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.

TELLTALE TELEMETRY
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.