Final Observations on the Survival of Planted Lake Trout in South Bay, Lake Huron

Abstract

Yearling lake trout were planted in South Bay, Lake Huron, an area with a sea lamprey population, each year from 1949 to 1955 with the exception of 1950. Fish were recaptured in pound and gillnets. Those recaptured in pound nets were tagged and released. Data from recaptures of tagged fish have been used to calculate yearly population estimates that were used to determine the annual mortality of certain year-classes. The fish were also examined for lamprey wounds and scars and the results tabulated according to the age of the fish.Before age IV annual mortality of South Bay lake trout does not appear to differ significantly from annual mortalities observed in lake trout populations in the absence of sea lampreys. Thereafter, annual mortality rates rise sharply and the population disappears at the age of VI or VII. No spawning population was maintained.Prior to age III no lamprey marks were observed on recaptured lake trout. From ages III to V the percentages of fish bearing lamprey marks increased from 5.2 to 38.8. This trend may continue through age VI but too few data are present to be certain. Before age VI there appears to be a direct correlation between annual lamprey marking rates and annual natural mortality rates.