Declining lake trout (Salvelinus namaycush) energy density: are there too many salmonid predators in the Great Lakes?

Abstract

This study used long-term biomonitoring data on lake trout ( Salvelinus namaycush ) collected from Lakes Erie, Ontario, Huron, and Superior between 1995 and 2004 to investigate latitudinal and temporal trends in body mass and energy density of this top predator in the Great Lakes. Lake trout average body mass and energy density were observed to have negative relationships with latitude that primarily reflected patterns in lake productivities. Temporal declines in energy density occurred for >80% of all lake trout age classes collected from each of the four lakes between 1995 and 2004. von Bertalanffy (VBL) growth models describing the relationships between fish energy density and age demonstrated decreased growth of lake trout energy density during 2000–2004 relative to 1995–1999. VBL growth coefficients (k) and the slopes describing the rates of change in lake trout energy density were negatively correlated with the total number of lake trout and salmonid individuals released into these lakes during this study. We hypothesize that the temporal declines in lake trout body mass and energy density are a manifestation of a bioenergetic bottleneck for this species due to their inability to efficiently compete with non-native salmonids for depleted prey populations.