Evaluating the application of scale frequency to estimate the size of pangolin scale seizures

Abstract

All eight species of pangolin are principally threatened by overexploitation, both for international trafficking and local use. Much illegal trade involves scales, but there is an absence of robust conversion parameters for estimating the number of different pangolin species in given seizures. Such parameters are critical in order to accurately characterize pangolin trafficking and understand the magnitude and impact of exploitation on populations. In this study, we calculated the number of scales on 66 museum specimens representing all eight extant pangolin species from the genera Manis, Phataginus, and Smutsia, and developed a method for estimating the number of pangolins in given seizures of scales based on scale frequency. Our statistical analyses found significant variation in scale number in inter-species terms (ranging from 382 for Temminck's ground pangolin to 940 for the Philippine pangolin), and in intra-species terms, with substantial variation in the giant pangolin (509–664 scales) and minimal variation in the Chinese pangolin (527–581 scales). We discuss application of the developed sampling method in a real world context and critically appraise it against existing methods. The knowledge generated in this study should assist in understanding pangolin trafficking dynamics, though there remains a need for accurate conversion parameters for estimating the number of pangolins in illegal trade, especially for the Indian and African species.