Abstract
Noise produced from a variety of human activities can affect the physiology and behaviour of individual animals, but whether noise disrupts the social behaviour of animals is largely unknown. Animal groups such as flocks of birds or shoals of fish use simple interaction rules to coordinate their movements with near neighbours. In turn, this coordination allows individuals to gain the benefits of group living such as reduced predation risk and social information exchange. Noise could change how individuals interact in groups if noise is perceived as a threat, or if it masked, distracted or stressed individuals, and this could have impacts on the benefits of grouping. Here, we recorded trajectories of individual juvenile seabass (Dicentrarchus labrax) in groups under controlled laboratory conditions. Groups were exposed to playbacks of either ambient background sound recorded in their natural habitat, or playbacks of pile-driving, commonly used in marine construction. The pile-driving playback affected the structure and dynamics of the fish shoals significantly more than the ambient-sound playback. Compared to the ambient-sound playback, groups experiencing the pile-driving playback became less cohesive, less directionally ordered, and were less correlated in speed and directional changes. In effect, the additional-noise treatment disrupted the abilities of individuals to coordinate their movements with one another. Our work highlights the potential for noise pollution from pile-driving to disrupt the collective dynamics of fish shoals, which could have implications for the functional benefits of a group's collective behaviour.
Highlights
Human activities, such as urbanization, resource extraction, transportation, and energy production, generate considerable noise
The distance between fish increased more, and the directional and speed organization of the shoals decreased more during the pile-driving playbacks compared with the ambient-sound playbacks
Noise from the pile-driving treatment caused significant changes to how individuals coordinated their movements with near neighbours, affecting the structure of the shoals
Summary
Human activities, such as urbanization, resource extraction, transportation, and energy production, generate considerable noise. We predicted that if the additional noise was perceived as a threat [57], the seabass would form denser, more directionally ordered shoals, with increased coordination of speed and direction changes, in the pile-driving treatment compared to an ambient-sound control treatment. The additional noise masks important information, or causes stress or distraction [4,58], the seabass would be predicted to form less cohesive and directionally ordered shoals, with reduced directional and speed coordination, in the pile-driving treatment compared to times with ambient-sound playback. One of the two sound treatments ( pile-driving noise; n 1⁄4 15 groups, or ambient sound; n 1⁄4 15 groups) was played to the fish for 5 min (termed ‘2nd half of trial’ hereafter), with filming continuing during this period. Owing to correlations between speed and maximum speed and directional correlations, and between speed and the time delay that maximized the directional correlation, the models that analysed these response variables were repeated with the fish’s speed as an additional main effect to control for the correlation of speed with the response variables
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