LIMITATIONS TO LAKE TROUT (SALVELINUS-NAMAYCUSH) REHABILITATION IN THE GREAT-LAKES IMPOSED BY BIOTIC INTERACTIONS OCCURRING AT EARLY-LIFE STAGES

We examine evidence that biotic factors, particularly predation, may b e limiting early survival of wild lake trout (Salvelinus namaycush) ju veniles in many areas of the Great Lakes. The Great Lakes contain nume rous potential predators of lake trout eggs and fry, some of which are recent invaders, and most of which were probably absent when lake tro ut most recently re-invaded the Great Lakes after the last ice age. Si mple quantitative models of predation suggest that plausible assumptio ns about prey densities, predator feeding rates, and duration of expos ure of predator to prey can lead to very high estimates of predation m ortality, in some instances approaching 100%. Indirect evidence from i nter-Great Lake comparisons and inland lake examples also suggest that biotic factors may impede successful lake trout colonization. Our syn thesis of the evidence leads to recommendations for research to better define field feeding rates of lake trout egg and fry predators and co mparative studies of densities of potential egg and fry predators on l ake trout spawning reefs. Management options should be designed to pro vide useful information as well as achieve short-term goals. From a ma nagement standpoint we recommend that: newly constructed lake trout re efs should be placed well away from concentrations of potential predat ors; offshore spawning reefs should be stocked; salmonine stocking, nu trient abatement, and commercial harvest of alewives should all be con sidered as options to enhance survival of young lake trout; hatchery l ake trout should nor be stocked at sites where wild lake trout are sho wing signs of recovery; and exotic species expansions or introductions must be curtailed to maintain or improve on our recent successes in l ake trout rehabilitation.