Quantification and characterizations of plastic debris ingested by sea turtles in Korean waters

Global production of plastics has steadily increased since 1950s. As a result, plastics are the most abundant type of marine debris on seafloor and coastal beach, and the prevalence of marine debris has detrimental impact on marine wildlife. The Convention on Biological Diversity (CBD, 2012) estimated that over 80% of adverse environmental impacts on marine life are associated with plastic debris. It is important to build up information on the amount and characteristics of plastic debris that damage marine species to devise strategies and set priorities to reduce their adverse impacts on marine life. This study investigated plastic debris ingested by sea turtles stranded, floating, or by-captured from 2012 to 2022 in the Korean coastal waters. The quantity, shape, color, size, origin, and polymer type of plastic debris (> 1 mm) ingested by sea turtles were analyzed after being sorted from gastrointestinal (GI) tract of 71 turtles: 41 loggerheads, 24 greens, 3 leatherbacks, 2 olive ridleys, and 1 hawksbill turtle. We found a very high frequency of occurrence of plastic debris in GI tract of sea turtles; 100% for greens, 83% for loggerheads, 67% for leatherbacks, 50% for olive ridleys, and 100% for hawksbill. The overall amount of plastics were in the range of 0－1.31 g/kg turtle (0－229 pieces/turtle). The ingested debris tended to be films and fibers (> 74%), light in color (white and transparent; > 60%), and light polymers (polyethylene, polypropylene, polypropylene[poly(ethylene:propylene)], expanded polystyrene; > 90%). Single-use or fishery-related plastics such as filmed packaging, plastic bags, twine, net, and rope were frequently found. Some debris were labeled with Korean (n=14), Chinese (n=10), English (n=2), and Vietnamese (n=1). The shape and origin of ingested debris varied between loggerhead and green turtles. Green turtles ingested commonly fibers (47%) such as rope, twine, and net. Conversely, loggerheads ingested frequently films (45%) such as plastic bag, and packaging. The difference in ingested plastics between greens and loggerheads may be related to feeding habit and geographical range of movement of each species. This study implies that sea turtles inhabiting around the Korean waters are severely affected by marine plastic debris, and that waste management of single-use and fishery-related plastics should be the top priority to effectively reduce the adverse impact of plastic debris on sea turtles.