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Restoring an endemic species to native tidelands: Olympia oysters in Swinomish pocket estuaries

Water property monitoring

This project is a continuation of a 2015 CREOi award.

Historically, Olympia oysters (Ostrea lurida) played an important ecological and cultural role as Washington’s only native oyster. In 2012, the Swinomish Indian Tribal Community (SITC) and regional partners began a small-scale Olympia oyster restoration effort on the Reservation’s tidelands with the intention of eventually establishing self-sustaining populations that could act as larval sources for the surrounding waters in the northern Whidbey Basin. Restoring native oyster beds does not just restore the population of oysters alone; instead, the return of these ecosystem engineers will help to reestablish the ecological community that likely co-evolved with these oysters.

In 2016, CREOi funds were used to purchase 34 bags of shell seeded with Olympia oysters from the Puget Sound Restoration Fund hatchery. This added approximately 17,340 oysters to each of SITC’s two restoration sites. The award also allowed SITC to continue monitoring water properties to quantify the temporal variability of conditions at the restoration sites and as a continuation of the baseline habitat assessment outlined in the Swinomish Olympia Oyster Monitoring Plan. Water property data were collected using HOBO temperature/conductivity loggers, sampling at 15-minute intervals. Additional weekly water property spot measurements were taken at the two enhancement sites and the surrounding bays (using a YSI 6920 sonde) by a summer intern from Northwest Indian College.

In early spring and late summer 2016 water temperatures were warmer than the previous year. Interestingly, the daily minimum water temperature at both sites reached 12°C 20 days earlier in 2016 relative to 2015. Warming water temperatures in the early spring could have cued the Olympia oysters to begin spawning in mid-April, earlier than SITC had expected from a previous survey. December 2016 also differed from the same period in 2015, with significantly colder water temperatures recorded at Lone Tree lagoon. Daily average salinity levels ranged from a low of 11 during the wet season to 26 psu.

Spot measurements revealed a positive relationship between water temperature and dissolved oxygen levels in the lagoons versus a more neutral relationship in the adjacent bays. Typically, as water temperatures increase the ability to hold oxygen decreases. Elevated levels of dissolved oxygen in the lagoons could be due to relatively higher phytoplankton productivity. Marine organisms, including Olympia oysters, can be sensitive to severe fluctuations in environmental parameters and further work is warranted to ensure our restoration sites will be able to provide suitable habitat into the future. ($10,400)