Swimming speed and morphological features of mixed populations of early maturing and non-maturing fish

Positional and temporal variations in swimming speed and some morphological attributes were assessed in various mixed populations of early maturing (grilse) and non-maturing Atlantic salmon (Salmo salar L.) to examine the potential of using such data to improve grilse management and predict the percentage of the grilse in a population. Bimodal distributions, which could have been used to estimate the percentage of the grilse, were not observed; the data from all the sets were normally distributed with a single mode. Significant positional and temporal variations in swimming speed and condition factor were found, which implied that the maturing and non-maturing salmon segregated from each other. An improved grilse removal system may be developed if the fish can be induced to segregate under controlled conditions.

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