A global ranking of the relative vulnerability of marine mammals to macroplastic pollution.

Plastic pollution poses a threat to marine mammals across the globe. However, quantitative research on the impacts of plastic pollution in marine mammals is lacking because of the ethical and practical issues that prevent experimentation on these species and the opportunistic nature of observational studies. Trait-based vulnerability indices offer a way to estimate the relative vulnerability of marine species to environmental stressors based on available knowledge about species life-history traits. To develop a relative global vulnerability index to macroplastic pollution for marine mammals (117 species), we applied an existing framework for assessing species vulnerability to macroplastic based on three components of vulnerability-likelihood of exposure, species sensitivity, and population resilience. We identified 11 traits to assess marine mammal species' likelihood of exposure (three traits), sensitivity (four traits), and population resilience to macroplastics (four traits). Using species trait data, we assigned each species a score for each trait. Weighting all three components of vulnerability equally, these scores were summed to provide each species a relative vulnerability score. On average, sirenians were most vulnerable to macroplastic interactions, whereas pinnipeds and fissipeds were least vulnerable, though within-order variation in vulnerability occurred. Through the global application of this vulnerability framework, we highlight its value for informing research and management needs to better reduce the impacts of macroplastic pollution on marine mammals and marine species more broadly.