Otolith‐based analysis of survival and size‐selective mortality of stocked 0+ year pike related to time of stocking
The effect of time of stocking on the extent and source of mortality in 0+ year pike Esox lucius was investigated in a lake (20 ha) and a drainable pond (0·5 ha) using pike with alizarin marked otoliths. The results indicated that pike stocked late relative to the recruitment of native 0+ year pike fell victim to cannibalism from these larger individuals. This resulted in very low survival through the first growing season (<2%). Pike stocked early in the season exhibited significantly higher survival (>12%). Analyses of the size distribution of the alizarin marks from these fish revealed that the largest 0+ year pike exhibited by a factor of 3·3, higher survival than the average 0+ year pike in the lake. In order for large 0+ year pike to exhibit such high relative fitness a minimum of 69·7% of the original population must suffer size dependent mortality. In the pond the survival of the largest pike was by a factor of 4·2 higher than the average pike, and the corresponding size dependent mortality was 76·4%. The substantial size‐dependent mortality was most probably due to intra‐cohort cannibalism or habitat segregation between large and small 0+ year pike that exposes the small pike to predatory fishes in the open lake. Cannibalism exerts a major influence on the survival of 0+ year pike post‐stocking although the magnitude and origin differ in relation to stocking time.
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Document Type: Regular Paper
Publication date: 2004-06-01