Steelhead and Their Habitat in the John Day River Basin

Livestock grazing in riparian zones affect many natural processes that are important in the formation and maintenance of steelhead (Oncorhynchus mykiss) habitat.  The loss of critical habitat for many steelhead populations led to the installation of riparian fencing with the objective of removing grazing to improve steelhead habitat in the John Day basin over the past 25 years.   We compared several riparian, biological, and physical responses between treatment (fenced) and control (unfenced and grazed) reach pairs that were selected based upon shared geomorphic reach types and stream basin. Juvenile O. mykiss were sampled and implanted with PIT tags.  Using electrofishing for marking and recapturing, as well as mobile PIT tag antennas, we were able to compare growth, survival, abundance, and habitat use, to increase our understanding of the mechanisms by which exclosures might influence steelhead.   We observed some differences in riparian vegetation and channel morphology between grazed and ungrazed reaches; however several expected changes were not observed.  Using time as covariate, suggests that given the high proportion of our sites that are in exclosures less than 15 years old, there has been insufficient time for these variables to show a response.  Fish site fidelity was high- suggesting independence between treatment and control pairs. O. mykiss used microhabitat features, such as pools and cover, which are expected to increase with exclusion of cattle. As with several habitat variables fish population responses were also not observed unless projects were greater than 19 years old.