Fishing gear modifications to reduce elasmobranch mortality in pelagic and bottom longline fisheries off Northeast Brazil

摘要

One of the biggest challenges of fisheries research is reducing the bycatch of unwanted species. The incidental fishing mortality of species with low reproductive rates, such as elasmobranchs (sharks, skates, and rays), is recognized as a key threat for their populations. In the present study, gear modifications related to the type of hook and position of the hook in the water column were tested to examine their effects on catch rates and mortality of elasmobranch species in both pelagic and coastal environments. Comparisons between circle (size 18/0,0 degrees offset) and J-style (size 9/0, 10 degrees offset) hooks demonstrated that the circle hooks have a greater efficiency in reducing the mortality of most species caught, both in pelagic and coastal longline fisheries. Internal lodging of the hook was significantly less frequent for the individuals caught with circle hooks, which likely contributed to their higher survival rate at haulback. Additionally, circle hooks also increased the CPUE of elasmobranchs caught in the pelagic longline fishery, which was particularly evident for Carcharhinus falciformis and Prionace glauca. The position of the hook in the water column exhibited a strong influence on the species caught in the coastal bottom longline fishery. Suspending hooks in the middle of the water column reduced the bycatch of common demersal species, such as Carcharhinus acronotus, Ginglymostoma cirratum, and Dasyatis americana, while increasing the CPUE of potentially aggressive species, such as Galeocerdo cuvier and Carcharhinus leucas. The interaction of the type of hook utilized with its position in the water column appears to be an essential factor in the optimization of longline selectivity and minimization of bycatch mortality