Diel vertical migration of adult burbot: a dynamic trade-off among feeding opportunity, predation avoidance, and bioenergetic gain

Diel vertical migration (DVM) of pelagic organisms is typically attributed to bioenergetic gain, foraging opportunity, predator avoidance, and multifactor hypotheses. While a number of benthic species perform nightly migrations into shallower waters, the function of these DVMs has largely been ignored in benthic fishes. We used depth and temperature sensing telemetry to investigate DVM function in burbot (Lota lota), a freshwater benthic piscivore. We modeled the influence of season, diel period, and body size on the depth, vertical activity, migration probability, and thermal experience of 47 adult burbot over 2 years in a reservoir in British Columbia, Canada. Burbot were found to occupy significantly shallower water at night than during the day. Our results, which showed elevated nightly activity and a seasonal size-structured depth distribution during DVMs, suggest these migrations likely provide a feeding opportunity “window” for this nocturnal predator, constrained by predation or cannibalism threats to smaller individuals. The observed thermal experience patterns suggest DVM may also provide a seasonal bioenergetic advantage. Our detection of within-individual plasticity in migration strategy is indicative of a partial migration. Taken together, our results suggest a multifactor DVM hypothesis: a dynamic trade-off among bioenergetic advantage, foraging opportunity, and predation threat.