Evaluation of differing anti-predator strategies of three juvenile north Pacific flatfish species

Abstract

Pleuronectid flatfish are generally thought to utilize stereotypical anti-predator behavior to reduce encounters with potential predators, including burial, maintaining a low profile on the bottom, cryptic coloration, and reduced activity. However, a series of laboratory experiments demonstrate significantly different predation rates on juvenile (Age-0) English sole (Parophrys vetulus), northern rock sole (Lepidopsetta polyxystra), and Pacific halibut (Hippoglossus stenolepis) by Age-2 Pacific halibut predators, suggesting differing anti-predator strategies and/or capabilities. Specifically, differences between the three species include their tendency to bury, their body posture relative to the bottom, as well as their activity levels both in the presence and absence of perceived predation risk. English sole, with the highest predation rates, tend to bury less frequently, exhibit an arched body posture (with head elevated off the bottom), and have generally higher activity levels in the presence of predators when compared to the other two species. Because of these behavioral characteristics, which render them more conspicuous, English sole are encountered more frequently by halibut predators than the other two species. Additionally, English sole are less likely to escape from these predators once pursued. As an estuarine dependent species, English sole are generally exposed to lower densities of predators in an environment that tends to be highly turbid. As a result English sole, may have "relaxed" anti-predator behaviors in comparison to northern rock sole and Pacific halibut which recruit to less turbid, predator rich, coastal nurseries.