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Tracking Flathead Catfish

By Joe Wilkinson

July 19, 2005

As we pushed upstream, fish 1702 was talking to us. Just above the new ramp on the Iowa River at River Junction, our radio receiver on board sounded clear, crisp 'beeps' to tell us we were closing in on the five-pound flathead catfish.

Steering the boat toward a jumble of trees on an inside bend, Iowa Department of Natural  Resources fisheries technician Greg Simmons was confident. "It's in that logjam. As we get closer, the beeping will get louder," said Simmons. Unplugging the electronic box from the mast, Simmons held it over the side of the boat. The beeps were loud and sharp. "It's right below us," offered Simmons. "1702 was tagged August 20 of last year. The last time we 'saw' it was this May (probably moving up from its wintering area) just above the mouth of the Cedar River. So it's moved up about ten miles since then."

As Simmons recorded depth and other details, it was easy to see why the fish was here. On the inside bend there would be a couple nice holes. The tangle of flood-carried trunks, stumps and limbs created blocked the current, creating a calm area, good habitat for smaller river fish...and the flathead catfish that would swallow them. Across the river, the outside bend showed sloughed-away dirt banks, a reminder of the changing nature of the stream and the multitude of organisms it supports.

Crews last year caught and implanted radio-transmitters in 35 flatheads. This trip was just for telemetry. "The receiver here will pick up signals from the fish," explains Simmons. "Each one is assigned a different frequency. If the scanner doesn't pick up a frequency in the two-second interval, it moves to the next one." It had been a pretty good day. Starting at the Burlington Street Dam in Iowa City on this day, Simmons had located 14 'electronic flatheads' by the time he pulled out at River Junction, east of Riverside. DNR biologist Greg Gelwicks had started there and was monitoring downstream. The research crew, out of Manchester, spent the night and completed their run down to the Mississippi the next day.

On a different trip, they might electroshock the same stretches; a method that brings up smaller flatheads. Or, they would set underwater hoop nets, especially during spawning, to get more of the monsters. They need to see a representative sampling of the flatheads to gauge just how many are out there. Concerns from anglers not seeing as many big flatheads prompted the multi-stream survey. As the top predator, a balanced flathead population is critical to a river's overall health. And if you've ever wrestled a five--or 45--pound flathead to the bank, you know why many river anglers prefer them.

Similar work is underway in the North Raccoon, Des Moines and Cedar River corridors in Iowa. That includes some attention to tributaries. Just prior to pushing off, Gelwicks talked by phone with a woman who had caught one of the transmitter-fitted fish on the English River, near North English. Though there is nothing illegal with taking one home-they know of four caught--biologists urge anglers to contact them to pin down location, movement and other data. Plus, they'll stop searching for that frequency.

In its second year now, the study is showing that habitat is critical...and that fish will move to get to that habitat. For instance, why did 1702 swim past 10 miles of the Iowa River to get back to that particular logjam above River Junction? "A fish might do well for ten months out of the year but if it lacks critical habitat, an over-wintering area for instance, it is going to have to (search for it)," cautions Simmons. "We just don't know a lot about flatheads on our interior streams. We are looking at how far they move at different times of the year. We want to learn about population, growth rates, too; some simple parameters to tell us more."

And through the implanted radio transmitters, the catfish are talking.


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