would die before they reached quality size.
Compared to the populations studied by Beamesderfer and North (1995), growth rates
and natural mortality of largemouth bass at Rodman Reservoir were average. Based on
these findings and the assumption that mortality rates of largemouth bass were additive,
harvest restrictions should serve as an effective means for manipulating the age structure
of the largemouth bass population at Rodman Reservoir.
Miranda et al. (2002) questioned the effectiveness of tagging studies as a means for
accurately assessing exploitation rates. They reported that the variability associated with
estimating reporting rates is so large that it precludes a manager's ability to accurately
assess exploitation, thus Miranda et al. (2002) recommended that managers seek an
alternate means for estimating exploitation. Because my exploitation rates were derived
from a tagging study, I introduced high error into my reporting rate estimates and used
the associated exploitation and natural mortality rates in simulation models to verify that
trends in the simulation results would remain constant regardless of the possible
variability associated with my reporting rate estimates. Simulations using exploitation
and natural mortality rates associated with + 50% variability in reporting rate showed that
trends in total catch remained constant. Trends in total harvest were moderately affected
by the extreme variation in reporting rates. Overall, variability in exploitation due to
reporting rate error did not significantly impact the relative value of each harvest
restriction.
The purpose of the simulation model was to identify trends in the population's
response to various harvest restrictions. Simulation models have error associated with
their estimates just as field data have associated error (Johnson 1995). Therefore, error
associated with specific predictions of the simulation model my recommendation to
implement a 510-mm minimum length limit at Rodman Reservoir was based primarily on
the trends reveled by the simulations, not the specific values.
FURTHER STUDY
Several factors could interfere with the success of the proposed 510-mm minimum
length limit. These factors include (1) a potential for reduced growth due to the proposed
high minimum length limit, (2) a potential for increased fish removal during tournaments
due to the re-opening of Buckman Lock, and (3) the potential elimination of the reservoir
due an ongoing debate to remove of the Senator George Kirkpatrick Dam.
The proposed high minimum length limit could potentially reduce the growth rates
of largemouth bass at Rodman Reservoir, thus interfering with the success of the
proposed regulation. Seidensticker (1994) found evidence that slow growth of
largemouth bass began 5-years after a 406-mm minimum length limit was implemented
at a Texas reservoir. I suggest conducting semi-annual age-and-growth surveys at the
reservoir to assess the potential effects of the regulation on fish growth rates. Age-and-
growth assessments would allow managers to identify potential problems as well as track
the success of the regulation as a means for altering the age structure of the population.
According to Allen and Pine (2000) the probability of detecting differences in the age
structure of a population due to an altered harvest restriction was higher under 5-year
evaluations than 3-year evaluations. Wilde (1997) concluded that data should be collected
for a minimum of three years following the implementation of a regulation in order to
detect differences. In either case, duration of evaluation was the key to determining the
effects of a regulation on a population. Based on these finding, I suggest monitoring age-
and-growth of the population periodically for 5-7 years.
The re-opening of Buckman Lock could lead to an increase in the number of
largemouth bass removed from the reservoir due to tournaments and potentially lead to
an increase in total annual mortality. Buckman Lock connects Rodman Reservoir to the
St. Johns River allowing boater access between the two water bodies. The lock is
commonly used by tournament anglers participating in fishing tournaments held outside
of the reservoir. Tournament anglers that lock through to fish the reservoir remove
largemouth bass from the reservoir when they return to the St. Johns River for weigh-ins.
Tournament anglers participating in tournaments outside of the reservoir do not release
fish back into the reservoir, thus tournament anglers could potentially contribute to the
total annual mortality of largemouth bass at Rodman Reservoir. Buckman Lock was
closed for the duration of this study except for a brief period in December of 2001 when
the lock was opened to allow anglers participating in the Citgo Bassmasters Eastern Open
to fish the reservoir. Buckman lock re-opened for regular operation in October of 2002.
Due to the re-opening of the lock, I recommend that managers assess effects of outside
tournament anglers on the abundance of largemouth bass at Rodman Reservoir. If
tournaments remove a significant number of fish, I suggest re-evaluating the harvest
restriction to ensure that the 510-mm minimum length limit is still the optimal regulation
for the reservoir.
Finally, the potential elimination of the reservoir due to an ongoing debate to
remove the Senator George Kirkpatrick Dam and restore the free flowing Ocklawaha
River could completely negate the findings of this study. The US Forest Service has
voiced its intention to initiate action by 2006 to restore the federal land which is currently
submerged beneath the reservoir and abuts the Senator George Kirkpatrick Dam. The
intentions of the US Forest Service would effectively result in the removal of the
reservoir. However, in response to the US Forest Service's intentions, the 'Save Rodman
Reservoir' advocacy group has voiced their plan to file suit against the US Forest
Service, should the US Forest Service take action to remove the dam. Managers should
consider the potential for dam removal when deciding whether to implement a new
harvest restriction. As previously stated, the effects of the regulation may not be visible
for five or more years, thus the removal of the dam could prevent the regulation from
ever taking full effect and if the dam was removed, a re-assessment of the fishery would
need to take place before a new optimal harvest restriction could be chosen. Managers
should take caution and consider all of these potential problems prior to implementing a
new harvest restriction.
APPENDIX A
REWARD SIGN-1
Reward sign posted at fishing access points around Rodman Reservoir and at local tackle
shops.
REWARD
$5 AND $50
Fishery biologists have tagged Largemouth bass in the Rodman Reservoir.
To receive a reward of $5 or $50, you must cut the tag from the fish and
mail the tag and the following information to the address listed below.
Send the following information with each tag:
NAME
ADDRESS
PHONE NUMBER
SOCIAL SECURITY NUMBER*
SIGNATURE
DATE CAUGHT
APPROXIMATE CATCH LOCATION
APPROXIMATE FISH LENGTH
COMMENTS
*Needed to receive reward.
Address information is also provided on the tag, and tag mailers are
provided at local tackle shops for your convenience.
S11 -. 1150 $5FReward I
Please mail tag and information to:
Florida Fish and Wildlife
Conservation Commission
7922 NW 71st St. Gainesville, FL 32653
(352) 392-9617 ext. 240
APPENDIX B
TAG-RETURN INVOICE
Tag- return invoice distributed to all anglers that returned largemouth bass tags.
Please mail tag and information to:
Florida Fish and Wildlife
Conservation Commission
7922 NW 71st St. Gainesville, FL 32653
(352) 392-9617 ext. 240
INVOICE
To: Florida Fish and Wildlife Conservation Commission
7922 NW 71st St.
Gainesville, FL 32653
TO BE FILLED OUT BY ANGLER
From: (Please Print)
Name:
Social Security Number: (Needed for reward)
Address:
Phone Number:( ) -
Approximate Fish Length (inches):
Date Caught:
Approximate Catch Location:
Was Fish Kept or Released
Comments:
Tournament : Yes/No (Circle)
Tournament Name:
Weigh-in Location:
APPENDIX C
REWARD SIGN-2
Informational sign posted at fishing access points around Rodman Reservoir beginning
January 2002. The sign was intended to alleviate confusion among anglers regarding the
number of tags that should be removed from double-tagged fish.
LARGEMOUTH BASS
TAGS
Please Cut All Orange Tags from Fish Regardless of
Whether the Fish is Kept or Released.
REWARDS: $5,$10,$50,$55,$100
Please mail Tags to:
Florida Fish and Wildlife Conservation Commission
7922 NW 71st Street. Gainesville, FL 32653
(352) 392-9617 ext. 240
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52
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populations in reservoirs: a computer simulation model. Pages 218-226 in Hall,
G. E. and M. J. Van Den Avyle, editors. Reservoir Fisheries Management
Strategies for the 80's. Reservoir Committee, Southern Division American
Fisheries Society, Bethesda, MD.
BIOGRAPHICAL SKETCH
Kristin Rene Henry was born on October 5, 1977, in Rochester, New York, the
daughter of Robert and Jacquieline Henry. She was raised in the small town of
Walworth, New York, with her brother Jason. She acquired a love for the ocean during
annual family camping-trips to the Atlantic coast, and decided to purse a degree in
marine science at Long Island University/Southampton College in the fall of 1995. She
graduated with a B.S. in marine biology in May 1999. After graduation she pursued an
interest in fisheries biology working with striped bass on the Roanoke River in North
Carolina. In June 2000, she began work as a fisheries technician for the University of
Florida and began her graduate work in the Department of Fisheries and Aquatic
Sciences at the University of Florida in January 2001. She will graduate with a Master of
Science degree in May 2003. Her future plans are to travel, spend time with her family,
and pursue a career in marine fisheries management.
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