In VIPERMAPS, the anadromous fish distribution matches the  distribution for anadromous habitats that is contained in the "streamnet" mapping (for confirmed fish bearing streams). However, the distribution is extended beyond that to all streams and rivers that are potential habitats based on gradient and flow thresholds in the intrinsic potential model, including those systems where fish are extinct or extirpated. In this approach, all channels that might have been accessible, but are no longer, are included. For source data, see: http://www.streamnet.org/mapping_apps.cfm

http://www.streamnet.org/gisdata/map_data_biological/FishDist_MSHv3_January2012/FishD_AllSpecies_January2012.xml

 

In Alaska, ADF&Gs Anadromous catalogue is used (for confirmed fish bearing) although the mapped distribution in the TerrainViewer extends beyond that to include all potential habitats as defined in the channel gradient and flow thresholds in available intrinsic potential models.

 

For resident fish, a channel gradient threshold cutoff of 20% is used.