Behavior, Ecology, and Restoration of Lake whitefish (Coregonus clupeaformis) and Arctic Charr (Salvelinus alpinus) in Maine Lakes

Artic charr (Salvelinus alpinus) and lake whitefish populations located in the contiguous United States lie at the southernmost limit of the species range, and can be found in a select few number of Maine lakes. These populations are under considerable stress for a variety of reasons and some have suffered extirpation. A number of strategies have been utilized to promote and enhance these vulnerable populations including chemical reclamation and stocking practices. It is unknown how these populations of these native fish species will function once reintroduced. This study assesses the seasonal vertical and thermal habitats of both reintroduced fish species in their respective waters using acoustic telemetry. In addition, I utilized otolith aging and back calculation methods to describe growth of the reintroduced lake whitefish population in relation to a source population. Arctic charr utilized deep and cold water habitats during daylight hours, during periods of stratification and inhabited shallower warmer waters at night. I discuss the bioenergetic implications of these movement patterns. Lake whitefish demonstrated reduced levels of activity during ice cover (December-March), while fish in the summer months (June-September) fish displayed the highest levels of activity. During periods of thermal stratification fish displayed diel vertical migrations, actively selecting depths and temperatures that may be more energetically profitable. During late season stratification, fish routinely utilized areas of warmer (\u3e15°C) than optimal temperatures for growth. Arctic charr and lake whitefish seasonal activity and depth use were driven by periods of ice cover during the winter months and thermal stratification during the summer months. To describe growth of a reintroduced lake whitefish population in relation to a source population age at length data were incorporated into a von Bertalanffy growth function and used to model lifetime growth in two lakes; additionally, growth trajectories from individual fish were examined to evaluate length at age variability within and among lake whitefish populations. Ages for lake whitefish from Clear Lake ranged from 8-30 years, and the oldest individuals demonstrate the slowest incremental growth when compared to younger cohorts. Lake whitefish from St. Froid Lake ranged from 2-9 years. Von Bertalanffy models suggest reduced growth in lake whitefish from St. Froid Lake when compared with Clear Lake. Findings suggest complex early life history interactions may limit the scope for growth in reintroduced populations from hatchery stocks