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Study investigates fish feeding habits

  • The Wichita Eagle
  • Published Saturday, July 20, 2013, at 8:33 p.m.
  • Updated Saturday, July 20, 2013, at 8:35 p.m.

— Fish not hitting your favorite bait lately? You might want to try a few lady bugs on a hook. Or maybe a big ol’ ball of sunflower seed hulls might do the trick.

Such are just two of the things Scott Brack and Brian Serpan have found in predatory fish at Cheney and El Dorado reservoirs this spring and summer. Using nets 80 feet long, the Fort Hays State graduate students are detailing all they find inside such species as walleye, wipers, flathead and blue catfish, largemouth bass and crappie.

“One main thing is that we want to see what predatory fish are best at eating white perch,” Brack said Wednesday morning at Cheney.

It’s been about 15 years since non-native white perch were inadvertently stocked into Cheney Reservoir with a load of little striped bass. Within a few years they were decimating the sport fishery at Cheney, gobbling up nearly all of the eggs and fry of other species and outcompeting them for food.

Biologists slapped the lake with restrictive limits of only two walleye or wipers of 21 inches or better per day. They did the same when white perch were found at El Dorado a few years ago.

“Now we’re checking to see if those regulations are working, if those size classes are eating more white perch or exactly what is eating white perch,” said Jason Goeckler, Kansas Department of Wildlife, Parks and Tourism fisheries research coordinator. “If we need to make adjustments we can …whoever is eating the most white perch, we want them to keep eating them.”

For about two months Brack and Serpan have been spending most of their days running up to six long nets that basically entangle fish. The nets are checked about every 30 minutes to reduce injuries to captured fish.

Everything is measured and logged. Many of the gamefish get their digestive system checked by a method that makes a trip to the dentist seem pretty tame.

After measuring and weighing a nice walleye, Brack reached for a bucket with clear plastic tubes of various diameters. “They make pumps specifically for this purpose, but this works just as well,” he said as he slowly inserted a tube’s beveled end down the walleye’s throat. A little water was poured in to loosen any contents, and the fish was tipped a few times. The young biologist plugged one end of the tube with his thumb, and eased it from the walleye. The tube had the water put in the fish, and the probable remains of a tiny shad. “It’s like sticking a straw into a glass of pop, making the vacuum then pulling it out,” he said. “It does a pretty good job.”

After removing some tissue from near the back of the dorsal fin, Brack placed the walleye back in the lake, where it eventually headed for deeper water. “Sometimes it takes a while, but most of them come out of it and swim off,” he said.

The study will also try to get an idea of the age structure of the various species of game and baitfish at Cheney and El Dorado. That’s easily learned by removing the fish’s otoliths, bone-like organs in their head that help fish hear and remain upright. They also contain growth rings, similar to a tree, that can later be counted by biologists. It’s a fatal procedure.

“When they’re really young, you can tell how old they are almost to the very day,” Serpan said. The researchers have small weekly quotas for various sizes of each species for fatal and/or invasive tests so they don’t needlessly kill too many fish.

Though it’s early in the study, Brack and Serpan have noticed some trends. Large walleye usually eat more white perch than white bass or wipers. Many fish have been eating burrowing mayfly nymphs, and an abundance of lady bug shells showed up after a highwater event flooded a lot of vegetation at Cheney.

Fish at both lakes have been relying heavily on this summer’s hatch of gizzard shad. Serpan described some of the first shad found in small game fish like “a short piece of thread with eyes on it.” As the shad have grown, they’ve shown up in larger gamefish.

Flathead catfish eat a varied diet. One day every small flathead they checked contained crayfish. The stomach of a foot-long flathead once held at least 30 tiny catfish fry.

There’s correlation between when the researchers are finding big fish with full stomachs and when local anglers are doing well. Another common trait: even fishing with nets is not always productive.

Wednesday morning’s first two nets, set at about 6 a.m., produced a dozen or so nice white bass, wipers and walleye. After those fish were worked up, Brack and Serpan set the nets five more times over about the next three hours. Even though an electronic locator showed fish on the spots, the nets were about void of gamefish when pulled.

“They’re there, but not active,” Serpan said. “It doesn’t matter if you’re using bait or nets. If the fish aren’t moving you’re just not going to catch much.”

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