Fish Sounds
Researchers study fish conversation
by Carolyn Lucas
West Hawaii Today
Monday, August 4, 2008 12:15 PM HST

University of Hawaii at Manoa professor Tim Tricas uses a closed circuit rebreather, which produces no bubble noise, to deploy hydrophones at a site of yellow tang spawning on the Kona coast. - Kelly Boyle | Special To West Hawaii Today

University of Hawaii at Manoa zoology professor Tim Tricas has been eavesdropping on "fish cocktail parties" occurring on the reefs of Puako and Pawai Bay since mid-April.

Tricas and his assistant, UH graduate student Kelly Boyle, are collecting hundreds of gigabytes of recorded grunts, clicks, pops, hums, pulses and other underwater racket.

Undergraduates Atma Bhawuk and Geraldine Cadalin are helping analyze the digital audio data in the lab at UH Manoa in Honolulu. They are doing spectrum analysis using sophisticated computer software to determine the frequencies in each sound and to determine what time of day the sounds are made.

So far the researchers have discovered at least 30 different sounds -- the beginnings of an acoustic library for Hawaii reef fish. It is possible to classify the types of sounds that can be produced by fish families whose calls are known, even though most of the fish sound producing mechanisms are unknown, Tricas said.

The yearlong project to Tricas' lab at Hawaii Institute of Marine Biology is funded by a $70,000 grant from the National Oceanic and Atmospheric Administration, Hawaii Undersea Research Laboratory and University. The undergraduates are supported by a National Science Foundation grant to promote study in math and biology research. The objective is to use progressive technology and acoustic activity of fish to asses biological activity on coral reefs. Monitoring wildlife behavior is important for resource management and conservation, Tricas said.

The research sites were chosen because of their distinct differences, accessibility and reputation for having lots of fish. As a fishery management area, Puako has a relatively undisturbed pristine reef. Pawai Bay is located at the far northern end of the runway at Old Kona Airport Park. More boat traffic, as well as commercial and recreation activities, tend to occur there.

Hawaii has more than 1,200 species of fish, many found on in coral reef ecosystems. Many -produce sounds associated with feeding, social behavior and reproduction. However only three or four species in Hawaii have been reported vocal in published scientific papers. Tricas attributed lack of funding, resources and interested researchers as reasons why.

The scientific community doesn't know how most fish make noises. However, some species produce weak low-pitched sounds by striking or rubbing together skeletal parts like teeth or fin spines; using muscles located on or near their swim bladder; slapping the water with their tail or fin; and quickly changing speed or direction while swimming, Tricas said.

Several species of mempachi that are common on Hawaiian coral reefs produce sounds that may be of use for remote monitoring of fish population activity. - Tim Tricas | Special To West Hawaii Today

To use fish sounds as indicators of coral reef health, the sound producer has to first be identified. Using innovative underwater breathing apparatuses called closed-circuit rebreathers, Tricas and Boyle are able to fade into the background of the aquatic landscape. They watch natural behaviors of various species without the noisy "freight train" air bubbles normally associated with scuba diving. While visually identifying species, these researchers record their low-pitched fish sounds with an underwater camera and hydrophone, which is basically a waterproof microphone.

One video clip, taken by Tricas, shows a hydrophone being held near a mempachi as if about to be interviewed. The fish with the large black eyes suddenly voices a series of pops and swims away. The hydrophone goes to the next mempachi and more pops are heard.

Closed-circuit rebreathers are proving to be highly beneficial to observing marine life. The devices do not release any bubbles into the open ocean, thus allowing the diver to get up close and personal with fish in a silent, outer space like environment.

Rebreathers completely recycle a diver's exhaled gas. Scrubbers clean out the carbon dioxide that can become toxic over time. Sensors add precise amounts of oxygen.

Conventional scuba gear is often used by researchers studying marine life, but is limited in depth, duration of dives and decompression times. Closed-circuit rebreathers, on the other hand, allow divers to go deeper and stay underwater longer. Approximately three hours of underwater time per day are possible with these systems. To use the closed-circuit rebreathers, Tricas and Boyle were trained by the UH Diving Safety Office.

An Environmental Acoustic Recorder records fish sounds on West Hawaii's coral reef. Researchers can download data and analyze patterns of fish sounds that may be of use in monitoring of fish populations. - Tim Tricas | Special To West Hawaii Today

During the dives, the researchers also use a Short Term Acoustic Recorder with four hydrophones that can be deployed at different locations. While the STAR is recording, Tricas and Boyle make timed observations about the behaviors of the fish.

Two-foot-long Environmental Acoustic Recorders, developed by UH, are also deployed. These passive acoustic devices simply listen to the sounds around them, including noise from marine animals and boats. EARs blindly record what is heard underwater for 5 minutes every hour. It can retrieve data this way for up to a year, Tricas said.

These long-term recordings can be used to monitor the behaviors of identified species, including when the fish are most active, feeding or undergoing important life cycles like reproduction.

Once a sound is classified to a species and managers know that it is associated with, for instance, spawning, they will be able to monitor the location, time, seasons and environmental conditions without being in the water and disturbing the fish or interfering with their behavior. Other future applications for the biological sounds include remote monitoring of population size, comparing behaviors of species on various reefs, or determining the effects of anthropogenic sounds on fish.

For more information about this research project, send an e-mail to Tim Tricas at tricas @ or visit