Genetic composition of loggerhead turtle feeding aggregations: migration patterns in the North Pacific

The loggerhead turtle Caretta caretta is highly migratory and undertakes trans oceanic migrations. In the North Pacific, loggerhead turtles that hatch on Japanese beaches reach the vicinity of Baja California in the eastern Pacific. As they grow, they return and recruit to the feeding areas around Japan. By using mtDNA control-region sequences, we identified the genetic composition of the feeding aggregation around the Sanriku coastal area (n = 107), > 500 km north of the main nesting beaches of Japan and located on the north of the Japanese mainland. Performing a mixed-stock analysis using the published data from 5 Japanese nesting rookeries ( n = 279 in total) as sources, the origin of the feeding aggregation was estimated with Bayesian statistics. The results indicated a high contribution from the southern rookeries (mean >= 82.10%), mainly the Yakushima rookery (mean >= 51.45%), to the Sanriku feeding aggregation, whether the number of nests was considered as an informative prior or not. Therefore, the Sanriku coastal area is estimated to be utilized by loggerhead turtles born in the southern nesting rookeries relatively far from Sanriku. The strong connectivity between loggerheads from the Sanriku feeding aggregation and the southern Japanese rookeries suggests that loggerhead turtles in the North Pacific generally settle in the Japanese coastal areas in the large juvenile stage, but not in the direct vicinity of their natal sites, and some juveniles that use an oceanic feeding strategy are recruited to the Sanriku coastal area.