The Influences of Body Size, Habitat Quality, and Competition on the Movement and Survival of Juvenile Coho Salmon during the Early Stages of Stream Recolonization

Abstract

AbstractUnderstanding the factors influencing the success of juvenile Pacific salmon Oncorhynchus spp. in newly colonized habitats is essential to their recovery in large areas across the West Coast of the United States and Canada. We studied biotic and abiotic factors associated with survival during the early stages of colonization and population establishment of juvenile coho salmon O. kisutch in Rock Creek, a tributary of the upper Cedar River in the Lake Washington basin of Puget Sound, Washington. The stream was occupied by resident fishes (e.g., rainbow trout O. mykiss, cutthroat trout O. clarkii, speckled dace Rhinichthys osculus, and several sculpins Cottus spp.), but adult coho salmon and other anadromous fishes had been excluded by a dam from 1901 until fish ladder installation in 2003. We defined logistic regression models and used an information‐theoretic approach to predict apparent survival with various combinations of individual fish condition, location competition, and local habitat quality. The best‐approximating models included measures of brood year, body size, habitat, and migration timing. Survival was positively associated with body size and habitat quality and negatively associated with competition. Survival from late summer to smolt migration varied among years (mean ± SD = 27 ± 11%) and was significantly higher within Rock Creek (73 ± 11%) than during seaward migration in the Cedar River and Lake Washington (38 ± 14%). Juvenile coho salmon established a population and outnumbered resident salmonid species by 40% in the lower 2 km of Rock Creek within 5 years of colonization. Overall, the results revealed the linkage between the colonization success of juvenile coho salmon and the biotic features and habitat quality in a newly accessible environment during the stream‐rearing phase of their life history.