Spatial and temporal variation in exploitation rates of the Louisiana blue crab spawning stock

Abstract

Objective Blue crabs Callinectes sapidus support one of our nation's most valuable fisheries, and Louisiana has led national landings from 2012 to 2021. Fishery‐independent estimates of abundance have declined in recent years; in 2015, the Louisiana spawning stock biomass reached the lowest point ever recorded. Management efforts for the blue crab spawning stock have been hindered by incomplete knowledge of the dynamics of natural and fishing mortality. The purpose of this study was to examine spatiotemporal variation in exploitation rates of the Louisiana blue crab spawning stock. Methods From 2016 to 2017, we conducted a mark–recapture study in three Louisiana estuaries. During this period, we tagged 6133 mature female blue crabs, of which 964 were recaptured. Exploitation rate estimates were calculated using recapture data. In 2018, Louisiana implemented a 2‐month female harvest prohibition; to examine impacts of this harvest prohibition on exploitation rates of female blue crabs, we tagged additional females before, during, and after the harvest prohibition. Result Overall exploitation rate estimates for 2016–2017 ranged from 0.27 to 0.30 (i.e., 27–30%), but significant spatial and temporal variation was observed. During 2018, estimated exploitation rate without the harvest prohibition was 0.16–0.18, but with the prohibition, exploitation rate decreased to 0.08–0.09, indicating that this management action was effective in reducing mortality of mature females. Conclusion Nearly one‐third of mature female blue crabs in southeastern Louisiana are captured in the fishery at some point during their life. The 2018 female harvest prohibition reduced exploitation rate of mature females by ~50%. These spatiotemporal estimates of exploitation rate will be directly applicable to future Louisiana blue crab management plans and stock assessments.