Influence of predation risk on individual spatial positioning and willingness to leave a safe refuge in a social benthic fish

Abstract

Abstract: Certain individuals tend to occupy frontal positions within social groups. Less is known about how predation risk can affect individual spatial positioning and group fidelity. We tracked individuals within groups goldfish (Carassius auratus) as they left a safe, covered, microhabitat to enter a risky, open-water, microhabitat over 2 days: one with and one without an avian predator (little egret—Egretta garzetta) present. For each day, an outing index was calculated to take into account both individual order of emergence from the refuge and the proportion of outings participated in. Prior to the experiment, fish were individually marked for identification, measured, and tested for boldness to enter a novel area. Body size did not predict individual outing index scores on either control or experimental days. Boldness index scores influenced outing index scores only on days with an egret present. We found individual outing index scores to be relatively consistent across both days, regardless of the presence of a predator. However, the presence of a predator increased the mean outing index score of the highest ranked fish and decreased the number of fish that occupied lead positions, suggesting that risk amplified the behaviour of the boldest fish. Furthermore, the presence of the predator decreased individual willingness to leave the safety of cover. Thus, we show that the introduction of a predator influenced social group movement and that the boldest individuals emerge at the front of the group under risk. Significance statement: Within social species, some bold individuals tend to occupy positions at the front of the group. Groups of goldfish were provided a safe covered refuge, and we recorded the order in which individuals left the refuge to enter an open water environment over multiple outings. We examined fish behaviour over 2 days: with and without a predator present. We found that the predator decreased the probability the fish would leave the safe refuge; however, relative individual fish behaviour and positioning were consistent over the 2 days. Interestingly, the presence of the predator amplified the behaviour of the boldest fish. Our results demonstrate that predation risk can influence group and individual prey behaviour and illustrate that bold individuals emerge at the front of groups when risk is high.