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


The Swinomish Indian Tribal Community (SITC) recently began a restoration project to establish, expand, and research Olympia oyster (Ostrea lurida) populations on Reservation tidelands. Olympia oysters are the only native oyster to the Puget Sound region and they traditionally played an important role in tribal culture. Yet, due to overfishing, pollution, and the widespread cultivation of non-native Pacific oysters (Crassostrea gigas), only ~5 % of their original population (circa 1850) remains in Puget Sound. In 2012 we began a small-scale O. lurida restoration project on Swinomish tidelands. The success of this pilot project encouraged us to expand our restoration project in terms of size and research effort. This larger restoration project has several broad objectives which include (1) developing a monitoring plan, (2) enhancing current native oyster populations and habitat in pocket estuaries, (3) establishing a long-term habitat monitoring survey, (4) investigating future oyster enhancement sites, and (5) disseminating information on SITC Olympia oyster restoration. We specifically used funding from CREOi to address components within Objectives 2, 3, and 5.

Oyster reefs can take decades to form because oyster larvae prefer to settle on previously existing oyster beds. Because fishing practices for oysters typically involve removing shell, overfished reefs and their related communities have struggled to recover even after cessation in fishing pressure. Indeed, lack of suitable habitat (i.e. oyster shell) is one of the main limitations to our Olympia oyster restoration efforts. To address this problem (Objective 2), SITC purchased enough UV-treated cultch to triple the size of our current restoration area. We anticipate that our pilot project oysters will be able to seed the cultch, helping us meet our goal of eventually creating a self-sustaining source population of native oysters on Reservation tidelands.

In the spring of 2015, SITC staff began surveying a set of metrics to assess restoration and enhancement success (Objectives 2 & 3). One key aspect of this monitoring included measuring reproductive benchmarks to determine population expansion potential. Our goal was to quantify the timing and environmental setting for peak brooding of oysters in the pocket estuaries. Brooding status was recorded weekly from May to early September 2015, capturing the entire reproductive cycle of the oysters. Also, surface water temperature and salinity were continuously logged using HOBO loggers at each of the two restoration sites. Our data clearly indicate that northern Puget Sound oysters located in pocket estuaries can begin brooding before May when daily temperatures are as low as 11°C, 2°C below the published thermal threshold. Olympia oysters in Lone Tree and Kiket Lagoons showed signs of reproduction during the first sampling event in early May. Peak brooding activity occurred in early June and the last brooding individual was observed in early September. These data were presented in a poster at the Pacific Coast Shellfish Growers Conference in September 2015.

OLYMPUS DIGITAL CAMERAOur team was able to fulfill our outreach goal (Objective 5) by designing and installing two interpretative signs at the Swinomish Marine Interpretive Center. These signs describe the historical importance of native oysters as well as current restoration efforts. Furthermore, our technician was able to present the results of the brooding study at the Pacific Coast Shellfish Growers Conference in September 2015. It is our hope that these educational opportunities will increase awareness and understanding of native oysters, which will lead to wider support and encouragement for additional restoration efforts and the sustainable management of this invaluable resource. ($10,300)