The Mediterranean and Black seas are among the most dangerous areas for threatened seabirds where they are at the greatest risk of ingesting or being entangled in plastic pollution, research suggests.

An international study has found that a quarter of all plastic exposure risk occurs in the high seas – areas that are not part of the territorial sea – which also includes the north-east Pacific, South Atlantic, and the south-west Indian waters.

The researchers said they found this risk to be “disproportionately high” for threatened seabird species who often travel long distances for food as well as migration.

Outside the high waters, they said plastic exposure risk was also highest in areas of the sea under the territorial ownership of the US, the UK, and Japan, also known as Exclusive Economic Zones.

The study, published in the journal Nature, is based on the tracking data from 77 species of petrel, a group of migratory seabirds including the Northern Fulmar, the European Storm Petrel, and the critically endangered Newell’s Shearwater.

The researchers said remote areas, such as the middle of the ocean, can accumulate plastic debris as a result of large systems of rotating ocean currents known as gyres.

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.”

Seabirds can mistake small plastic pieces for food, or ingest plastic that has already been eaten by prey, causing injury, poisoning and starvation.

Some often end up entangled in plastic while looking for food.

Petrels are particularly vulnerable because they cannot regurgitate the plastic easily, the scientists said.

Ms Pearmain said: “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.”

For the study, the researchers assessed the movements of more than 7,000 individual seabirds – including shearwaters, fulmars, and prions – to create maps of plastic concentration across the oceans worldwide.

Study co-author Dr Maria Dias, a researcher at the Centre for Ecology, Evolution and Environmental Changes at the University of Lisbon, said: “The data allows us to conclude that the risk is not uniformly distributed, as a result of the accumulation of plastic in areas where ocean current and tides favour it.

A Great Shearwater
A Great Shearwater (Bethany Clark/BirdLife International)

“When both regions overlap [high concentration of birds and plastic], the risk is much greater.”

They found that threatened species — such as Balearic shearwater, Newell’s shearwater, and Hawaiian petrels — have greater risk because of the structure of their digestive tracts.

Based on their findings, the experts said international cooperation is essential to address the issue.

Dr Bethany Clark, seabird science officer at BirdLife International and joint corresponding author of the study, said: “Many petrel species risk exposure to plastic in the waters of several countries and the high seas during their migrations.

“Due to ocean currents, this plastic debris often ends up far away from its original source.”

European Storm Petre on the water
The study is based on tracking data from 77 different species including the European Storm Petrel (AGAMI Photo Agency / Alamy Stock Photo/PA)

Commenting on the study, Dr Louise Gentle, a wildlife conservation expert in Nottingham Trent University’s School of Animal, Rural and Environmental Sciences, said: “This is a very timely study, highlighting the need for global goals such as Nature Positive where organisations pledge to halt and reverse biodiversity loss.

“Plastic ingestion or entanglement can be lethal.

“This study demonstrates that certain species are more susceptible to plastic pollution than others, due to their ecology, feeding behaviours and movements.

“The study used tracking devices to identify areas where the seabirds are foraging and see if these coincide with areas of high plastic pollution such as the Mediterranean sea or gyres, where debris accumulates.

“Microplastics have been found in every single species that I have looked for them, from bats to badgers to barn owls.”