Field measurements reveal exposure risk to microplastic ingestion by filter-feeding megafauna

Combining microplastic data from the California Current Ecosystem with high-resolution foraging measurements from 191 tag deployments on blue, fin and humpback whales, this study quantifies plastic ingestion rates and routes of exposure risk in filter-feeding megafauna. Microparticles, such as microplastics and microfibers, are ubiquitous in marine food webs. Filter-feeding megafauna may be at extreme risk of exposure to microplastics, but neither the amount nor pathway of microplastic ingestion are well understood. 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. We find that baleen whales predominantly feed at depths of 50-250 m, coinciding with the highest measured microplastic concentrations in the pelagic ecosystem. 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. 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. 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.

Automated summary

This study combines microplastic data and foraging measurements on whales to quantify plastic ingestion rates and exposure risk in filter-feeding megafauna. Baleen whales predominantly feed at depths coinciding with high microplastic concentrations, with almost all microplastic ingestion occurring through trophic transfer. Fish-feeding whales are less exposed to microplastic ingestion compared to krill-feeding whales.