COMPENSATION IN INDIVIDUAL GROWTH-RATES AND ITS INFLUENCE ON LAKE TROUT POPULATION-DYNAMICS IN THE MICHIGAN WATERS OF LAKE-SUPERIOR

The role of compensatory mechanisms in the population dynamics of lake trout in the Michigan waters of Lake Superior was explored during thr ee time periods: the pre-sea lamprey period, prior to 1950 when lake t rout were at a relatively high abundance and the fishery was the prima ry source of lake trout mortality; the sea lamprey dominant period, fr om 1951 to 1961 when lake Grout were at a very low abundance due to se a 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 changes in growth and fecundity rates of lake trout i n the Michigan waters of Lake Superior was evaluated using a life tabl e approach. Individual growth and fecundity rates were calculated and compared between time periods. These rates were used to determine age- specific fecundity which, along with age-specific survival, were incor porated into a Leslie projection matrix to calculate the finite rate o f population increase (lambda). Individual growth rates and age-specif ic fecundity rates changed in response to the different levels of lake trout abundance during each of the study periods. Lake trout during t he sea lamprey dominant period, which experienced the lowest abundance and highest mortality levels, exhibited the fastest individual growth rates and the highest age-specific fecundity. These high rates contri buted to the relatively large compensatory scope exhibited by lake tro ut during the sea lamprey dominant period as compared to lake trout du ring the pre-sea lamprey or the current periods which are associated w ith higher levels of abundance. (C) 1996 The Fisheries Society of the British Isles