Effects of size-selective catch-and-release angling on population size structure of two Black Bass (Micropterus spp.) species in an Alabama Reservoir

Abstract

The potential for size-selective catch-and-release angling to affect the size distributions of black bass (Micropterus spp.) populations is not well understood. Angling is highly size-selective, and competitive fishing events, may be particularly size-selective by incentivizing the capture of large fish. These competitive events (i.e., tournaments) are increasing in popularity which leads to more angling effort that might be size-selective. We conducted research on Largemouth and Alabama Bass at Neely Henry reservoir in Alabama to assess the potential for size-selective angling to affect population size structure. This system is characterized by high fishing effort and a high proportion of fish captured in tournaments. Size-selectivity of tournament and non-tournament angling was estimated from a high reward tagging study. Size-specific vulnerability estimates from angler tag returns revealed that vulnerability of 300 mm Largemouth Bass was 0.75 and vulnerability of the same size class of Alabama Bass was 0.66. Variation in growth among individual fish was estimated by ageing samples of fish from the creel and from standardized electrofishing surveys. A pairwise comparison between gears for each age class was conducted for both Alabama Bass and Largemouth Bass. Alabama Bass collected from tournaments were on average 55 mm longer at age 1, 19 mm longer at age 2, and 25 mm longer at age 3 than fish from electrofishing surveys. Largemouth Bass collected from tournaments were on average 28 mm longer at age 1 and 13 mm at age 2. A Bayesian hierarchical growth model was fit to age samples to estimate von Bertalanffy growth parameters for individuals. The mean posterior growth parameters estimated from electrofishing samples of Largemouth Bass estimated from electrofishing samples were 563 (95% CI: 561 - 565), 0.279 (95%CI: 0.277 – 0.282), and -0.348 (95% CI: -0.359 – -0.336) for L, k, and t0, respectively. For Alabama Bass the mean posterior growth parameter estimates across individuals collected via electrofishing were 566 (565 – 567) for L, 0.25(0.248 – 0.252) for k, and -0.25(-0.26 – -0.23) for t0. An age- and size-structured equilibrium model was used that accounted for individual variation in growth within these populations under encounter rates developed from Neely Henry. The Ricker stock-recruitment model and Beverton-Holt model, along with variation in natural mortality, and maximum lifetime reproductive rate were modeled to assess influence on the abundance of quality (≥305 mm) and memorable (≥508 mm) fish of both species. Under high encounter rates the model predicted angling could reduce the abundance of quality sized Largemouth and Alabama Bass by 6% and 12% relative to the unfished condition, respectively. A decline of 48% in memorable size Largemouth Bass abundance and 79% in memorable size Alabama Bass abundance was predicted relative to the unfished condition. This study provides information on the level of impact that catch-and-release angling can have on population size structure in a reservoir system.