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Factors that influence the distribution and movement of Yellowstone cutthroat trout (Salmo clarkii lewisii) fry in Kiakho Lake outlet, British Columbia Shapley, Sanford Philip

Abstract

In May, adult Yellowstone cutthroat trout (Salmo clarkii lewisii) moved from Kiakho Lake into its outlet to spawn. Upon emergence from the gravel, most young fry descended at night from the fast flowing, gravel bottom areas into slow flowing, mud and sand bottom regions where they spent the summer. The majority of fry over-wintered in the creek before ascending to the lake. The research was conducted in the summers of 1959 and 1960. It had two objectives: (1) to describe fry distribution and (2) to examine some characteristic fry "behavior" including movement. Traps and an experimental trough were operated. Behavior was observed, movements of marked fish were studied, and fry distribution was determined. Temperature, barometric pressure, water level, and light were recorded. Darkness apparently influenced the downstream movement of recently emerged fry for 90% of it occurred at night. A slow current apparently greatly slowed the rate of descent. The gradual descent of these fry in the "sluggish" Beaver Meadow during July evidently produced the late July uniform Beaver Meadow fry density. Long distance upstream and downstream movement of "healthy" fry in August was quite limited though short temporary movements of fry from their "home", may have been common. At least 60% of the fry held the same "home" for two weeks. Fry defended territories. The August 1960 Beaver Meadow fry population decrease was due to natural mortality. Month-old Beaver Meadow descending fry were characterized by small size and "physical weakness". In a week, the number of day versus night descenders was about equal, but within a 24 hour period, there was no correlation between the two. Bright moonlight appeared to depress night downstream movement, a fluctuating water level may have increased it, and a week long drop in creek temperature apparently depressed all downstream movement. Fry moving upstream were generally larger than average size fry. There was a moderate association between rising daily maximum water temperature over a period of several days and increased upstream movement. Fry in a trough ascended more at 20°C. than at 9°C. A week long drop in water temperature likely depressed movement. Because more than 80% of the movement occurred in the day, a certain minimum light intensity may be required before fry ascend much. The Kiakho outlet observations were compared to the findings of other researchers. Generally, stream dwelling Salmoninae appear to exhibit territorialism, homing, and limited movement,, Several other generalizations about stream dwelling trout, were suggested,,

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