Underwater noise impairs social communication during aggressive and reproductive encounters

Human-generated noise pollution is of global concern, as designated by the World Health Organization ( WHO, 2011 , Burden of disease from environmental noise: Quantification of healthy life years lost in Europe. https://www.who.int/quantifying_ehimpacts/publications/e94888/en/). Increases in shipping, sonar use, pile driving, and more have all contributed to a rise in ambient underwater sound levels. Unfortunately, continuous low-intensity sounds, like shipping noise, are pervasive in shallow-shore environments where many social species live and correspond to the frequency ranges at which many fishes produce and detect acoustic stimuli. Noise has the potential to alter the sender's production of the signal, mask the signal itself (if acoustic), or change the receiver's physiology. We hypothesized that continuous tonal noise would impair social interactions and communication. To test this, we used highly social African cichlid fish, Astatotilapia burtoni, to examine inter- and intrasexual interactions that occurred in a control or noisy environment (pure tones of 100–2000 Hz). During reproductive interactions, we found that males changed the location of their courtship behaviours. Instead of producing courtship quivers (and associated sounds) immediately next to gravid females, males produced these behaviours inside their spawning shelter. This change in location decreases the likelihood of the female detecting it. Also detrimental to acoustic communication, we found that noise-exposed gravid females had lower hearing sensitivity at 100–200 Hz, a major component of male courtship sounds. In addition, males changed their visual displays during male–male territorial interactions such that they spent more time with their eyebar displayed, suggesting an increase in visual signalling. Together, these data indicate that noise may impact all three components of social communication: signal production, signal reception and the signal itself, and highlights a possible cross-modal impact of noise on visual signalling. Subtle changes to social behaviours and communication, rather than dramatic effects such as injury or mortality, are important to evaluating sublethal impacts of noise on reproductive success and species survival.