Monique Keiran: Native oysters make unexpected comeback

Beneath the quiet surface of the Gorge Waterway and Portage Inlet, life, death and survival play out in a drama affecting a rare, tasty B.C. marine species.

The Olympia oyster is the only oyster species native to the province. Once abundant from Alaska to Panama, it disappeared from much of its habitat by the early 20th century, a victim of its own tastiness, overfishing and waters contaminated with sewage, chemicals and sediment that poisoned and suffocated the oyster beds.

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The fished-out waters included the Gorge Waterway, from which the oyster was considered locally extinct by the 1920s. The state of Olympia oyster populations in the province remains such that Canada’s Species at Risk Act lists it as a species of special concern.

However, the oyster has surprised everyone. Some years back, researchers found the small mollusk had returned to the Gorge.

Individual oysters had cemented themselves onto seafloor reefs in the waterway’s upper reaches, and then multiplied and spread. They even — uncharacteristically for this species — established a colony on the sandy bottom of Portage Inlet. While ecologists, fisheries people and oyster farmers were working hard to re-establish the Olympia oyster up and down the coast and in Puget Sound, the bivalve was quietly creating its own oyster garden of happiness in our backyard.

By 2009, 28 of 31 sites surveyed in the Gorge Waterway and Portage Inlet supported Olympia oysters. They were particularly abundant near the old Craigflower Bridge. Each square metre between the bridge’s pilings contained as many as 400 of the homegrown bivalves, compared to 250 per square metre nearby.

The Gorge now has one of the largest known populations of Olympia oysters in the province.

In the coming weeks, divers will be checking on the most recent, hoped-for expansions to the native oyster beds. Last June, staff and volunteers from the World Fisheries Trust transplanted sections of the oyster reefs out of harm’s way of the new Craigflower Bridge’s construction. New reefs were established just off Esquimalt Gorge Park and at Christie Point in Portage Inlet.

Initial assessments last September indicated mixed results.

“We found a lot of sediment collecting on the patch we’d transplanted in front of the nature house,” says World Fisheries Trust executive director Joachim Carolsfeld. The not-for-profit organization operates out of the Esquimalt Gorge Park Nature House. “But the oysters seemed to be doing fine at the Christie Point site.”

As well, Carolsfeld says, young oysters were settling at the new reefs. This means the reefs were attractive to the oysters.

Only patches of colonies from around the old Craigflower Bridge had been transplanted. The project focused on moving sections that had colonized the bridge’s pilings and where the work on the new bridge would disturb the seafloor. This left most of the original oyster beds untouched. Carolsfeld says divers will also check to see how those are faring, now that the new bridge is open.

The company that replaced the bridge installed screens around the construction site to keep sediment that was stirred up during the work from drifting away from the site. It also hired a fisheries ecologist to monitor the remaining oyster beds’ health.

And the new bridge contains oyster-friendly features. Olympia oysters like shallow, horizontal grooves to attach to and shelter in. Carolsfeld says: “We persuaded the construction company to texture the concrete cladding on the footings in a way that these oysters would find attractive. We hope to see young oysters settling there.”

As oyster-spawning season progresses and draws to a close for the year, the success of the oyster-salvage-and-transplant project will become clear. We will no doubt learn more about what it is that makes the Gorge such an attractive address for our native oysters. And that information will help us ensure this treasured waterway remains a garden of happiness for oysters, as well as for people.  World Fisheries Trust staff and volunteers invite you to visit their displays and mobile aquarium at Fisherman’s Wharf Sunday, as part of World Oceans Day.

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