Anthropogenic noise increases fish mortality by predation

Anthropogenic noise increases fish mortality by predation

Noise-generating human activities affect hearing, communication and movement in terrestrial and aquatic animals, but direct evidence for impacts on survival is rare. We examined effects of motorboat noise on post-settlement survival and physiology of a prey fish species and its performance when exposed to predators. Both playback of motorboat noise and direct disturbance by motorboats elevated metabolic rate in Ambon damselfish (Pomacentrus amboinensis), which when stressed by motorboat noise responded less often and less rapidly to simulated predatory strikes. Prey were captured more readily by their natural predator (dusky dottyback, Pseudochromis fuscus) during exposure to motorboat noise compared with ambient conditions, and more than twice as many prey were consumed by the predator in field experiments when motorboats were passing. Our study suggests that a common source of noise in the marine environment has the potential to impact fish demography, highlighting the need to include anthropogenic noise in management plans.

Since the Industrial Revolution, anthropogenic (man-made) noise has changed the soundscape of many terrestrial and aquatic ecosystems1, 2, 3. International legislation, such as the US National Environment Policy Act and the European Commission Marine Strategy Framework Directive, recognizes the need to assess and manage the biological impacts of noise-generating human activities. However, while recent studies have demonstrated that anthropogenic noise can detrimentally affect animal hearing thresholds, communication, movement patterns and foraging3, 4, 5, it is often difficult to translate these effects into meaningful predictions about individual fitness and population-level consequences6, 7. This is because animals may be able to move away from noise sources, acoustic disturbance may be sporadic, and compensation by organisms may prevent long-term impacts3, 6, 8. Recent correlative evidence suggests that naval sonar may cause mortality in beaked whales9, but it is impossible to test this directly. Thus, there is a clear need for experimental studies on tractable organisms that investigate directly whether common sources of anthropogenic noise reduce survival.

In marine environments, noise pollution is derived from a variety of sources including pile-driving, seismic surveys, shipping and motorboat traffic3, 4. Much of this noise occurs in coastal regions, which are experiencing unprecedented human population growth10 and thus significant rises in transportation, fishing and recreation activities that involve boating11. For example, there were >12.5 million registered motorboats in the USA in 2013 (ref. 12) and there are expected to be 0.5 million recreational motorboats using the Great Barrier Reef by 2040 (ref. 13). Motorboats are therefore a prevalent and increasing source of anthropogenic noise, with emerging evidence that this noise could affect communication, orientation and territorial behaviour in fish14. Unlike industrial sources of noise such as pile-driving and commercial shipping, it is relatively straightforward to design studies that use motorboats in controlled experiments to test impacts of noise on marine organisms.

Here, we examine the effect of motorboat noise on predator–prey dynamics and survivorship using a model coral reef system that lends itself to manipulation, observation and replication: the Ambon damselfish Pomacentrus amboinensis and its predator, the dusky dottyback Pseudochromis fuscus. Damselfishes share life-history traits with the majority of benthic and coastal fishes and invertebrates, typified by demersal, site-attached adults that produce pelagic larvae that develop in open water before settling to suitable habitat where they will live as juveniles and adults15. On settlement to reef habitat, young naïve fish encounter a suite of novel predators and suffer high rates of mortality that make the first few days post-settlement a critical population bottleneck16. We tested the impact of motorboat noise on the post-settlement survival, physiology and performance of P. amboinensis when exposed to the predator P. fuscus, thus providing a direct assessment of the fitness consequences of anthropogenic noise. We found that both motorboat noise and direct disturbance by motorboats elevated stress and reduced anti-predator responses, more than doubling mortality by predation.



Nature Communications
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