Micheal S. Allen

Differential Growth and Survival of Weekly Age-0 Black Crappie Cohorts in a Florida Lake

Abstract Black crappies Pomoxis nigromaculatus exhibit highly variable survival to adulthood because of their 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-d cohorts of juvenile black crappies in Lake Wauberg, Florida (a 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 by means of an otter trawl. Based on daily otolith rings, hatching occurred over a 12-week period (1 March−18 May). The mean daily growth rate (DGR) was positively related to water temperature, which increased over the hatching season. Common prey taxa included calanoid copepods, Daphnia and Bosmina spp., and cyclopoid copepods. The total density of these taxa did not differ significantly among collection dates. Mean hatching date shifted from mid-March for fish collected in mid-April to ...

Temporal Trends in Largemouth Bass Mortality, with Fishery Implications

Abstract We reviewed estimates of annual exploitation (u) and total mortality (Z) for populations of largemouth bass Micropterus salmoides and used a simulation model to explore how temporal changes in u have influenced those populations. The review produced 32 estimates of u and 30 of Z spanning 51 years. Fishing mortality was roughly parabolic through time, with a mean of 0.35 for 1976–1989 and a mean of 0.18 for 1990–2003. Thus, average fishing mortality rates have declined by about one-half since about 1990. Total mortality declined with the decline in u, suggesting that changes in u caused lower overall total mortality rates. The evidence further suggests that the decline in u was caused by the voluntary release of fish by anglers rather than by changes in overall fishing effort. The simulation model showed that the decline in exploitation increased adult largemouth bass abundance but reduced the ability of size and bag regulations to improve population metrics owing to low rates of directed harvest....

Temporal Trends in Voluntary Release of Largemouth Bass

Abstract We used creel survey data collected from 1975 to 2006 to evaluate temporal changes in the voluntary release of legally harvestable largemouth bass Micropterus salmoides at four Texas reservoirs and two Florida lakes noted for providing high-quality largemouth bass fisheries. The voluntary release rate increased substantially over time at all six water bodies and reached asymptotic levels exceeding 0.90 in two Texas reservoirs in the early 2000s. Year explained from 68% to 96% of the variability in voluntary release rates. The level of voluntary release ranged from 0.53 to 0.99 among Texas reservoirs in the early 2000s. The increase in voluntary release over time was similar at the two Florida lakes, which had identical largemouth bass harvest regulations, but the levels differed. Catch and release of legally harvestable largemouth bass was more prevalent than harvest at five of the six water bodies included in this study but also varied across small spatial scales. Fishery managers should measure...

RELATIONS BETWEEN HYDROLOGICAL VARIABLES AND YEAR-CLASS STRENGTH OF SPORTFISH IN EIGHT FLORIDA WATERBODIES

Hydrological variables have influenced fish recruitment in lakes, reservoirs and rivers. We evaluated how annual and seasonal hydrological variables were related to year-class strength (i.e., residuals from catch curves) of sportfish across eight Florida waterbodies (four rivers and four lakes). Multiple regression equations computed for black bass Micropterus spp. were combined across rivers and year-class strength was negatively related to spring median flow rates and in some cases positively related to winter median flow rates (all p ≤ 0.10). Conversely, Lepomis spp. residuals combined from the rivers indicated that year-class strength was positively related to median flow rates in the fall prior to spawning and negatively related to post-spawn fall median flow rates (all p ≤ 0.10). Fish recruitment combined across lakes were not related to water levels in this study, although within lake relationships did occur in some instances. Ecological implications of this work include regulations such as minimum flows and levels (MFLs) regarding sportfish species. Impacts of hydrology on year-class strength of sportfish were stronger in rivers than in lakes for these Florida systems. High flows at least once every 3 years in the fall may allow inundation of floodplain habitat, providing favorable environmental conditions for Lepomis spp. reproduction. Setting MFLs during periods of drought (i.e., 3 years or more) should consider impacts to short-lived species such as Lepomis spp.

Comparison of Trap Nets and Otter Trawls for Sampling Black Crappie in Two Florida Lakes

Abstract We compared the effectiveness of a recreational shrimp trawl (used for Penaeus spp.) with that of trap nets for assessing populations of black crappie Pomoxis nigromaculatus. Lakes Griffin and Monroe were sampled with both gears simultaneously during Oct–December 1997. Coefficients of variation (CV = 100 × SD/mean) on mean catch per effort (CPE) values ranged from 105 to 161 for trap nets and from 62 to 96 for trawls. Both trawls and trap nets collected fish less than 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 than trawl sampling (up to 4 times as much) to obtain precise estimates of mean CPE. 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 mac...

Recruitment of Largemouth Bass in Alabama Reservoirs: Relations to Trophic State and Larval Shad Occurrence

Abstract 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 densities of larval threadfin shad Dorosoma petenense and gizzard shad D. cepedianum from Mar to Jul from nine Alabama impoundments. Using shoreline rotenone sampling and daily otolith rings, we estimated density, age, and growth of age-0 largemouth bass Micropterus salmoides in late Jun–Jul. Density and growth of larval gizzard shad, larval threadfin shad, and age-0 largemouth bass 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 that were 40% or less of mean age-0 largemouth bass total length (i.e., the size at which they would probably be vulnerable to predation) in late Jun–Jul, whereas larval shad were generally not collected in late Jun or Jul i...

Exploring Population-Level Effects of Fishery Closures during Spawning: An Example Using Largemouth Bass

Abstract We used an age-structured model to evaluate the impacts of recreational angling during spawning on populations of largemouth bass Micropterus salmoides and the potential benefits of seasonal fishing closures. We simulated fisheries with average and high capture rates (i.e., fractions of the stock caught by anglers). We manipulated mortality rates to mimic the effects of various regulations, including (1) an open fishery with no closures, (2) a full fishery closure during the spawning season, (3) a catch-and-release fishery during the spawning season, and (4) a year-round catch-and-release fishery. We simulated two hypothetical populations: a high-productivity, low-latitude population and a low-productivity, high-latitude population. Spawning season closures produced the largest relative increases in adult abundance when applied to low-productivity populations and when capture rates were high (e.g., 70%) and harvest rates were relatively low (20%). This resulted because very high capture rates imp...

A REVIEW OF LITTORAL VEGETATION, FISHERIES, AND WILDLIFE RESPONSES TO HYDROLOGIC VARIATION AT LAKE OKEECHOBEE

Variation in hydrologic regimes in subtropical lakes and wetlands strongly influences biodiversity and value to human users. Lake Okeechobee, Florida, has a 450-km2 littoral landscape that supports a diverse assemblage of aquatic vegetation that provides critical habitat for fish and wildlife. Water level is one of the primary factors affecting the composition of aquatic vegetation and its associated faunal assemblages at Lake Okeechobee. We summarized published literature regarding the effects of water-level variation on subtropical wetland and littoral plants, as well as the fish and other biota supported by those plant communities, with an emphasis on shallow lakes and wetlands occurring at latitudes generally similar to Lake Okeechobee. The objective of this study was to enhance the information base that supports the CERP (Comprehensive Everglades Restoration Plan) hydrologic performance goals for this large lake ecosystem. Our results demonstrate that high water/prolonged flooding at lake stages exceeding 5.1m msl (mean sea level) will cause substantial loss of aquatic and wetland plants at Lake Okeechobee, which will negatively impact fish and wildlife populations. Conversely, very low water (< 3.7 m msl) on a regular basis may favor expansion of native plants but also torpedograss, Panicum repens (a non-native), which would require more intensive control programs. If Okeechobee lake stage varies between 3.7 and 4.6 m msl in most years, littoral and near-shore zones can be expected to develop diverse and widespread stands of emergent and submerged aquatic vegetation. If these changes occur, we predict that largemouth bass (Micropterus salmoides) and other fish species, alligators (Alligator mississippiensis), wading birds, and snail kites (Rostrhamus sociabilis) would all positively respond due to enhanced habitat structure and food resources.

Evaluating the Potential for Stock Size to Limit Recruitment in Largemouth Bass

Abstract Compensatory changes in juvenile survival allow fish stocks to maintain relatively constant recruitment across a wide range of stock sizes (and levels of fishing), but few studies have experimentally explored recruitment compensation in fish populations. We evaluated the potential for recruitment compensation in largemouth bass Micropterus salmoides by stocking six 0.4-ha hatchery ponds with adult densities ranging from 6 to 40 fish over 2 years. Ponds were drained in October each year, and the age-0 fish densities were used as a measure of recruitment. We found no relationship between stock abundance and recruitment; ponds with low adult densities produced nearly as many recruits as the higher-density ponds in some cases. Both prey abundance and the growth of age-0 largemouth bass declined with age-0 fish density. Recruit abundance was highly variable both within and among the adult density groups, and thus we were unable to identify a clear stock–recruit relationship for largemouth bass. Our re...

Spawning Site Selection and Potential Implications of Modified Flow Regimes on Viability of Gulf Sturgeon Populations

Abstract Rapid human population growth and an associated increase in consumptive water demands within the ecologically diverse Apalachicola–Chattahoochee–Flint (ACF) River basin of the southeastern United States have led to a series of highly publicized water wars, exacerbated by recent drought conditions, between the states of Alabama, Georgia, and Florida. A key issue is how managing riverine flows to meet human water needs will affect the viability of species that are federally listed as threatened or endangered, including the Gulf of Mexico sturgeon Acipenser oxyrinchus desotoi. Our present understanding of Gulf sturgeon ecology within the Apalachicola River basin indicates that altered riverine flow regimes may affect spawning success and possibly the recruitment patterns of the population. Through intensive field work, we documented Gulf sturgeon spawning site selection in the Apalachicola River and then evaluated the relationship between river stage and the available spawning habitat at these sites...