Kjetil Hindar

Resource utilization of sympatric and experimentally allopatric cutthroat trout and Dolly Varden charr

SummaryResource utilization by cutthroat trout (CT) and Dolly Varden charr (DV) was studied 8 years after experimental transfers from sympatry had established reproducing allopatric populations in two nearby fishless lakes. Allopatric DV significantly increased their utilization of shallow-dwelling zoobenthos, and increased their vertical distribution in comparison to that in sympatry. In contrast, allopatric CT showed little change in the proportions of major prey types utilized, and, if anything, restricted their vertical distribution in comparison to that in sympatry. The results can be explained by the hypothesis that the resource use of DV is strongly influenced by interspecific competition from CT, whereas CT largely remains unaffected by this interaction. An alternative hypothesis, that lake differences can explain the differences in resource use between sympatry and allopatry, was evaluated by comparing food resource availability and other biotic and abiotic characteristics of the three study lakes. None of these could account for the shift in resource use by DV between sympatry and allopatry, but lake differences may explain why allopatric CT showed a restricted habitat use in comparison with their sympatric donor stock. The results of this whole-lake transfer experiment are consistent with earlier reported field and laboratory studies, and suggest that the aggressive dominance of CT is the most important mechanism by which DV are displaced from littoral and near-surface habitats in sympathy with CT.

Optimal age at sexual maturity of sympatric and experimentally allopatric cutthroat trout and Dolly Varden charr

SummaryReproductive potentials of transplanted curthroat trout (Salmo clarki) and Dolly Varden charr (Salvelinus malma) and of their donor stocks were estimated from life history data. We found good agreement between observed and predicted age at maturity in all populations, and cannot reject the hypothesis that the fish matured at the age maximizing the overall lifetime reproductive potential (n

Genetic differentiation among local populations and morphotypes of Arctic charr, Salvelinus alpinus

Delta mu _{iota } = 0 = In left( {{{a_i^p } mathord{left/ {vphantom {{a_i^p } {a_i^L }}} right. kern-nulldelimiterspace} {a_i^L }}} right) + A_i + {{B_i } mathord{left/ {vphantom {{B_i } T}} right. kern-nulldelimiterspace} T}

Changes in use of lake habitat by experimentally segregated populations of cutthroat trout and Dolly Varden char

n). Our estimates were insensitive to probable variations in female fecundity, adult mortalityrate and maximum body length. Small changes in either juvenile mortality-rate or individual growth-rate had marked effects on the estimations, as did changes in the Malthusian parameter (r). Three alternative mechanistic explanations of how age at maturity is determined could be rejected. We suggest that fish are able to adjust the maturity age non-genetically to changes in growth-rate, and that temporal variations in juvenile survival-rate allow coexistence of genotypes coding for different ages at maturity at the same growth-rate.