THE CARRYING CAPACITY FOR JUVENILESALMONIDS IN SOME NORTHERNCALIFORNIA STREAMS 1

Abstract

Standing crops of juvenile coho (silver) salmon (Oncorhynchus kisutch), steelhead rainbow trout (Salmo gairdneri), and coast cutthroat trout (Salmo clarki) were examined in seven coastal streams to define the natural carrying capacity of these streams, and to develop methods of population comparison and prediction which could be used to determine the effects of road construction and logging on salmon and trout production. Biomass per unit of surface area was the best method of expressing carrying capacity, because biomass was better correlated with stream surface area than with other parameters tested. Volume of streambed sediments, total dissolved solids, alkalinity, and total phosphate in six streams were not satisfactory predictors of carrying capacity. only livingspace variables correlated significantly with biomass. Not all streams reached carrying capacity in the summer and salmonid biomass was highly variable. Even with 3 years of prelogging study, it would be difficult to attribute a change in carrying capacity under 50% to anything but natural variation.