AUTHORS: Dylan K. Undlin, UW-Stevens Point; Justin A. VanDeHey, UW-Stevens Point; Joshua K. Raabe, UW-Stevens Point; Nick R. Peterson, Minnesota Department of Natural Resources
ABSTRACT: Salmonids represent an ecologically, culturally, and economically important fishery in Lake Superior and its tributaries. However, current fluvial conditions and climate projections forecast significant reductions in cold-water habitats in these systems. Salmonids such as native Brook Trout Salvelinus fontinalis, and non-native Steelhead Oncorhynchus mykiss depend on these volatile tributaries for at least a portion of their life. Therefore, our research aims to 1) identify critical habitat (i.e. thermal refugia) for resident and migratory Salmonids across two watersheds, and 2) determine if movements of Salmonids are related to water temperature, dissolved oxygen, and discharge. Salmonid movement was investigated in the Knife and Stewart River watersheds using 16 stationary Passive Integrated Transponder (PIT) arrays and active radio telemetry techniques. Data loggers measuring water temperature, dissolved oxygen, and discharge were dispersed across watersheds, and stratified among sub watersheds and natural habitat breaks. To date, we have PIT tagged 1100 wild Salmonids and implanted 15 radio transmitters. Preliminary results suggest Salmonids sought headwater tributaries with groundwater influence and overhead cover during periods of warmer air temperatures. Salmonids used precipitation events and cold fronts as windows for movements during times of low flows and relatively warmer water. Water temperature profiles in the lower reaches of the Knife River periodically surpassed the lethal threshold for Brook Trout, indicating an ephemeral thermal barrier between tributary headwaters and Lake Superior. More data are currently being collected to further assess movement and habitat use in these riverscapes to inform management and restoration efforts.
