Canadian and American researchers are studying harbour seals to find out what kind of contaminants are polluting the water.

The harbour seals along the B.C. and Washington coasts are ecosystem sentinels offering clues to the health of the oceans.

Tiny samples of blood, blubber, hair and skin will tell researchers about pollutants in the waters in which the seals feed.

Researchers take a blood sample.

"These harbour seals are telling us what types of persistent chemicals are circulating in the environment and accumulating in high concentrations at the top of the food chain," said Peter Ross of the Department of Fisheries and Oceans.

The seals are surrogates or stand-ins for a much more vulnerable species: the killer whale or orca.

Canada has declared the whales moving between southern Vancouver Island and Washington state endangered. There are 82 left – a drop of 20 per cent in less than a decade.

Biologists need more data to explain the decline so they're turning to the seals, who share the whales' space and snacks.

"Any chemical that we find in a killer whale or a harbour seal is coming from their food," said Ross. "So the key, or the secret, to finding where their contaminants are coming from is studying their diet."

Steve Jeffries of the Washington state Department of Fish and Wildlife said the main study area in southern Puget Sound is contaminated with PCBs.

British Columbia contributed dioxin and furan pollutants until pulp mills were forced to clean up in the 1980s.

But the orcas eat salmon that grow fat in the open Pacific, far from the local sources.

Ross compared juveniles as they swam downriver to the ocean to adult salmon returning to the river years later. He found 98 per cent of the chemicals in their flesh were acquired after they left their spawning grounds.

The results suggest salmon are importing contaminants from the Pacific Ocean, which receives a steady plume of contaminants transported in the atmosphere from Asia.

Scientists say once the pollutants are emitted into the atmosphere, no one can do much to fight them.

Ross and his colleagues will examine the samples to see if any of the chemicals are produced or used in North America, and whether they remain unregulated.