Native Olympia Oysters
We have been looking after the Olympia oyster population in the Gorge Waterway of Victoria, BC since 2009. The Gorge population is quite large compared to most on our coast. This is likely due to a combination of factors including the large fluctuations in temperature and salinity with the tides and a lack of predation from sea stars and crabs. Due to these tidal fluctuations however, the Gorge oysters don’t grow as large or live as long as they do in other areas, but they sure make up for it in numbers!
Olympia oysters on a rock from the Gorge Waterway
This species of oyster is quite small, growing at most to 9cm in length over the course of their 3-10 year lifespan. They can be found from British Columbia to Baja California in the very low intertidal and high subtidal zones of estuaries, lagoons, bays and channels. They are often found attached to other shells, rocks, docks or pilings.
Their breeding season in BC starts as early as May and goes as late as September. Male Olympia oysters release sperm into the current and the female oysters filter the sperm from the water to fertilize their eggs. The fertilized eggs develop into larvae, which are brooded by the female for approximately 10-12 days before being released – which likely reduces their sensitivity to ocean acidification. Roughly two weeks later the free-swimming larvae attach themselves to hard substrates and within 5 months are able to reproduce.
Olympia oysters start their life off as male but change their sex each year, sometimes multiple times in a single season!
Pollution associated with urbanization, pressures from global warming, introduced oysters that compete for space, introduced predators and invasive fouling organisms are some of the major threats to Olympia oysters. One of the largest issues in the Gorge is sediments that wash down from streams, roads, and subdivisions to settle out in the Gorge. This smothers oysters already struggling to stay above the mud and buries the hard surfaces new oysters require to settle on.
Divers doing an assessment of adult Olympia oysters on the Craigflower Bridge footings
Why do we care?
The Olympia oyster is the only native oyster species on British Columbia’s coast. These small oysters were once an important food source for local First Nations people but over harvesting during the Gold Rush and the introduction of invasive species resulted in population crashes up and down the coast, many of which have never recovered. In 2003 the Olympia oyster was added to the Canadian Species at Risk Act as a species of “Special Concern.”
Oysters are important “ecological engineers.” They filter large volumes of water and provide habitat and food for many other animals. As they filter water for food they help clean the water and incorporate carbon dioxide in their shells, contributing to the fight against climate change.
What are we doing?
From May to September you will find us in the Gorge switching out settling stakes to monitor Olympia oyster recruitment patterns, doing a survey of the adult oysters on the Craigflower Bridge, checking on our artificial reefs and more! We are one of the only NGOs monitoring these oysters in BC making our work crucial to the understanding of how the population changes over the years, compared with environmental conditions, to better predict what is needed for successful restoration elsewhere.
We have been testing enhanced substrates in the Gorge Waterway and at Fisherman’s Wharf. These have included artificial reefs of Pacific oyster shells (2013), reef balls (2017), oyster castles and cut rock (2019). These substrates increase the settling habitat available to Olympia oysters and help raise them out of the mud. Our hope is that they will one day help to increase the total breeding population of Olympia's.
In 2019 we started our first reintroduction project by taking over 400 Olympia oysters salvaged from a boat ramp construction site in Portage Inlet and moving them to an oyster cage at Fisherman’s wharf. Initial results show an 83% survival rate a couple months after deployment. These oysters will continue to be monitored, as will any settlement of new oysters on surrounding substrates. If successful, we will look at reintroducing them into other areas where they were traditionally found.
Eel Grass Planting
Artificial oyster reefs, installed in 2013, got covered in sediment. When they were assessed in 2019 one reef was nearly clear of sediment and full of Olympias, the only change was the growth of eel grass around the reef. In 2020 we partnered with SeaChange Marine Conservation Society to plant eel grass next to one of the sediment-laden reefs in Portage Inlet to see if we can replicate the same results. We are also testing a new way of transplanting eel grass using Pacific oyster shells instead of washers or rebar.
We are part of a coast-wide collaborative of organizations working on Olympia oysters called the Native Olympia Oyster Network (NOOC). This allows us to better compare the Gorge oyster population with those in different environments, as well as keep up to date on restoration efforts elsewhere. It also opens up lots of potential for collaboration!
We have developed both an in-class and a field program on the Olympia oyster and its ecosystem with our sister division, Seaquaria Ocean Education. These programs bring the oysters to you or you to the oysters and focus on different aspects of their lives and ecosystem!