Natural reproduction by rainbow trout was substantial. I estimated that the average annual densities in November of age-0 and age-I rainbows per 305-m study section were 0. 69/m2 or 1, 072 trout and 0.09/m2 or 136 trout, respectively, and that this number of age-0 fish were produced by 16 adult rainbow trout.

Natural reproduction by coho salmon was moderate, but was without trend and was extremely variable. Young were produced by adults of hatchery origin in 1968-1970 and by adults of hatchery and wild origin in 1971-1974. I estimated that the average annual density per study section in November was 0. 22/m2 or 317 age-0 salmon and that a population of 4-14 adults was associated with this juvenile population.

The newly established populations of juvenile coho salmon did not have a detectable effect on numbers and growth of rainbow trout. Linear regressions of the biomass of age-0 rainbow trout or of age-I rainbow trout biomass on the biomass of coexisting age-0 coho for each study section showed that the populations of rainbow trout were independent of coho populations.

The data are suggestive of a depressant effect by coho salmon on brook and brown trout populations. In the three streams where small numbers of brook trout occurred, their numbers were lower when age-O coho were abundant than when salmon were absent or nearly so. The same was true for a small population of brown trout in the single stream where they occurred. Additional investigations are needed on the relationship between coho salmon and brook and brown trout.