Genetic diversity and source rookeries of loggerhead turtles Caretta caretta from bycatch and strandings around the Korean Peninsula

Understanding the origins and habitat connectivity of sea turtles with wide habitat ranges is essential for their conservation. Although loggerhead turtles Caretta caretta are found annually in the seas around the Korean Peninsula, their genetic diversity and origins remain unclear. We analyzed partial sequences of the mitochondrial DNA (mtDNA) control region (808 bp) of 62 loggerhead turtles collected in Korean foraging grounds (East, West, South, and Jeju Seas) between 2014 and 2022 to determine their genetic diversity, phylogenetic relationships, and rookery origins. The sampled loggerhead turtles had 5 haplotypes, with haplotype diversity of 0.439 ± 0.075 and nucleotide diversity of 0.00228 ± 0.00052, which originated from 3 Northwest Pacific management units (MUs): Ryukyu Islands (RYI), Yakushima Island (YAK), and mainland Japan (MLJ). In distance-rookery size-weighted mixed stock analysis, mean (±SD) contributions of sampled loggerhead turtles to Korean foraging grounds were 4.2 ± 1.6% for RYI, 71.6 ± 16.7% for YAK, and 24.2 ± 15.2% for MLJ. These contributions varied depending on the season and Korean feeding grounds. Our findings on the connectivity of loggerhead turtles between Korea and Japan highlight the necessity for international cooperation in their conservation.