OLYMPIA OYSTERS IN THE GORGE
The Olympia oyster is the only native oyster on British Columbia’s coast. Traditionally these small oysters were an important food source for local First Nations people and from the late 1800s until the 1930s they were harvested commercially. Introductions of non-native oysters (e.g. Pacific, Atlantic and European flat oysters) - starting in the 1910s - have brought diseases and parasites that may also have affected Olympia oyster populations. Historically, Olympia oysters were found in many bays and lagoons along the BC coast, but today few locations exist with healthy native oyster populations. The Gorge Waterway is one of these unique locations where there is a significant, stable population.
OLYMPIA OYSTER LIFE CYCLE
Reproduction in Olympia oysters is regulated by temperature threshold which induce spawning. After fertilization, larvae are brooded in the mantle cavity for 10 to 12 days and released as veliger larva into the water column. The specific cues for settlement are unknown, however, the availability of hard substrate and presence of conspecifics may play a role. Recruitment of juvenile oysters - known as spat - are affected by the vertical and longitudinal gradient at which they settle. Stressors such as air exposure, temperature fluctuations and tidal range all have impact on juvenile survival.
WHY WE CARE
British Columbia's only native oyster, the Olympia oyster, is found right here in the Gorge Waterway and Portage Inlet. In 2003 this species was added to the Canadian Species At Risk Act as a species of "Special Concern." In the past, these small oysters were an important food source to local First Nations people. They were also commercially harvested in the late 1800's and early 1900's. Overharvest and habitat altercation are believed to be the causes for the decline of this species. Despite the lack of harvest since the mid 1900's, Olympia oyster numbers have not rebounded to historic numbers.
Oysters are important "ecological engineers." They filter large volumes of water and provide important habitat and food sources for many other animals.
WHAT WE'RE DOING
In July 2009, World Fisheries Trust started a project to examine the population of Olympia oysters that remains in the Gorge despite years of heavy agricultural, industrial, and urban activities – factors that have caused extirpation in other locations.
Over the summer months of May to September, we monitor biweekly and seasonal settlement rates at three key sites on the Gorge using stakes consisting of Pacific oyster shells - a hard substrate known to promote Olympia oyster settlement. We have been able to determine the peak settlement time for Olympia oysters throughout this time period, and infer environmental and physical factors impacting their settlement, growth, and overall survival. We are currently analyzing the 2016 data.
Our dedicated team also monitors the water quality of the Gorge throughout the year to correlate these factors with oyster survival. We measure temperature, salinity, turbidity.
In partnership with Environment Canada's Habitat Stewardship Program for Species at Risk
Due to the construction of the new Craigflower Bridge, an Olympia oyster relocation project was required in the Gorge Waterway during the spring of 2013.
An environmental assessment highlighted the need to relocate the particularly high density of Olympia oysters living on and around the original bridge. World Fisheries Trust has been monitoring the Gorge Waterway population of Olympia oysters for many years and was granted the contract for this relocation.
Desired outcomes from relocation project:
- Relocate Olympia oyster population endangered by Craigflower Bridge construction
- Encourage Olympia oyster population stability and growth by creating quality habitats for future larvae settlement and maturation
- Determine Craigflower Bridge oyster demographics including size variance, population density, and general biodiversity of area
- Monitor survivorship and relocation outcome for five years
The Olympia oysters from the Craigflower Bridge site were transferred to two locations in the Gorge Waterway: Christie Point and near Esquimalt Gorge Park.
Throughout the transplantation process samples from the population were measured for shell size, density, live specimen to shell ratio, and biodiversity. These parameters are important in creating a data baseline that will be used in future monitoring efforts.
Outreach & Education
Our team of educators works with the community to spread the word about Olympia oysters. Our 'Seaquaria In Schools' education project reaches hundreds of local students every year.