DISCARD MORTALITY, RECRUITMENT, AND CONNECTIVITY OF RED SNAPPER (LUTJANUS CAMPECHANUS) IN THE NORTHERN GULF OF MEXICO
Curtis, Judson Matthew
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Red Snapper (<italic>Lutjanus campechanus</italic>) is the most economically important reef fish species in the Gulf of Mexico. Despite being intensively managed, stocks have been slow to recover from overharvest and the population is still rebuilding. One possible reason is that Red Snapper experience high discard mortality after catch-and-release. Additionally, there is a decoupling of the stock-recruit relationship in the fishery with high levels of recruitment despite low spawning stock biomass. This dissertation addressed these gaps in knowledge in three principal chapters. In Chapter II, I evaluated if certain release methods reduced discard mortality of Red Snapper at different depths and temperatures. I used acoustic telemetry to determine the best-release practices for enhancing survival and to estimate the extent of delayed mortality. Venting and rapid recompression release methods were more beneficial for enhancing survival, and delayed mortality events occurred within a 72-hour time period. In Chapter III, I used novel acoustic transmitters to analyze the post-release behavior and activity patterns of Red Snapper that survived catch-and-release. Red Snapper had different acceleration and depth activity over diel time periods, and increases in acceleration were correlated with higher depth in the water column. Release treatments did not affect long-term behavior and activity. In Chapter IV, I examined the stock-recruit relationship for the Red Snapper fishery by assessing whether localized cryptic spawning stock biomass is responsible for maintaining high recruitment levels. Acoustic telemetry and catch data were used to show that large, sow Red Snapper have high site fidelity and residency patterns in the western Gulf of Mexico, suggesting high recruitment observed in the stock may be originating locally from non-targeted sites. By identifying the source of the high spawning stock biomass, protection measures and regulations can be implemented to ensure that the current high recruitment to the fishery is sustained. Determining the best-release practices to enhance survival of discarded fish will result in larger stock sizes. Ultimately, implementation of findings from this dissertation into the management process will further assist and expedite the rebuilding of Red Snapper stocks and promote the recovery towards sustainability in this historically important Gulf of Mexico fishery.
Submitted in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY in MARINE BIOLOGY