Influences of Lake Trout on Lake-Resident Arctic Char in Northern Quebec, Canada

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Abstract
Arctic char Salvelinus alpinus that were sympatric with lake trout Salvelinus namaycush in three northern Quebec lakes had faster growth rates, lower survival, and shorter longevities and yielded lower catches per unit effort than a population of Arctic char that was sympatric only with threespine sticklebacks Gasterosteus aculeatus. In lakes that contained lake trout, Arctic char were not piscivorous, whereas lake trout were. In the absence of lake trout, Arctic char were piscivorous, the rate of consumption of prey fish was positively correlated with length of Arctic char and, from the age of 6 years onward, each age-class of Arctic char exhibited a bimodal length distribution. We concluded that the growth rate of a small proportion of small, slow-growing Arctic char accelerated when the fish became piscivorous. Internal parasite load was significantly greater in Arctic char when the threespine stickleback was the only other fish species in the community; parasite loads were positively correlat...