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Researchers Track Hammerhead Shark Fins To Source Using DNA Barcodes

NEW YORK (GenomeWeb News) – In a paper appearing online today in the journal Endangered Species Research, scientists used DNA barcoding to determine the geographic origin of scalloped hammerhead shark fins being sold by vendors in Hong Kong and to identify genetic subgroups within living sharks in the western Atlantic.

A trio of researchers from Florida's Nova Southeastern University used DNA barcodes based on about 500 base pairs of mitochondrial DNA sequence to determine the haplotype for dozens of scalloped hammerhead shark fins in a Hong Kong market. Their results suggest that the fins came from scalloped hammerheads throughout the Indo-Pacific and Atlantic oceans — including the western Atlantic, where the scalloped hammerhead shark populations are thought to have all but collapsed.

"We found sequence from everywhere, basically," lead author Demian Chapman, formerly at Nova Southeastern University's Guy Harvey Research Institute and now a researcher at Stony Brook University's Institute for Ocean Conservation Science, told GenomeWeb Daily News. "It just attests to the fact that the [fin] trade is sourced from everywhere."

Chapman and his colleagues also improved on existing mitochondrial haplotype classification schemes for western Atlantic scalloped hammerheads, sampling almost 200 living sharks.

An estimated 26 million to 73 million sharks are killed for their fins each year, including between one million and three million hammerheads. Much of the shark fishing that supplies the shark fin markets is unregulated, the team noted, and conservationists are concerned that over-fishing could take a toll on shark populations.

"Inadequate protection, combined with inexorable pursuit, has placed many shark species at grave risk," Ellen Pikitch, a marine science researcher at Stony Brook University and executive director of its Institute for Ocean Conservation Science, who was not directly involved in the research, said in a statement.

For the current study, Chapman and his co-workers used DNA barcodes based on 547 bases of mitochondrial DNA as part of their "genetic stock identification" to track the origin of scalloped hammerhead fins back to their source.

They focused on the scalloped hammerhead because it is in particularly high demand in due to its large fins and ample fin needles, part of the fin used as a thickening agent in shark fin soup.

Past studies suggest scalloped shark populations have already collapsed in parts of the North Atlantic and Gulf of Mexico and the shark has been classified as endangered by the International Union for the Conservation of Nature.

When the researchers sequenced mtDNA from 62 scalloped hammerhead shark fin samples collected from 11 fin traders in a Hong Kong market, they found 18 different mitochondrial haplotypes with some 21 percent of the fins corresponding to haplogroups in the endangered western Atlantic region.

Of the 62 samples tested, 57 belonged to haplogroups identified in previous studies while three resembled Indo-Pacific haplogroups, one was similar to haplogroups in West Africa and another grouped with sharks from the Caribbean. The five new haplotypes clustered very deep within the Atlantic and Pacific groups, Chapman explained, making the classification unambiguous.

To get a better handle on the genetic patterns in the western Atlantic, the team also assessed data for 140 live scalloped hammerheads sampled in the region, incorporating data for 37 samples collected as part of previous studies. In so doing, they identified three distinct groups: a northern group in the US Atlantic and the Gulf of Mexico, a central group found near Belize and Panama, and a southern group near Brazil.

"The fact that scalloped hammerhead shark DNA shows strong population DNA signatures means that we can trace the geographic origin of most of their fins sold at markets," senior author Mahmood Shivji, director of the Guy Harvey Research Institute, said in a statement. "From a broader perspective, this type of DNA forensic testing of fins will be an incredibly useful tool to prioritize areas for conservation and ensure sharks aren't wiped out in particular regions by excessive fishing."

In particular, the researchers would like to see changes to the Convention on International Trade in Endangered Species, or CITES, oversight of scalloped hammerhead and other sharks. Chapman and Pikitch plan to attend next year's CITES meeting in Qatar in March to push for so-called Appendix II designation for six shark species, including the scalloped hammerhead. Such a classification would require permits for international trade of the species.

In the future, the researchers hope to further refine their understanding of genetic patterns in the scalloped hammerhead and other shark populations. And along with mitochondrial patterns, Chapman is also looking at parts of the hammerhead genome that contain evidence of location-specific selection pressures.

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