Thermal habitat of Brook Trout in lakes of different size

摘要

We assessed thermal habitat use of lake-dwelling Brook Trout (Salvelinus fontinalis) populations in 39 lakes of varying size with short-set duration, stratified-random netting surveys in Algonquin Park, Ontario, Canada. Temperature at capture depth was determined from vertical temperature profiles and used as a proxy of Brook Trout temperature selection. Almost all Brook Trout observations fit within their aerobic scope, indicating that our approach adequately captured the distribution of body temperature for this species. However, we found a bimodal distribution of temperatures at capture depth. Most fish occupied a cold mode at capture, but a smaller subset of fish was captured in a warm-temperature mode that occurred in all lake-size categories, indicating Brook Trout that appeared to be actively moving into the warm-temperature mode. Adult Brook Trout occupied colder thermal habitats, on average, than published literature estimates and were found in significantly-colder temperatures than subadult Brook Trout within the same lake. Variation in thermal habitat use increased as lake size decreased. For lakes <100 ha, temperatures at capture depth were highly variable and ranged from 7.2 to 17.7 degrees C. We report weighted means and distributions of thermal habitat boundaries because these boundaries may aid future efforts to project the influence of climate change on Brook Trout. Dissolved oxygen at capture depth suggested that fish occupy either an upper mode >5 ppm or a lower mode, including individuals captured at depths where dissolved oxygen is <2 ppm.