Evaluation of Age-0 Survival and Its Effect on Lake Trout Rehabilitation in the Michigan Waters of Lake Superior

Efforts to rehabilitate lake trout in the upper Great Lakes have met with limited success. One key factor hypothesized to impede progress towards rehabilitation is inadequate age-0 survival (from egg deposition to age-1). We evaluated age-0 survival rates for lean lake trout populations in the Michigan waters of Lake Superior during three periods of significantly different abundance levels and mortality regimes: pre-sea lamprey (1929–1950), sea lamprey-dominant (1951–1962), and current (1988–1993). Current age-0 survival rate was calculated to be 0.00118 which is lower than age-0 survival rates corresponding to the pre-sea lamprey (0.00372) and sea lamprey-dominant (0.00416) periods. Population growth rates of lake trout were found to be extremely sensitive to changes in age-0 survival rates. We found that if the current lake trout population in the Michigan waters of Lake Superior exhibited an age-0 survival rate similar to that of the pre-sea lamprey population, the current population would be increasing in numbers rather than decreasing. As increasing age-0 survival will greatly increase the population growth rate and facilitate the rehabilitation process, we recommend that future research and management efforts place a high priority on evaluating the factors that are currently depressing survival rates of age-0 lake trout in Lake Superior in order to develop strategies to overcome these impediments.