M. S. Allen, K. I. Tugend, and M. J. Mann.   In Press.  Largemouth bass abundance and angler catch rates
following a habitat enhancement project at Lake Kissimmee, Florida.  North American Journal of Fisheries Management.

A habitat enhancement project was conducted at Lake Kissimmee, Florida, during 1995-1996 to remove dense inshore vegetation caused by stabilized water levels and improve fish habitat. We evaluated age-1 (i.e., fish less 250 mm TL) and adult largemouth bass Micropterus salmoides abundance (i.e., fish over 356 mm TL and all sizes of fish caught by anglers) before and after the habitat enhancement. Mean electrofishing catch-per-hour (CPH) of age-1 largemouth bass increased significantly after the 1995-1996 habitat enhancement, suggesting strong year classes for two years after the habitat enhancement (i.e., 1997-1998 year classes). Growth of age-1 largemouth bass also increased following habitat enhancement, with mean TL at age-1 fish averaging 143 mm TL before enhancement and 186 mm TL after enhancement. Catch curves conducted in 2001 and 2002 corroborated historical electrofishing data indicating that the 1997 and 1998 year classes were abundant as adults compared to other year classes in the age frequencies. Age-1 largemouth bass electrofishing catch rates were not related to seasonal water levels or hydrilla Hydrilla verticillata coverage. Despite the rapid growth rates and high abundance of the 1997 and 1998 year classes, neither electrofishing catch rates of harvestable largemouth bass (i.e., $ 356 mm TL) or angler catch rates of largemouth bass (fish/h, all sizes of fish, harvested and released) from creel surveys differed significantly between pre- and post-habitat enhancement time periods. Thus, we were unable to detect a change in adult largemouth bass abundance or angler catch rates following the habitat enhancement. Fishing effort directed toward largemouth bass declined after enhancement for the winter period (Nov-Feb) but did not differ significantly between pre- and post-enhancement periods for the summer (May - Aug) period. Benefits of muck removal concurrent with lake drawdowns include increased recreational opportunities and improved habitat. However, our results indicate that fish-population responses to drawdowns and muck removals may vary, and detecting effects on the adult largemouth bass populations can be difficult. Therefore, habitat enhancement efforts should focus on lake-wide recreational benefits rather than benefits to a single preferred species (e.g., largemouth bass).

Effects of a large-scale habitat enhancement project on habitat quality for age-0 largemouth bass at Lake Kissimmee, Florida. Pages 265-276 in D. Phillipp and M. Ridgeway, editors. Black Bass: Ecology, Conservation and Management. American Fisheries Society, Bethesda, Maryland.

A habitat enhancement project was conducted in 1995-1996 to remove macrophytes and organic matter from about half of the 80-km shoreline of Lake Kissimmee, Florida. We evaluated habitat quality in enhanced and control (i.e., debilitated areas left intact after enhancement) areas, and largemouth bass density and growth in enhanced sites during 1998-2000. Control sites were characterized by low dissolved oxygen throughout the day (mean < 2 mg/L), high aquatic macrophyte biomass (> 50 kg/m2), and percent coverage of aquatic macrophytes (PAC) of 100%. Qualitative fish sampling in control sites yielded no sport fishes. Enhanced sites generally had mean DO > 4 mg/L, relatively low aquatic macrophyte biomass (mean < 5 kg/m2), and intermediate PAC (5-90%). Mean density of age-0 largemouth bass in enhanced sites averaged about 100 fish/ha from May - August of both years and was positively related to PAC in block nets in 1998. Growth rates of age-0 largemouth bass in 1998 and 1999 were rapid compared to historical records at Lake Kissimmee and a database of 56 Florida lakes. Diet analysis of age-0 largemouth bass revealed that fish were important prey (> 30% of diets by weight) from June - March of both years. Early piscivory of age-0 largemouth bass probably resulted in rapid growth rates. The habitat enhancement project created quality habitat for age-0 largemouth bass at Lake Kissimmee, and benefits were prolonged relative to previous enhancement efforts at another lake.

Allen, M. S., W. Sheaffer, W. F. Porak, and S. Crawford. 2002. Growth and mortality of largemouth bass in Florida waters: implications for use of length limits. Pages 559-566 in D. Phillipp and M. Ridgeway, editors. Black Bass: Ecology, Conservation and Management. American Fisheries Society, Bethesda, Maryland.

We reviewed growth and total mortality data for largemouth bass populations in Florida waters and used a simulation model to assess potential benefits of harvest restrictions. Mean total length (TL)-at-age across 32 populations was TL = 626(1 - e-0.246(age+0.139)) for females and TL = 419(1 - e-0.435(age+0.107)) for males. Total annual mortality (A) averaged 51% for 45 water bodies, and 70% of the estimates were between 40-60%. Simulation results suggested that length limits would improve total catch (fish harvested and released) if growth was at least average for the water bodies we evaluated and natural mortality was not substantially higher than exploitation. Very restrictive minimum length limits (e.g., 457-mm minimum length limit, 381-610 mm slot limit) reduced harvest regardless of growth rate. Yield responses were variable among length limits, but yield generally decreased with use of a length limit unless natural mortality was low. Given observed growth and mortality values, simulations suggested that length limits would improve angler catch rates (fish harvested and released) for most largemouth bass fisheries in Florida.

Wheeler, A. P., and M. S. Allen. In Press. Habitat and diet partitioning between shoal bass and largemouth bass in the Chipola River, Florida. Transactions of the American Fisheries Society.

We investigated the macrohabitat use, microhabitat use and food habits of shoal bass Micropterus cataractae and largemouth bass M. salmoides in the upper Chipola River, Florida. We electrofished two macrohabitats (pools and shoals) during the summer (May-August) and fall (September-December) of 1999 and 2000. The ratio of shoal bass to largemouth bass differed among the macrohabitats and was highest in the shoals and lowest in the pools. Age-0 and adult shoal bass were collected in areas of higher than average rocky substrate in both shoals and pools. Age-0 and adult largemouth bass were associated with areas of reduced current velocity and areas with higher than average amounts of woody debris. The diets of age-0 and adult shoal bass and largemouth bass were similar, however a few differences were apparent. Age-0 largemouth bass diets contained grass shrimp, whereas age-0 shoal bass diets contained mostly mayflies. Crayfish and fish dominated the diets of adult shoal bass and largemouth bass, with crayfish becoming more dominant in the diets with increasing fish size. Largemouth bass transitioned to a crayfish-dominated diet at a smaller size than shoal bass. Given the evidence for habitat partitioning, maintaining habitat diversity may be important for coexistence of shoal bass and largemouth bass in rivers and streams.

W. B. Tate, and M. S. Allen.  In press.  Simulated impacts of juvenile mortality on Gulf of Mexico Sturgeon populations.  The Scientific World.

We used an age-structured computer model to assess the impact of changes in juvenile mortality on the Gulf of Mexico sturgeon population in the Suwannee River, Florida.  We simulated population trends under four levels of annual juvenile mortality (20, 25, 30, and 35%).  As the rate of mortality increased, population size decreased and rates of population growth shifted from positive to negative.  Our models indicated that juvenile survival is important to the success of gulf sturgeon populations and mortality estimates are needed to predict population viability.   We suggest that life history studies in estuaries should be conducted and bycatch rates for commercial fisheries should be quantified to aid in the management and conservation of gulf sturgeon.

Pine, W. E. III, M. S. Allen, and V. Dreitz.  In Press.  Population viability of Gulf of Mexico sturgeon in the Suwannee River, Florida.  Transactions of the American Fisheries Society.

The Suwannee River, Florida population of the Gulf of Mexico sturgeon Acipenser
oxyrinchus de sotoi was evaluated using the capture-recapture software MARK and an age-structured model to examine population trends from 1986-1999. The MARK software revealed a positive rate of change in the adult population (8) indicating that the Gulf sturgeon population in the Suwannee was slowly increasing during the mid-1980's to mid-1990's. The age-structured model revealed that the population was highly sensitive to changes in egg to age-1 mortality, percent of females that spawn annually, and adult mortality. The model predicted that even slight increases in annual adult mortality (from 16% to 20%) resulted in population decline for Suwannee River Gulf sturgeon. Although this population is currently growing, caution should be taken not to increase mortality of adult fish and especially females. Managers should be patient and willing to monitor populations for extended periods of time (~20 years) before detecting changes in the adult population given attributes of Gulf sturgeon such as late sexual maturation, few mature females spawning each year, and high egg to age-1 mortality.

Allen, M. S., and L. E. Miranda.  2001.  Quasi-cycles in crappie populations are forced by interactions among population characteristics and environment.  Canadian Journal of Fisheries and Aquatic Sciences 58:594-601.

Crappie Pomoxis spp. populations have been characterized as cyclic, with strong year classes recurring at 2-4 year intervals. We evaluated the potential for cyclic trends in crappie populations using a population model that included a density-dependent stock recruitment function and random environmental variation. Slow, medium, and fast growth were simulated over 100-years.  The model predicted highly variable recruitment that was strongly influenced by environmental fluctuation at low and intermediate stock densities. At high stock density, recruitment was low even if environmental conditions were favorable. Significant quasi-cycles occurred, but they were not sustained throughout the time series due to random environmental fluctuation. Quasi-cycles occurred because intermediate stock density and favorable environmental conditions occasionally combined to produce a very strong year class that greatly increased stock density in the following 1-3 years and produced low recruitment, even if environmental conditions were favorable. Empirical data from 32-years of sampling age-0 crappies at Ross Barnett Reservoir showed trends similar to the simulated fluctuations.  We conclude that crappie populations likely do not exhibit true cycles, but may show quasi-cycles as a result of the interaction between random fluctuations in environment and density-dependent mechanisms. The frequency of such quasi-cycles may be enhanced by rapid growth and high exploitation.

Pine, W. E. III, and M. S. Allen.  In Press.  Differential growth and survival of weekly age-0 black crappie cohorts in a Florida Lake.  Transactions of the American Fisheries Society 130:80-91.

Black crappie Pomoxis nigromaculatus exhibit highly variable survival to adulthood due to varying larval and juvenile abundance, growth, and mortality during early life.  We examined how growth and mortality changed with hatch date, prey density, and water temperature for 7-day cohorts of juvenile black crappie in Lake Wauberg, Florida (150-ha hypereutrophic natural lake)during spring and summer 1998.  Fish were collected once per week from March through June and twice per month during July and August 1998 using an otter trawl.  Based on daily otolith rings, hatching occurred over a 12-week period (01 March-18 May).  Mean daily growth rate (DGR) was positively related to water temperature that warmed through the hatching season.  Common prey taxa consumed included calanoid copepods, Daphnia, Bosmina, and cyclopoid copepods.  Total density of common prey taxa did not differ significantly among collection dates.  Mean hatching date shifted from mid-March for fish collected in mid-April to early-April for fish collected in late May.  Early-hatched fish had lower DGRs (early= 0.72 mm/day, middle = 0.76 mm/day, late = 0.82 mm/day), higher mean daily instantaneous mortality rates (early = 0.25, middle- and late-hatched = 0.09), and lower survival to the end of the first summer than did middle and late-hatched fish.  As such, the 1998 year class of black crappie in Lake Wauberg was likely dominated by middle- and late-hatching individuals by the end of the first summer.

Allen, M. S., M. V. Hoyer, and D. E. Canfield Jr.  2000.  Factors related to gizzard shad and threadfin shad occurrence and abundance in Florida lakes.  Journal of Fish Biology 57:291-302.

Gizzard shad Dorosoma cepedianum and threadfin shad D. petenense are important prey species in many lentic systems and can potentially influence recruitment of other fishes via interactions during early life.  We evaluated 60 Florida lakes to identify factors related to   gizzard shad and threadfin shad occurrence and abundance.  We measured gizzard shad and threadfin shad density and biomass using block nets, catch-per-effort in gill nets, percent of lake volume inhabited by aquatic macrophytes (PVI), chlorophyll concentrations, and total zooplankton density from each lake.  Gizzard shad were collected in 23 and threadfin shad were collected in 22 of the 60 lakes sampled.  Logistic regression equations were 94% effective for predicting gizzard shad occurrence from chlorophyll and lake surface area, and 84% effective for predicting threadfin shad occurrence from lake surface area and PVI.  Occurrence of both shad species was positively related to lake size.  In lakes where gizzard shad or threadfin shad were collected, shad density and biomass of both shad species were positively related to chlorophyll.  Gizzard shad populations were generally vulnerable to predation in lakes where they occurred, with the percent of gizzard shad 200 mm TL values exceeding 60% with few exceptions.  Effects of gizzard shad and threadfin shad on fish community dynamics may be confined to relatively large (> 100 ha) and fertile (chlorophyll > 20-30 ug/L) Florida lakes.  Where gizzard shad occurred in Florida lakes, the were usually composed predominantly of individuals  less than 200 mm TL and were probably
vulnerable to predators.

Allen, M. S., and W. E. Pine III.  2000.  Detecting fish-population responses to a minimum length limit: effects of variable recruitment and duration of evaluation.  North American Journal of Fisheries Management 20:672-682.

We used a simulation model to evaluate how recruitment variability and evaluation duration would affect fisheries managers' ability to detect fish-populations responses to a minimum length limit.  Length limits modeled were 254-mm for white crappie Pomoxis annularis, and 305, 356, and 457-mm length limits for largemouth bass Micropterus salmoides.  Simulations were conducted at recruitment variation (coefficient of variation, CV= SD/  * 100%) in recruits to age 1 of 20-100%.  We evaluated how population density, population biomass, total catch (fish harvested and released), yield, and proportional stock density (PSD) would differ in response to a single three-year or five-year length limit evaluation.  For white crappie, simulations suggested that a 254-mm length limit would not provide detectable differences (P > 0.10) in any population parameter if recruitment variability exceeded 90% for either evaluation period.  Mean CV in recruits to age 0 or age 1 for empirical crappie populations was 82% (range 55-124, N=14).  Simulations revealed that largemouth bass populations would not exhibit detectable differences unless recruitment variability was less than or equal to 40% for a 305-mm and  65% for a 356-mm length limit, respectively.  Values of CV in recruits to age 0 or age 1 for largemouth bass populations averaged 66% (range 11-189, N = 13).  A 457-mm length limit for largemouth bass provided detectable differences in total biomass and PSD up to recruitment variabilities of 100%.  Detectable differences were more likely using five-year evaluations than with three-year evaluations.  Proportional Stock Density was the variable most likely to change in response to the size limit for both white crappie and largemouth bass.  However, at recruitment variabilities over 90%, detectable differences did not occur in three-year or five-year evaluations unless the size limit was
457 mm for largemouth bass.  Fishery managers should consider effects of variable recruitment and duration of evaluation period when evaluating the success of a minimum length limit.

Tugend, K. I., and M. S. Allen.  2000.  Temporal dynamics of zooplankton community composition and mean size at Lake Wauberg, Florida.  Florida Scientist 63(3):142-154.

Patterns of mean zooplankton abundance were observed during January - August 1998 in Lake Wauberg, Florida.  Zooplankton size structure was evaluated from April - August. Total zooplankton density, cladoceran density, copepod density and rotifer density varied significantly among months (P<0.01).  Zooplankton abundance was lowest in January and February, peaked in April and May, then declined throughout the summer.  Cladocerans peaked in abundance in May and were dominated by Daphnia, Eubosmina, Bosmina, and Diaphanosoma at varying times throughout the study.  Mean length for cladocerans ranged from 0.30 mm to 0.52 mm depending on which genera dominated at any given time.  Mean copepod abundance varied among months and was generally highest in spring.  Mean copepod length did not vary significantly (P>0.05) among months due to the dominance of nauplii (>70% by number).  Mean rotifer density in May was significantly higher than all other months except April (P<0.05) with Conochilus/Conochiloides (grouped together) and Brachionus comprising the dominant taxa.  Rotifers ranged in size from 0.06 mm to 0.15 mm and monthly mean size was greatest in late summer due to the presence of larger-bodied rotifers.  Our results suggest that Lake Wauberg is more characteristic of tropical systems containing smaller adult cyclopoid and daphnid species than those found in more temperate climates. Fish predation may also play a role in structuring the zooplankton community in Lake Wauberg.

Allen, M.S., M.M. Hale, and W.E. Pine III.  1999. A comparison of trap nets and otter trawls for sampling black crappie in two Florida lakes.  North American Journal of Fisheries Management 19:977-983.

We compared a recreational shrimp Penaeus spp. trawl to trap nets for assessing black crappie (Pomoxis nigromaculatus) populations. Lakes Griffin and Monroe were sampled with both gears simultaneously during October-December 1997. Coefficients of variation (CV=SD/ *100) on mean catch-per-effort (CPE) values ranged from 105 to 161 for trap nets and from 62-96 for trawls. Both trawls and trap nets collected fish < 150 mm total length (TL), but trawls sampled significantly more adult fish (> 250 mm TL). Variable catches in trap nets would require more sampling effort (up to four times as much) to obtain precise estimates of mean CPE than trawl sampling. Trawl sampling was preferable to trap nets based on size of fish captured, precision of abundance estimates, cost of the gear, and required sampling effort to estimate mean CPE. However, trawl sampling may be impractical in water bodies with excessive submerged structures, debris, and submersed macrophytes. We are encouraged by the effectiveness of the trawl for assessing black crappie populations in lakes where it is possible to use a bottom-sampling trawl.

Allen, M.S., J.C. Greene, F.R. Snow, M.J. Maceina, and D.R. DeVries. In Press.  Recruitment of largemouth bass in Alabama impoundments: relations to trophic state and larval shad occurrence.  North American Journal of Fisheries Management.

Factors affecting recruitment of largemouth bass have frequently been evaluated, but few studies have assessed recruitment potential among a range for reservoirs of varying trophic states.  We examined larval threadfin shad and gizzard shad densities from March-July from nine Alabama impoundments. Using shoreline rotenone sampling and daily otolith rings, we estimated density, age, and growth of age-0 largemouth bass in late June - July. Larval gizzard shad, larval threadfin shad, and age-0 largemouth bass density and growth increased with chlorophyll-a across impoundments.  Duration of occurrence for larval gizzard shad and threadfin shad was positively related to chlorophyll-a. Eutrophic reservoirs contained larval shad 40% of mean age-0 large-mouth bass total length (i.e., size where they would likely be vulnerable to predation) in late June - July, whereas larval shad were generally not collected in late June or July in oligo-mesotrophic impoundments.  Thus, piscivory on age-0 shad by age-0 largemouth bass was most likely to occur in eutrophic reservoirs for this study. Mean swim-up date of age-0 largemouth bass was not related to chlorophyll-a. However, eutrophic impoundments had length frequencies composed of larger age-0 largemouth bass than oligo-mesotrophic impoundments. Eutrophic impoundments have high chlorophyll-a values, and high larval threadfin shad and gizzard shad densities, and therefore may provide greater recruitment of largemouth bass than oligo-mesotrophic impoundments.

Allen, M. S., M. V. Hoyer, and D. E. Canfield, Jr.  1998.  Factors related to black crappie occurrence, density and growth in Florida lakes.  North American Journal of Fisheries Management 18:864-871.

Occurrence, density and length-at-age of black crappie Pomoxis nigromaculatus in 60 natural Florida lakes were described from aquatic macrophyte densities, chlorophyll-a concentrations (CHLA), chlorophyll-a values adjusted to include nutrients encompassed in macrophytes (ACHLA), and zooplankton abundance in each lake. A logistic regression equation predicted 90% of black crappie occurrence from log10 lake surface area and log10CHLA. Probability of black crappie occurrence increased with both variables. Density of black crappies was positively related to zooplankton abundance but was highly variable unrelated to lake surface area, CHLA, ACHLA or macrophyte abundance.  Length-at-age 3 was quadratically related to fish density. Length-at-age 3 was unrelated to trophic indicators (CHLA, ACHLA, zooplankton abundance), lake surface area or macrophyte abundance. Lakes with the most promise for sustaining high catch rates of harvestable-sized black crappies were relatively large (> 50 ha), contained high CHLA (>10 ug/L), and had relatively high
(> 200 fish/ha) black crappie densities. Low-density populations exhibited rapid growth, but would likely provide low catch rates to anglers. Small (< 10 ha), oligotrophic (CHLA < 3 ug/L) lakes were characterized by low frequency of black crappie occurrence. Growth and density of black crappies was not strongly affected by presence or density of aquatic macrophytes. Potential effects of fish density on growth rates should be considered in managing black crappie populations.

Allen, M. S., and L. E. Miranda.  1998.  An age-structured model for erratic crappie fisheries.  Ecological Modelling 107:289-303.

White crappie Pomoxis annularis and black crappie P. nigromaculatus are important freshwater sportfishes in North America. Because of erratic recruitment (the number of fish that survive to age 1 each year) fishery yields are inconsistent. We developed a simple age-structured model to help manage crappie fisheries. The model changes population biomass by age-specific somatic growth, and population abundance through recruitment and age-specific natural and fishing mortalities. Using empirical stock-recruitment data and a stochastic component to simulate effects of abiotic environmental fluctuations on recruitment, the model simulated empirical recruitment dynamics of a crappie population over 30 years in a large impoundment. Effects of density-dependent growth and natural mortality were modeled, but did not substantially affect yield given the observed magnitude of recruitment fluctuations. Model predictions of population biomass and yield tended to be high relative to empirical estimates, but not unrealistic.  Erratic recruitment of crappie populations has made development of management strategies elusive; this model should help fishery managers examine potential management alternatives.

Allen, M. S., L. E. Miranda, and R. E. Brock.  1998.  Implications of compensatory and additive mortality to the management of selected sportfish populations.  Lakes and Reservoirs: Research and Management 3:67-79.

The compensatory mortality hypothesis postulates that a population's total mortality remains unchanged at low to intermediate exploitation rates because natural mortality decreases to compensate for reduced density, whereas the additive mortality hypothesis postulates that any increase in exploitation mortality results in an increase in total mortality. Fishing and natural mortality rates have generally been assumed to be additive rather than compensatory. We reviewed mortality estimates for some prominent sportfish populations to identify evidence for compensatory or additive mortality. For largemouth bass Micropterus salmoides, total annual mortality (A, %) increased with annual exploitation (u, %) suggesting additive mortality. For crappies Pomoxis nigromaculatus and P. annularis, u did not seem to affect A at low to moderate u, but A increased with u as u increased beyond 40%, conforming to the compensatory mortality hypothesis. Northern pike Esox lucius mortality estimates revealed no relation between A and u, and highly variable A for a given u. Evidence from the literature suggests that mortality of northern pike may be compensatory for fish smaller than 40 cm total length, but additive for larger fish.  Because compensatory natural mortality reduces the managers' ability to control A, we suggest that further consideration of the compensatory mortality hypothesis be given to species that have shown variable mortality responses to reductions in u.