Behavioral responses of juvenile white sturgeon (Acipenser transmontanus) to manipulations of nutritional state and predation risk

Predation and reduced energetic intake have been highlighted as potential mechanisms of recruitment failure in sturgeon populations. These two factors may interact, as foraging carries with it costs of increased predation risk, requiring behavioral trade-offs. We expect that juvenile sturgeon should express predator avoidance behaviors while they are within vulnerable size ranges, yet these behaviors should be modified by nutritional state. To evaluate behavioral trade-offs of juvenile white sturgeon, we designed an experiment to test the interacting effects of acute nutritional state and predation risk on the spatial distribution and movement of small groups (n = 6). Groups were assigned to one of four treatments, designed as a full factorial of nutritional state (well-fed or starved 24-h) and predation risk (largemouth bass present or absent), and eight replicates were conducted for each treatment. Juvenile sturgeon displayed a predicted and adaptive response to predation risk and predator aggression levels by reducing activity levels and displaying marked freezing behavior. Sturgeon responded strongly to nutritional deprivation through increased activity and increased near-neighbor distance, which was likely an adaptive response to increase encounter rates with benthic food items. Both of these responses to starvation were suppressed in the presence of predators. This study has provided experimental evidence that predators can abruptly reduce the foraging activity of white sturgeon, possibly reducing growth rates and extending the period of juvenile vulnerability. Future conservation planning should consider the interacting effects of multiple stressors experienced by sturgeon at early life-stages, as introduced predators and degraded foraging habitats may have interacting effects.