Plastic pollution poses a threat to the health and well-being of marine mammals across the globe. This paper takes a previously developed trait-based risk assessment framework and applies it to all 118 species of marine mammals worldwide, to help create a relative ranking of vulnerability of species to plastic ingestion and entanglement. After extensive data collection on 13 traits related to each species’ relative likelihood of exposure to plastics, species sensitivity to plastic ingestion and entanglement, and overall population resiliency, the initial trait framework was adapted and scored to calculate the relative vulnerability of marine mammals to marine microplastic pollution. Results indicate that the Hawaiian Monk Seal has one of the highest relative vulnerabilities to macroplastic pollution among all marine mammals. Furthermore, this exercise highlighted several areas where future research is needed, including expanding the framework to microplastics, applying the framework to coastal human populations, and further investigation of unknown life history traits of various marine mammals.

In an industrialized world that relies heavily on low cost production and packaging produced without a viable end-of-life strategy, the accumulation of non-biodegradable plastics in the environment and particularly the oceans today is an urgent problem of global proportions. Plastics pose a significant threat to marine mammals due to mistaken ingestion as well as potential release of plasticizers and other chemicals. However, the interactions and consequences of ingestion of oceanic plastics by marine mammals have not been thoroughly studied. In this literature review, information regarding plastic ingestion by marine mammals was compiled to estimate the magnitude of adverse impacts and identify major knowledge gaps. Using comprehensive Boolean search terms in Web of Science of literature published between 1960 and 2020, it was determined that there were large discrepancies in the amount of research conducted among 10 different categories of marine mammals, with cetaceans being the primary focus group of most studies (70.3). In addition, different areas of the world, such as southern Africa, were found to have a disproportionately small number of studies on plastic impacts on marine mammalian life in their surrounding marine waters. Differences were found in the amount of plastics ingested by marine animals and a hypothesis of explaining these observations was formulated, attributing potential ingestion of plastic to the debris resembling different food sources in the mammals’ diets as well as different feeding mechanisms.