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Some aspects of the winter ecology of juvenile salmonids with reference to possible habitat alteration by logging in Carnation Creek, Vancouver Island Bustard, David R.

Abstract

Juvenile coho, steelhead, and cutthroat trout commonly spend from one to three or more years in coastal streams before migrating to the sea. Much of this time is spent in streams during the winter, making a study of these fishes' winter habitat requirements, distribution, behavior, and the possible influences of stream habitat alteration on them a useful undertaking. Some physical characteristics of areas selected by juvenile coho and steelhead were observed by snorkeling in a small west coast of Vancouver Island stream between September 1972 and April 1973. Observations revealed that with lowering water temperatures from 9°C to 2°C coho and older steelhead tended to move into deeper water while most steelhead fry remained in shallow, marginal sections of the stream. As water temperatures dropped in the winter, juvenile fish fed less and moved closer to areas offering low water velocities and cover. Steelhead fry were most often found under rubble while coho and older steelhead were most often found within upturned roots and under logs. Results from fish traps located on the lower ends of two small tributary streams indicated that juvenile coho, steelhead and cutthroat trout moved upstream into these tributaries in the late fall. Overwinter survival of coho in one tributary was 3-6 times as great as the estimated survival of coho in the main stream. Together the two tributaries contributed between 15 and 25 per cent to the total coho smolt production of the larger system. A series of experiments comparing coho and cutthroat preference for alternative habitat types in sidepool areas as may occur before and after stream disturbance were carried out during the winter. Both coho and cutthroat demonstrated a strong preference for bay areas offering overhanging bank cover as opposed to bays without cover, and for bays offering clean rubble substrate as opposed to silted rubble substrate. The impacts of timber harvesting on overwintering fish as suggested by the results from the underwater observations, winter movements, and the sidepool experiments are discussed and management recommendations are made.

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