Early Observations from Monitoring of a Reintroduction Program: The Return of Sockeye Salmon to a Nursery Lake of Historical Importance
The historical distribution of Sockeye Salmon (Oncorhynchus nerka) in the Columbia River Basin has been constrained by the species dependence on nursery lakes for juvenile rearing. Several productive lake systems that were impounded by dams during the last century lead to the extirpation of Sockeye Salmon from many nursery lakes in the region. Recent efforts to re‐establish populations in historically natal areas are exemplified by the Cle Elum Lake reintroduction program. The program is founded on outplanting of adult fish from two donor populations in the middle Columbia River with different adaptive potentials. We used genetic stock identification methods to differentiate stock origins between Osoyoos Lake (OSO) and Lake Wenatchee (WEN) donor stocks, and to evaluate the relative productivity from two brood years (2011 and 2012) of natural spawning in the novel environment. Spawning ground surveys revealed assortative mating between earlier spawning WEN fish that were more abundant farthest upstream and later spawning OSO fish that were concentrated (82%) downstream nearest the lake. Hybrids accounted for only 5% of sampled smolts and 4% of adult returns. Smolts rearing in Cle Elum Lake were significantly larger overall (OSO‐ 140 mm, WEN – 129 mm) than smolts in either donor population (84 mm). However, the average size of OSO smolts varied among emigration years, suggesting slow growth in some years, and relative smolt abundances favored the WEN stock (70% overall), indicative of a rearing survival advantage. In relation, the WEN stock exhibited a better average rate of replacement (0.80) in adult‐to‐adult escapement compared to OSO (0.17). Continued monitoring will focus on trends in productivity and potential demographic shifts that may arise in the Cle Elum Lake population, and will help inform managers concerning limiting factors in the environment that might impact similar approaches to reintroductions in other lake systems.
Matala, A.P., S.R. Narum, B.P. Saluskin, M.V. Johnston, J.E. Newell, D.E. Fast, and P.F. Galbreath. 2018. Early observations from monitoring of a reintroduction program: the return of Sockeye Salmon to a nursery lake of historical importance. Transaction of American Fisheries Society 148(2):271-288. Online at https://doi.org/10.1002/tafs.10133.