Life History Influence on the Sublethal Effects of Sea Lamprey Parasitism on Lake Trout

Sea lamprey invasion of the Great Lakes has been linked directly to lake trout population decline through parasitism mortality. Less well understood are the sublethal effects. Current lake trout population models do not incorporate the likely decrease in growth and reproductive ability due to sublethal sea lamprey parasitism and may be underestimating the full effects on lake trout. This study aims to identify sublethal effects of parasitism and to determine if life history can influence such effects. We examined the effects of parasitism on the lean and siscowet lake trout morphotypes.  Siscowets have higher muscle lipid levels and inhabit the depths of Lake Superior. Leans inhabit shallow waters throughout the Great Lakes and have been the focus of conservation and re-stocking efforts.  Both morphotypes were subjected to sea lamprey parasitism for one to five days and analyzed for fecundity, muscle lipid levels, plasma sex steroids, and gonadotropin. Lake Superior lake trout were also collected and sampled similarly to determine the range of responses experienced in the wild. Results suggest differential reaction to sublethal parasitism between morphotypes. Siscowet response was largely immune-related while lean response was energetics-related. Future plans include incorporating these changes in plasma sex steroids, gonadotropin, and lipids levels into models that link to population-relevant endpoints such as changes in fecundity and growth.