Population biology of lake trout (Salvelinus namaycush) of Lake Superior before 1950

Scale samples collected in 1948 were used to estimate the instantaneous total mortality rate (0.70) and growth for lake trout (Salvelinus namaycush) in Lake Superior before the population had been significantly reduced by the sea lamprey (Petromyzon marinus). Indirect evidence indicates that the instantaneous natural mortality rate was probably 0.10–0.25. The Ricker model was used to calculate yield per recruitment, which varied with natural mortality and growth. Natural mortality was more critical than growth; yield per recruitment increased 183.3% with a 60% decrease in instantaneous natural mortality (from 0.25 to 0.10). For the prelamprey lake trout population the yield per recruitment was about 12–34 lb; the recruitment of about 3.6–10.1 million lake trout of age 1.5 resulted in an annual commercial production of 4 million lb.