Historical evidence indicates that Olympia oysters (Ostrea lurida)† are indigenous to at least three of Oregon's estuaries. Populations of O. lurida occur in Yaquina Bay, Netarts Bay, and Coos Bay, although only the population in Yaquina Bay seems likely to have been continuous since prewestern settlement. The historical occurrence of Olympia (native) oysters in Yaquina and Netarts Bays is confirmed by numerous records of fishery landings. In contrast, historic populations in Coos Bay are inferred by the presence of large shell deposits buried in sediments throughout the polyhaline (salinity > 18–30) region of the estuary. Other Oregon estuaries (such as Tillamook, Alsea, and Umpqua/Winchester Bay) may have had ambient environmental conditions suitable to support self-sustaining populations of O. lurida, but none of these estuaries are currently inhabited by natural populations, nor do they exhibit clear historical records of occupation in the past. We conducted searches of background information on many estuaries to summarize knowledge about the status of O. lurida populations in Oregon. The information presented here is based on a literature search, analysis of internal agency documents, and personal contacts with individuals most familiar with specific estuaries. As a case study, the Oregon Department of Fish & Wildlife (ODFW) repeated intertidal field surveys previously conducted in 1997 in an effort to document changes in O. lurida populations within Coos Bay. Field surveys conducted in 2006 followed methods that were similar to the 1997 intertidal surveys. Using previously published results as a baseline, we found that populations of native oysters exhibited spatial expansion throughout the mesohaline and polyhaline regions of the estuary, and that the intertidal oysters occurred at increased densities, over a wider range of sizes, and over a broader range of habitats. Further recovery of O. lurida populations in other regions of Coos Bay is most likely limited by the availability of suitable substratum for attachment and growth of the juvenile oysters.
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Vol. 28 • No. 1