The Lake Trout of Lac la Ronge, Saskatchewan

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Abstract
The lake trout, Salvelinus namaycush, of Lac la Ronge was studied in the years 1948 to 1959 using gill netting, tagging, creel census and sampling of the spawning run. The trout spawned on shallow rocky reefs in the first week of October, when water temperatures were about 10 °C (50°F). Of the spawning run, 82% were from 7 to 12 years old. Possibly 10% of the mature trout failed to spawn in any single year.Growth rate varied widely in individuals and the average rate produced, at 10 years, a trout of 26 inches (66 cm) fork length and weighing 8 lb (3.6 0kg). No difference was found between growth rates of males and females and there was no change in average growth rate during the 10-year study. However, trout in the main lake grew considerably faster during their first 5 years than those in the deeper, colder Hunter Bay. Thirty-three trout weighing from 30 to 43 lb were examined.Ciscoes, whitefish, ninespine sticklebacks and other fish made up 90% of the food of adult trout. The crustaceans Mysis and Pontoporeia were eaten in moderate quantities, especially by trout in their third and fourth years. Two cestode parasites were found in the intestine and the larvae of a third in the muscle of trout.The trout were widely scattered from break-up of ice in mid-May to late June. As the upper water warmed above 10 °C (50°F) they moved down and were concentrated in areas deeper than 20 m (65 ft) during July and August. As the water cooled they again spread into shallow water about mid-September. Of 429 tagged, 60 or 14% were recovered during the first, second and third years after tagging. Recoveries showed extensive movement throughout the lake and a moderate exchange between the main lake and Hunter Bay.In standard gill-net catches plankton-feeding and bottom-feeding fish outweighed piscivores by 3 to 1 in the main lake and 1.8 to 1 in Hunter Bay. Catch data suggest that the trout population was greater in 1958–59 than in 1948–49. The average size of trout caught and the year-class composition were unchanged after 10 years.By diverting commercial fishing from trout to whitefish the average commercial catch in the 10-year period has been maintained at 250,000 lb per year, as compared to 316,000 lb in the previous 30 years. The anglers' catch of trout now averages 30,000 lb per year and this could be doubled without exceeding the known capacity of the lake for trout production. The creel census shows no decrease in average size of trout caught, average catch per angler, and number of very large trout taken.

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