Dynamics of a polyphagous lake trout, Salvelinus namaycush (Walbaum), population in a Northwestern Ontario lake

Abstract

Tagging studies, index gill netting and an experimental winter fishery were used to investigate the dynamics of a polyphagous lake trout (Salvelinus namaycush population in Squeers Lake of northwestern Ontario. The density and standing crop of mature lake trout in Squeers Lake is higher than reported for other lake trout populations. Lake trout in Squeers Lake exhibit a bimodal length distribution with a wide range in length at age, suggesting recruitment of juveniles into the adult population is regulated. Observed depth distribution of lake trout indicates adults may limit young juveniles to deep water. Exploitation in the 1970's may have produced several strong year classes, but recruitment into the adult population did not occur. The slow growth of lake trout in Squeers Lake appears to result from the lack of available pelagic forage fishes. Thermal regimes limit foraging activity to Mysis relicta and Pontoporeia hovi during the summer months resulting in suboptimal growth. In Squeers Lake, scales underestimate the age of lake trout; the magnitude of the error increases with age. In slow growing polyphagous populations, age should be assessed using otoliths. The wide range in size of fish at a given age suggests the choice of aging tissue should be based on age rather than length. The Ricker Yield model indicates Squeers Lake can withstand the removal of four to eight times the allowable yield of lake trout recommended by the Morphoedaphic Index. . This model accurately reflected actual yield of the 1986 winter fishery. The lottery system is Useful for experimental management projects because it allows strict control and monitoring of effort and harvest. Anglers thought the lottery system was an unacceptable method for managing lake trout populations. Rotational pulse fishing appears to be a simple and acceptable system for managing polyphagous lake trout populations.