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RESEARCH PRODUCT

Assigning Elephant Ivory with Stable Isotopes

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The international ivory trade remains one of the world’s most controversial wildlife trade issues. One of the main arguments for the trade prohibition is the fact that it is very difficult to distinguish legal from illegal ivory in the markets, so that the legal ivory trade would provide a perfect cover for smuggling. The purpose of this study was to analyze the variability of isotope ratios in ivory samples from Appendix I and II elephant populations in Africa to validate their potential for forensic purposes more quantitatively. We selected a subset of 293 data of ivory samples from the www.ivoryid.org database that stores isotopic ratios of δ13C, δ15N, δ18O, δ2H, and δ34S from more than 500 geo-referenced ivory tusks. In order to address the problem of cutting natural variation due to limited sample size, we calculated the mean and standard deviation for each CITES Appendix statistical population and simulated n = 1000 isotopic ratios per class. We then applied the k-nearest neighbor (NN) rule as pattern classification algorithm and cross-validated the data. Our results showed that the geographic structure of isotopic signatures of current CITES listing of elephant populations is about nine times more informative than the random case. Therefore, our isotope-based results are promising for the aim of classifying elephant ivory according to its regional provenance under current CITES listing of elephant populations. Where knowledge of isotopic differences between elephant ivory is important for conservation activities and better control of contrabanded ivory trade, cost-effective isotopic markers and the statistical methods examined here may be used.