Sound’s harbor seals help scientists track pollutants

TACOMA – For more than three decades, scientists have been rounding up harbor seals from Puget Sound, drawing their blood, sampling bits of blubber and running other tests to check for signs of disease.

Their goal: to track how harmful concentrations of toxic chemicals are affecting the animals’ health.

For researchers trying to pin down the scope and effects of toxic contamination, harbor seals perform a canary-in-a-coal-mine service, said Peter Ross, a Canadian marine mammal toxicologist, who collaborates with state fish and wildlife scientists in Washington.

“They are the laboratory animal of the ocean around here,” Ross said.

The sleek, spotted critters – the state’s largest population of marine mammals – have helped biologists create Puget Sound’s longest scientific record of pollution in aquatic animals.

Over the years, scientists have found harmful concentrations of toxins like PCB, or polychlorinated biphenyl, an industrial compound that can cause cancer, in the blubber of seals. PCBs have been shown to affect seals’ metabolism and make them vulnerable to illness, scientists say.

Some researchers recently found a link between South Sound harbor seal contaminants and impaired immune system response. In addition to making harbor seals more vulnerable to disease, chemical contaminants appear to be affecting the animals’ thyroid hormones, Ross said.

Disease-causing bacteria – likely waste runoff from people and livestock – also affect the seals.

Harbor seals don’t migrate, and they are reclusive. They shy away from people and can be fierce, making it difficult to examine them up-close. So every fall, biologists go out in fast boats and use strong nets to catch them. Researchers haul the seals to shore, hold them still, then brand them.

“By branding animals we get to follow individuals throughout their lifetime. It’s a mark they don’t lose,” said Harriet Huber, a biologist at the National Marine Mammal Laboratory in Seattle.

The federal Marine Mammal Protection Act has safeguarded seals since 1972. It requires federal officials to manage marine mammals based on population work such as Huber’s. Scientists in Canada and Alaska used to base their analyses on animals that were killed.

The statewide seal population numbered about 5,000 in 1970, said Steve Jeffries, who coordinates a state Fish and Wildlife Department team of marine mammal biologists. It began to recover after passage of the Marine Mammal Protection Act, which banned killing.

Concentrations of contaminants in south sound seals have declined since the 1970s, but scientists say the levels remain high enough to cause harm.

Also, newer chemicals, like flame retardants, have begun to show up in harbor seals. “The big concern is that not only are there still legacy contaminants, but new ones are being created and used that are essentially unrestricted, but similar to ones that have been banned that we know cause problems,” Jeffries said.