Fish come back for water music

New Zealand researchers have helped to prove that dead coral can be restocked with fish, using artificial noise to mimic a living reef.

Experiments at Lizard Island on Australia's Great Barrier Reef showed that underwater speakers emitting high- and low-frequency sounds could attract fish to patch reefs of dead coral dropped on the sea floor.

The chair of marine science at Auckland University, Professor John Montgomery, said earlier work at the Leigh marine reserve, north of Auckland, had shown that young fish were attracted to sound.

"We then had to go up to the Tropics to do work on coral reefs to show it was a genuine phenomenon and establish the amount of settlement."

The findings of Professor Montgomery and Dr Andrew Jeffs of the National Institute of Water and Atmospheric Research have been published in the April volume of Science magazine.

The research started in New Zealand and continued with the help of the Australian Institute of Marine Science, Edinburgh University and the Curtin University of Technology.

It has implications for regenerating failing coral reefs and identifying potential adverse effects of man-made noise in the marine environment, such as that from recreational boating, ships, wharves and coastal industry.

Professor Montgomery said there was a risk that if fish didn't differentiate between sounds there could be problems "like, bizarrely, fish following boats out to sea", or being confused about where reefs were.

For example, there were suspicions that crayfish had settled near the New Plymouth power station because of the noise from the coastal plant, and at Gisborne because of noise from the wharves.

Professor Montgomery said there was "a hint" from the work at Lizard Island that different fish were attracted to different frequencies.

In the research the reefs were squirted with fish anaesthetic so any overnight settlement could be recorded in daylight.

More research was needed to develop a three-dimensional sound record to map out an acoustic footprint of a reef, he said.

If it was known what sort of noise a healthy reef made its condition could be monitored, or artificial noise could be used to help re-populate reefs that had been fished out.

Dr Jeffs suggested healthy reefs sounded like loud static or two bits of sandpaper rubbing over each other. The noise came the animals moving around, scratching, rasping, calling and feeding, along with wave action.

"The reef is a very noisy place, like the hum of a city."

Dr Jeffs said the sound in water was transparent and could travel large distances. Fish could pick up noise many kilometres away.

Dr Jeffs said noise was clearly a clue young fish used to return to reefs.