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Calculations of fish lengths from scales. 2. Growth rates of Kamloops trout in Paul Lake, British Columbia. Smith, Stuart Boland

Abstract

The logarithmic scale/body relationships of Kamloops trout has been discussed with particular reference to its use in the calculation of fish lengths prior to capture. Growth of scales relative to body growth exhibits strong positive heterogony in the fork length range 3.5 cm. to 4.5 cm., above which the scale/body ratio is isometric. Calculation of fish lengths, using only the diameter of the first growth ring (placode) of the scale and total scale diameter, shows close statistical agreement with actual measured lengths for the same specimens. In the population studied, the intense sport fishery is highly selective with respect to rate of growth for all age-classes. In all comparisons, longer-lived fish were slower-growing and samples drawn from anglers’ catches may not, in this case, be considered as representative of the population as a whole. In some years statistical differences exist in the mean lengths of spawning and non-spawning trout of the same age. It is suggested that attainment of sexual maturity and rate of growth may be closely associated. A change in lake ecology may be detected by growth comparisons of trout from various year-classes. Lowered growth rates of Paul lake trout are attributed to the effects of the recent introduction of the redside lake shiner, Richardsonius balteatus Richardson. Effects of the increase in numbers of shiners also are manifested in the increased variability in growth rates of Paul lake trout.

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