Distribution, abundance, and emigration of juvenile steelhead (Oncorhynchus mykiss), and analysis of stream habitat in the Steamboat Creek Basin, Oregon

Graduation date: 1991Presentation date: 1991-03-15Snorkel dive estimates and an inventory of stream habitat of the juvenile steelhead (Oncorhynchus mykiss) population in the Steamboat Creek basin were made in the summers of 1987 and 1988. Emigration was\ud monitored by fish trapping from spring through fall of 1988. Distribution, abundance, and habitat utilization of juvenile steelhead were affected by stream size and temperature. The majority (65%) of\ud age >1 fish were in two mainstem channels, whereas numbers of age 0 fish were more evenly distributed throughout the basin. Age >1 fish significantly (P<O.005) increased their use of riffles with depth, and avoided shallow riffles. Where riffles were apparently too shallow, age >1 steelhead utilized pool habitat to a greater extent. Age >1 steelhead greatly avoided glides in all sizes of channels. Age 0 steelhead appeared to be less restricted in their choice of habitat than age >1 fish. Age 0 fish, presumably by virtue of a smaller body\ud size, showed only slightly increased use of riffles with depth. Both age 0 and >1 steelhead increased their use of riffles in streams with higher temperature regimes. Densities of age >1 fish in channels with\ud large boulder substrate increased significantly (p=O.02) with mean riffle depth, probably as a function of more wetted area being useable in streams with deep riffles, and more feeding microhabitats being\ud afforded by rough channels. Densities of age 0 fish did not appear to be affected by the range of stream sizes studied, or by channel\ud roughness, but were low in all channels with high stream temperatures. Compared to other steelhead producing streams, Steamboat Creek\ud had low summer rearing densities, small smolts, and an exceptionally high proportion of fish emigrating as parr (considered to be at least one year away from development of smolt characteristics). Roughly 120,000 age 0 steelhead, 60,000 parr, and 4,100 steelhead smolts were estimated to have emigrated from the basin. Most parr emigrated in the spring when stream flows were high, whereas the majority of age 0\ud fish emigrated during summer base flow recession. I suggest that parr emigration from Steamboat Creek may be a life history adaptation that takes advantage of rearing conditions downstream in the North Umpqua\ud River