Olympia Oysters in the Gorge Waterway

A Natural Native Oyster Hatchery in Your Backyard.

The Olympia oyster is the only native oyster on British Columbia’s coast. These small oysters were an important food source for local First Nations people. Overharvesting and introduction of invasive species have affected the species in many areas. The Gorge Waterway is a unique location where there is a significant, stable population.


Olympia Oysters nestled among surf grass in the Gorge Waterway.

OLYMPIA OYSTER LIFE CYCLE

Reproduction in Olympia oysters is regulated by a temperature threshold which induces 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 and salinity fluctuations and tidal range all have impact on juvenile survival.

Fun Fact! Did you know what Olympia oysters alternate sexes from year to year? That’s right, one year they are female and the next male!

Why We Care

In 2003 the Olympia Oyster was added to the Canadian Species At Risk Act as a species of “Special Concern.” Over harvest and habitat alteration are believed to be the causes for the decline of this species. Despite the lack of harvest since the mid 1900’s, Olympia oysters 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. As they filter water, they remove excess Nitrogen, which is a powerful green house gas in our atmosphere. This means oysters play a part in the climate crisis!

Monitoring

In July 2009, World Fisheries Trust began to examine the population of Olympia oysters that remains in the Gorge. These populations persisted despite years of heavy agricultural, industrial, urban activities and huge fluctuations in temperature and salinity with the tides. All of these factors have caused extirpation in other locations.

  1. May to September, we monitor biweekly and seasonal settlement rates using Pacific Oyster shells.
  2. We have been able to determine the peak settlement time for Olympia oysters.
  3. In the summer we conduct adult Olympia oyster surveys at three index sites in the Gorge Waterway.
  4. We monitor the water quality (temperature and salinity) of the Gorge throughout the year to correlate these factors with oyster survival.

Projects

Craigflower Bridge Olympia Oyster Relocation

An environmental assessment showed the need to relocate the Olympia oysters living on and around the original bridge. During the transplantation process samples from the population were measured for shell size, density, live specimen to shell ratio, and biodiversity. This information was important in creating a data baseline for future monitoring efforts.

The Olympia oysters from the Craigflower Bridge site were transferred to oyster shell reefs at two locations in the Gorge Waterway: Christie Point and near Esquimalt Gorge Park. Unfortunately these were largely silted out by 2017 due to increased levels of silt. Now WFT is searching for alternative options that could raise they oysters out of the mud.

Reefballs

Reefballs are 350lb hollow concrete artificial reefs with large holes to promote water flow. They are known to promote oyster settlement and provide oysters with habitat well above muddy substrates.

In 2017 WFT put three reefballs into the Gorge Waterway to test if they would be a viable option for the Olympia oysters in the Gorge. Initial settlement of any organism was very slow however, in the spring of 2018 growth of various types of algae, tunicates and sponges could be observed from land. In the summer of 2019 we will be doing a full assessment of the Gorge reefballs.

In the spring of 2018 four bare reefballs with bolts for the attachment of settling plates (PVC plates that can be removed and easily monitored for settlement of organisms) were moved to Fisherman’s Wharf in the Victoria Harbour.

Two reefballs covered in algae

Outreach & Education

Our team of educators works with the community to spread the word about Olympia oysters. Our ‘Seaquaria Ocean Education’ education project reaches hundreds of local students every year.