![]() ![]() In many ecosystems, forage fish and zooplankton-the most common prey items of baleen whales-are regularly found to ingest microplastics, as the sizes of microplastics and the biological particles available for consumption are similar 23, 24, 25, 26, 27. The foraging behavior of filter-feeding megafauna including baleen whales is driven by the presence of dense but ephemeral patches of prey 21, 22. Recent studies investigating stomach contents and fecal samples from baleen whales agree that plastic ingestion is ubiquitous, but disagree on the magnitude of plastic consumption 19, 20 (Table 1). Baleen whales (Mysticeti) are perceived to be at high exposure risk of microplastic ingestion due to their diet, habitats, and filter-feeding behaviors 16, 17, 18. ![]() While some taxa have been extensively studied for plastic ingestion, including marine fish 13, sea turtles 14, and seabirds 15, this information is limited for marine mammals, particularly cetaceans. This ingested plastic may have deleterious effects on marine consumers however, most of these threats are poorly understood 12. For top predators in particular, secondary ingestion of plastics via trophic transfer can be a dominant exposure route 11. Wildlife can confuse plastic for food but may also inadvertently ingest plastic that is adjacent to, attached to, or within food items. However, the route of exposure, the extent, the effects, and the bioaccumulation of ingested plastic are understudied or unknown in most natural systems.ĭetermining exposure route and intensity are crucial first steps to projecting risk and mitigating harm for individuals and populations. At least 1500 species have been reported to ingest plastic 9, particularly microparticles including microplastics (plastic pieces 0.001–5 mm) and microfibers (pieces 0.8–0.9 mm with a median diameter of 16.7 µm) 10. Plastic consumption by wildlife, either directly by ingestion from the environment or indirectly via trophic transfer from prey, has become a pervasive phenomenon since plastic debris was first reported in marine food webs half a century ago 7, 8. ![]() Plastic production and disposal has risen more than twentyfold over the last half century and is projected to worsen through at least 2050 5, 6. The Anthropocene Ocean is marked by the rapid proliferation of pollution, including noise 1, chemical 2, biological (e.g., biotoxins and pathogens) 3, and plastic pollution 4. For species struggling to recover from historical whaling alongside other anthropogenic pressures, our findings suggest that the cumulative impacts of multiple stressors require further attention. Per day, a krill-obligate blue whale may ingest 10 million pieces of microplastic, while a fish-feeding humpback whale likely ingests 200,000 pieces of microplastic. Nearly all (99%) microplastic ingestion is predicted to occur via trophic transfer. We predict that fish-feeding whales are less exposed to microplastic ingestion than krill-feeding whales. We find that baleen whales predominantly feed at depths of 50–250 m, coinciding with the highest measured microplastic concentrations in the pelagic ecosystem. Here, we combine depth-integrated microplastic data from the California Current Ecosystem with high-resolution foraging measurements from 191 tag deployments on blue, fin, and humpback whales to quantify plastic ingestion rates and routes of exposure. Filter-feeding megafauna may be at extreme risk of exposure to microplastics, but neither the amount nor pathway of microplastic ingestion are well understood. Microparticles, such as microplastics and microfibers, are ubiquitous in marine food webs.
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