Bycatch and mortality of three prohibited shark species in northeast U.S. commercial gill-net and trawl fisheries

Objective Incidental capture in nontarget fisheries can contribute to mortality of prohibited shark species with low productivity and slow population growth. In the U.S. northwest Atlantic Ocean, the Dusky Shark Carcharhinus obscurus, Sand Tiger Carcharias taurus, and White Shark Carcharodon carcharias have been prohibited from retention for more than two decades, yet incidental captures persist. Methods Using National Marine Fisheries Service observer data from 1993 to 2024, we estimated annual bycatch in gill-net and trawl fisheries and evaluated predictors of at-vessel mortality. Annual fleetwide bycatch and mortality were estimated by expanding observer catch per unit effort to total commercial effort using Vessel Trip Report records (1996–2024). Results Gill nets accounted for 71.5% of observed bycatch, driven largely by Dusky Sharks. Mean annual expanded bycatch in gill-net fisheries was 128 ± 287 Dusky Sharks, 20 ± 17 Sand Tigers, and 4 ± 3 White Sharks compared with 85 ± 160 Dusky Sharks, 45 ± 88 Sand Tigers, and 4 ± 3 White Sharks in trawl fisheries. Mean annual at-vessel mortality was higher in gill nets (72 ± 191 Dusky Sharks, 5 ± 7 Sand Tigers, 3 ± 3 White Sharks) than in trawls (34 ± 85, 3 ± 6, and 1 ± 1, respectively), with anchored sink gill nets producing the highest mortality rates. Species-specific binomial models indicated higher mortality with increasing shark size for Dusky Sharks and Sand Tigers and consistently higher at-vessel mortality in gill nets than trawls. Expanded bycatch and at-vessel mortality generally declined over the time series for Dusky Sharks and Sand Tigers, whereas no consistent temporal trend was evident for White Sharks. Observed bycatch was dominated by young-of-the-year and juvenile individuals across all three species. Spatial analyses identified recurring clusters of incidental capture in the Middle Atlantic Bight and southern New England that overlapped extensively with juvenile Essential Fish Habitat. Conclusions Together, these results provide a multidecadal quantitative baseline for prohibited shark bycatch and at-vessel mortality and illustrate how long-term observer data sets can be used to characterize rare incidental capture and mortality of protected sharks in nontarget fisheries. As a case study, this work highlights the broader value of underutilized fishery observer data for management of shark species where direct assessment data remain sparse.