|
Winter Catfish
Scuba divers have made discoveries about wintering
river catfish which could be
important to future river management.
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 pro posed 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 air 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 sad "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 lay was
little or no
current, while a foot above them it 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 arid 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 visibility was 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 many of these areas have been.
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't 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.
SUBMITTED BY: Member JimHS
Read more free catfishing articles on our forums -
Catfish in the news
Enter Forum |
