Investigations of Lake Trout Salvelinus namaycush Ecology and Behaviour in Relation to Fragmented Thermal Habitats to Inform a Multifaceted Management Strategy

Freshwater ecosystems have been experiencing rapid changes including altered thermal habitats.Natural processes and manmade disturbances can fragment and disrupt thermal habitats that can be detrimental to freshwater organisms.Thermal habitats are one of the largest drivers of biological processes for fish because they influence physiological mechanisms that dictate movement and behaviour, growth, reproduction, and survival.Lake Trout (Salvelinus namaycush) are a cold-water fish that inhabits oligotrophic ecosystems in northern North America.The species holds cultural, ecological, and economic value as it facilitates several ecological processes and supports subsistence, indigenous, recreational, and commercial fisheries.However, as alterations to thermal habitats occur, Lake Trout populations might experience declines in population health, affecting ecosystem stability and the sustainability of fisheries.The overall goal of my thesis was to gain knowledge on how changing thermal habitats influence the movement and behaviours, trophic relationships, growth, reproduction, and bioenergetics of Lake Trout.My thesis studied Lake Trout in a complex multibasin lake in western Quebec, Canada.Acoustic telemetry, stable isotope analysis, diet analysis, growth structures, and bioenergetic models, were used to meet the goals of my thesis.Lake Trout were captured for biological sampling and transmitter implantation and released near the site of capture within their capture basin.My observations suggest thermal habitats become seasonally fragmented forcing Lake Trout to limit movement to their capture basin.Depending on their capture basin, thermal habitats might be limited causing the use of suboptimal habitats (≥ 10°C).Changes in thermal habitat use resulted in reduced movement and feeding on pelagic and/or benthic food more than littoral sources.Pelagic and benthic food sources, in the study system, are limited to low energy sources (e.g., zooplankton and aquatic insects).Furthermore, iv constrained movement resulted in reduced energetic costs (i.e., lower active metabolism) that could be beneficial for Lake Trout.However, if food quality is poor, then an individual might expend more energy feeding to meet basic requirements thus, potentially affecting survivorship, growth rates, and reproductive capacity.My observations indicated that the size and availability of thermal habitats drives energy transfer in this freshwater ecosystem potentially having compounding consequences for Lake Trout and the ecosystem.In the context of management, incorporating methodologies and mitigation tactics to ensure thermal habitat stability could assist in maintaining Lake Trout populations and sustainable fisheries.v

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