Seasonal Abundance and Length Patterns of Brown and White Shrimp in Texas Estuaries and Nearshore Waters: Implications for Population and Fishery Dynamics

Abstract

Penaeid shrimp are a major contributor to commercial landings in the Gulf of Mexico, with white shrimp Litopenaeus setiferus and brown shrimp Farfantepenaeus aztecus making up the bulk of the landings off Texas. In this study, we examined seasonal trends in white and brown shrimp population demographics (relative abundance, monthly proportion of catch, and length) and their relationship with water quality parameters (water temperature and salinity) across a 36-year fisheryindependent data set for Texas estuarine and nearshore waters. The primary findings of this analysis were consistent negative trends in seasonal mean TL (April-August) for brown shrimp. These negative trends resulted in decreases in mean TL of up to 20 mm across the time series. Additionally, growth coefficients calculated on an annual scale for brown shrimp showed negative trends as well. White shrimp did not show the same consistently negative trends in mean length or growth. Although expected seasonal trends in CPUE and monthly proportions of catch were observed, the analysis showed few convincing or consistent annual trends in these metrics for either species. We suggest that the differing trends in mean length (i.e., between species) may be explained by summer water temperatures exceeding the optimum growth range for brown shrimp in the latter part of the time series examined here. Such trends in mean length for the brown shrimp population may have implications for population fecundity and may affect the value and efficiency of shrimp harvest in commercial fisheries, though this has yet to be seen. Nevertheless, managers should remain vigilant to any continued negative trends in brown shrimp length and their potential impact on the population and fishery dynamics.