Dynamics of a polyphagous lake trout, Salvelinus namaycush (Walbaum), population in a Northwestern Ontario lake / by Helen Elizabeth Ball

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

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