The incidence of plastic in the diets of Antarctic seabirds

We investigated the diets of seabirds at sea in the Antarctic from 1976 to 1988. During the study period, on eight cruises in the Ross, southern Scotia, and Weddell Seas and Drake Passage, we collected or pumped the stomachs of 1,223 seabirds of 23 species. The stomach contents of species that feed below the sea surface contained little plastic, as expected; these birds live entirely on live prey. Among species that feed a t the surface, most of which eat both live and dead organisms, incidence of plastic was highest among the smaller ones and those that are omnivores, or feed on zooplankton and micronekton. This includes the majority of Southern Ocean flighted birds. Incidence of plastic among them was a function of the degree to which their populations frequented waters outside of the Antarctic during the winter. Among those species that live south of the Antarctic Convergence year-round there was little evidence of plastic ingestion. Among those species that are summer visitors to the Antarctic, incidence of plastic in the diet decreased with increased latitude. These results indicate either that the Antarctic Convergence blocks plastic debris, which is commonly found a t the sea surface in the north, from entering the Southern Ocean, or that other factors such as the northward movement of pack ice sweeps the sea clear of plastic. Results also suggest that floating plastic debris is not yet the problem in the Antarctic that it is in more northern waters.