DNA zip codes helps scientists track endangered sharks

Posted by Lydia Leavitt

With the popularity of shark fin soup in Asia, shark populations all over the globe are being threatened with slow extinction.

Considering sharks swim internationally and others are transported to the Asian market, it’s hard for scientists to track exactly where these sharks come from, and which are at the highest risk of being killed. Searching for a way to protect these sharks, scientists have decided on DNA "zipcodes."

By examining a shark’s DNA makeup, scientists can determine where a shark was born and identify how high the risk is.

"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," said Demian Chapman, assistant director of sciene of Stony Brook University’s Institute for Ocean Conservation Science.

"This research shows that adult females faithfully give birth along the continental region where they were born."

Researchers from across the world took samples of nearly 400 dusky and copper sharks from fishing boats, research cruises, and beach meshing nets as well as from samples found in Hong Kong’s marketplaces.

The two sharks in the study are both extremely popular in Hong Kong and face widespread finning. The International Union for Conservation of Nature labels the dusky shark off the East Coast and in the Gulf of Mexico as endangered, because it has declined by more than 80 percent over the past 20 years despite being protected by 2000. The same organization lists the copper shark as "near threatened."

The findings allow experts to estimate how intensely a certain population of sharks is being targeted by fin trade fishermen. The goal is to ultimately curb finning, a practice in which operators cut off a shark’s fins and toss the "invaluable" body back overboard.

Dusky sharks are in particular trouble because it takes them up to 20 years to sexually mature and reproduce. To add to their low odds of survival, female dusky sharks will only breed and give birth in their own territory.

"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," explained Martin Benavides, who worked on the study and is a research assistant at the Institute for Ocean Conservation Science.

"The sight of a dusky shark swimming off our shores will be a rare experience for generations to come."

(Via Washington Post)