Little change in plastic loads in South Atlantic seabirds since the 1980s.

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. Both at-sea surveys and ingested plastic loads in seabirds show inconsistent evidence of significant increases in the amount of plastic since the 1980s. We use 3727 brown skua Catharacta antarctica regurgitations, each containing the remains of a single seabird, to monitor changes in plastic loads in four seabird taxa breeding at Inaccessible Island, Tristan da Cunha in nine years from 1987 to 2018. Frequency of occurrence in plastic ingestion and types were compared across four near-decadal time periods (1987-1989; 1999-2004; 2009-2014 and 2018) while loads were compared among years. 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. 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. Plastic loads in great shearwaters Ardenna gravis, which spend the austral winter in the North Atlantic Ocean, increased in 2018, but the proportion of shearwaters containing plastic decreased. We conclude that the density of plastic floating at sea has not increased in line with global production over the last 30 years.