Movement ecology of adfluvial bull trout (Salvelinus confluentus)

Ecologists are recognizing that organism movement can be explained by a combination of inter-related variables that are derived from an individual’s internal state, environment, motion capacity, and navigation capacity. To reveal aspects of movement ecology of free-ranging adfluvial bull trout (Salvelinus confluentus), I used acoustic telemetry and tested hypotheses about thermal resource selection, diel vertical migration, and size and sex-related effects on movement. I tagged 187 adult fish and monitored these individuals for up to two years (2010-2012) in the ~ 425 km2 Kinbasket Reservoir, BC. Correlates of movement included combinations of variables representing the internal state (e.g., phenotypic traits including sex and body size), the external environment (e.g., temperature and diel period), and the navigation capacity (e.g., the way in which an organism perceives and navigates its environment). Over the two-year period, temperature experience was similar for all body sizes (~ 400-800 mm total length). During summers, bull trout were predicted to experience temperatures that were within ~1°C of their lab-derived thermal optimum for metabolism and growth for juveniles. Bull trout occupied temperatures between approximately 11-15°C and selected higher temperatures as these temperatures became less available with the progression of summer and autumn. Diel vertical migration (DVM) was evident, with the largest individuals occupying the shallowest water. Significant DVM continued to occur during winter when the thermal profile was presumably isothermal. Winter DVM, and a significant effect of body size, indicated that multiple inter-related factors were responsible for vertical movements. Body size and season were significant predictors of home range size, with the largest home ranges predicted during autumn and spring in fish greater than 700 mm total length. A significant sex x body size interaction predicted horizontal movement such that in a given month, large females moved significantly farther than large males and small females, whereas there was no difference between large and small males. This work provides novel insight into thermal resource selection, diel vertical migration, and the correlates of horizontal movement. This research generates new information on the movement ecology of adfluvial bull trout in a hydropower reservoir which is relevant to understanding entrainment risk.