Spatial Variability of Coastal Cutthroat Trout Abundance and Lidar-Derived Channel Morphometry in Headwater Catchments

Understanding the linkages among physical and biological processes across scales is vital to understanding the diversity and heterogeneity of headwater streams.  Most research investigating fish–habitat relationships in headwater catchments has been conducted over a limited extent and at a small spatial scale.  We conducted spatially continuous single-pass electrofishing and physical stream habitat surveys, sampling all habitat units possible, within the fish-bearing portions of 16 catchments where coastal cutthroat trout are the sole salmonid species present.  Each catchment was surveyed twice, first in the autumn and then again the following spring, prior to the emergence of young-of-the-year cutthroat trout.  Spatial and temporal (seasonal) variability of cutthroat trout abundance within each study catchment was assessed at coarse (catchment), intermediate (stream segment), and fine (channel unit) spatial scales.  Fine-scale fish–habitat associations were assessed using stream habitat and fish count data collected during field surveys.  Stream segments were identified and grouped by analyzing intermediate-scale stream channel characteristics (channel gradient, confinement, and size) derived from high-resolution (≤2 m) LiDAR digital elevation models.  Geostatistical analysis techniques were used to quantify spatial structure in the distribution of cutthroat trout as it relates to these stream segments, and also to identify the range of distances over which trout abundance is autocorrelated.  Preliminary results indicate associations between intermediate-scale habitat characteristics and areas of locally high cutthroat trout abundance.  By better understanding the relationships between fish abundance and stream habitat, land managers can better identify areas of high biological potential where specific habitat protection or restoration efforts may be warranted or most productive.