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

We evaluated how microhabitat complexity structured a fish assemblage and influenced microhabitat selection by the northern leatherside chub Lepidomeda copei, a recent candidate for listing under the Endangered Species Act. Fishes were sampled using pre-positioned areal electrofishing (~1 m²), 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 northern leatherside chub used more heterogeneous depths and flows in addition to the low velocity, deep habitats often considered to be the species’ habitat. Additionally, chubs were almost certain to occur in deep-water habitats when overhead cover – often from mature riparian vegetation – was present. The complex microhabitats observed during our study were often directly linked to boulders, mature riparian vegetation, and beaver dams – stream features with direct ties habitat restoration. Incorporating measures of complexity in habitat studies will result in models that are more informative to stream restoration practitioners.