CANCELLED - The fate of regulatory discarded red snapper in the Gulf of Mexico: Insights into delayed post-release mortality and behavior

Background/Question/Methods

Red snapper (Lutjanus campechanus) is considered ecologically and economically one of the most important reef fish species in the Gulf of Mexico. Populations are heavily managed but have failed to recover as expected and stocks remain at an all time low (97% decline). One possible reason for this is that red snapper are susceptible to pressure related injuries (barotrauma) that could contribute to delayed mortality after catch-and-release. Delayed mortality may occur from behavior alterations such as reduced fitness, predator evasion capability, or foraging efficiency. To determine the extent of delayed post-release mortality, we tagged 40 red snapper with Vemco© V9AP accelerometer tags and released them at an oil platform at 50m depth. Acoustic receivers attached to the platform at depths of 30m and 50m recorded acceleration and pressure (depth) data for approximately 45 days. Two trials were performed with 20 fish tagged in summer and 20 fish tagged in winter. Three treatments for each trial included: 1) surface, non-vented; 2) weight descended hook; and 3) surface-released control. Control fish were captured and held for two weeks to allow recovery from barotrauma symptoms prior to experimental release. To prevent incidental venting from suturing, fish were externally tagged through the anterior dorsal fin with stainless steel wiring.  

Results/Conclusions

There was a significant difference in delayed mortality between the summer and winter trials with more tagged fish surviving past day four during the winter. There was also a difference in receiver detections among release treatments for the winter trial, with the weight descended hook treatment registering fewer mean detections per fish per day than surface released treatments. Acceleration rates and depth varied depending on season and release treatment. These results suggest that temperature plays a critical role in determining post-release survival or mortality. The method of release may also dictate the fate of discarded fish. Results from these experiments enhance our understanding of post-release mortality and behavior of red snapper and provide useful information that documents the fate of regulatory discards. Estimates of delayed post-release mortality from this study can be integrated into current stock assessment models to achieve better calculations of overall post-release mortality and ultimately more accurate estimates of population size.