High frequency of occurrence of anthropogenic debris ingestion by sea turtles in the North Pacific Ocean

Ingestion of anthropogenic debris can have deleterious effects on sea turtles. To study diet content of sea turtles, four species were opportunistically collected as deceased bycatch over 18 years (1993–2011) from pelagic longline fisheries based in American Samoa and Hawaii (North Pacific between 140°–170°W and 20°S–50°N). Diet contents were analyzed from 71 sea turtles: 45 olive ridleys (Lepidochelys olivacea), 22 greens (Chelonia mydas), 2 loggerheads (Caretta caretta), and 2 leatherbacks (Dermochelys coriacea). This study reports some of the highest frequencies of anthropogenic debris ingestion documented for sea turtles, with 83 % of all the sea turtles sampled ingesting anthropogenic debris. Within species, 91 % of greens and 82 % of olive ridleys ingested anthropogenic debris. This is the first published report of anthropogenic debris ingestion by olive ridleys outside of the Atlantic Ocean. Neither of the leatherbacks ingested anthropogenic debris. The average dry weight of anthropogenic debris ingested by individual olive ridleys and individual greens was 4 and 7 g, respectively. The total dry weights of anthropogenic debris ingested by the two loggerheads were 9 and 120 g. Plastics were the most prominent anthropogenic debris ingested, making up 95 % (405 g dry weight) of the total 427 g ingested. Increased ingestion of anthropogenic debris was found in olive ridleys collected during the winter, which corresponds with the wintertime increase in anthropogenic debris accumulated in the North Pacific Subtropical Convergence Zone. This study highlights the need to better understand the factors affecting anthropogenic debris ingestion and its sublethal effects.