Effects of Improved Water Quality and Stream Treatment Rotation on Sea Lamprey Abundance: Implications for Lake Trout Rehabilitation in the Great Lakes

Efforts over the past 25 years to improve water quality in the Great Lakes basin may be counteracting progress toward lake trout rehabilitation that has been made possible by sea lamprey control. Improved water quality in streams has been linked to increased amounts of suitable sea lamprey spawning and ammocoete habitat leading to increased sea lamprey production. To assess the impact of improved water quality on sea lamprey production, we simulated transformer (young adult stage) production in a model stream assuming 50%, 75%, and 100% habitat availability. We also assessed the effect of lengthening the lampricide treatment cycle in streams; a proposed solution to inadequate funding of the sea lamprey control program. Increasing habitat availability dramatically increased the number of transformers produced in the stream; for example, doubling the available sea lamprey habitat resulted in a 2.5 fold increase in sea lamprey production. In addition, we found that the combined effects of improved water quality and lengthened lampricide treatment rotation caused transformer production to increase at a faster rate than either factor acting alone. Increased sea lamprey production directly impacts lake trout mortality and retards efforts toward achievement of lake trout rehabilitation goals. To counteract the improvement of sea lamprey habitat in tributaries, sea lamprey control efforts must be increased in order to enable lake trout rehabilitation to succeed.