A team of scientists from a Japanese research institute have performed a molecular analysis of shark fins sold in the Hong Kong food trade in an attempt to determine which species are being targeted by the trade.
The trade in shark fins involves a fishing technique known as 'finning' in which the cartilaginous pectoral and dorsal fins are cut off live sharks, which are then thrown into the sea and left to die. The practise is believed to be a contributing factor in the decline of many shark species, but little is known about the species being exploited, as the fins sold come from a number of species and are hard to identify to species level.
Experts from the Joint Institute for Marine and Atmospheric Research and the National Research Institute of Far Seas Fisheries designed a sampling strategy to enable them to collect statistically significant numbers of fins from traders in Hong Kong - the world's largest market for shark fins - that would allow them to access the fins without arousing the suspicion of the traders, who are sensitive to criticism of the trade.
"Our approach to marketplace monitoring of wildlife products is particularly applicable to situations in which quantitative data at the source of resource extraction are sparse and large-scale genetic testing is limited by budgetary or other market access constraints", the authors wrote.
The scientists were able to find shark fins sold under 11 common Chinese trade names, and studied the structure of the fins as well as the DNA of the species to determine which species were being targeted by the trade.
The results showed that a small number of species were being used in the trade, with one species - the Blue shark, Prionace glauca - forming the bulk of the catch:
"Only 14 species made up approximately 40% of the auctioned fin weight. The proportion of samples confirming the hypothesized match, or concordance, varied from 0.64 to 1 across the market categories.
"We incorporated the concordance information and available market auction records for these categories into stochastic models to estimate the contribution of each taxon by weight to the fin trade. Auctioned fin weight was dominated by the blue shark (Prionace glauca), which was 17% of the overall market. Other taxa, including the shortfin mako (Isurus oxyrinchus), silky (Carcharhinus falciformis), sandbar (C. obscurus), bull (C. leucas), hammerhead (Sphyrna spp.), and thresher (Alopias spp.), were at least 2-6% of the trade."
Shark fin soup is a delicacy in China, and in Chinese restaurants around the world, but environmental groups are putting pressure on the public to stop eating the dish to prevent further decline in shark populations. An alternative "imitation shark fin soup" is available at some restaurants, which is made from mung bean vermicelli shaped to resemble shark fin and is served in a chicken broth-like soup.
For more information see the paper: Clarke SC, Magnussen JE, Abercrombie DL, McAllister MK, Shivji MS (2006) - Identification of shark species composition and proportion in the Hong Kong shark fin market based on molecular genetics and trade records. Conservation Biology, 2006 Feb;20(1):201-11.