The Origins of Lake Washington Sockeye Salmon: What Can Genetic Data Tell Us?

Currently, four well-established populations of sockeye salmon (Oncorhynchus nerka) spawn in the Lake Washington basin. These include beach spawners (primarily at Pleasure Point), and populations spawning in the Cedar River, Issaquah Creek, and the Sammamish River tributaries (principally Bear Creek). The origin of the Bear Creek population (i.e., native or non-native) is uncertain. Historical records of sockeye in Bear Creek are limited, and the genetic data, though suggestive of a native origin, are not conclusive. Early reports (Evermann and Meek 1898; Rathbun 1900; Evermann and Goldsborough 1907) indicate that O. nerka spawned in Lake Washington’s tributaries at the turn of the century. Most of these reports are now believed to be of kokanee, the nonanadromous form of O. nerka (Shaklee et al. 1996). The presence of kokanee suggests that anadromous sockeye must have inhabited the basin at some time in the past (Wood and Foote 1996), perhaps even in the early 1900’s. Nonetheless, these populations may not have survived the dramatic changes to the watershed following the 1916 completion of the Lake Washington ship canal, which permanently dried the lake’s former outlet (the Black River, a tributary of the Duwamish) and established the Ship Canal as the watershed’s only link to the Paciflc. Such changes might reasonably have had negative impacts on any contemporary, anadromous sockeye populations, and, indeed, the few historical records from that period suggest that anadromous sockeye were not present in the Lake Washington drainage during the 1920’s and ‘30’s (Cobb 1927; Rounsefell and Kelez 1938). This suggests that sockeye inhabiting the basin today descended entirely from introduced flsh from Bake