SaSI Stock Distribution
The SSHIAP method for mapping fish distribution is designed to document fish use by stream segment at the 1:24,000 scale for each SaSI stock. The SSHIAP approach starts by compiling information from stream surveys, StreamNet, the WDF Stream Catalog, Watershed Analyses, Washington Conservation Commission (WCC) Limiting Factors Analyses, and field biologists. Known fish distribution includes habitat that is documented to presently sustain fish populations and areas that have historic records of fish use, even if the fish have been extirpated. In addition, SSHIAP uses stream segment data to identify presumed fish distribution, which includes stream segments that have no records of fish use but that are below natural barriers and otherwise conform to stock-specific habitat criteria. Stream segments located above artificial barriers that have the potential to support specific stocks are included in order to identify habitat that could be used if the barriers were removed.
Peterson (1982), Kozel et al. (1987), Benda et al. (1992), and Montgomery et al. (1999) illustrate the strong linkage between segment-level habitat features (stream gradient, habitat type, stream network position) and fish use. For this reason, the SSHIAP segmenting scheme provides a powerful tool for determining presumed fish distribution. This allows resource managers to avoid some limitations associated with only using documented observations of fish use. Fish distribution information is entered into the SSHIAP database for each segment, allowing queries to determine habitat conditions for known or presumed distributions. A key use of this information is to identify appropriate areas for restoration and protection efforts.