Solving the Mystery of Wintering Catfish
by Donna Sanders
Fins and Feathers:February 1981
Flathead Catfish (Pylodictis olivaris)
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 al 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 waler 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.
