Estimating Delayed Mortality of Gray Triggerfish Using Surface and Bottom Tagging

The number of discarded gray triggerfish (Balistes capriscus) in the US southeast has nearly doubled in recent decades, perhaps as a result of stricter management measures and increased effort.  High numbers of discards represent large sources of uncertainty in stock assessments, necessitating robust estimates of discard mortality.  We used conventional tagging of gray triggerfish in depths of 35-40 m of water on the seafloor (by SCUBA divers via traps) and at the surface (via traps and hook-and-line) to estimate discard mortality by observed condition.  At 35-40 m, proportional discard mortality in best-condition surface-released gray triggerfish was low (~ 4%) relative to the assumed zero mortality for seafloor tagged fish but was much higher for fish with outward signs of barotrauma (~ 51%).  Preliminary application of these condition-specific values to numbers-by-condition from a survey of for-hire vessels indicates a substantial increase in overall discard mortality with depth of capture.  On average, discard mortality may be 30% or higher for triggerfish discarded in the US southeast.  These findings will be important in calculating the number of dead discards required as input into stock assessments for gray triggerfish in the US southeast and other areas of the world where they are fished.