Microplastics in large marine animals stranded in the Republic of Korea.

Microplastics (MPs) are found in every ocean and are frequently ingested by marine animals. This study analyzed MPs in the stomachs and intestines of 12 large marine animals comprising one fin whale (Balaenoptera physalus), seven finless porpoises (Neophocaena asiaeorientalis), two loggerhead turtles (Caretta caretta), one Indo-Pacific bottlenose dolphin (Tursiops aduncus), and one common dolphin (Delphinus delphis) that were stranded off the Republic of Korea between 2019 and 2021. MPs were detected with a mean abundance of 3.42 ± 3.2 items/g and were predominantly of transparent-white, fragment-shaped polypropylene smaller than 200 µm. The abundance of MPs found did not correlate with the biological information (maturity, body length) of the finless porpoises and there were no significant differences in the abundance of MPs between the stomachs and intestines. These results cannot accurately assess the impact of MPs on large marine animals, so further studies are necessary to understand how MPs can potentially affect them.

Possible link between derelict fishing gear and sea turtle strandings in coastal areas.

Ghost fishing via a derelict fishing gear (DFG) is a critical threat to marine organisms. To explore the effect of DFG on sea turtle strandings, the DFG distribution was compared at two sites on Jeju Island (South Korea) with a contrasting number of strandings. Coastal areas in northern Jeju Island were surveyed during dives with scuba equipment, and the DFG from two sites, Gwideok-ri and Sinchang-ri was collected and compared in terms of quantity and size of the items. Fishing line was more common, longer, and thicker in Gwideok-ri than in Sinchang-ri, while other types of DFG did not differ between the two sites. In addition, necropsies on two loggerhead sea turtles discovered on Jeju Island found fishing lines with fishing hooks in the oral cavity of both carcasses. This suggests that derelict recreational fishing lines may pose a significant threat to sea turtles in coastal areas.

Seafloor litter generated by coastal and offshore fisheries operations in the South Sea of Korea.

Seafloor litter sources, distribution and density were assessed in a bottom trawl survey of the South Sea around Jeju Island by the Ara-ho training ship of Jeju National University. Samples were taken from 14 transects at a depth range of 60-120 m in areas with sandy and muddy substratum. Generally, mean densities varied from 26.9 items/km2 to 62.4 items/km2 and 104.8 kg/km2 to 370.9 kg/km2. Mean densities of total litter sampled was 46.3 items/km2 and 228.6 kg/km2. Derelict gears were the most common litter items (92 % of total litter) with mean densities of 44.3 items/km2 and 228.1 kg/km2. Gillnets and traps were the most derelict with densities reaching 4.9 items/km2 and 99.2 kg/km2 and 25.0 items/km2 and 89.1 kg/km2 respectively. The results of this study indicate that significant level of pollution in the South Sea are generated from commercial fishing activities and gillnets and traps being high risk derelict gears.

First record of plastic debris ingestion by a fin whale (Balaenoptera physalus) in the sea off East Asia.

Marine pollution caused by plastic litter can threaten the survival and health of marine organisms. In 2019, a juvenile fin whale (Balaenoptera physalus, length: 13.02 m, weight 12,000 kg) was found dead floating on the sea near Jeju Island, Republic of Korea. During the dissection, 45 plastic particles were found in the body of the whale, including fishing lines, plastic filaments, pieces of fishing nets, and Styrofoam particles. The largest item found was a piece of fishing line (1180 mm in length and 1.15 mm in thickness). Filaments, both bundled and separated, were more frequent. Some of the filaments found were entangled with the baleen plate bristles. These observations suggest that plastic pollution is a potential risk for baleen whale species. This is the first record of plastic ingestion by a vulnerable baleen whale species in the sea off East Asia.

First record of Ginkgo-toothed beaked whale (Mesoplodon ginkgodens) stranded in Korea.

Two stranded whales were found dead on the coast of Jeju, South Korea. Based on the outer appearance and autopsy findings, one was determined to be an adult and the other a calf. The carcasses were dissected for species identification and pathological examination. A genetic analysis was performed, and the morphological characteristics of the skull observed. Then, 448 bp of the 5' half of the mitochondrial (mt) DNA control region and 413 bp of the mtDNA cytochrome b gene were sequenced. A BLAST search revealed that the whales were ginkgo-toothed beaked whales (Mesoplodon ginkgodens). Morphological comparison of the adult skull with the holotype specimen confirmed the result. This is the first record of a stranded ginkgo-toothed beaked whale in Korea.