Ecology of Juvenile Coho Salmon in a Glacial-Fed Estuary: Transitional or Rearing Habitat?

We examined how variability in estuary habitat conditions can be translated into life history variability in coho salmon.  This poster presents preliminary results from our work that focused on site-scale variability in environmental conditions and the resulting patterns of abundance, size, age, and condition in juveniles that occupied channel habitats within a glacial estuary.  We evaluated how abundance and life history traits (age, size, condition) corresponded to seasonal conditions in channel environments.  Juvenile coho salmon were found using the estuary channels throughout the sampling period (early May through late September), and preliminary diet analysis suggests active feeding within these habitats.  Three age classes of coho salmon were found using the estuary habitats, with larger, older fish becoming scarce by the end of June and smaller, younger fish becoming more prevalent. Two kinds of habitats with corresponding differing patterns of use were apparent: transitional refuge habitats (short term use by few age classes, little or less feeding activity) and rearing habitats (long term use by all age classes, greater feeding activity). Patterns of use most greatly correspond with variability in channel depth (covaried with temperature).  These data provide support for our hypotheses that estuary channels serve important roles both as rearing and as and refuge habitats and that these roles are different across various stages of development and potential life histories in coho salmon.  Future work includes determining estuary rearing time and comparisons between patterns of use, phenotypic traits, and corresponding genetic diversity in juveniles occupying glacial and spring-snowmelt fed estuary habitats.