Estuarine Environments As Rearing Habitats for Juvenile Coho Salmon in Contrasting South-Central Alaska Watersheds

For Pacific salmon, estuaries are typically considered transitional staging areas between freshwater and marine environments, but their potential as rearing habitat has only recently been recognized. The objectives of this study were: (1) to determine if Coho Salmon were rearing in estuarine habitats, and (2) to characterize and compare the body length, age, condition, and duration and timing of estuarine occupancy of juveniles between the two contrasting estuaries. We examined use of estuary habitats with microanalyses of sagittal otoliths in two watersheds of south-central Alaska. Juvenile salmon with evidence of estuary rearing were greater in body length and condition than individuals lacking evidence of estuarine rearing. Salmon captured in the glacial estuary had greater variability in body length and condition, and were younger compared with the nearby snowmelt-fed, smaller estuary. Glacial estuary-rearing fish arrived later and remained longer (39 versus 24 d of summer growth) than did fish using the snowmelt estuary. We observed definitive patterns of overwintering in estuarine and near shore environments in both estuaries. This information refutes the notion that estuaries function as only staging or transitional habitats in the early life history of this species.