Stable isotope analysis successfully identifies wild-caught individuals of threatened Asian freshwater turtles in illegal trade

Laundering of wild-caught animals as captive-bred is a frequent practice in the illegal wildlife trade. Stable isotope analysis is a promising tool for distinguishing wild and captive-bred animals. We use Hong Kong freshwater turtles to test the effectiveness of using stable isotopes to differentiate wild and captive-bred individuals. In this study, we compared five stable isotope signatures (δ¹³C, δ¹⁵N, δ³⁴S, δ²H, and δ¹⁸O) in claw samples across four highly threatened species: Cuora trifasciata, Mauremys reevesii, Platysternon megacephalum, and Sacalia bealei. We found non-overlapping δ¹³C and δ¹⁵N values for all species; combined δ¹³C and δ¹⁵N isotopic profiles resulted in a 100 % accuracy in identifying the sources of turtles. Through repeated sampling of seized P. megacephalum, we estimate 95 % turnover rates of 46.3 months for δ¹³C and 32.8 months for δ¹⁵N, suggesting that wild-caught individuals can be identified up to two years after capture. Lastly, we apply the stable isotope method in true wildlife seizures. These seizures are unique because some individuals possessed microchips from our long-term population study, so were unambiguously from the wild. The isotopic profiles of seized turtles clustered with those of wild populations, providing forensic evidence that supported the prosecution of suspects for illegal trade and/or possession. Overall, our study demonstrates the effectiveness of δ¹³C and δ¹⁵N in differentiating wild and captive freshwater turtles. We advocate for using isotopic profiling in future seizures and expanding its application to more taxa and geographic locations to support wildlife trade management and prevent illegal exploitation of wild organisms globally.