Altered Prey Responses in Round Goby from Contaminated Sites

Although prey must move to forage, escape predation or gain information about predation risk, movement itself enhances the risk of predation by increasing visibility of prey and encounter rates with predators. Animals subjected to stressors often show altered behaviour; a widely cited effect of contaminant exposure is an increase in vulnerability to predation, which may be mediated by an increase in risky behaviour. Round goby are invasive fish that typically rely on crypsis and sheltering (low-activity behaviours) to avoid predators. We collected round goby from contaminated sites and tested whether they showed signs of altered risk-taking compared with fish from a less contaminated reference site. We subjected the fish to a simulated predation event (a motor-operated model bass) under both diurnal and nocturnal conditions. Fish from contaminated sites showed lower overall activity levels, but also failed to reduce activity following an attack, unlike fish from the reference site. The intensity of effects varied with diel period. Males, but not females, from contaminated sites showed reduced likelihood of darting during an attack, while females, but not males, from contaminated sites were less likely to approach the predator. Sex differences in round goby risk-taking may reflect sex-specific selection pressures on activities promoting predation risk. With the exception of post-attack activity, round goby from contaminated sites generally showed signs of reduced risk-taking. If contaminant exposure increases goby vulnerability to predators, it may be occurring through behavioural mechanisms other than impacts on risky prey responses.