Risk-taking behaviour in foraging perch: does predation pressure influence age-specific boldness?

In fish, predation risk is often size-specific due to gape limited piscivores and visibility constraints. We have investigated whether risk-taking behaviour in perch varies in accordance with size-specific predation risk in their natural habitat. In our two study lakes, the risk of cannibalism was estimated from fishing survey data. In Lake Fisksjön, the relative risk for juvenile perch was much higher than in Lake Ängersjön in the early stages, but after reaching a body length of approximately 70 mm the situation was reversed, with higher predation risk in Ängersjön than in Fisksjön. Groups of perch, from either of the two lakes and of two age classes (0+ or 1+ years), were given the choice of foraging in an open area or hiding in the vegetation in the presence of a predator. Three measures of boldness were estimated: proportion of time spent in the open area, latency to start feeding and duration of first feeding bout. A principal component analysis was used to calculate individual boldness scores from a combination of the behaviour estimates. Differences in boldness scores within age classes corresponded well with the relative attack rates in the two lakes. In the youngest age class, perch from Fisksjön were less bold than those from Ängersjön. In the older age class, the Fisksjön perch were bolder than those from Ängersjön. Within lakes, boldness differed between age classes. Seemingly, perch adjust risk-taking behaviour to perceived predation risk.