Evaluating protected species bycatch in the U.S. Southeast Gillnet Fishery

Abstract Incidental capture or ‘bycatch’ of non-targeted species is a global fisheries issue that threatens ocean ecosystems and the conservation and recovery of protected species. Many protected species are at a high risk of incidental capture and mortality in commercial fisheries, which could have an impact on already decreasing populations. From 1998 to 2017, U.S. federal fisheries observers aboard fishing vessels in the U.S. Southeast Gillnet Fishery collected data on captures of encountered protected species. Data collected by the observers were used to describe protected species incidental capture within this fishery. A generalized linear zero-inflated negative binomial two-part model (GLM-ZINB) was applied to determine which environmental and fishing characteristic factors influence the probability of incidental capture of protected species including leatherback, Dermochelys coriacea, and loggerhead, Caretta caretta, sea turtles, bottlenose dolphins, Tursiops truncatus, and giant manta ray, Manta birostris. While a variety of factors were considered in our models, no one single factor was found to influence all protected species. Incidental capture of leatherback turtles was influenced by season, depth, and gillnet depth, while loggerhead turtles were influenced by season, sea surface temperature, and target species of the fishery. Bottlenose dolphin bycatch was most influenced by soak duration, gear type, and season, while giant manta ray captures were influenced by soak duration, gear type, and depth. Environmental factors and fishing characteristics associated with incidental capture of protected species can be used to help guide fishery managers as to what species-specific regulations could be implemented to help mitigate capture.