Estimating Delayed Mortality of Discarded Red Snapper in the Gulf of Mexico with Acoustic Telemetry

Discard mortality in Red Snapper (Lutjanus campechanus) may be one impediment towards a more rapid stock recovery for this economically important Gulf of Mexico fishery. Red Snapper are highly susceptible to pressure-related injuries (i.e., barotrauma) that compromise survival after catch-and-release. Barotrauma afflicted fish may not only experience immediate surface mortality but also delayed mortality upon returning to depth, and this unknown fate leads to uncertainty in stock assessment models and rebuilding plans. To generate better estimates of immediate and delayed mortality, Red Snapper were tagged with ultrasonic acoustic transmitters equipped with accelerometer and pressure sensors. We estimated survival rates and delayed mortality events in a series of temperature, depth, and release treatments. Results from field trials showed strong depth effects resulting in increased barotrauma injuries, more impaired reflexes, and greater mortality as depth increased. Venting and rapid recompression strategies showed greater survival than non-vented, surface released fish. However, interactions between release treatment and season suggest that using these release strategies may only be necessary during summer. Estimates from this study can be integrated into stock assessment models to achieve better calculations of overall mortality and inform managers on effective release methods to maximize survival in discarded Red Snapper.