Study seeks to ID what species make meals of white perch
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BY JOE DUGGAN / Lincoln Journal Star
Electrodes dangle into the dark waters of Branched Oak Lake as the research boat rounds the tip of a rock jetty. Within seconds, stunned fish pop to the water’s surface.
...white perch, white perch, white perch, a little bluegill, another white perch...
“That’s a hybrid,” says the boat’s driver, Kevin Pope, referring to a striped bass-white bass hybrid, known more commonly as a wiper.
“Get it, get it, get it!”
Jeff Stittle, a fisheries and wildlife student at the University of Nebraska-Lincoln, stands on the front of the boat, his hands protected inside insulated gloves and spread wide along the plastic handle of a dip net. The hybrid violently breeches the surface, clearly trying to escape the electrical current. Stittle scoops up the fish and deposits it into the boat’s livewell.
Over the next 90 seconds, the pair capture several more hybrids, a walleye, two catfish and a black crappie. All of the fish have just become subjects in a two-year study to find out what game fish are feeding on at Branched Oak, north of Malcolm, and Pawnee Lake, north of Emerald.
Specifically, the study aims to find out what game fish most readily eat white perch. The upshot for anglers: The study will hopefully allow fisheries managers to minimize the effect of white perch and improve fishing at both lakes.
The white perch problem has been like a recurring bad dream in the Salt Valley since the early 1970s, a few years after the brackish water species common in East Coast estuaries was inadvertently released into Wagon Train Lake.
The small, spiny fish have invaded both Branched Oak and Pawnee and state fisheries biologists believe white perch have had a serious effect on the recruitment of desirable game fish. Not only do white perch feed on young game fish, scientists also believe they compete for the microscopic insects that allow young fish to survive and grow.
White perch have particularly hurt natural walleye recruitment at Branched Oak, eastern Nebraska’s largest reservoir and one of the most popular camping and fishing destinations in the state. Stocking attempts also have proven unsuccessful at getting a solid walleye population established.
To make matters worse, the white perch in Branched Oak have become stunted, making them practically worthless to anglers.
Not wanting to spend the money for a lake renovation, which may only temporarily solve the problem, Game and Parks leaders hope freshwater predators can control the white perch. Since 1999, the commission has made Branched Oak a catch-and-release fishery for wipers and flathead catfish and allowed only one walleye over 22-inches to be kept per day.
Still, it seems for every white perch that ends up in a wiper’s stomach, thousands more swim free to inflict the lake. To complicate matters further, Branched Oak also has gizzard shad, a smooth-bodied fish with a higher fat content than perch that species like walleyes and wipers would prefer to eat if given the choice.
At Pawnee Lake, the situation isn’t as dire. The perch density isn’t as high at Pawnee and they aren’t stunted, not yet anyway. Nor does the lake have shad, which means predators there are more likely to eat perch because they don’t have a choice. Still, Pawnee also suffers from a low walleye population and instead of hybrids, it has white bass.
Now biologists want to know what, if any, game fish are feeding on white perch. Enter the fish food study.
The study is being overseen by Pope, assistant unit leader of Nebraska’s Cooperative Fish and Wildlife Research Unit. The unit is a joint effort between the U.S. Geological Survey, the Game and Parks Commission and the University of Nebraska-Lincoln School of Natural Resources.
Using primarily an electrofishing boat, Pope and Stittle started collecting game fish last March at each lake. The study, which will be taken over by a graduate student in a few weeks, will continue into November. They will collect data during the same eight-month period in 2007 as well.
The study is budgeted to cost $102,000, Pope said. The Geological Survey contributed $25,000 while the commission committed 77,000.
After their pass along the Branched Oak jetty that resulted in a good catch, Pope beached the boat so they could work up the fish.
They started with one of the wipers, which they measured for length and weight. Then Stittle held the fish upside down as Pope carefully inserted a clear, plastic hose down its throat. With a few flips of a pump switch, Pope pulsed water into the fish’s stomach forcing the contents into a metal pail.
The procedure left a partially digested fish carcass in the bucket. While he was hesitant to say before the remains were examined in the laboratory, he said it was most likely a white perch. He knew for sure it wasn’t a gizzard shad.
After ensuring the fish’s stomach was empty, Stittle released it. He then he used a squeeze bottle to swish all of the stomach contents into a plastic lab bottle, which will be analyzed in the lab later.
The same procedure on another wiper and a nice walleye produced samples that Pope was even more confident were perch. Often the researchers get only bones, but under the microscope, bones can usually reveal the species.
If the samples they collected do turn out to be white perch, they will be some of the first in the study. Before the jetty pass, the researchers had pumped 200 stomachs at both lakes and found only two suspected white perch.
The researchers worked fast to gather their data and get the fish back in the water as quickly as possible. Pope said they take every precaution to keep a study fish, especially the valuable big predators, alive.
“There’s always the chance that some of them aren’t going to make it,” he said. “We have to be willing to sacrifice a few for the sake of research, nonetheless, we’re doing everything we can to minimize the impact.”
Researchers intend to flush stomachs on hybrids, walleye, flathead catfish, channel catfish, white and black crappie, white bass and largemouth bass. They’re shooting for a goal of 50 of each species at each lake per month, although they know that won’t always be possible.
They’ll be at one lake or another Monday through Thursday, sometimes in the morning, sometimes at night.
Shocking the water.
Netting fish.
Pumping stomachs.
And finding answers.
Reach Joe Duggan at 473-7239 or jduggan@journalstar.com.
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