Seasonal use of habitat by juvenile steelhead trout in Hurdygurdy Creek, California, and implications for stream enhancement

Seasonal shifts in macro- and microhabitats chosen by age 0+ steelhead (Oncorhynchus mykiss) were used to assess the effects of boulder structures placed in a fourth-order, coastal stream to increase rearing capacity for juvenile steelhead. Microhabitats identified by direct observation by divers were used to quantify microhabitat used during summer 1985 and the following winter. Macroinvertebrate drift was also monitored with monthly, 24-hour collections to determine if there were seasonal limitations in food supply. Microhabitat data were collected for totals of 227 and 24 age 0+ steelhead in summer and winter, respectively. Microhabitat characteristics for 0+ steelhead (with respect to water depth, average water column velocity and substrate type) were found to be similar to previously reported values. An attempt to discriminate seasonal groups of age 0+ steelhead via multivariate analysis of these and additional variables (maximum water velocity within average foraging distance from focal points, and focal height) was inconclusive. During winter, age 1+ steelhead virtually disappeared while age 0+ steelhead were numerous only in secondary channel pools. Invertebrate drift was at its low-point from late October to mid-December. Winter is the season most likely to limit the production of juvenile steelhead. Because secondary channel pools, which appeared to offer the most preferred winter habitat are extremely limited in this stream, enhancement of this habitat type is recommended.