‘Zip codes’ keep track of sharks

STONY BROOK (US) — A taste in the Asian community for shark fin soup is claiming tens of millions of animals each year. Now scientists are using shark DNA to determine origins of fins turning up in markets around the world.

An international team of scientists used DNA to determine that groups of dusky sharks (Carcharhinus obscurus) and copper sharks (Carcharhinus brachyurus), both large apex predators living in different coastal regions across the globe, are separate populations of each species.

“By analyzing part of the genome that is inherited solely through the mother, we were able to detect differences between sharks living along different continents—in effect, their DNA zip codes,” says Demian Chapman, assistant professor of marine and atmospheric sciences at Stony Brook University.

“This research shows that adult females faithfully give birth along the continental region where they were born. If fished too much, the population will collapse, and it is extremely unlikely that it will be replenished from immigration of sharks from another region.”

Studies, reported in the journals Endangered Species Research and Marine and Freshwater Research.

Dusky sharks, once common along the U.S. eastern seaboard, showed an 80 percent decline in a recent stock assessment, despite being protected since 2000.

The species reaches the age of maturity at 20 years, has a reproductive cycle that occurs only every three years with a two-year pregnancy, and has relatively small litter sizes, so species recovery is extremely slow.

“Here in the United States, it took only a few decades to nearly wipe out our dusky sharks, and it will probably take a few centuries for their stocks to be replenished,” says Martin Benavides, lead author of both studies and research assistant at the Institute for Ocean Conservation Science.

“Our results dash any hopes that dusky sharks from other areas of the world will replenish the depleted U.S. stock. The sight of a dusky shark swimming off our shores will be a rare experience for generations to come.”

“We know very little about the shark fin trade, but by using DNA-zip coding we can identify source populations that are contributing most to the trade, and prioritize them for management,” Chapman says.

“We, therefore, really need to establish sampling programs of fins on their way to Asia or in the markets to regulate the global trade before many more populations suffer the fate of the dusky shark in the United States.”

More news from Stony Brook University: www.stonybrook.edu/news