Diel vertical migration of larval and early-juvenile burbot optimises survival and growth in a deep, pre-alpine lake

Abstract

Burbot larvae (Lota lota) perform a substantial diel vertical migration (DVM) of increasing amplitude in the pelagic zone during a 3-month period before migrating to the littoral zone as early-juveniles. We hypothesised that feeding in the warm surface layers at night and then spending the day in cold water below the thermocline reduces metabolic costs and earns burbot larvae an energetic advantage. 2. To test our hypothesis, we mimicked the temperature conditions experienced by vertically migrating burbot in the pelagic zone. We also simulated three further scenarios, in which temperature remained constant. 3. Burbot showed the best performance (defined as specific growth rate multiplied by the probability of survival) in the treatments simulating DVM. The high temperature treatment, simulating permanent residence in the warm epilimnion, resulted in high growth combined with high mortality. At a permanently low temperature, simulating life in the hypolimnion, growth was poor and activity reduced. 4. In a deep, temperature-stratified lake, where the apparently beneficial overall medium temperature is found in a restricted layer within the thermocline, DVM optimises performance in young burbot. Various ultimate factors might act synergistically in selecting for DVM in larval and early-juvenile burbot.