It was April 2017 in a large fish market northwest of Mumbai. Shark fins destined for China were piled onto tables, with a good dose of blood to go around. Tens of millions of sharks are killed for the fin trade every year, primarily destined to become shark fin soup, and a quarter of the world’s sharks, rays, and chimaeras (a cartilaginous fish also known as ghost sharks) are considered to be threatened. The international trade in many species is prohibited, but it can be nearly impossible for law enforcement, and even for experts like Shaili Johri, a post-doctoral biology researcher at San Diego State University, to tell whether the fins are from protected species once they’re