For all his interest in fish
and other underwater creatures,
man's efforts to observe them in their
mysterious watery medium have met with
limited success. Fish biologists have
always relied heavily on electrofishing,
netting,creel counts and commercial fishing
records to increase their knowledge of fish
behavior. Information gathered from these
sources tells where the fish are, but it seldom
tells why the fish are there
While it would seem that scuba diving
would be an ideal way to gain first hand knowledge
of a fish's world, it is a tool that has seldom been
used in scientific research. An exception to this
is a current study to find out more about catfish
in the Upper Mississippi River. For the past two years
biologists have been diving to the bottom of the Mississippi
to study the winter behavior of flathead and channel cats.
For years it has been known that each winter catfish gather
in the Mississippi's main channel in deep scour holes on the
outside bends where there are strong currents
But knowing why the catfish are attracted to these areas
has become increasingly important, since the US Army Corps of
Engineers has proposed dumping dredge spoils in the river.
Exact dump sites have not been identified, but traditional
catfish wintering areas seem to be the pre ferred location
as the dump site must have currents strong enough to move
the spoils down river
The Corps has conducted engineering and
hydraulic studies to determine if spring runoff will carry
the spoils down river, but they have done no research on its
effects on fish.
Little catfish research of any sort, in fact, has been done
by Upper Mississippi River state natural resource departments.
Traditionally, fish biologists have relied heavily on commercial
fishermen as an important source of information about catfish
behavior
Commercial fishermen report catfish movement out of
backwater areas into the main river as early as October, with
the aggregations forming from the middle to the end of November
and break up in March. These aggregations are collections of
catfish that are found together, but do not react as a group
In the past Minnesota and Wisconsin fish biologists have
done conventional shocking and netting studies on some catfish
wintering sites. Using these techniques in 1977, Wisconsin DNR,
fish biologist Tim Larson and Richard Ranthum reported 2,732
catfish per acre at a wintering area in Pool 7 near Trempealeau.
But still unanswered was the question of why the fish congregate
in particular areas.
To find out, Minnesota DNR fish biologists Bruce Hawkinson
and Gary Grunwald suggested scuba diving to the river bottom to
see what the fish were doing, what the bottom looked like and
how the wintering site differed from other areas of the river
Exploring the Mississippi in 33 degree water took special
equipment and the combined efforts of the Minnesota DNR,
Wisconsin DNR and the University of Wisconsin-Madison Marine
Studies Center
Making the first dive on February 26, 1979. were Mike Talbot,
a Wisconsin DNR fish biologist stationed at Alma, and Doug
Stamm, an experienced diver and photographer from the UW-Madison
Marine Studies Center.
To swim in the frigid water Talbot and Stamm used dry suits
instead of the usual wet suits. While wet suits rely on a layer
of water to keep the diver warm, dry suits are waterproof and
use a layer of air to insulate the swimmer. In spite of the
extra warmth of the dry suit. Talbot said he had to fight the
rage to get out and warm up. Each of their five dives lasted
about 30 minutes.
Even if the divers had not wanted to study the winter lives
of cats, late winter would still be the best time to examine
the Mississippi's bottom.
"Visibility is best during the winter as the current is
slowest and the sediments less, Talbot said "I've done some
diving in the Mississippi in the summer and 10 feet down you
can't see your hand in front of your face. On our catfish dives
we were in depths up to 25 feet and could see eight to 10 feet
away."
And what they saw were catfish lying on the silt free sandy
bottom, always behind rocks. The rocks ranged in size from as
small as a fist to as large as a basketball
"We dived at Diamond Island near about a half mile below
Lock and Dam #3. The shoreline had been riprapped (rocks placed
on a river bank to stop erosion) by tile Corps in the late
thirties. Some of the rocks from the riprap were on the flat
sandy bottom of the river. Almost every rock had a fish behind
it," Talbot said.
"We were surprised to see the number of fish we did and that
all these fish were behaving the same way."
The cats were lying on the bottom with little or no body
movement--no gill movement, no eye movement, no fin movement.
Some of the fish even had a fine layer of silt on their backs.
The catfish allowed the divers to approach and touch them...
something that would be impossible in summer. While they were
submerged the divers estimated catfish numbers and measured
oxygen levels and current speed. In an area about 300 yards long
the population varied from about 250 per acre to as high as
2,350 per acre. This compared quite well with the 1977 study by
Larson and Ranthum.
Why were all the fish found so close to rocks? Behind the rocks
there was little or no current, while a foot above themit was
one third to one half foot per second.
There was no segregation by size or species. At times the
fish were lying almost on top of each other. In some cases they
seemed to use one another as protection from the current. Divers
estimated that 75 percent of time catfish had white, fluffy
nodule like infections on their fins. The fish averaged 25 pound.
About 85 percent of the fish were flatheads, with the rest
channel cats. Besides the catfish, the divers saw only one dead
shad and one live freshwater drum.
In addition to diving in the riprap area and near a wing dam,
Talbot and Stamm investigated a portion of the river with a
naturally eroded bank. The current was less than half that of
the main river. At that site a layer of silt covered the sand,
there were no rocks on the bottom and only four catfish.
Bottom depth wasn't so much a factor as the bottom features.
Level sandy areas behind rocks appeared to offer the fish what
they needed, for all fish chose such areas. Catfish were not
found behind rocks along the irregular and steeply sloping bank
or wing dam face.
While the 1979 dives answered some important questions,
several others remained. Was this wintering site typical? Would
it vary from year to year and site to site? To help answer these
questions, and also to tag the catfish so their movements could
be studied, more dives were planned for 1980
Because of weather and scheduling difficulties, the divers
did not plunge into the icy water until nearly a month later
than the previous year. On March 19 Talbot dove with Bill Horns,
a UW Madison Department of Zoology teaching assistant, about
one mile south of Lock and Dam #4 at Alma. Spring runoff had
already started. They saw only 22 catfish and three walleyes.
"One of the things we found out was that the aggregation was
not unique to the Red Wing area," Talbot said. "This year there
were rocks on the bottom and the catfish were much the same way
as last year.
"The fish were smaller and more active. Their orientation to
the current was not as strong as at the Red Wing site. But I
think the differences were mainly because we dove so much later
this year. It was close to time for them to break up. There was
so much sediment we could only see three to four feet in front
of us and the water temperature and current speed were different
than last year."
During the next day's dive, Talbot and Horns saw no catfish
although they were in an area known to harbor wintering cats.
The current was so strong the divers had to pull themselves
along the bottom and visibilitymwas even worse than on the day
before. However, they confirmed that the river bottom resembled
the other dive sites with rocks scattered across the sandy
bottom
Talbot and Horns did not see enough fish to do the scheduled
tagging, but they tagged a few to see if it was possible to do
it underwater. They were successful, although they disturbed
the catfish more than they would have liked.
All of the cats were observed in areas where rocks were
deposited on the river bottom from riprapped banks or from wing
dams. However, Talbot pointed out that both flatheads and channel
cats are native, and winter aggregations occurred before human
engineers redesigned the Mississippi. Rocky areas were in the
river naturally, although in different locations.
From their observations, the biologists are convinced that
catfish require a silt free, level location combined with
shelter from the current for their wintering site. Strong
currents are necessary to keep the area clear of silt.
In their dormant state, silt would cause the fish problems
by plugging up their gills. Silt also harbors microorganisms
that could cause diseases. Even in the chosen areas the fish
had problems with fin infections in the silt free areas where
the divers saw them. They also must have rocks to lie behind so
they can hold a position without using energy.
Isn' it hard to see how these findings reflect on the Corps'
proposal. Under the Corps proposal, sand dredge spoil would be
pumped into deep scour-holes and river bends during spring and
summer when dredging requirements are greatest. These sand
deposits would remain throughout the fall and winter until
scouring action during spring runoff carried them downstream.
Thus, the rocks used by the catfish would be covered by sand
during the winter, forcing the fish to other areas. If there is
only one suitable catfish wintering area in a pool, burying it
with sand would probably doom all the fish in that pool
Talbot hopes to continue his under water research into the
lives and habits of Mississippi River cats. And he would like to
expand his research to other fish species. He feels that scuba
diving has generally been overlooked as a useful fish
management tool.
Divers could assess spawning areas, determine fish usage of
artificial structures, investigate fish kills and help
population studies by observing tags.
While certain specific things can be learned by diving, a
less tangible but certainly important benefit is the "fish eye"
perspective the biologists now have of underwater problems.
