Fish Sounds
Researchers
study fish conversation
by Carolyn
Lucas
West Hawaii Today clucas@westhawaiitoday.com Monday, August 4, 2008 12:15 PM HST |
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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.
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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.
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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 @ hawaii.edu or
visit http://www.hawaii.edu/fishlab.