Modeling the Population Response of Alligator Gar in Texoma Reservoir to Harvest and Discard Mortality

Abstract

AbstractThe popularity of angling for Alligator Gar Atractosteus spatula is an essential component of fisheries management and can affect population resilience. In most cases with Alligator Gar, development of biological assessment models to assess stocks is often unavailable. For this reason, we aimed at describing Alligator Gar demographic rates and population size in Texoma Reservoir, Oklahoma. We used these data to parameterize an age‐structured simulation model to determine population responses of maximized yield, total catch, catch of trophy fish, and fishery sustainability to a range of instantaneous finite fishing mortality rates (FM) and discard mortality rates (D) in approximating ideal harvest strategies. Our simulations suggest that the Alligator Gar population is highly sensitive to increases in exploitation. Under the current management regulations, an FM of 0.00–0.05 would have a limited impact on sustainability, which would result in negligible growth as an effect of stochastic recruitment. If FM reaches or exceeds 0.06, the current regulations would not be effective at sustaining the population (spawning potential ratio <0.30). At FM values greater than 0.10, the probability of the population declining from the current population estimate (1,947 fish) to less than 500 individuals would increase from 20% to 100%, resulting in the collapse of the population over 100 years, especially if D is greater than 0.10. Use of a 1,524‐mm minimum length limit had the potential to allow FM values of up to 0.10 while absorbing a low amount of D. The use of length limits may provide some options for sustaining the Alligator Gar population, although their efficacy is limited by D when FM exceeds 0.06. Given the sensitivity of long‐lived, periodically recruiting fishes to exploitation and given the benefits that possible length‐based regulations or a tag/lottery system can provide, we encourage managers to continue monitoring Alligator Gar populations, and when concerning trends are observed, managers should consider such regulations to increase resilience to FM and increase sustainability.