ANACORTES — As empty clamshells crunched and tidal mud squished under their rubber boots, Christine Woodward and Pamela Maxwell scrutinized their finds, looking for signs that the native Olympia oyster is reproducing in Fidalgo Bay.

Woodward, director of natural resources for the Samish Indian Nation, measured the size of each live native oyster. Maxwell, a volunteer with Beach Watchers, a shoreline stewardship group, recorded the measurements and tracked the number of living and dead native oysters.

The two women watched for signs — such as a smaller oyster growing on a larger one’s shell — that the half-dollar-sized bivalves “seeded” in the bay between 2002 and 2006 had reproduced.

“It’s a question of do we have enough seed in the right place to reproduce and repopulate the bay, or do we need to put more out or in a different place,” said Paul Dinnel, a marine scientist who volunteers with the Skagit County Marine Resources Committee.

Dinnel and other volunteers took advantage of low tides earlier this week to check on the progress of the marine committee’s effort to re-introduce the oysters to the bay. They checked at least 14 areas along the trestle on the Tommy Thompson Parkway over the bay.

Known for their slight coppery taste, the Olympia oyster is prized by shellfish lovers, Dinnel said.

“They are definitely good eating oyster,” Dinnel said. “They are a gourmet oyster.”

But the species is in trouble. The number of oysters in Washington has declined from historic levels by as much as 90 percent, said Dinnel, who specializes in marine invertebrates and toxicology at Western Washington University’s Shannon Point Marine Center.

In Canada, the species has been identified as at risk of extinction. But in the United States, no one has petitioned the National Marine Fisheries Service to place the Olympia oyster on the Endangered Species List, according to Brian Gorman, a federal fisheries service spokesman.

Olympia oysters were once found from Baja, Calif., to Sitka, Alaska. In Fidalgo Bay, the native oysters were eaten by indigenous people between 2,400 and 3,400 years ago, according to a 2006 report by Cascadia Archeology, a contractor that evaluated a midden site on the shore.

The hunger of Gold Rush millionaires in the late 19th Century and pollution from paper mills in the early 20th Century decimated the Olympia oyster population, Dinnel said.

“Schooners full of oysters would head south to San Francisco in the gold mining days,” Dinnel said. “They wiped oysters out in San Francisco and worked their way north. An Olympia oyster, which is a small little guy, went for $1 apiece, in those days.”

The annual harvest of Olympia oysters in Washington reached 130,000 bushels by the 1890s, according to The Nature Conservancy. By 1910, the harvest had dropped to 16,000 bushels a year, similar to declines in Oregon and California, according to the conservancy.

Then water pollution took its toll.

“There was enough untreated waste from paper mills in Bellingham to kill oysters living here,” Dinnel said.

The Olympia isn’t the only native oyster species at risk. Around the world, oyster reef habitat has declined by at least 90 percent from historic levels, and 85 percent of the oyster reefs have been lost, according to “Shellfish Reefs at Risk,” a report by The Nature Conservancy. “Based on these data, we conclude that shellfish reefs are one of, and likely the most, imperiled marine habitat on earth.”

The conservancy is calling for resource managers to recognize that shellfish habitats need protecting and have asked government agencies to expand the listing of oysters as an imperiled species.

“Perhaps the biggest challenge is the perception among managers that there is not a problem,” the authors wrote.

The conservancy and the Puget Sound Restoration Fund have partnered to re-introduce the oyster to South Puget Sound.

The Skagit marine resource committee’s project is the first such effort in the North Sound and was funded by the Northwest Straits Commission, Dinnel said. Besides efforts made by marine resource committees and environmental groups, commercial and hobbyist shellfish growers also are working on bringing the Olympia back at various locations in the Sound.

Sheltered from storms and extreme temperature ranges, the firm tidal flats of Fidalgo Bay offer an ideal site for the oysters, Dinnel said. The Skagit committee planted 1.5 million “seeds” of the bivalves in the bay annually from 2002 to 2006, Dinnel said.

Volunteers also shoveled yards of empty Pacific oyster shells into various spots along the bay to provide places for the Olympia oyster larva to attach to and grow. Laboratory tests indicate that oysters prefer to attach to oyster shells, rather than rocks or other structures, Dinnel said.

As the Olympia oyster species re-establish, each subsequent generation of oysters will attach to the shells of deceased or older oysters, forming flat reefs. Pacific oysters build freeform sculptural reefs of the Pacific oyster colonies. Reefs of that species, imported from Japan by shellfish growers, can be seen at Bay View State Park at low tide.

On Wednesday, Dinnel’s volunteers counted all the oysters found in a quarter-meter-square area at one of the sites.

Woodward, who represents the Samish on the Skagit marine resources committee, said that the tribe, the Port of Anacortes and various state agencies have been working hard to improve the bay’s water quality. Recovery of the native oyster beds could be an indicator of improved water quality, she said.

“To the Samish people, being able to harvest native oysters once again will kind of be like recreating what was here during pre-settlement times,” Woodward said. “We’re just really supportive of the efforts of the (marine resources committee) and Shannon Point.”

Over the past few years, volunteers also have placed nylon net bags of oyster shells at various spots, including the Guemes Channel, Padilla Bay and nailing them to the Thompson trestle pilings.

The volunteers later check the oyster bags, counting the new oysters they found inside. They’ve also found native oysters along Crandall spit and other places in the bay that weren’t seeded, Dinnel said. Those are signs that the seeded Olympia oysters have reproduced in the wild.

But Dinnel said that he and the marine committee don’t know whether they have seeded enough oysters or placed them in the best spots to ensure that the bivalves will repopulate the bay without human help. It could take four or five years to have those answers.

“It takes a long time with a population like this,” Dinnel said.

Marta Murvosh can be reached at 360-416-2149 or .