The number of plastic in petrels breeding at Inaccessible Island in the central South Atlantic Ocean has remained constant since the 1980s, a new study has revealed. (Photo by: Martin Zwick/REDA&CO/Universal Images Group via Getty Images)
The number of plastic in petrels breeding at Inaccessible Island in the central South Atlantic Ocean has remained constant since the 1980s, a new study has revealed.
Marine seabirds can be used as indicators of plastic pollution at sea, the researchers from the University of Cape Town’s FitzPatrick Institute of African Ornithology said.
“For instance, in the Northern hemisphere, fulmars [tube-nosed seabirds] breeding close to densely-populated areas contain more plastic than those breeding in remote Arctic regions,” they said.
The findings were published in the journal Science of the Total Environment. Given the steady increase in the global production of plastics since the 1950s, the authors expected the amount of plastic in petrels to increase over time.
Large amounts of mismanaged plastic waste have leaked into marine environments, and continue to do so. And once at sea, plastic litter may drift for years. The physical degradation of plastic items has led to tiny plastic particles becoming ubiquitous around the world, with especially high concentrations in the sea.
Seabirds frequently consume these plastic fragments directly or in their food, said Vonica Perold, a PhD student, who led the study.
“Among seabirds, the highest ingested plastic loads typically are found in petrels, which can store plastics in their stomachs for weeks or months. Indeed, petrels were among the first organisms found to contain plastics in 1960, and since then, almost all petrel species examined have been found to contain plastic.”
Yet despite growing concern about the large amounts of waste plastic in marine ecosystems, evidence of an increase in the amount of floating plastic at sea has “been mixed”, they said. Both at-sea surveys and ingested plastic loads in seabirds show inconsistent evidence of significant increases in the amount of plastic since the 1980s.
The study examined plastic loads in 3 727 brown skua pellets containing the remains of four petrel species. Skuas are predatory seabirds that mainly feed on other seabirds while breeding at Inaccessible Island, and regurgitate the indigestible remains of their prey – including the plastic they contain.
This was to monitor changes in plastic loads in the four petrel species breeding at Inaccessible Island, Tristan da Cunha, in nine years from 1987 to 2018.
“The number and proportions of industrial pellets among ingested plastic decreased consistently over the study period in all four taxa, suggesting that industry initiatives to reduce pellet leakage have reduced the numbers of pellets at sea,” the study says.
“Despite global plastic production increasing more than four-fold over the study period, there was no consistent increase in the total amount of ingested plastic in any species.”
Perold took advantage of samples collected since 1987 by Peter Ryan, an emeritus professor at the FitzPatrick Institute and co-author of the study, who started researching the island while he was a student.
“Global plastic production increased more than four-fold over the study period, so the failure to detect an increase in the amount of plastic in petrels sampled in the same way at the same site for over 30 years is surprising,” Ryan said.
“Our findings suggest that efforts to limit waste plastic entering the environment have been at least partly successful, reducing the proportion of plastic leaking into the sea over this period.”
When the study started, dumping of plastics at sea was still legal, and lax controls on plastic converters resulted in huge numbers of industrial pellets reaching the sea. Since then, numerous initiatives have been implemented to reduce plastic leakage and clean up plastics in the environment.
For the seabirds in the South Atlantic, the authors found that these measures appear to have more or less balanced the increase in the amount of plastic now being produced. “Clearly there is room for even stricter controls to reduce waste plastic leakage, and in particular to reduce the amount of plastic used in single-use applications,” Ryan said.
He added that continued monitoring of plastic in seabirds will help to determine the efficacy of further efforts, including the United Nations plastic treaty that is being negotiated.
The study noted that if global plastic production was the primary driver of plastic at sea, “we would expect the density of floating plastic at sea to have increased four to six times from 1989 to 2018.
“This is in sharp contrast to the limited change in plastic loads in petrels breeding on Inaccessible Island over this period, and in the other long-term studies. Either petrels do not track the density of floating plastic at sea, or the density of plastic in the South Atlantic Ocean has not increased in line with global plastic production.”
Growing awareness of the dangers posed by plastics in the environment over the past three decades has resulted in many interventions to reduce plastic leakage. “Together, these efforts might explain why plastic loads in seabirds (and by extension, floating at sea) have not increased as fast as the growth in plastic production.”
Their study provides further support for long-term reductions in the numbers of industrial pellets at sea, presumably at least in part from mitigation measures to reduce the leakage of pellets into the environment.
“The lack of marked increases in plastic loads in four seabird species over 30 years, despite four to six-fold increases in global plastic production over this time, is consistent with other studies tracking the density of floating plastic at sea.”
Such long-term monitoring studies highlight the value of seabirds as sentinels of ocean health by tracking changes in plastic loads in the marine environment. “Continued monitoring of plastic pollution trends is important to assess the efficacy of intervention measures and understanding the dynamics behind the densities recorded at sea,” the study says.