Lost at sea: determining geographic origins of illegally traded green sea turtles (Chelonia mydas) rescued on Hainan Island, China

Context. Green sea turtles are threatened by exploitation for food and medicine markets, with Asian populations facing the heaviest pressures. Sea turtle confiscations that happen out at sea can give a general area that poachers are targeting, but it can be difficult to determine the impact on specific nesting rookeries. Previous studies circumvented this difficulty by using genetic markers to identify nesting rookery origins of confiscated green turtles. Aims. To determine the impact on nesting rookeries from the illegal harvesting of green sea turtles by Hainan fishermen and describe the genetic diversity of the Paracel Islands' green sea turtle population. Methods. In the present study, we sequenced 384 bp of mitochondrial DNA control region from 85 illegally traded green sea turtles rescued on Hainan Island, China, to investigate their population of origin. For reference-source data, we used previously published mtDNA haplotype data from rookeries from Australasian waters and mtDNA haplotype data from 16 newly collected samples from the Paracel Islands in the South China Sea, a previously unsampled area. Key results. Ten and four mtDNA haplotypes, all being reported before, were detected from the Hainan confiscation and Paracel Islands rookery respectively. However, CmP19, an infrequent haplotype that has been found only in 10 green sea turtles previously, made up,45% of our rescued samples and,62% of the Paracel Islands sample, suggesting a potential association between CmP19 and the Paracel Island rookery. Haplotype diversity of the rescued green sea turtles was relatively high (h = 0.7143 +/- 0.04), whereas nucleotide diversity was relatively low (p = 0.0031 +/- 0.00), compared with other rookeries. Mixed-stock analysis suggested that the rookeries in the Paracel Islands (similar to 57%) and the Sulu Sea (similar to 29%) are experiencing the greatest impact from illegal harvesting by fishermen from Hainan and neighbouring countries. Conclusions. The Paracel Islands population contains a unique genetic makeup compared with other studied rookeries, particularly the high frequency of the previously rare CmP19 haplotype. The current harvesting of green sea turtles by Hainan fishermen affects not only protected local populations (Paracel Islands), but also distant populations (Sulu Sea) in protected international waters. Implications. Establishment of a large-scale Sea Turtle Nature Reserve in the South China Sea, including a special law enforcement team to monitor this National Marine Park, needs to be top priority to help curb illegal harvesting. The Paracel Islands represents a newly defined population, and conservation measures need to be taken immediately to preserve this distinct population.