Captive dolphins have less toxic mercury than wild animals

Study by JHU, National Aquarium suggests different diet explains contaminant levels

  • Sue Hunter, the National Aquarium's director of animal programs and marine mammals, checks a dolphin.
Sue Hunter, the National Aquarium's director of animal… (George Graul/National…)
May 22, 2012|Tim Wheeler

People aren't the only ones at risk from eating mercury-contaminated fish, since coal-burning power plants have liberally sprinkled the toxic metal across the earth's waters.  But it appears that captive dolphins have a little less to worry about in that regard than their wild counterparts.

A new study by researchers from Johns Hopkins University and the National Aquarium in Baltimore found that the aquarium's captive bottlenose dolphins have lower levels of mercury in their bodies than wild dolphins tested off the Atlantic and Gulf coasts of Florida.

Mercury is a potent neurotoxin. High mercury levels have been linked to liver abnormalities in stranded Atlantic bottlenose dolphins and with infectious diseases in stranded harbor porpoises.

Differences in contamination levels likely stem from differences in diet, researchers said. The aquarium dolphins were fed capelin and herring caught in North Atlantic waters off Newfoundland and New England, where mercury in the water is relatively low.  Much higher mercury levels were measured in wild dolphins tested off Indian River and Sarasota in Florida, where in-state power plants have been blamed for higher mercury levels in the environment.

The study, published in a recent issue of Science of the Total Environment, found a smaller difference in mercury contamination between the aquarium dolphins and animals tested off the coast of South Carolina. Researchers cautioned that the findings are limited by the relativley small number of dolphins tested, just seven from the Baltimore facility.

“This is just one snapshot, one puzzle piece,” said Edward Bouwer, co-author of the study and chairman of JHU's geography and environmental engineering departments. He and the other researchers, including lead author Yong Seok Hong of JHU, would like to compare mercury levels in other aquarium dolphin populations with wild counterparts.

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