Occupancy of young-of-year Arctic grayling (Thymallus arcticus) in Barrenland streams

Arctic grayling (Thymallus arcticus) is an iconic fish species that is present across the remote subarctic Barrenlands, yet our lack of understanding of their distributional patterns constrains predictions of anthropogenic effects on Barrenland populations. These adfluvial fish rely on seasonal lake-stream connections to migrate, spawn, and rear. We address knowledge gaps on what Barrenland stream attributes are suitable for rearing young-of-year Arctic grayling. Visual surveys of young-of-year Arctic grayling were conducted in 48 streams near Baker Lake, Nunavut, Canada. Occupancy modeling was used to relate stream habitat and landscape variables to fish presence/absence. The best predictors of occupancy were total area of contributing upstream lakes and landcover (upland/lowland); stream basins with larger contributing upstream lake area and more lowland cover were more likely to be occupied. Results suggest that occupancy reflects reliability of stream connectivity throughout the open water season and across years. The occupancy model developed here can adequately predict stream suitability for young-of-year Arctic grayling using lake area and land classification data that are remotely accessed. This may lessen the considerable financial and logistical constraints of conducting field research on Arctic grayling in the vast Barrenlands and facilitate more directed field programs to inform conservation and mitigation plans.

Using Video to Evaluate Depth and Velocity Selection by Arctic Grayling (Thymallus arcticus) in Pools of an Engineered Tundra Stream

We evaluated pool use by Arctic grayling (Thymallus arcticus) in an engineered stream in the Canadian Barrenlands at the summer background flow (1.0 l/s) and at enhanced flows (9.9 l/s and 21.9 l/s) similar to those during the spring spawning period. We used an acoustic Doppler velocimeter to measure and map out point velocities (horizontal and vertical) in five study pools. The positions of adult Arctic grayling were monitored for each flow condition using visual surveys and a novel video assessment technique. Although fish mobility limited pool selection at the summer background flow, the highest use of pools by fish during enhanced flows occurred where pool designs incorporated scour holes or downstream sills to provide larger amounts of relatively deep water. Within those pools, grayling selected for locations with depths between 0.20 m and 0.30 m and near-zero vertical velocities (−0.02 m/s to 0.04 m/s). Fish selected near-zero horizontal velocities(0.00 m/s to 0.04 m/s) for resting and higher velocities (0.12 m/s to 0.20 m/s) for feeding. In contrast, grayling tended to show local avoidance of areas with horizontal velocities above 0.2 m/s or vertical velocities above 0.04 m/s. Although findings are likely site specific, our study contributes towards the development of size, depth, and velocity criteria for Arctic grayling habitat; this information can promote effective designs for habitat compensation and fish passage projects. We also present a novel video monitoring method that can be easily deployed at remote locations.

Mechanics of foraging success and optimal microhabitat selection in Alaskan Arctic grayling (Thymallus arcticus)

Most fishes residing in temperate streams in the Northern Hemisphere are drift-feeders. Despite this fact, little is known about the mechanisms of drift-feeding itself. We used Alaskan Arctic grayling (Thymallus arcticus), an abundant boreal drift-feeder, to examine the effects of water velocity on several aspects of drift-feeding behavior and test predictions of the Grossman et al. (2002) net energy intake model for microhabitat choice. Water velocity had a negative effect on prey capture, a positive effect on holding velocity, and little effect on reactive distance. We also found that dominance was a better predictor of prey capture success than size rank, although neither of these variables influenced holding velocity or reactive distance. The Grossman et al. (2002) model successfully predicted holding velocities of grayling in one Alaskan stream, but not another. Model failure might have occurred due to higher turbulence, increased predation, or interspecific competition with Dolly Varden (Salvelinus malma). These results help inform the study of habitat selection in drift-feeding fishes as well as management and conservation of Arctic grayling.