Distributions of Juvenile Steelhead and Cutthroat Trout (Salmo gairdneri and S. clarki clarki) Within Streams in Southwestern British Columbia

Abstract

Trout were collected and identified from 66 streams or stream systems of different size and gradient. Total dissolved solids (T.D.S.) and pH were determined on most streams. Size and profile of streams to a large degree determined the species of trout present. Large streams, with drainage area over 130 km2, were predominantly occupied by steelhead. Small streams, drainage area under 13 km2, were predominantly occupied by cutthroat. Streams less than 120 km2 in drainage area with steep gradients, and emptying directly into the sea, usually supported steelhead, as did large rivers. Those which dropped steeply and then levelled and ran through several miles of sloughs usually supported cutthroat. Where both species occurred, cutthroat were most often predominant in the small tributaries and headwaters, and steelhead in the lower reaches of the main stream. Stream pH's were usually lower in winter than in summer, but had no obvious effect on trout distribution. Many cutthroat streams had high T.D.S. readings in the lower reaches in summer and low T.D.S. readings in these areas in winter. Otherwise there were no marked differences between steelhead and cutthroat streams in terms of T.D.S.