Assessing vulnerability of marine megafauna to global anthropogenic threats

Marine megafauna (large marine vertebrates that are highly mobile and at or near the top of food webs including bony fishes, elasmobranchs, mammals, seabirds, and turtles) are exposed to a wide range of anthropogenic threats both offshore and in coastal regions, especially areas near urban population centers. However, understanding how these threats might affect marine megafauna populations remains a key question in Ecology. We used an expert elicitation approach to quantify the vulnerability of 256 marine megafauna species to 23 anthropogenic threats from four categories: ‘climate change’, ‘coastal (urban) impacts’, ‘fishing’, and ‘maritime disturbances’. We assembled 307 marine megafauna experts from existing global networks and completed a total of 38,962 vulnerability ratings to calculate vulnerability weights for 5,888 species-threat combinations across all individual marine megafauna species and each anthropogenic threat considered. We found that, on average, marine megafauna species have maximum vulnerability weights of 0.740 (out of 1) for a single threat and an average of 0.334 across all threats considered. Across all taxa, species have highest vulnerabilities to temperature extremes, plastic pollution, maritime pollution, drifting longlines, and direct human intrusions. Per taxon and across threat categories, pinnipeds have highest vulnerability to ‘climate change’, turtles to ‘coastal (urban) impacts’, bony fishes, elasmobranchs, and flying birds to ‘fishing’, and all other groups (cetaceans, polar bear, penguins, and sirenians) to ‘maritime disturbances’. However, all taxa face a range of threats from all categories, and the wide breadth of threats per species suggest mitigating manageable threats in coastal urban areas may alleviate the cumulative risk faced by these species across diverse threats. Further, our clear and reproducible methods to evaluate species vulnerability to a diverse set of anthropogenic threats can be applied across species from diverse ecosystems.