Role of Complexity in Habitat Use and Selection by Stream Fishes in a Snake River Basin Tributary

Impacts from grazing, agriculture, and other anthropogenic land uses can decrease stream habitat complexity that is important to stream biota and often is the goal of stream habitat restoration. We evaluated how microhabitat complexity structured a fish assemblage and influenced habitat selection by the Northern Leatherside Chub Lepidomeda copei , a recent candidate for listing under the U.S. Endangered Species Act, in Trapper Creek, a tributary to the Snake River in Idaho. Fishes were sampled using prepositioned areal electrofishing (about 1 m ²), and microhabitat conditions were measured within a 1-m-diameter circle centered on the electrofishing anode. Constrained correspondence analysis showed complexity in water depths and velocity to structure the fish assemblage and partition habitat use by Northern Leatherside Chub, Rainbow Trout Oncorhynchus mykiss , and Redside Shiner Richardsonius balteatus . Habitat selection models showed that the chub used areas of heterogeneous depths and flows in addition to the low-velocity, deep habitats often considered to be the species’ habitat. Additionally, chub were almost certain to occur in deep-water habitats when overhead cover—often from mature riparian shrubs—was present. The complex depths and flows structuring the fish assemblage, and selected by chub, were often directly tied to other structural stream features such as boulders, mature riparian vegetation, and beaver Castor canadensis dams, stream features that have direct ties to active and passive instream habitat restoration techniques. Our study suggests that habitat complexity should be routinely incorporated into studies evaluating fish habitat use, occupancy, and abundance. Doing so will result in models that are more informative to practitioners conducting stream restoration with a goal of improving habitat complexity. Received January 9, 2014; accepted April 29, 2014