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Influence of physical habitat on the seasonal movement, growth, and habitat association of individual coastal cutthroat trout Roberge, Michelle

Abstract

A multi-stream comparative study conducted in southwestern British Columbia revealed that juvenile coastal cutthroat trout (Oncorhynchus clarki clarki) were found at highest density in narrow (< 3 m), shallow (< 40 cm) streams with non-coarse substrate. To assess how cutthroat trout grow and behave within different physical habitats, I selected three streams for intensive examination from the physical structure gradient that I derived in the multi-stream study: (A) narrow width, shallow, fine substrate; (B) narrow width, shallow, coarse substrate; (C) wide width, deep, coarse substrate. I used radiotelemetry and bi-monthly recapturing of PIT tagged fish from set trap locations to examine individual growth and movement among the stream types over the fall, winter and spring of 1998/99. Individual PIT tagged fish tended to be heavier and grew faster during the spring than the winter or fall in all streams. Growth rate did not seem to be dependent on the physical habitat of the stream. During normal seasonal flood events, movement rate of fish from each of the three stream types was not affected. During a major flood event that occurred in stream types (C) and (B), fluctuations in water depth in stream type (C) displaced several radiotagged fish (> 100 m) and caused a general downstream movement in PIT tagged individuals. Almost no movement was detected during the winter in the three streams for PIT tagged fish (< 0.09 m/day). Density was lowest in stream (C) and highest in stream (A). Past and current provincial forestry practices usually result in removal of riparian vegetation on small streams. This can alter their physical habitat, usually by widening and aggrading the stream bed. Therefore, in streams where riparian logging has occurred, displacement of cutthroat trout during major floods may be a concern.

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