Since their introduction into the Laurentian Great Lakes, sea lamprey have had serious negative effects on lake trout populations contributing to population decline. Although the consequences of sea lamprey introduction for lake trout have been studied for decades, there are critical unknowns that remain challenges for lake trout and sea lamprey management. My work focuses on some of these critical unknowns through a combination of experiments addressing the physiology of parasitized lake trout, the accuracy and reliability of sea lamprey wound assessments, and the quantification of the sublethal effects of sea lamprey parasitism in a modeling framework useful for management applications. My first chapter provides a background and description of the critical unknowns surrounding the interactions between sea lamprey and lake trout that my dissertation addresses. My second chapter focuses on problems related to the process of collecting and aggregating sea lamprey wound data from wild fish. The assumptions of consistent and accurate wound classification and reliable wound healing progression that are required for the use of this data is not met. Fisheries management in the Great Lakes depends heavily on these data and models for determining lake trout harvest thresholds, stocking strategies, estimating sea lamprey damage, and for assumptions about lake trout survival that are used in sea lamprey population estimates. Highlighting deficiencies in this process is critical as it allows us to rethink how wound data is collected and used, and provides potential avenues for improving its use going forward. My third chapter addresses the sub-lethal effects of sea lamprey parasitism on lake trout growth, reproduction, and energy storage. Much research on the interactions between sea lamprey and lake trout has focused on estimating direct mortality on lake trout populations, but an estimated 45-75% of lake trout survive a sea lamprey parasitism event. In our study, severe sea lamprey parasitism resulted in considerable alterations to reproduction and energy storage for siscowet lake trout, but lean lake trout were far less susceptible to these parasitism-driven effects. The difference in response is likely driven by life history differences between these two ecomorphs. This work provides crucial missing information about the effects of sea lamprey parasitism on lake trout in the Laurentian Great Lakes. My fourth chapter focuses on the development of dynamic energy budget (DEB) model to enhance our understanding of the energetic consequences of sea lamprey parasitism. While empirically measured sub-lethal alterations to lake trout reproductive physiology are interesting, it is difficult to understand the implications of stressors in the context of the whole organism. I developed a DEB model that tracks energy allocation for siscowet lake trout, and accounts for parasitism-driven life history alterations. This allows for a better understanding of the energetic mechanisms that lead to skipped spawning following sea lamprey parasitism. Simulations using our developed model highlight the relative importance of parasitism and individual variation in muscle lipid and plasma estradiol concentrations for ovarian development, and closely match empirical observations. This work advances our knowledge of the sub-lethal influences of sea lamprey parasitism and provides tools and guidance for how to measure and estimate these effects going forward.
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