Juvenile green turtles on the northern edge of their range: mtDNA evidence of long-distance westward dispersals in the northern Pacific Ocean

Abstract

Understanding the dispersal pathway and connectivity of an endangered species plays an essential role in the development of strategies for its effective conservation and management. By using mtDNA control region sequences, we identified the genetic composition and estimated the origin of the northernmost feeding aggregation of green turtles Chelonia mydas around the Sanriku coast of Japan. Significant differences in haplotype frequencies between Sanriku and southern Japanese feeding aggregations, a significant correlation between genetic distance and geographical distance in Japanese feeding aggregations, and estimated contribution to the Sanriku, mainly from the Japanese rookery of Ogasawara, indicate compositional changes from the south to the north along the Japanese Archipelago and suggest that the northern feeding aggregations were occupied by turtles born mainly in Japanese rookeries. However, haplotypes specific or similar to Hawaiian and eastern Pacific rookeries were detected, and substantial contributions from Hawaii or the eastern Pacific to the Sanriku feeding aggregation were estimated. Combined with the observation of specimens with phenotypic features of the subspecies ‘black turtle’ nesting in the eastern Pacific, the results indicate the long-distance dispersal of hatchlings born in Hawaii or the eastern Pacific to Japanese coastal waters, possibly through the North Equatorial Current. Although the level of contribution may be small, this study genetically supports the occurrence of the westward long-distance dispersal of green turtles in the Pacific.