Efforts to Control Lake Trout and Further Ecological Change in Flathead Lake, Montana

Flathead Lake in Montana first received non-native lake trout (Salvelinus namaycush) in 1905.  A relatively small population dominated by older fish developed that preyed on non-native kokanee (Oncorhynchus nerka) and had seemingly minimal disruptive ecological effects.  Also present were abundant adfluvial bull and westslope cutthroat trout that utilized the interconnected system of rivers and lakes emanating largely from pristine lands.  Mysis diluviana appeared in Flathead Lake in the 1980s rapidly triggering cascading trophic changes.   Lake trout greatly expanded, the popular kokanee fishery collapsed abruptly, followed by alarming declines of native trout.  A misguided hatchery-based rescue of the kokanee fishery failed, leading to the realization that predation by lake trout was reshaping the fish assemblage.  Initial attempts by state and tribal managers to stem the deleterious role of lake trout consisted of liberalizing fishing regulations and promoting subsidized fishing contests.  These efforts doubled harvest of lake trout, but have been insufficient to meaningfully reduce abundance.  Managers are currently evaluating new control methods, such as netting, and a range of harvest targets identified through population and bioenergetics modeling.  The new targets are predicted to reduce lake trout abundance and with it their predatory effects on other species by specific modeled amounts.