A new study finds that the amount of plastic in the bodies of petrels breeding on Inaccessible Island in the central South Atlantic has remained constant since the 1980s (Photo: Martin Zwick/REDA&CO/Universal Images Group via Getty Images)
A new study finds that the amount of plastic in the bodies of petrels breeding on Inaccessible Island in the central South Atlantic has remained stable since the 1980s.
Researchers from the University of Cape Town's Fitzpatrick Institute of African Ornithology said marine seabirds could be used as indicators of plastic pollution in the oceans.
“For example, in the Northern Hemisphere, [tube-nosed seabirds] “Otters breeding near populated areas contain more plastic than otters breeding in the more remote Arctic,” the researchers said.
The findings were published in the journal. Science of the Total Environment. Global plastic production has been steadily increasing since the 1950s, and the authors predict that the amount of plastic in petrels' bodies will also increase over time.
Large amounts of poorly managed plastic waste have been and continue to be released into the marine environment, where it can remain adrift for years. Due to the physical degradation of plastic products, microscopic plastic particles have become ubiquitous around the world, with particularly high concentrations in the oceans.
Seabirds often ingest these plastic particles either directly or in their food, says Vonica Peroldo, a doctoral student who led the study.
“Among seabirds, the highest plastic ingestion is usually seen in petrels, who can store plastic in their stomachs for weeks or months. In fact, petrels were one of the first organisms found to contain plastic in 1960, and since then, nearly every petrel species that has been studied has been found to contain plastic.”
But despite growing concern about the amount of discarded plastic in marine ecosystems, the evidence of an increase in the amount of floating plastic in the ocean is “mixed,” the researchers said. Both at-sea surveys and the amount of plastic ingested by seabirds show inconsistent evidence of a large increase in the amount of plastic since the 1980s.
The study looked at the amount of plastic in 3,727 skua pellets containing remains from four petrel species. Skuas are predatory seabirds that feed primarily on other seabirds while breeding on Inaccessible Island, and regurgitate the indigestible remains of their prey, including plastic.
This was to monitor changes in plastic loads in four species of petrels breeding on Inaccessible Island in Tristan da Cunha over a nine-year period, from 1987 to 2018.
“The number and proportion of industrial pellets in ingested plastics consistently decreased across all four taxa over the study period, suggesting that industry efforts to reduce pellet leakage have reduced the number of pellets at sea,” the study said.
“Despite a more than four-fold increase in global plastic production during the study period, the total amount of plastic ingested by any species did not increase consistently.”
Perold used samples that have been collected since 1987 by Peter Ryan, professor emeritus at the Fitzpatrick Institute and co-author of the study, who began studying the island as a student.
“Global plastic production increased more than fourfold during the study period, so it is surprising that we did not detect an increase in plastic load in petrels sampled in the same way in the same places for more than 30 years,” Ryan said.
“Our findings suggest that efforts to limit the input of waste plastic into the environment have been at least partially successful, reducing the proportion of plastic ending up in the ocean over this period.”
At the time the study began, dumping plastic into the ocean was still legal and regulations on plastic processors were weak, meaning large amounts of industrial pellets ended up in the sea. Since then, numerous efforts have been made to reduce plastic runoff and clean up the environment.
For South Atlantic seabirds, these measures appear to more or less offset the increase in the amount of plastic currently being produced, the authors found. “Clearly, there is scope for further stringent regulation to reduce the flow of waste plastic, particularly to reduce the amount of plastic used for single-use applications,” Ryan said.
He added that continued monitoring of plastics in seabirds would help determine the effectiveness of further efforts, including the UN plastics treaty currently under negotiation.
The study noted that if global plastic production is the main cause of plastic in the oceans, “the density of floating plastic in the oceans is expected to have increased four to six times between 1989 and 2018.”
“This is in stark contrast to limited changes in plastic loads in Inaccessible Island breeding petrels over this period, and in other long-term studies. Either petrels are not tracking the density of floating plastic in the ocean, or plastic densities in the South Atlantic are not increasing in line with global plastic production.”
Over the past 30 years, there has been growing awareness of the dangers that plastics pose to the environment and many interventions to reduce plastic runoff. “Together, these efforts may explain why the plastic load on seabirds (and therefore drifting plastic in the ocean) has not increased as fast as plastic production has.”
Their study provides further support that the number of industrial pellets at sea will decline in the long term, probably at least in part due to mitigation measures to reduce pellet leakage into the environment.
“Despite a four- to six-fold increase in global plastic production over the last three decades, we have not observed a significant increase in plastic burden in the four seabird species, consistent with other studies tracking the density of floating plastic in the ocean.”
These long-term monitoring studies highlight the value of seabirds as sentinels for ocean health by tracking changes in plastic loads in the marine environment. “Continuous monitoring of trends in plastic pollution is important to assess the effectiveness of interventions and understand the dynamics behind recorded densities in the ocean,” the study states.