Mortality estimates for gray triggerfish (Balistes capriscus) in the northern Gulf of Mexico based on acoustic telemetry

Abstract

— Gray triggerfish ( Balistes capriscus ) is a common resident of reef habitats in the northern Gulf of Mexico. It is targeted by fishermen and recently considered not overfished. However, stock status is highly depen- dent on indirect mortality estimates from sport and commercial fishery landings that may have errors. To enhance management efforts, we used acoustic telemetry to directly estimate fishing mortality ( F ), natural mortality ( M ), and total mortality ( Z ) for gray triggerfish on artificial reefs in the northern Gulf of Mexico. Over the study period, 30 fish emigrated, 4 fish were caught by fishermen, 4 fish died of natural causes, 8 fish were active when their transmitter battery expired, and 3 fish were still active at the end of the study. Annual F was 0.23 (95% confi- dence interval [CI]: 0.07–0.50) and was lower than in past stock assessments. This rate indicates that earlier man- agement efforts were successful. However, our F estimate is possibly greater than a recent management goal of 0.17 based on a 30% spawning potential ratio. Therefore, gray triggerfish stocks may still be experiencing overfishing. Annual M was 0.25 (95% CI: 0.07–0.57) and supports the management applied M of 0.28. Annual Z was 0.48 (95% CI: 0.18–0.85), which was not considered sustainable under the most recent stock assessment and supports the management decision to increase fishery restrictions.