Salmon Habitat

Intrinsic Potential: A Tool for Identifying Salmon Habitat at the Watershed Scale

G.H. Reeves, A.L. Bidlack, L.E. Benda, T. Miewald and K.M. Burnett

Ecosystem management requires information on habitat condition across large scales; however, in Alaska comprehensive environmental surveys are often impractical and expensive to carry out. Intrinsic Potential (IP) models provide a means to identify at a large scale those portions of the landscape that can provide essential habitat for various fish species. These models are derived from watershed patterns and processes that operate at broad temporal scales and are not readily affected by human activities. In the lower 48 states, these typically include valley constraint, channel gradient, and mean annual flow. Stream attributes obtained from remotely-sensed data are translated into index scores for each species, based on empirical evidence from the published literature, existing field data, and professional judgment. The IP for a reach is calculated by multiplying the un-weighted species-specific index scores together and then taking the geometric mean of the product. This reflects the assumption that the attributes are approximately equally important and only partially compensatory, and that the lowest index score has the greatest influence on the intrinsic potential. IP modeling has been used to estimate historic distributions of coho (Oncorhynchus kisutch) and Chinook (O. tshawystcha) salmon in Oregon and northern California to prioritize areas for salmonid conservation and restoration efforts, and in the Pacific Northwest, Japan and Taiwan to assess potential land management impacts on salmon populations.

We are developing an IP habitat model for Chinook salmon juveniles in major tributaries of the Copper River in southcentral Alaska, utilizing existing digital elevation models (DEMs), salmon radio telemetry and aerial survey data, expert opinion, and field surveys. Our preliminary model indicates that Chinook juveniles prefer rearing habitats in complex (or braided), low gradient, non‐glacial streams, with medium to high flows. In general, there are greater numbers of Chinook juveniles in areas which have high IP scores, although the variability is also higher in these areas. This model will eventually help resource managers map critical habitat for Chinook throughout the Copper watershed, will help direct field research to appropriate stream reaches, and will assist managers in prioritizing restoration actions, such as culvert replacement. It is our hope that this type of modeling will be broadly applicable and will also inform future research into the ecological impacts of climate change in Alaskan river systems.

© 2011 Copper River Knowledge System