"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 Dr. Demian Chapman, leader of the research team and assistant director of science of the Institute for Ocean Conservation Science. "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."
This is precisely what has happened along the U.S. Eastern Seaboard, where the once common dusky shark is now rare and a species of concern for listing under the Endangered Species Act. At one time, these animals were common in ocean waters off the United States; however, a recent stock assessment of the sharks along the U.S. East Coast and in the Gulf of Mexico showed an 80 percent decline even though they have been protected since 2000. The recovery of the species is extremely slow because the average age of maturity is 20 years, its reproductive cycle only occurs every three years including a two-year pregnancy and its litter size is relatively small (three to 14 offspring).
"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," said 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 lit
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Stony Brook University