While fish don't have ears that we can see, they do have ear parts inside their heads that can pick up sounds in the water.

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Not only do fish and invertebrates make their own sounds, but wind, waves and currents also create other background noise. And reefs especially are naturally noisy places.

Add this noise to the engines and horns of shipping vessels and military sonars, and we have a full-blown orchestra of marine sounds.

Consequently, fish react to the noises they hear and according to new research, boat noise can disrupt orientation behavior in larval coral reef fish.

Researchers from the Universities of Bristol, Exeter and LiÃ¨ge conducted a sound study in French Polynesia and found that while reef fish are normally attracted by reef sound, they are more likely to swim away from recordings of reefs when boat noise is added.

Sophie Holles, a PhD researcher at the University of Bristol and one of the study's authors, said: "Natural underwater sound is used by many animals to find suitable habitat, and traffic noise is one of the most widespread pollutants. If settlement is disrupted by boat traffic, the resilience of habitats like reefs could be affected."

Co-author, Dr Steve Simpson, a marine biologist at the University of Exeter, said: "Boat noise may scare fish, affecting their ecology. Since one in five people in the world rely on fish as their major source of protein, regulating traffic noise in important fisheries areas could help marine communities and the people that depend on them."

The study used controlled field experiments with settlement stage coral reef fish larvae. Larvae in a long plastic tube could decide to swim towards or away from a speaker playing back different sounds. In ambient noise equal numbers of fish were found in each section of the tube and in reef noise most fish swam towards the sound. But when boat noise was played along with reef noise more fish swam away from the sound than in reef noise alone.

Co-author, Dr Andy Radford from the University of Bristol, said: "This is the first indication that noise pollution can affect orientation behaviour during the critical settlement stage. Growing evidence for the impact of noise on fish suggests that consideration should be given to the regulation of human activities in protected areas."

The research is published in the Marine Ecology Progress Series.

See more at the University of Bristol.

Underwater image via Shutterstock.