An Assessment of Juvenile Salmon Feeding Ecology in Alaskan Upland and Lowland Streams Using Stable Isotope Analysis

Over the last 20 years, stable isotope analysis has been applied to ecological studies to analyze food webs and the feeding ecology of many animals from insects to humans. Limited research has used stable isotopes to analyze the feeding ecology of juvenile salmon, with little or no research conducted in Alaskan streams. We aimed to pinpoint basal energy sources and compare food energy pathways to juvenile salmon in wetland and upland Alaskan streams. In particular, we wanted to determine if allochthonous or autochthonous energy contributed more to juvenile coho salmon diets and if their relative importance differed between site types. The study was conducted in 13 streams within the Matanuska- Susitna Valley region of Alaska. Each stream was classified as either wetland or upland based on location, topography, and physical characteristics. Coarse particulate organic matter (CPOM), fine particulate organic matter (FPOM), algae, and fish samples were collected from each of the stream sites and analyzed for dual (carbon and nitrogen) stable isotope analysis. C:N ratio plots and MIXSir mixing models were run for each of the site types in order to determine the relative contribution of each basal energy source to juvenile coho salmon diet. Physical chemical parameters were also measured in each of the study streams. Links between these parameters and differences in salmon stable isotope signatures were examined with Pearson correlation and multiple linear regression analyses. Although juvenile coho salmon rear in very different habitats, we found that allochthonous energy played a key role in wetland streams and is likely important in upland streams as well. The more information that is gathered about the feeding ecology of juvenile salmon, the better researchers and managers will be able to understand the important factors that contribute to rearing healthy salmon populations.