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Examination of sonar as a tool for studying catfish behavior
BY C. DOUGLAS MINCHEW AND
KENNETH K. MCDILL
MSU National Warmwater Aquaculture Center
An obvious difference between production of catfish and terrestrial animal
production such as cattle farming is the difficulty of observing the animals living in the
aquatic environment. Cattle farmers can visually assess their stock . They can count them,
weigh the, tag them, sort them into groups, look for new born calves, or do any number of
other things which will help them make informed management decisions. Catfish farmers are
not so fortunate. They can evaluate the condition of their levees and equipment, observe
whether or not fish eating birds are causing a problem, and make some judgments about the
condition of the quality of the water in the ponds. However, unlike the cattle farmer, the
catfish can not tell much about his fish. They know what was stocked, what has been
harvested, how much feed has been fed, and therefore has some idea about what the standing
crop should be in a pond. They have a general idea about when they will be able to harvest
but they probably do not know for certain how many pounds of food-size fish are ready for
harvest. Unfortunately, catfish farmers can't see their fish unless the fish are sick, up
at the surface due to low oxygen or feeding, or have died. Further complicating management
decisions, the catfish farmer usually has 6,000 - 12,000 of multiple year class fish in
each of their ponds. Generally the crop will include small fingerlings, stocker-size
fingerlings, small adults, food-size fish, and some large fish which have managed to
escape harvest. Because they cannot see their stock they are never sure what they estimate
is in there is actually there in the right numbers and the right sizes. Sometimes when the
catfish farmers seine their fish, they are surprised to find the fish are smaller or
largest then they should be or that the number of pounds that they expected to catch
simply were not there. In some cases, even after multiple seine hauls, the fish are not
accounted for. They simply appear to have been lost to the "black hole", which
is a term coined to describe the fate of all unaccounted for fish.
IN order to help the catfish farmers address some of these problems, researchers at the
Thad Cochran National Warmwater Aquaculture Center have initiated a fish behavior program.
The research objectives of this program focus on improving production and harvesting
methods and technologies in the catfish industry through the study of of the behavior of
catfish in ponds under normal production conditions. Like catfish farmers, we are limited
in our ability to design pond experiments to observe fish behavior because catfish pond
waters are generally turbid and have very poor light penetration. These conditions
preclude the possibility of using ambient-light photography or video recording to study
fish activities or to estimate their numbers or sizes. To overcome these difficulties, we
are evaluating the possibility of using sonar to study fish behavior.
During the past year, we have been using a modified marine sonar unit which we have on
loan form the National Center of Physical Acoustics at the University Of Mississippi to
evaluate its potential for use in our behavior program. The system consists of a tripod
mounted sonar dome which is placed in the middle of the pond with the dome at middle of
the water column. Data from the dome is transmitted back to a mobile laboratory where the
signal is converted to a standard television type signal which can be viewed in real time
or recorded on a time-lapse video recorder. The design of this particular sonar is not as
sophisticated as needed for our research; thus, we have restricted its use to making
general observations about fish movements and to help evaluate the capabilities of our
mobile laboratory. Even with its limitations, this type of equipment has great potential.
As a point of interest, we have observed the fact that not all of the fish feed during a
given feeding period. We have also observed the fish lining up behind the aerators during
periods of low oxygen before the acrators are actually turned on.
Based on the information we have obtained using the modified sonar until, the center is
participating in the development of a state-of-the-art side-scanning sonar system, a
multi-channel pulse-echo down-looking sonar system, and a specially designed software
package which will integrate the output of the two systems into a usable format which can
be stored on a laptop computer. These systems will make it possible for us to record and
analyze the vertical and horizontal movements of the fish in the ponds. When evaluated
along with information on farm activities (feeding, mowing and noises of various kinds)
and environmental factors such as temperature and dissolved oxygen concentrations, data
form studies using this equipment should provide a much clearer understanding of "why
fish do what they do and when they do it". We expect the results from our studies to
help catfish farmers make more informed management decisions.
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