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The Energy Budget, Niche Shift, Reproduction and Growth in a Population of Arctic Charr, Salvelinus alpinus
T. Forseth, O. Ugedal and B. Jonsson
Journal of Animal Ecology
Vol. 63, No. 1 (Jan., 1994), pp. 116-126
Published by: British Ecological Society
Stable URL: http://www.jstor.org/stable/5588
Page Count: 11
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1. We studied age at niche shift and sexual maturity of Arctic charr Salvelinus alpinus (L.) from a Norwegian lake in relation to their energy budget. 2. Young Arctic charr (age -2) fed successfully on zooplankton giving them a significant energy surplus for somatic growth. Energy intake, however, levelled off at age -3 to -4, and decreased with age among older fish. Similarly, energetic costs increased from age -2 to -3 and then the costs levelled off and decreased, probably as a consequence of a niche shift from zooplankton to zoobenthos feeding in deeper water. This shift did not increase energy intake, but reduced costs, probably through higher feeding efficienty on the larger zoobenthos in the deeper water and reduced metabolism at lower ambient temperature. 3. Growth rate influences the age at niche shift and maturity. Fast-growing males attained maturity, and changed feeding niche, younger and at a smaller body size than their more slow-growing conspecifics. By contrast, female size at maturity was largely independent of age. The association between growth rate and these life-history traits is probably an effect of the close connection between growth rate and rate of metabolism in fish. We develop a model where the timing of niche shift and sexual maturation are a function of metabolic rate. 4. The estimated maximum weight from energy budget considerations was very close to the observed asymptotic size for Arctic charr in this population. Females matured at a size above the estimated optimum (c. 30 g) and close to maximum size (c. 61 g). Male size at maturity, however, was more variable; some matured close to optimum size while others matured at twice that size. The concept of optimal size thus appears irrelevant in connection with size at sexual maturity of wild fish.
Journal of Animal Ecology © 1994 British Ecological Society