October 04, 2010
Thanks to a handful of transmitters and a few antennas, Iowa anglers can catch a fleeting glimpse of the secret lives of the Hawkeye State's ramblin' whiskerfish. (July 2008)
IDNR radio telemetry studies show that flathead catfish like this one hoisted by the author embark on seasonal migrations as long as 75 miles.
Photo courtesy of Ted Peck.
Grandpa's catfishing tactics used to change drastically when "cotton" started drifting into the Mississippi River off the cottonwood trees along its banks -- an annual phenomenon that should occur any time now.
He didn't have a thermometer to use for monitoring water temperature, but if the technology had been available, Grandpa would have switched from aged clams and fresh chicken livers near the channel edge to a big minnow under a bobber back in the stumps when the mercury hit 78 degrees.
We now know that when water temperatures approach this "magic" number, the forktails forgo the feedbag to concentrate on carrying on the family name by building nests in root systems and similar habitat that they defend aggressively until another generation is ensured.
If that big white spinnerbait you intended for bass finds the whiskered mouth of a catfish this month, take a quick look at the electronics on that fancy boat and note the water temperature -- odds are that it's pretty close to 78 degrees.
Generations of catfishermen on the Mississippi held as sacred truth that "cotton" on the Father of Waters signaled the movement of cats to the riffles at dusk and towards the bank on a rising river, and that theory paid dividends in the form of weighty stringers. But recent studies by the Iowa Department of Natural Resources on channel and flathead catfish on the Mississippi and several of its tributaries have revealed more about catfish movement than even Grandpa knew.
A pair of radiotelemetry studies on the Turkey and Wapsipinicon rivers in 2004 and a third survey on the Iowa River last summer -- all spearheaded by IDNR research biologist Greg Gelwicks -- tell us more about seasonal catfish movement than Grandpa could have imagined in his wildest dreams. Agency biologists captured a number of adult catfish, smallmouth bass and walleyes, implanted tiny radio transmitters in the fish, and then returned them to the rivers to track their movement.
The outlines of the seasonal movement of walleyes have been common knowledge for years, but documentation of similar migration among smallmouth bass and catfish dispels long-held notions that smallies and cats were relative homebodies.
The Iowa studies began in October 1995 as part of the federal Aid to Fish Restoration initiative. The goal of this effort was to identify the importance and abundance of suitable fish habitats in our state's interior rivers.
Back in 1995, a number of channel catfish, northern pike, smallmouth bass and walleyes of various sizes were fitted with tiny radio tags and tracked through several seasons on the Wapsipinicon River.
The study revealed nearly all radio-tagged catfish and walleyes wintered in one of two areas in a 15-mile stretch of the Wapsi between Independence and Quasqueton bordered by low-head dams at either end. These spots were generally the deepest runs of river available. According to the IDNR report, almost 100 percent of the catfish in the Wapsipinicon -- and the lion's share of the walleyes -- spent the winter in a single deep sandpit in this stretch of river.
Smallmouths in the initial study spent their winters in one of three areas. With the smallies, water depth was not the most important consideration as to their choice of locale for spending the winter months' coldwater period.
In the fall of 2000, the IDNR tagged various sizes of channel catfish, walleyes and smallmouths on the lower Turkey River in the 39-mile run between Elkader and its confluence with the Mississippi River. Signals from the diminutive devices implanted in these fish indicated that individuals of all species moved a considerable distance down into the Mississippi River to spend the winter. Every catfish made this trip as winter approached; all of the catfish that didn't die or get caught by commercial fishermen returned to summer haunts on the Turkey in the spring. From this study biologists concluded that a lack of deepwater habitat on interior rivers limited sportfish populations in these fisheries.
Initial studies also revealed the need to take an additional step when securing transmitters in channel catfish: stitching the pricey little gadgets to the cat's pectoral girdle through a surgical incision to prevent "rapid expulsion of the transmitters from the body via the intestinal tract."
Truly modern marvels, the transmitters are designed such that each broadcasts on a slightly different frequency. To optimize battery life, they're programmed to turn on every Monday, Wednesday and Friday. Monitoring took place via two types of receiving antennas -- a large boat-mounted antenna that looks like the TV antenna seen atop many houses and a smaller handheld loop antenna similar to the UHF antenna found on the back of a small portable television.
Once the general location of a tagged fish was documented, biologists would use an electric trolling motor to sneak up on the subject so that its exact location could be pinpointed. Technicians then made careful note of habitat parameters in the general vicinity, including water temperature, depth, current velocity, visibility and the presence or lack of any woody or rocky structure.
During winter months, biologists tracked fish movement from an airplane. These data indicate very little movement in catfish until spring, when warming waters goad them to move back up inland rivers.
In the Wapsi study, 45 channel catfish, 17 northern pike, 16 smallmouth bass and 31 walleyes were tagged and studied from 1995 until 2001. The monitoring on the Turkey River of 24 catfish, 23 smallmouths and 18 walleyes began in September 2000 and ran through the summer of 2003.
When final results were tallied, note was made of each fish's fate. In many cases, the batteries in the transmitters expired; in some cases, the fish were caught by sport anglers, commercial anglers or natural predators. In a few instances, the transmitters and the fish that carried them were still active when the studies concluded.
Individual specimens of all three species monitored in the Turkey River study made long-distance movements between their initial tagging location and the Mississippi. According to the survey report, the migration trend w
as "most evident in channel catfish."
During the autumn of 2000, 2001 and 2002, all active channel cats moved 28 to 35 miles from summer haunts in the Turkey down to the Mississippi. Twenty-one catfish completed the initial fall migration; eight fish made the trip in consecutive fall periods. In every instance, surviving fish "made return movements into the Turkey River to positions near the initial tagging location in the spring."
The travels of two Turkey River cats designated T-34 and T-39 are typical of most other forktails in this study. T-34 called a relatively small stretch of Turkey River home during the summer, moving down to the Mississippi in late autumn to spend the winter, returning to the same stretch of this interior river in the spring. T-39 was more of a ramblin' sort, moving down to the Mississippi in the fall, returning to the Turkey in the spring with the other catfish, and then deciding to head back down to the Mississippi with his companion, T-38, in May. He remained in the Mississippi until August, when the urge arose to return to the Turkey for a couple of months before moving back downstream again as winter approached.
Water temperature appears to be a driving force in catfish migration, with movement back into interior rivers occurring during April each year. During 2001, the Turkey River warmed from 44 to 60 degrees between April 18 and April 27, and all of the catfish being monitored moved into the warmer water. By mid-May, all of these fish were in or near the areas in which they were initially tagged.
Northeast Iowa had more difficulty shaking winter off in the spring of 2003. That year, two channel catfish moved into the lower reaches of the Turkey by March 24, drawn by 51-degree water -- much warmer than the 38 degrees out in the river. By April 9, several more catfish were also staging in the lower Turkey as they waited to move inland.
Around that time, a major cold front hit, causing water temperatures to tumble to 39 degrees in the Turkey. The sheer volume of the Mississippi enabled this awesome river to maintain a temperature of 39 degrees. All of the cold-blooded creatures moved to the warmest water, staying in the Mississippi until spring arrived in earnest about 10 days later.
The Turkey River study also indicates that depth provides a key to catfish location throughout the year, as does preference to bottom substrata. During the summer months, catfish swimming in the Turkey River are found most frequently in 2 to 4 feet of water. Between November and March, they locate in water greater than 10 feet deep over 75 percent of the time -- a fact that biologist Gelwicks found "most significant."
Wintering areas for channel catfish in the Mississippi are almost always over hard bottom or sand devoid of much structure. During the summer, woody structure is a major key to catfish location in the Turkey River.
The IDNR study also concluded that current velocity is a major key to catfish location throughout the year. Channel catfish tend to set up housekeeping in areas with low current velocity near the bottom year 'round. The key to catfish location lies in middepth current velocity: Fighting current requires energy. Lying in relatively slack water and allowing the river to bring food overhead in a current's perpetual virtual conveyor belt is a natural course of action.
Data from radio-tagged channel catfish indicate a preference on the part of whiskerfish spending the winter in the Mississippi for near-zero current velocity on the bottom and very low current velocity at middepths.
A DIFFERENT CRITTER
Serious cat-chasers will tell you that flathead catfish are critters entirely different from their forktailed cousins. A study completed on the Iowa River last summer by Gelwicks and his assistants seems to confirm this contention.
Prior to 2004, when Iowa's flathead monitoring program commenced, precious little information was available on these big, powerful fish. Studies ongoing at 12 different sites on four Iowa rivers will add to biologists' knowledge base of this species in the future; to date, IDNR biologists have sampled flathead populations on 22 tributaries of Iowa's larger interior rivers.
According to the project report published in December 2007, Iowa's fish managers only started monitoring changes to interior river fish habitats about 20 years ago. The old adage "big water, big fish" applies to flatheads of leviathan proportions. But recent research indicates the significance of riffle areas on interior streams to growing flatheads.
In total, 55 flatheads were monitored in the Iowa River study completed in 2007 that covered a 70-mile run of river from the downstream dam in Iowa City to the confluence with the Mississippi. The study also included the English River tributary and Pool 18 of the Mississippi.
Catfish in the study ranged in size from less than 3 pounds to monsters weighing more than 30 pounds -- and two of them are still swimming. The dreadnought wearing radio tag IA47 weighed 30.8 pounds when she was released near the River Junction sample site, just south of the Iowa's confluence with the smaller English River in June 2006.
According to the data, seasonal movements of the 18 flatheads radio-tagged at this site "are more mobile than catfish tagged at the other two sites." Catfish IA47 illustrates this point. It and IA27, a 12-pounder tagged and released the previous June, disappeared from the Iowa River after spawning; the following winter, they were located by aerial surveillance almost 75 miles away in the Mississippi. Catfish IA48 was tagged the same day at the River Junction site. Radiotracking data revealed that this whopper, which weighed more than 32 pounds when tagged, continues to find local habitats suitable. Her tag is still active. Her dimensions are no doubt larger, and her attitude is probably worse.
Flatheads tagged at the Hills site, about halfway between the Burlington Street dam in Iowa City and the confluence with the English River downstream, are "generally more sedentary" than cats tagged at the River Junction site.
According to Gelwick's report, the 11 catfish tagged here in 2004 and 2005 migrated an average of 19.4 miles through the seasons. One fish moved nearly 75 miles. Conversely, catfish IA12 moved only three-tenths of a mile in the 34 months during which her tag was monitored. The behavior of this catfish, which was nearly 20 pounds when tagged in September 2004, is similar to six other catfish monitored at the Hills site.
Odds are good that a fish that moved only 0.3 miles in nearly three years is probably still pretty close to home -- and considerably larger today. Flatheads are carnivores, unlike their forktailed cousins, which will eat anything from Ivory soap to shrimp. Bluegills and frogs are probably the best baits for flatheads.
The Iowa River study indicated that not all catfish move downstream towards the Mississippi as winter approaches. Flathead IA25 -- at more than 39 pounds when tagged the biggest cat in the study -- disappeared from the Iowa River in June and was located in the English River by ai
rplane in December. According to Gelwicks, "(I)t is not known when this fish died, but the transmitter was recovered from the English River the following May."
Could it be that this old fish knew the end was near and returned to the area in which it was born to die? It's anyone's guess.
A NEW PERSPECTIVE
Future studies involving this species will certainly provide more insight. "We have learned a great deal about catfish habits," Gelwicks said, "but there is so much more to learn."
The study completed in 2007 demonstrated convincingly the Iowa River flathead catfish population is more mobile than are populations studied in other states. Several flatheads from several different sites in the study were not year-round residents of the Iowa River. These fish apparently moved inland to spawn and then slid back downstream once their procreative mission was accomplished.
"Our studies indicate that movements between sites and rivers indicate population densities of flathead . . . and channel catfish in particular locations may vary through the year," Gelwicks reported. "Additional tagging and tracking will help further define extent and timing of seasonal movements. This will aid in determining population boundaries and give greater insight on overall populations."
The IDNR catfish studies have provided an epiphany to me regarding long-held notions of catfish behavior. Grandpa's observation that channel cats spawn when "cotton" falls off of cottonwood trees is still on target, but subsequent spring outings on interior rivers tested Grandpa's wisdom and produced less-than-spectacular results. Given Gelwick's findings, that's not altogether surprising.
This backs up another of Grandpa's homilies regarding whiskerfish of all persuasions: "Ya gotta remember, Sonny -- them critters ain't tied up!"