The Last Oyster

The West Coast’s native Olympia oyster serves an important role as an ecosystem builder. But owing to reasons that are still somewhat unclear, over the last few millennia native oysters have largely disappeared from the San Francisco Bay.

May 20, 2014

They’re basically just small rocks out in Bay, stuck to bigger rocks that anchor them in place for their entire lives. The tides come and go, and they just sit there, unmoving and sometimes opening and closing their shells. If you aren’t looking closely, you might think the oyster doesn’t do much at all. But its apparent inactivity belies its true nature: the oyster actually works pretty hard for us.

The West Coast’s native Olympia oyster plays an important role as an ecosystem builder with its ability to filter the water and serve as substrate for other organisms. Its habitat once ranged from Baja California to north of British Columbia.

But owing to reasons that are still somewhat unclear, over the last few millennia native oysters have largely disappeared from the San Francisco Bay.

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Native Americans in the coastal parts of the Bay Area ate shellfish and fashioned the shells into currency, jewelry and tools, and shells of all kinds have been found in mounds and middens dating back 7,000 years.

But there’s a small historical mystery: the farther back you go, the more oyster shell you find. The shift suggests oysters were either declining in importance or declining in abundance well before the Gold Rush.

Oyster shell appears in the archeological record all over the Bay Area, from Tomales Bay down to Montara State Beach in San Mateo County, even in places you might not expect. Like modern-day San Francisco.

Archaeologist Tim Spillane, while surveying for the Golden Gate National Recreation Area, discovered a few unrecorded indigenous sites in the dunes of southwest San Francisco, near Lake Merced. People lived on the high coastal bluffs seasonally, where they had access to nearby wetlands where they could harvest tule plant to make clothing and boats.

On the coast, mussels made up the “lion’s share” of people’s shellfish diet, Spillane said, but according to the archaeological record from the area near Lake Merced, the Yelamu Ohlone clearly preferred the native oyster, thought to be the scarcer of the two shellfish.

“(Merced Valley is) one of the least explored areas in San Francisco –- I think a lot of archeologists assume there’s so much dune movement that it’s a frustrating place to do work because it’s always changing,” he said. “These recent discoveries in the Merced Valley show definitely oyster was native to that area, and no longer are.

Still, oysters remained reasonably abundant in the Bay until the Gold Rush, which brought much greater change: a wave of people with an appetite for oysters moving to California and the peninsular boomtown of San Francisco.

The oysters that the new settlers found in the Bay were different than the ones they were used to. San Francisco oysters were smaller and had a coppery taste, compared to the white meat of the larger Eastern oyster.

In the 1850s, people began bringing shiploads of Olympia oysters from Willapa Bay and Puget Sound in Washington, and planting them in the Central Bay close to San Francisco’s markets. (Even though they were the same species as local oysters, the Washington oysters were larger and had a milder flavor.) By this time, it’s possible local oysters were already becoming harder to find.

Oyster farming in San Francisco Bay was short-lived, though, due to pollution and the completion of the transcontinental railroad, which allowed people to bring in live Eastern oysters.

Around the same time, sediments from hydraulic mining began washing into the North Bay, burying the hard surfaces that make good oyster habitat. Ships brought not only people but invasive species that eat or outcompete the native mollusk.

Once the Pacific oyster from Japan became available to California aquaculture in 1931, farming resumed in the cleaner waters of Drakes and Tomales bays. Interest in the native oyster as a food source waned. But to this day, the population has not recovered.

“After over a hundred years of no fishing, they still haven’t come back,” said Ted Grosholz, a UC Davis biologist who studies ecology and native oyster restoration.

Part of the problem, though, is figuring out how much they’ve declined. “We don’t really have good estimates that would make us happy about what oyster populations looked like prior to the Gold Rush,” he said.

It’s safe to say oysters were relatively abundant pre-Gold Rush, Grosholz said, considering there was an oyster fishery and “people don’t build fisheries for rare species.”

oyster reefs in San Rafael
The artificial reefs on the San Rafael shoreline. (Photo by Stephanie Kiriakopolos, San Francisco State)

While we don’t know perfectly about the oysters of the past, we know enough about the oysters of today to know we want them back. They’re highly desirable for habitat and water quality.

Scientists and government agencies, including Grosholz and the State Coastal Conservancy, want to restore 8,000 acres of oyster reefs by the year 2060. In doing so, scientists believe oysters can improve the health of the estuary by filtering sediments and restoring nutrient cycles for underwater plants. That’s good for everything else up the food chain, from small invertebrates to crab to fish to birds. (I wrote about one such project, the Living Shoreline Project, in the April issue of Bay Nature.)

To do that, we don’t need to know what things were like back then. In fact, the Bay is so altered by human impacts that restoration in the fullest sense of the word is no longer feasible. But that doesn’t mean we shouldn’t try.

“There’s not really a sense that we can restore back to a point of time, even if we know what the point of time is,” Grosholz said. “Restoration isn’t, nor should it be, constrained by what things looked like 100 years ago. The system probably couldn’t support things like they were 100 years ago.”

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