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Recordings of coral reef sounds attract fish
Pied Pipers of the Reef
Tina Butler, mongabay.com
May 24, 2005


According to an international team of researchers based in Australia's Great Barrier Reef, using recordings of reef sounds may increase reef fish stocks depleted by shipping traffic, underwater drilling and overfishing. Scientists have discovered that some species of young coral reef fish are lured back to home reefs by sounds they hear while still developing in the egg. By piping in convincing ‘reef music,' consisting of recorded fish and shrimp noises through underwater speakers, marine biologists have been able to attract reef fish to artificial reefs to start new colonies. In the future, researchers hope to employ the same tactics to lead young reef fish to natural reefs where fish stocks have been decreased by outside factors or to populate newly established conservation areas.

Many coral reef fish species are spawned on the reef, with eggs developing under the care of parent fish until hatching, but mature elsewhere. Some species of larval reef fish relocate to the open sea after hatching to avoid predation by other reef organisms. Previous studies have discounted the belief that reef fish larvae are merely passive passengers on ocean currents. Feeding on plankton, the larvae mature into juveniles, moving back onto the reef when they are larger and less vulnerable. Even though these young fish spend at least four weeks at sea, traversing significant distances, young coral reef fish eventually find their way back to a reef to make a permanent home.

Heron Island on Australia's Great Barrier Reef

Although just millimeters long initially, reef fish larvae can consistently swim faster than the currents they float in. In some cases, researchers recorded young fish swimming as far as 125 miles from their reef of origin. Scientists had determined that they were exceptional swimmers for their size, but the question remained--how did they know which way to go? Information from the study, recently published in the April 8, 2005 issue of Science, suggests that fish take auditory cues from specific animal sounds to guide them back to their home reefs. By acting as ‘Pied Pipers' of sorts, researchers have discovered they can draw fish into artificial reefs for settlement. What is more, marine biologists have found that by playing similar noises made by the reef fish and other organisms of the habitat to fish eggs, fish embryos actually hear the noises before hatching and register the recognition of sound as they mature.

The research team behind the study, headed by Dr. Stephen Simpson, from the University of Edinburgh's School of Biological Sciences, was stationed on Lizard Island, located near the northern end of the Great Barrier Reef. After building 24 patch reefs near the island, researchers broadcasted imitation reef noises on half of the patch reefs using an innovative submersible speaker system developed in New Zealand. The noise the marine biologists simulated consisted of a series of pops, bangs, whoops and trumpet sounds used by nocturnal fish to communicate as they hunt. There was an additional recording used that played a background crackle noise, like that made by the claws of snapping shrimp.

Simpson and his colleagues studied two families of reef fish, damselfish and cardinal fish, believed to be most important in the reef habitat. Experimenting on both silent and ‘noisy,' speaker-assisted artificial reefs produced illuminating evidence on fish behavior. Fish not only locate settlement sites using reef sounds, but also discriminate between different sounds. Their aural memories from inside the egg, known as acoustic conditioning, may imprint the particular noises of their natal reef on fish. The marine biologists found that the studied damselfish, also known as clownfish, were drawn to the high frequency noise of snapping shrimp, while the cardinal fish responded to both high and low frequency noises produced by shrimp and other fish. Whatever the frequency, the affect of the noise is so strong that the number of fish arriving on noisy reefs was six times that for the silent reefs.



Researchers behind the study warn that foreign and unnatural noises created by shipping and drilling may be depleting fish stocks in sensitive areas. Overfishing and damage to natural habitat are also serious threats to coral reef fish. In order to manage these fish species effectively, scientists need to understand their behavior, especially during the open water developmental stage in relation to sound. Reefs are noisy environments, full of crackles and snaps from other inhabitants like shrimp and various fish species, combined with the ambient sounds of surf, wind and rain. The underwater cacophony of clicks, clacks and pops is a powerful navigation tool for juvenile reef fish to find their way home. Scientists hypothesize that larval crabs and rock lobster probably use the same acoustic cues to find the coast from out at sea. In light of these findings, human activities such as drilling may be seriously impacting fish populations that can no longer rely on their aural memory because it is drowned out by foreign sounds.

Great Barrier Reef fish. Photo by Brian Mathy.

In recent years, sounds made by everything from fishing boats to naval sonar tests have been making the world's ocean much noisier places than they used to be. There are several adverse effects of increasing marine noise pollution on sea life. Most notably, whales are becoming disoriented by sonar signals, which interfere with their navigation. In the case of young reef fish, there are several factors of increased risk. Considering fish are attracted by the noises of their peers, it is likely that areas emptied of other reef organisms through overfishing and other disturbances may be slow to re-colonize. Or, if fish only sense less specific noise, there is a danger that other noises could draw them into unsuitable areas. Scientists believe that a better understanding of the underlying sensory and behavioral mechanisms will aid in the active management of reef fish populations in the future. With this new information, marine biologists have gained crucial insight that will undoubtedly aid in protecting this fish populations as well as the health of reef habitats.





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