A Potential Enforcement Tool for Regulating Trade in Tortoises: Stable Isotope Analysis

Abstract

Tortoises of the genus Testudo are imported to the UK in large numbers. It is currently legal to trade both wild-caught and ranched Testudo horsfieldii, however there are incentives to fraudulently claim wild-caught specimens as ranched. In addition, only captive-bred Testudo graeca and Testudo hermanni specimens can be traded legally. Currently, it is difficult to ascertain the breeding source of tortoises in trade and a forensic tool that distinguishes between them is called for. I verified that tortoise scute keratin can be non-invasively longitudinally sampled for stable isotope analysis. I sampled 30 T. horsfieldii specimens that died on import to the UK and found that whilst they were from a single batch they clustered into two groups. I associated these groups with a known morphological measure of breeding origin (degree of scute pyramiding) and compared the two nominal groups using general linear mixed models (GLMMs). I found differences in δ15N at all ages of growth, and in δ13C and δD in old growth. I also longitudinally sampled 8 mature T. graeca and 4 mature T. hermanni specimens of unknown origin, and 1 mature T. graeca and 2 juvenile T. hermanni known to be imported. GLMMs revealed a shift in δD, δ13C and δ15N between old and recent growth of T. graeca but not T. hermanni specimens. δD of the T. hermanni specimen known to be imported did however appear to differ between old and recent growth. The greatest potential for stable isotope analysis as a regulatory tool for the tortoise trade appears to be in determining 1) if batches of captive specimens also include wild-caught individuals, and 2) if wild-caught specimens have been fraudulently claimed as UK captive-bred. However, the majority of specimens available for this thesis were of unknown origin so the conclusions I have drawn are based on assumptions and conjecture and will need further testing. Stable isotope analysis can be used to distinguish between individuals that have experienced different conditions, and it has potential to facilitate understanding of the scale of the illegal tortoise trade and identify areas to which further resources should be directed.