Researcher verifies that shark meat can contain excessive mercury

A doctoral researcher has determined that shark meat sold in San José and Heredia can contain high levels of mercury.

The researcher is Jason R. O’Bryhim who studied the shark trade for his doctoral dissertation at Geroge Mason University in Fairfax, Virginia. He defended his work last November.

Among the goals, he said in the dissertation abstract, was that knowledge about contaminants might reduce the demand for shark meat and aid in the conservation of threatened species.

His work was distributed Monday by the environmental organization the Programa Restauración de Tortugas Marinas.

Fish consume methyl mercury when they eat algae because the substance is found in small quantities in sea water. Fish much higher in the food chain, like shark, tuna, swordfish and other predators accumulate the substance.

O’Bryhim reported that he and a colleague collected 170 shark, ray, and fish muscle tissue samples from Costa Rican markets in San José and Heredia over a five-day period in September 2014.

They analyzed the amount of total mercury in each sample using standard U.S. Environmental Protection Agency-approved procedures.

“It is very concerning to find that samples for three shark species tested exceeded U.S. health guidelines,” said O’Bryhim in a release issued by the local environmental organization. “Silky sharks are a special concern since they account for 70 percent of all the shark sold to the public in those markets and a number of the samples tested exceeded the U.S. health threshold.”

“This is yet another reason why Costa Ricans should reduce their annual consumption of 2,000 tons of shark meat, most of which consists of silky shark chops,” said Randall Arauz of the Programa Restauración de Tortugas Marinas and the Turtle Island Restoration Network. “Don’t eat shark. Mercury contamination is a known risk to women and children,” he said in the release.

Total mercury concentrations in the shark products being sold were highest in smooth hammerheads and blacktip sharks, which exceeded U.S. Food and Drug Administration mercury limits of 1.0 part per million for wet weight. Individual samples of silky sharks and scalloped hammerhead sharks also exceeded the FDA threshold, the release said.

Mercury in fish is not new. U.S. residents have been discouraged for years from eating swordfish because it accumulates mercury. The U.S. Environmental Protection Agency urges pregnant women to eat fish like tilapia that are lower in mercury.

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