Effects of Hook Size and Type on Northern Gulf of Mexico Red Snapper Catch Metrics and Stock Assessmen

The reef fish fishery in the northern Gulf of Mexico (GOM) produces millions of discarded fish annually due to traditional management regulations concomitant with high effort. Circle hooks were mandated in 2007 when targeting GOM reef fishes to reduce traumatic hooking and subsequent discard mortality. However, little was known regarding potential impacts of circle hooks specific to reef fishes in the northern GOM. In this study, recreational charterboat trips were observed for two years to characterize differences in fishing behavior between open and closed red snapper seasons, an overfished species and the most targeted reef fish in the northern GOM. Two field experiments were conducted to test the effect of hook size and type on traumatic hooking, catch composition, and catch rates of reef fishes, as well as to directly estimate contact selectivity of red snapper, Lutjanus campechanus, and gray triggerfish, Balistes capriscus. Results from field experiments were then used to inform deterministic simulations conducted in the red snapper stock assessment model to evaluate the effect of hypothetical hook-size regulations for recreational fleets on estimates of spawning stock biomass (SSB), the overfishing limit (OFL), retained catch, and discards.;Charterboat fishers used a combination of gear configuration and adaptive spatial targeting during open seasons to target large red snapper almost exclusively at artificial reef sites but were unable to significantly decrease red snapper discards during closed seasons. Fishers increased the frequency of larger, older red snapper in the retained catch via live high-grading. Compared to J hooks, circle hooks significantly reduced traumatic hooking rates of red snapper but did not affect catch rates or contact selectivity. Circle hooks did not affect traumatic hooking or catch rates of gray triggerfish but did shift contact selectivity to smaller size classes below the current minimum length limit. Empirical data suggest that increasing circle hook size provides a small increase (900 mm TL). Simulation results indicate that size-at-peak selectivity need only be shifted to approximately 400 mm TL to provide dramatic reductions in discards. Large circle hooks (15/0) did increase size-at-peak selectivity above 400 mm TL in this and other empirical studies. Hook regulations had a modest, positive effect on estimates of projected SSB but little effect on projected OFLs. Estimates of projected retained catch and discards were more sensitive to hook regulations but were dependent upon contact selectivity during the recent past and the recreational fleet upon which the regulations were imposed (i.e., eastern vs. western GOM). Results of this study suggest that mandating large circle hooks could improve fishery efficiency, but the magnitude of change is dependent upon live high-grading behavior and catch constraints of recreational fishers during red snapper open seasons.