Arctic Grayling Movements through a Nature-Like Fishpass in Northern Canada

Using a PIT detection system and two in-stream, swim-through antennas, we examined the movements of Arctic Grayling Thymallus arcticus through a low-gradient (< 1%), nature-like fishpass that connected two small lakes in the Barrenlands region of northern Canada. We used an ensemble of generalized linear mixed models to evaluate whether passage events (1) were related to fish FL, water depth in the fishpass, and/or temperature in the fishpass; and (2) exhibited any diel patterns. During two seasons, passage events were not related to fish FL or fishpass water temperature; however, the probability of a passage event occurring increased with increases in fishpass depth, which likely served as a proxy for velocity and/or discharge. Most notably, 95% (n = 193/204) of Arctic Grayling passages occurred at night (1800-0559 hours) throughout our study. Although the cause(s) of this diel pattern were not examined directly, we hypothesized that it represented a response to avian predation given the shallow depth of the fishpass and given our observations of daytime avian predation events on Arctic Grayling in the littoral zones of the study lakes. Our results offer novel insights into correlates of Arctic Grayling passage through a fishpass and lay the foundation for future studies to address the hypotheses supported herein with well-designed experiments to determine the mechanisms behind the patterns we observed.