Growth and distributional correlates of behavior in three co-occurring juvenile flatfishes

We explored whether anti-predator behavior and intrinsic growth are co-evolved traits in 3 co-occurring juvenile flatfish species: English sole Pleuronectes vetulus, Pacific halibut Hippoglossus stenolepis and northern rock sole Lepidopsetta polyxystra. English sole are risk prone, adopting behavior that renders them more vulnerable to predation, while northern rock sole are more risk averse. Pacific halibut are risk sensitive and modulate behavior to match perceived threats. We hypothesized that risk-taking behavior and intrinsic growth rate would be positively correlated in these species. We examined the willingness of each species to feed, both in the presence and absence of risk, and in separate experiments we measured their intrinsic growth rates under a range of temperatures. As predicted, risky behavior in English sole was accompanied by high intrinsic growth, while risk aversion in rock sole was accompanied by low growth. Pacific halibut confounded predictions, combining moderate risk-taking behavior with high growth. Lastly, we examined the depth distribution of each species. We expected English sole would be restricted to the shallows (<5 m), where predators are less common, while rock sole would have a deeper distribution, being better able to co-exist with predators. Halibut were expected to present an intermediate depth distribution. Again, English sole and rock sole conformed to predictions, while Pacific halibut confounded them by having a deeper depth distribution, comparable to that of rock sole. We suspect that the behavioral plasticity of Pacific halibut, combined with refuging behavior and well-developed escape capabilities, may allow them to have both high intrinsic growth as well as the ability to coexist with the predators. Thus, our results provide only partial support for our hypothesis that behavior and growth are co-evolved traits that together control the distribution of juvenile flatfishes across predation gradients.