Noisy oceans may lead fish astray

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Human-generated noise may have dangerous consequences for young fish, according to researchers working on the Great Barrier Reef.

While it is already know that both fish and corals used the symphony of sounds generated on a reef to navigate towards their territories, new research shows that recent experience is key for fish in terms of deciding which noises to follow.

Given that larval fish spend their larval stage in the open ocean and must return to the reefs to live out their juvenile and adult lives, being able to follow the correct sound cues is crucial to survival.  

Dr Stephen Simpson and colleagues conducted their research off Lizard Island, Australia. The team caught young pomacentrids from the reef, and then transferred them to the lab for acoustic conditioning.

The fish were divided into three groups and played a continuous loop of either reef sounds (invertebrate clicks and fish vocalisations previously recorded on the Great Barrier Reef) or tonal sounds (an artificial mix of sounds of varying amplitudes), or were kept in silence.

After the noise conditioning, the fish were returned to choice chambers in the ocean where they were played a variety of sounds via underwater speakers, and it was here that the researchers saw clear differences how fish behaved, based on their previous acoustic experience.

Fish that had previously heard reef noises responded positively to reef noise payback, swimming towards the source of the sound.

In contrast, when played tonal sounds, they generally swam away from  its source. When the same tests were carried out on fish previously played tonal sounds, a similar pattern was seen for reef sounds – the fish swam towards them – but they also swan towards tonal sounds.

The results have a potentially huge impact, as Dr Simpson explains: "Anthropogenic noise has increased dramatically in recent years, with small boats, shipping, drilling, pile driving and seismic testing now sometimes drowning out the natural sounds of fish and snapping shrimps.

"If fish accidentally learn to follow the wrong sounds, they could end up stuck next to a construction site or follow a ship back out to sea."

The true impact of this on maintaining healthy fish population at reef sites is not yet clear, but the research group warn that its effects are potentially devastating and clearly merit further investigation.

More details are contained in the full research paper: Stephen D. Simpson, et al.  Behavioral plasticity in larval reef fish: orientation is influenced by recent acoustic experiences. Behavioral Ecology August, 2010.