Longitudinal Patterns of Juvenile Coho Salmon Distribution and Densities in Headwater Streams of the Little Susitna River, Alaska

Headwater streams contribute to overall production and life history diversity in river systems. These relatively small streams represent an alternative rearing habitat for juvenile fish, including Coho Salmon Oncorhynchus kisutch. To determine the extent that juvenile Coho Salmon use headwater habitats, we used a spatially continuous sampling approach to investigate the distribution and density patterns of juvenile Coho Salmon in three headwater streams of the Little Susitna River, Alaska. We related the distribution patterns to environmental and biological variables, which are important for informed management of this species. Juvenile Coho Salmon were continuously distributed along the length of headwater streams, with upstream limits of 4-5km from the main stem, at about 250m elevation, with slopes between 4% and 5%. For all juvenile Coho Salmon, elevation and dominant substrate type (e.g., boulders) were negatively related to fish density; both variables may be related to adult spawning habitat and the proximity of juveniles to their point of emergence. Age-1 Coho Salmon, which overwinter in the Little Susitna River basin before smolting, represented only 2% of all juvenile fish captured; no environmental variables related to age-1 fish density. Yet, their presence in the headwater streams represented an opportunity to determine what factors relating to conservation and fisheries management (i.e., culverts) may limit their distribution. Headwater stream habitats may increase the variability in life history and juvenile traits, and given ongoing climate change and human development this type of variability is likely to be increasingly important for the persistence and continued productivity of this population of Pacific salmon.