A quantitative risk assessment approach for longline fishing gear impacts on seafloor habitats

Bottom longline fishing gear used worldwide to capture fish and invertebrate species can impact seafloor habitats, leading to increased use of spatial closures (e.g., MPAs) in areas where habitat risks are considered high. However, such closures often rely on limited data, because fishing impacts on habitat are rarely quantified and fine-scale habitat maps are often unavailable. In this paper we develop fine-scale species distribution models for coral and sponge habitats and demonstrate a quantitative risk assessment framework for habitat impacts from bottom longline trap and hook fisheries, using the British Columbia Sablefish fishery as a case study. We estimate a 4% (95%CI: 2-7%) reduction in coastwide sponge habitats due to Sablefish fishing from 1965 to 2024, compared to pre-fishery levels. Habitat status at finer spatial scales of 1 km2 shows similar trends to the coastwide aggregate status, with habitat declines less than 10% for 99% of fishing grounds. Our analysis provides fine-scale information on habitat distribution and the impacts from Sablefish longline trap and hook fishing gear, providing key information for conservation planning and fisheries management. Our risk assessment approach provides quantitative metrics (relative benthic status) for ecosystem objectives focused on fishery impacts on habitat. Such habitat metrics can be incorporated into fisheries management strategy evaluation, allowing resource managers to compare performance of alternative strategies against a broader suite of sustainability objectives that include habitat, fish stocks, and fisheries catch.