Context-dependent impacts of anthropogenic noise on individual and social behaviour in a cooperatively breeding fish

Anthropogenic (man-made) noise is a global problem and present in virtually all terrestrial and aquatic environments. To date, most studies investigating the potential impact of this pollutant have focused on individual behavioural responses and simply considered whether noise has an effect. However, most animals engage in social interactions, which may be vulnerable to the adverse effects of noise, and work in other fields suggests that individuals might react differentially to comparable noise stimuli depending on their own characteristics and the current situation. We used controlled experiments and standardized tests to investigate the impacts of playback of the noise of a passing boat, a dominant acoustic stressor in the aquatic environment, on nest-digging behaviour, antipredator defence and social interactions in small groups of Neolamprologus pulcher, a territorial and cooperatively breeding cichlid fish. Our results show that, in comparison to ambient noise, playback of boat noise: (1) reduced digging behaviour, which is vital to maintain hiding and breeding shelters; (2) decreased defence against predators of eggs and fry, with direct consequences for fitness; and (3) increased the amount of aggression received and submission shown by subordinates. Moreover, the context (presence or absence of eggs) affected individual and social behaviours in response to the same noise source. Our results demonstrate the need to consider whole behavioural repertoires for a full understanding of the impact of anthropogenic noise, and indicate that the effects of this global pollutant are likely to be context dependent.