Tracking the Confiscated Green Sea Turtles in the South China Sea: Where Did They Come From? Where Will They Go?

The population of the green sea turtle (Chelonia mydas) is under decline, threatened by bycatch and illegal acquisition despite worldwide protection efforts. However, the confiscation of illegally acquired sea turtles could aid in tracking their origin and movement patterns, crucial for effective conservation strategies. Combining satellite tracking and genetic analysis offers an opportunity to investigate the relationship between the origins and migration directions of green sea turtles in the western Pacific. Here, we applied two methods to investigate the spatial ecology of 18 green turtles caught as bycatch in the South China Sea. Our results revealed the genetic origins and diverse movements of the turtles. Bayesian Mixed Stock Analysis (MSA) suggested that these turtles originated from the rookery of the Xisha Islands (49.6%), central Ryukyu (24.6%), NE Borneo (8%), and the Sulu Sea (5.2%), with other rookeries in meagre proportions (<2% each). Satellite tracking showed the ranges of their travel were smaller than the whole contributed rookery range, but diverse. The haplotype diversity of these turtles is high, and CmP19 stands out as both the most frequent and the most diverse haplotype in terms of swimming destinations. These results indicate that the South China Sea is likely an important transportation hub and mating spot for green turtles. Our findings provided evidence for the rehabilitation of these green turtles in the wild and illustrated the complexity of movement during the green turtle’s life history, and the “mixed backgrounds” of the green turtles also highlight the need for joint conservation efforts of neighbouring countries in the South China Sea.