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Temporal and spatial differences in movement of cutthroat trout in Placid Lake, British Columbia Shepherd, Bruce Gordon

Abstract

The temporal and spatial variations in the activity of cutthroat trout in a small coastal British Columbia lake (49°19'N, 122°34’W) were examined in order to determine the Impact of activity on the production of fish, and the factors controlling activity. Sonar tracking, diving, netting and tagging, rise observation, stomach content-prey distribution comparision, and echo sounding were used in the Investigation. Average activity levels were at least an order of magnitude below any published values. Energy values were correspondingly low; the maximum estimate of annual energy expenditure in activity (including routine metabolism) was 2330 kCal/kg/yr, which is well below the accepted 'rule' of field metabolism being twice the routine metabolism (3860 kCal/kg/yr). Fish behavioral problems and methodological shortcomings are considered responsible for this result. Activity over 5 min intervals was quite variable. Daily activity peaked during dawn and dusk. The level of activity decreased in late fall and early spring, and there was a shift from the littoral zones during summer. The cutthroat in the lake appear to maintain home ranges-for up to 5 months. Factors affecting activity can be broken into 3 categories: Temperature, light, and oxygen primarily determine the depth zones that are accessible to fish. Substrates such as Potamogeton beds and logs may act to concentrate fish within accessible depth zones; attraction is likely due to the higher food levels and/or increased cover found in these areas. Bottom slope, by affecting foraging efficiency in the productive littoral areas, might also affect the summer offshore distribution of fish within an accessible depth zone. It is suggested that the indirect effects of activity (specifically, the offshore movement of fish in summer) can be equally or even more important to the production of fish than is the direct use of energy for activity. higher food levels and/or increased cover found in these areas. Bottom slope, by affecting foraging efficiency in the productive littoral areas, might also affect the summer offshore distribution of fish within an accessible depth zone. It is suggested that the indirect effects of activity (specifically, the offshore movement of fish in summer) can be equally or even more important to the production of fish than is the direct use of energy for activity.

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