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Pawnee Reservoir Low-Dose Rotenone Treatment Re-visited

Some of you may remember that fisheries managers for the Nebraska Game & Parks Commission tried an experimental fisheries management technique at Pawnee Reservoir a year ago last fall, Pawnee Renovation.  Unlike typical rotenone renovations where all fish are removed from a body of water, the effort at Pawnee was one where we hoped that a relatively low dose of rotenone would selectively eliminate gizzard shad and white perch.

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Let me share some more of what we know about that fisheries management effort:  Nathan Stewart is a graduate student at the University of Nebraska-Lincoln and he did a lot of work on the shad and white perch populations in Pawnee Reservoir as part of his Master’s research.  I have not seen a published copy of Nathan’s thesis yet, but I have an executive summary and some very interesting results to share with you.

Nathan estimated that there were 1.5-1.7 million white perch and 0.6-0.7 million gizzard shad in Pawnee Reservoir in 2013.  He also estimated that the low-dose rotenone treatment in the fall of 2013 eliminated 83% of the white perch and nearly all of the gizzard shad!  YES!  Those were the kind of results we were hoping for!  As a result, the size of white perch in Pawnee increased from an average of 5.2 inches in 2013 to 7.8 inches in 2014 (the surviving fish had less competition for food resources and therefore grew much faster).

There are some quality-sized white perch in Pawnee right now, and anglers might as well take advantage of that!  White perch are basically a smaller version of white bass (they are members of the same fish family, temperate basses) and white perch of nearly 8 inches or larger are absolutely big enough to clean, big enough to eat.  In addition to the increase in average size, the “plumpness” of the surviving white perch in Pawnee also increased dramatically.

Of course the question is whether this reduction in white perch and gizzard shad numbers in Pawnee can be maintained and if so, for how long?  In addition to the removal of white perch and gizzard shad, additional walleye, largemouth bass and even northern pike were stocked in Pawnee last year to take advantage of the opportunity to perhaps “get on top” of the white perch population and control numbers by predation.  Human predators could perhaps apply some more predation to Pawnee white perch by harvesting even more of those fish, especially now when they are “big enough to keep”/big enough to clean.  I will not tell you that anglers would ever harvest enough white perch from any body of water to impact white perch numbers, but if the white perch are big enough to eat, anglers might as well take all they want.  At Pawnee right now I would tell you to harvest white perch, all you catch if you wish, but please release all predator fish, regardless of size–those fish will do us all a lot more good by being left in the reservoir than by sizzling in someone’s frying pan.

We expected some mortality of desirable sport fish during the low-dose rotenone treatment at Pawnee, and there was some.  Freshwater drum and common carp appear to have been the hardest hit, but there are still fishable-numbers of channel catfish, flathead catfish, crappies and even largemouth bass present right now.

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Let me mention one more thing before I quit. . . . Absolutely, we want folks to take advantage of the white perch in Pawnee or other waters–if you can catch some large enough to take a fillet knife to, harvest all you want.  However, please remember that no live white perch can be transported away from any water body.  Bring a cooler of ice with you, throw the white perch in there, take ’em home or to the fish-cleaning station and clean them.  Besides being completely legal, they will taste better if they are handled that way.

Why such restrictive regulations on white perch?  Simply put they are an invasive species and we do not want them spreading anywhere.  Unfortunately, we suspect that there are still too many “anglers” who are capturing white perch in one body of water and then illegally transporting them to another body of water to use as live bait.  If you are aware of any activity like that, any unauthorized stocking of any fish into any public body of water (and unless there is an official Nebraska Game & Parks Commission stocking truck and staff stocking the fish, it is unauthorized!) report it immediately, Nebraska Wildlife Crimestoppers 1-800-742-7627.  The fishing that will be ruined due to the introduction of white perch and other undesirables will be YOUR fishing, MY fishing!  A “fish pox” on every person who does this.

About daryl bauer

Daryl is a lifelong resident of Nebraska (except for a couple of years spent going to graduate school in South Dakota). He has been employed as a fisheries biologist for the Nebraska Game and Parks Commission for 25 years, and his current tour of duty is as the fisheries outreach program manager. Daryl loves to share his educational knowledge and is an avid multi-species angler. He holds more than 120 Nebraska Master Angler Awards for 14 different species and holds more than 30 In-Fisherman Master Angler Awards for eight different species. He loves to talk fishing and answer questions about fishing in Nebraska, be sure to check out his blog at outdoornebraska.org.

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