Shark finning continues seemingly unabated, despite some gains in protection for threatened shark species. The scope of the trade is staggering, more than 70 million fins per year are thought to move globally. What species are targeted for these fins? This is a difficult question. Once removed from the shark and stripped of their skin, fin identification to a certain species is difficult. The authors of this work undertook an enormous task, the genetic identification of 4800 fins offered for sale in Hong Kong seafood districts during 2014-2015. The composition of species in the shark fin trade was last assessed in Hong Kong during 1999-2001, so they asked if and how the trade has changed since then.
The authors avoided purchasing shark fins by analyzing the “trimmings” left behind when fins are prepared for sale. They visited 334 of the 373 stores selling shark fins in two Hong Kong markets, obtaining 480 bags of trimmings from 92 shops, and randomly sequencing 10 samples per bag. (Think about this for a moment — in two markets in a single Asian city there are 373 shops selling shark fins!) They performed a barcoding procedure, sequencing a region of the mitochondrial cytochrome oxidase I gene that can identify a tissue to its species.
They found 76 different species of sharks, rays and chimeras represented, and 1/3 of these were species are listed as Vulnerable or Endangered by the IUCN. Most prominent were blue sharks, comprising one third of the samples, followed by silky sharks, which represented 10% of the fins. The two species of rays identified were both guitarfish, a batoid that has large dorsal fins. They found equal numbers of small and large sharks, and while many of the species were coastal, 50% of the trade was in oceanic sharks.
The numbers and representation of the 6 most prominent shark species, and their IUCN status are:
Blue shark (Prionace glauca), 34% of fins, Near Threatened
Silky shark (Carcharhinus falciformis), 10% of fins, Near Threatened
Scalloped hammerhead shark (Sphyrna lewini), 4% of fins, Endangered
Blacktip sharks (Carcharhinus limbatus, amblyrhynchoides, leiodon, tilstoni), 4% of fins, Near Threatened
Smooth hammerhead shark (Sphyrna zygaena), 3% of fins, Vulnerable
Shortfin mako shark (Isurus oxyrinchus), 3% of fins, Vulnerable
Interestingly these were the same species represented in the 1999-2001 study. To explain why these vulnerable species have not been fished out over the intervening nearly 20 years, the authors suggest that as one region is depleted of sharks the fishers may simply move to different areas to find their desired species. The authors note that the majority of these heavily traded species are managed in no or few areas, and they suggest ongoing monitoring of the fin trade composition could detect incipient population declines and/or a hopefully positive effect of recent conservation measures.
The paper is: Fields AT, Fischer GA, Shea SKH, Zhang H, Abercrombie DL, Feldheim KA, Babcock EA and Chapman DD. (2017) Species composition of the international shark fin trade assessed through a retail-market survey in Hong Kong. Conservation Biology, DOI: 10.1111/cobi.13043