Hierarchical Assessments of Fish and Their Habitat

Changes to fish habitat are driven by geomorphic processes occurring at the catchment, landscape (immutable and human induced characteristics), geomorphic reach, and geomorphic unit (pools, riffles, and bars) scales.  The geomorphic processes shaping fish habitat need to be strongly considered in order to determine the effects of management practices and stream restoration on fish populations. While these hierarchical considerations are often acknowledged, many ecological and geomorphic studies of streams occur at the reach scale. Continuous surveys, via remote sensing or rapid assessments, have changed our perceptions of the spatial frameworks that have been used to describe ecological and geomorphic processes. To further this growing understanding of importance of the spatial and temporal context, we are assessing stream habitat and fish populations at multiple scales in several different watersheds in the Columbia basin. At the reach scale we are conducting high resolution surveys with total station and Real Time Kinematic GPS to describe stream bathymetry, while also delineating geomorphic units and microhabitat features. Specific fish habitat features, such as large wood and substrate, are collected in association with the delineated geomorphic units. We combine reach scale surveys with watershed level rapid ground-based surveys and multispectral aerial photography from small autonomous unmanned aerial vehicles to assess fish habitat. These reach scale surveys are used to calibrate and validate aerial imagery information, such as water depths, channel form, large wood and substrate types. We conduct seasonal juvenile steelhead surveys at site and watershed scales using PIT tag mark-recapture methods and mobile and passive PIT tag antennas to determine how these reach and watershed scale geomorphic features and processes influence steelhead populations. From our fish surveys we determine response variables such as abundance, movement, growth, survival, and production and use the multi-scale habitat information to help explain spatial and temporal patterns.