Whole-lake food web model indicates alewife invasion fueled lake trout restoration and altered patterns of trophic flow Lake Champlain

Abstract

Food web responses to invasion can be context-dependent and therefore difficult to predict based only on invasion histories. Alewives (Alosa pseudoharengus) had generally negative impacts on the native fish communities of the Laurentian Great Lakes after they invaded in the 19th century and were thus expected to negatively impact the Lake Champlain food web after entering the lake in 2003. We evaluated the impact of alewives on the Lake Champlain food web by compiling 25 years of biomass, abundance, and diet data and constructing an Ecopath with Ecosim model of the coldwater food web. Model projections indicated that, contrary to the Great Lakes experience, biomass of native predators increased, mortality rates decreased, and overall trophic level of the pelagic fish community decreased after alewife entered the system. Consequently, the amount of primary production supporting predator biomass increased in response to the addition of prey fish production. The model suggests that alewife invasion in Lake Champlain could have altered food web structure by transferring more energy to tertiary consumers via pelagic pathways at the expense of other energy pathways and “jump started” wild lake trout recruitment by expanding the forage base. In contrast to the Great Lakes response to alewife invasion, Lake Champlain may represent an alternate trajectory for alewife invasion and demonstrates that alewife impacts are context-dependent.