An analysis of global tracking data for 77 species of petrel has revealed that a quarter of all plastics potentially encountered in their search for food are in remote international waters – requiring international collaboration to address. Today’s guest blog by Dr Bethany Clark, Seabird Science Officer at BirdLife International, and study’s first author explains.
Our study, published today in the journal Nature Communications, assessed the movements of 7,137 individual birds from 77 species of petrel, a group of wide-ranging migratory seabirds including three species that breed on RSPB reserves in several places around the UK: the Northern Fulmar, European Storm-petrel and Manx Shearwater.
Manx Shearwater adult in flight at sea (c) Greg Morgan (rspb-images.com)
What harm does plastic pollution cause?
Seabirds accidentally eat plastic that resembles their food and ingest plastic that has already been eaten by their prey. This can lead to internal injury, poisoning from toxic chemicals, inflammation from microplastics, and starvation due to blockages or by filling up their stomachs. Petrels are particularly vulnerable because they can’t easily regurgitate the plastic, except for when they inadvertently feed plastic to their chicks.
Plastic pollution is not evenly spread around the world’s oceans. It becomes trapped in enclosed coastal areas and in remote mid-ocean gyres fed by massive currents that transports plastic thousands of miles from the source. Likewise, petrels travel vast distances on their foraging trips and migrations, and they spend more time feeding in specific locations. Petrels are found across the globe and they can be studied when they return to land to raise their chicks, making them important ‘sentinel species’ when assessing the risks of plastic pollution in the marine environment.
Petrels are already one of the most threatened groups of birds due to climate change, bycatch, competition with fisheries, and invasive species such as mice and rats on their breeding colonies. While the population-level effects of plastic exposure are not yet known for most species, exposure to plastics may reduce the populations’ resilience to these other threats.
Where are petrels most exposed to marine plastic?
We overlaid global location data, taken from location tracking devices attached to the birds, onto pre-existing maps of estimated marine plastic distribution. We identified the areas on the birds’ migration and foraging journeys where they are most likely to encounter plastics. We calculated an ‘exposure risk score’ for each species to indicate their risk of encountering plastic during their time at sea.
Our study found that many species of petrel spend a lot of time in high plastic density areas including around remote mid-ocean gyres. The five areas of highest plastic exposure risk are in the Mediterranean and Black Seas; the north-east Pacific; north-west Pacific; South Atlantic and the south-west Indian oceans.
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, the Hawaiian Petrel also scored high for plastic exposure risk, as did three species classified by the IUCN as Vulnerable: the Yelkouan Shearwater, which breeds in the Mediterranean; Cook’s Petrel, which breeds in New Zealand, and the Spectacled Petrel, which only breeds on an extinct volcano called Inaccessible Island, part of the Tristan da Cunha archipelago, a UK Overseas Territory.
Cook's Petrel is already classed as Vulnerable (c) Paul Donald
Even species with low exposure risk such as the Northern Fulmar and Snow Petrel have been found to eat plastic by previous studies. This shows that plastic levels in the ocean are a problem for seabirds worldwide, even outside of these high exposure areas.
This is 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. This dataset allowed a big leap forward in our understanding and has provided priorities for conservation and future research. The next steps are to investigate the links between exposure, ingestion and impact. We recommend new plastic ingestion and tracking studies for species in data-poor areas, such as southeast Asia and parts of the Pacific.
International collaboration required.
The Pacific, Atlantic, and Indian oceans have mid-ocean gyres full of plastic waste, where many species of threatened seabird forage. Much of the plastic in these areas is concentrated in the high seas – areas beyond the jurisdiction of any one country. Many petrel species risked exposure to plastic in the waters of several countries and the high seas during their migrations. We found that 25% of exposure risk across all 77 species occurred in the high seas, and the majority of plastic exposure risk occurred outside of the waters of the country where the birds breed.
Due to ocean currents, plastic debris often ends up far away from its original source, highlighting the need for international cooperation to tackle marine plastic pollution, both directly from boats and from plastic waste on land reaching the oceans.
Solutions could include reducing the use of disposable plastics, improving recycling and waste management, and improving compliance with the existing ban on discarding any plastic from boats. Regional treaties and global treaties on plastic and biodiversity in national waters and the high seas are important for applying solutions on the large scales needed.
Acknowledgements
The study was led by a partnership between BirdLife International, the University of Cambridge, and the British Antarctic Survey, in collaboration with Fauna & Flora and the 5 Gyres Institute. The study was made possible by the collaboration of over 200 seabird researchers around the world, including scientists from the RSPB and other BirdLife partner organisations around the world: SEO/BirdLife (Spain), SPEA (Portugal), LIPU (Italy), BirdLife Malta, BIOM (Croatia), BirdLife Norway, Nature Seychelles, Mauritian Wildlife Foundation and Birds Canada.
This research was funded by the Cambridge Conservation Initiative’s Collaborative Fund for Conservation, sponsored by the Prince Albert II of Monaco Foundation, and the Natural Environment Research Council.
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