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 dependent 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% confidence interval [CI]: 0.07–0.50) and was lower than in past stock assessments. This rate indicates that earlier management 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.