The effects of climate change on north-temperate lake trout (Salvelinus namaycush) populations
Guzzo, Matthew Michael
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Aquatic ecosystems are expected to undergo major changes in response to climate change. Lake trout (Salvelinus namaycush) is predatory fish found in oligotrophic lakes of Canada and is considered a sentinel species for studying the impacts of warming on lakes due to its requirement for cold water. The objective of this thesis was to determine the impacts of warming on north-temperate lake trout populations. In Chapters 1-3, I used long-term datasets collected from small lakes near the southern extent of lake trout’s distribution to determine how warming impacts thermal habitat and how these habitat changes cascade to alter the behaviour and growth of individuals and ultimately population-level characteristics of this species. I found that over a period when annual air temperatures increased by ≈ 2 ˚C there was a 14-day reduction, on average, in the ice-free season and an equal extension of summer — a period when littoral zone temperatures exceed the metabolic optimal for lake trout. Years with shorter springs and longer summers negatively impacts lake trout by limiting access to littoral prey, resulting in slower growth and reduced condition. I also found that the growth and size structure of an unexploited lake trout population shifted during this warming period; the population is now made up of a larger number of small individuals with lower condition and reduced life span. Lake trout also began to mature at younger ages and had reduced maximum size. Results suggest these changes in size-structure were not due to changes in the amount or size of prey fish or density-dependence, as the biomass of adult lake trout remained constant over time. In Chapter 4, I collected data from a northern lake to describe the seasonal ecology of this northern lake trout population and predict how warming might alter growth. I found that lake trout displayed similar seasonal cycles in habitat use and diet as in southern lakes, but that the use of littoral habitat was far reduced, likely due to the presence of pelagic prey fish and northern pike (Esox lucius) in this lake. Lastly, bioenergetic simulations indicated that the under a 2 ˚C warming scenario, the growth and consumption of lake trout would increase in this northern lake assuming prey was readily available.