Lake trout (SALVELINUS NAMAYCUSH) populations in Lake Superior have exhibited differing levels of abundance through time and thereby provide an opportunity in which to study the effects of compensation on population regulation. I explored the role of compensatory mechanisms in the population dynamics of lake trout in the Michigan and Wisconsin waters of Lake Superior during three time periods: the pre-sea lamprey period, prior to 1950 when lake trout were at a relatively high abundance and the fishery was the primary source of lake trout mortality; the sea lamprey dominant period, during the 1950šs and 1960šs when lake trout were at a very low abundance due to sea lamprey predation and over-exploitation; and currently, from 1985 to 1993 when wild lake trout abundance was at a moderate level.

The role of compensatory mechanisms was evaluated using a life table approach. Age-specific fecundity and survival schedules were incorporated into a Leslie projection matrix to calculate the finite rate of population increase (lambda). Individual growth, fecundity, and age-0 survival rates were calculated for each lake trout population and compared between time periods. Elasticity analyses were performed to determine the proportional contribution of each matrix parameter to the population growth rate during the three periods.

I found that individual growth rates, age-specific fecundity, and age-0 survival rates changed in response to the different levels of lake trout abundance during each of the study periods in both sites. Lake trout during the sea lamprey dominant period, which experienced the lowest abundance and highest mortality levels, exhibited the fastest individual growth rates, the highest age-specific fecundity, and the highest age-0 survival. These high rates contributed to the relatively high production potential exhibited by lake trout during the sea lamprey dominant period as compared to lake trout during the pre-sea lamprey or the current periods. Survival, particularly during the pre-reproductive ages, made a greater contribution than fecundity to the population growth rate of lake trout during the current time period. Reducing fishing mortality, which has its greatest impact on lake trout that are about to become mature, has a greater effect on the population growth rate than reducing sea lamprey induced mortality by an equal percentage.