Analysis of tracking data for different species of seabird has revealed that a quarter of all plastics potentially encountered while foraging are found in remote international waters.
The extensive study assessed the movements of 7,137 individual birds from 77 species of tubenose, marking the first time that tracking data for so many seabird species has been combined and overlaid onto global maps of plastic distribution in the oceans.
The results, published in Nature Communications, show that plastic pollution threatens marine life on a scale that transcends national boundaries: a quarter of all plastic exposure risk occurs in the high seas. This is largely linked to gyres – large systems of rotating ocean currents – where vast accumulations of plastics form, fed by waste entering the sea from boats, and from many different countries.
Balearic Shearwater was one of the species studied during the research (Kris Webb).
Lizzie Pearmain, a PhD student at the University of Cambridge's Department of Zoology and the British Antarctic Survey, and joint corresponding author of the study, said: "Ocean currents cause big swirling collections of plastic rubbish to accumulate far from land, way out of sight and beyond the jurisdiction of any one country.
"We found that many species of petrel spend considerable amounts of time feeding around these mid-ocean gyres, which puts them at high risk of ingesting plastic debris. When petrels eat plastic, it can get stuck in their stomachs and be fed to their chicks. This leaves less space for food, and can cause internal injuries or release toxins."
Petrels and other species are already threatened with extinction due to climate change, bycatch, competition with fisheries, and invasive species such as mice and rats on their breeding colonies. The researchers say exposure to plastics may reduce the birds' resilience to these other threats.
To get their results, the researchers overlaid global location data, taken from tracking devices attached to the birds, onto pre-existing maps of marine plastic distribution. This allowed them to identify the areas on the birds' migration and foraging journeys where they are most likely to encounter plastics.
Species were given an 'exposure risk score' to indicate their risk of encountering plastic during their time at sea. A number of already threatened species scored highly, including the Critically Endangered Balearic Shearwater, which breeds in the Mediterranean, and Newell's Shearwater, endemic to Hawaii.
Another Endangered species, Hawaiian Petrel, also scored high for plastic exposure risk, as did three species classified by the IUCN as Vulnerable: Yelkouan Shearwater and Cook's and Spectacled Petrels.
Reference
Carneiro, A P B, Clark, B L, Clay, T A, Cowger, W, Eriksen, M, González-Solís, J, Hazin, C, Manica, A, Pearmain, E J, Phillips, R A, & Rouyer, M-M. 2023. Global assessment of marine plastic exposure risk for oceanic birds. Nature Communications. DOI: https://doi.org/10.1038/s41467-023-38900-z
