To better understand the effects of debris flows on salmonid populations, we studied juvenile steelhead/rainbow trout (Oncorhynchus mykiss) populations in six streams in the Klamath Mountains of northern California: three affected by debris flows on 01 January 1997 and three that experienced elevated streamflows but no debris flows. We surveyed habitat and fish in study reaches on all six streams in September for three years following the disturbance. Pool depths, substrate size and substrate embededdness varied among streams but with no clear patterns to distinguish debris-flow from no-debris-flow streams. However, the debris-flow streams had significantly less canopy cover and significantly more woody debris. Debris-flow streams did not differ from no-debris-flow streams in biomass and numeric densities of both young-of-year and age 1 and older (age 1 ) O. mykiss. In debris-flow streams in the first year following the debris flows (1997), we observed low numbers of age 1 O. mykiss and variable year-class strength of young-of-year fish. In 1997, the young-of-year cohort in one debris-flow stream exhibited exceptional growth. In all three debris-flow streams, age 1 biomass increased each year through 1999 when total O. mykiss biomass in the debris-flow streams exceeded that in the no-debris-flow streams. Surprisingly, we collected larval coastal giant salamander (Dicamptodon tenebrosus) in all streams in all years. We suspect the recovery of juvenile O. mykiss following the debris flows may have been hastened by increased productivity stimulated by clearing of dense, alder-dominated riparian corridors while salamanders likely recolonized from nearby unaffected tributaries.
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Vol. 91 • No. 3