A global meta-analysis of gillnet bycatch of toothed whales: Mitigation measures and research gaps

Odontocetes are globally distributed and are foundational to the structure and function of marine food webs, and hence bycatch impacts from gillnet fishing need to be considered in the context of their conservation and population viability. Currently, global gillnet bycatch numbers are unknown yet are estimated to be the greatest in Asia, East Africa, and the west coasts of North and South America. Here we provide the first global meta-analyses of small- and large-scale gillnet bycatch estimates of odontocetes during 1990-2020, compiling population size, estimated gillnet bycatch, and conservation status in support of geographical and species-specific risk estimates. We estimate that annual gillnet bycatch is ∼50,000 from 1990 to 2020, and, combined with overfishing, pollution, and noise, it has been shown to be a serious threat to these long-lived and slow-reproducing species with heavy offspring investment. The global gillnet bycatch of odontocetes is a difficult challenge to address and mitigate and requires improved species and regional-based management strategies including collaborations between fishers, fisheries managers, marine mammal experts, and marine spatial planners. This has been worked on for decades, yet more attention is needed for successful management of odontocete gillnet bycatch to ensure their sustainable future in the Anthropocene Ocean, in accordance with local subsistence dynamics and the relevant United Nations (UN) sustainable development goals.