Noisy neighbours threaten reef fish

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You might think noise pollution is only a problem for humans, but it also influences fish’s choice of territory.

New research has suggested artificial sounds like engine noise are hampering their house-hunting efforts by leading them away from good habitats.

Baby tropical fish spend the first few days or to weeks of their lives out at sea. When they reach a certain age they use the sounds of coral reefs – fish calls and the clicks produced by invertebrates like crabs – to guide them towards safe habitats where they can settle down.

However, artificial sounds like boat engines could confuse them, attracting them to these dangerous noise sources instead.

These findings, published in Behavioral Ecology may have serious implications efforts to protect coral reefs. Dr Steve Simpson, Senior Researcher in the University of Bristol’s School of Biological Sciences, argues that the damage caused to fish populations if they are distracted from their natural habitat will ‘only further the harm reefs are already suffering at the hands of pollution and global warming’. He says the cumulative effects could be devastating.

Simpson and his team carried out the study on the Great Barrier Reef. They collected baby damselfish as they returned to coral reefs. They then put them in tanks with speakers playing either natural reef noise or a synthesised mix of pure tones.

The next night they moved the fish into tube-shaped tanks. Both tones were played into these tanks. Both groups of fish were attracted to natural reef noise. However, the ones that had not heard artificial noise swam away from it, while the ones that had been exposed to it moved towards it.

The study debunks the common assumption that fish have a three-second attention span. The fish’s reactions to the noises suggest that they remembered events from the previous day.

Simpson explains ‘it also shows that they can discriminate between sounds’, and this in turn shows fish’s minds adapt to their environment.

It might be possible to teach them through sound; this would have important implications for environmental conservation. Scientists could train fish to swim towards or away from particular sounds, guiding them to better environments.

Simpson himself carried out a study into this in the Philippines. Though he was hampered by the quality of the coral reefs and the small number of fish larvae available the idea is also being looked at by companies that run ocean power-stations, who are developing techniques to prevent fish being sucked into their mechanisms.

These studies highlight the rich research potential of the relationship between sounds and the oceans, and its potential implications for the environment.

Simpson also calls for the creation of ‘acoustic sanctuaries’ for fish. He argues that important locations like hatcheries should be protected from dangerous sounds.

Another potential solution to the problem of noise pollution is the development of quieter engines on boats or power-plants, and on techniques like ‘bubble curtains’ where a thick stream of bubbles is produced to insulate against sound.