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Study identifies Morro Bay Estuary as site to restore native oysters

Grassy Bar Oyster Company grows Pacific oysters in Morro Bay. They occasionally see native Olympia oysters.
Beth Thornton
Grassy Bar Oyster Company grows Pacific oysters in Morro Bay. They occasionally see native Olympia oysters.

A recent study identifies Morro Bay Estuary as a priority location for restoring the native Olympia oyster population through conservation aquaculture. It's a project that unites shellfish lovers and conservationists on the Central Coast.

April Ridlon, a post-doctoral researcher at UC Santa Barbara, said oysters are not as charismatic as other marine organisms she has studied, but they are a foundation species — meaning they create a habitat for other animals that live on or near their shells. They are also a source of food for crabs, birds, and humans.

Ridlon said Olympia oysters are native to the West Coast, but populations have struggled since the 1850s.

“Originally, Olympia oyster populations declined during the Gold Rush era because people who came to California and the West Coast searching for gold, also found delicious Olympia oysters and went about eating their way through Olympia oyster populations,” Ridlon said.

She recently published a study on using conservation aquaculture techniques to replenish the population.

“The way our group is defining conservation aquaculture is any type of aquaculture that supports conservation goals and species recovery for wild populations of native species,” Ridlon said.

A small number of Olympia oysters still exist, but Ridlon said the numbers are so low that some intervention is needed.

“Just like we used captive breeding programs to bring the California condor back from the brink of extinction, for example, aquaculture techniques can be used to rapidly increase the number of oysters that are in a particular estuary or at a particular site, so that the population can sustain itself,” Ridlon said.

Beth Thornton

The study identified ten priority locations where conservation aquaculture might support both oysters and people. Ridlon evaluated the sites for water quality, oyster populations, community engagement, and more.

The Morro Bay Estuary made the list. Lexie Bell, executive director of the estuary program, is not surprised.

“The Morro Bay Estuary is recognized as an estuary of national significance in the Clean Water Act. Our bay represents many important, unique natural areas,” Bell said.

Bell said increasing native oyster populations aligns with their goals to restore natural habitats and support wildlife. They are in the early stages of researching the project.

“Having a robust oyster population would help maintain clean water here, and help the bay be more resilient,” Bell said.

She said there is a long history of oyster farming in Morro Bay, and that local commercial farmers share the goal of clean water.

“In order to be able to have an economic endeavor where they can sell oysters, the water in the Bay needs to be clean enough to support that, so from the perspective of the estuary program, the ability to even permit oyster aquaculture is an indicator of clean water,” Bell said.

George Trevelyan, owner of Grassy Bar Oyster Company, raises oysters in the mudflats of Morro Bay.

“We manage the beds so there’s always young ones coming up, and we protect them from predators by growing them in mesh pouches,” Trevelyan said.

Trevelyan grows Pacific oysters to sell at his oyster bar and market, and to local restaurants. He said Pacific oysters are not native to the California coast. He does, on occasion, see an Olympia oyster.

“There are native oysters already here in Morro Bay, but they are rare, and few and far between,” he said.

Trevelyan’s process for farming starts with a quarter million tiny oysters from a hatchery flown in from Hawaii. He grows them in a protected nursery under the dock. We took a look inside:

“I’m going to open up one of these hatches here, this is a good example because the red tape one has new babies that were planted in August, they’re about a 1/4 inch long or 1/8 of an inch long. In this one, they arrived and looked like that in May, and now that it’s September, they’re ready to go to the grow out area,” Trevelyan said.

The grow out area is the approximately 150-acres of mudflats where Trevelyan is permitted to operate his business. The oysters will grow for another year or more before they are ready to harvest and sell.

Trevelyan said Olympia oysters are delicious, and he’s definitely interested in restoring and growing the native population.

Whether that happens is yet to be determined. Kevin Marquez Johnson is a California Sea Grant aquaculture specialist and teacher at Cal Poly San Luis Obispo. He said the first step is to bring stakeholders together.

“From people that work in the area to the Chumash, Indigenous First Nations, we’re looking to bring them into the conversation at the ground floor level to say, “how do we do this here?” Johnson said.

He said the next likely step is to move a few of the existing Olympia oysters to a hatchery.

“We can bring them into a hatchery facility like the one that we’re building at the Cal Poly pier in Avila, where we would be able to do the spawning in controlled conditions. Then those animals would be the ones actually planted in Morro Bay as the restoration effort,” he said.

Johnson said restoring the native oyster population in Morro Bay Estuary is a lengthy process, but he’s confident something can happen in the next five years.

This story is made possible by a grant from the Community Foundation of San Luis Obispo County.

Beth Thornton is a freelance reporter for KCBX, and a contributor to Issues & Ideas. She was a 2021 Data Fellow with the USC Annenberg Center for Health Journalism, and has contributed to KQED's statewide radio show The California Report.
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