Hawai‘i's pelagic longline fishery demonstrates the need to consider multispecies impacts in bluewater time-area closures

Abstract Cap-based time-area closures can reduce the incidental capture of specific non-target species in fisheries by temporarily closing fishing areas when bycatch exceeds a threshold. The displacement of fishing effort can result in bycatch tradeoffs by increasing interactions with other species or even negate the intended effect of the closure. Here, we assessed the change in bycatch risk for a suite of species of concern resulting from the Southern Exclusion Zone (SEZ), a 343 796 km2 bycatch cap-based time-area closure designed to protect false killer whales from mortality and serious injury in the Hawaiʻi deep-set longline fishery. The SEZ was enacted twice between 2018 and 2020. We found that during the SEZ closures, fishing effort increased along the eastern and southern SEZ border, where species like oceanic whitetip sharks, giant manta rays, and olive ridley sea turtles showed the most concentrated risk, indicating high susceptibility to overlap with displaced effort. Scalloped hammerhead sharks and green and leatherback sea turtles faced moderate risk near heavy fishing, while loggerhead turtles and false killer whales showed diffuse risk. These results highlight that while cap-based closures aim to protect a single species, effective Ecosystem-Based Fisheries Management should consider the entire species portfolio in conservation strategies.