September 27, 2018 - EMPORIA – In a cooperative study with Kansas State University to evaluate the influence of gizzard shad on food webs in small impoundments, the Kansas Department of Wildlife, Parks, and Tourism (KDWPT) will be conducting partial fishery renovations on four small impoundments this winter. Selected impoundments are Neosho State Fishing Lake, Pottawatomie State Fishing Lake No. 1, Shawnee State Fishing Lake, and Washington State Fishing Lake.

In a partial renovation, the fish population is not completely eliminated as it is during a full renovation. The first step in a partial renovation is lowering water levels, which will occur in late October when levels in these four impoundments will be lowered approximately 3 feet below normal lake elevation. When weather conditions permit in November or December, a fish toxicant called Rotenone will be applied at a concentration of 7.5 parts per billion, which is much less than the 40 parts per billion allowed in municipal water supplies. The low-dose of Rotenone is designed to target gizzard shad while not affecting sport fish. No salvage order will be issued, and sport fishing equipment and harvest regulations will remain in effect. However, anglers will be permitted to collect deceased gizzard shad from the shoreline following treatments for personal use only.

Gizzard shad present a challenge to managing small impoundments, which are designed to provide close-to-home fishing opportunities. While many anglers may recognize gizzard shad as a food source for sport fish, this mostly applies to large reservoirs where open-water fish such as walleye and wipers prey on shad. In smaller impoundments, open-water predators are rare or non-existent and gizzard shad populations can expand to levels that cause problems for more desirable sport fish.

One example is direct competition for food resources between gizzard shad and young bluegill, which typically favors gizzard shad and causes a reduction in bluegill numbers. These changes can cause a chain reaction in the food web because bluegill are a preferred prey of sport fish like largemouth bass and white crappie. The result is an unsustainable sport fishery.
When gizzard shad populations exceed acceptable levels, a complete lake renovation is often prescribed to reset the fish community and rebuild a sustainable balance.

A complete renovation entails draining the reservoir as much as possible, then treating the remaining water with Rotenone at levels of  2,000-3,000 parts per billion to remove all fish. A major downside of renovation is the amount of time needed for newly-stocked fish to grow to sizes sought by anglers. The partial renovation to remove gizzard shad is a new strategy that shows promise. Other fish species are more tolerant of the chemical, although unintended mortality may occur in a small portion of the population. Reservoirs will be restocked following treatment if larger than expected loss occurs.

Rotenone is a plant-based compound used primarily as an insecticide or piscicide. It is toxic to fish and other gill-breathing animals, but does not harm humans, birds, or other air-breathing animals. Similarly, animals that consume fish exposed to Rotenone will not be affected. Rotenone breaks down rapidly in sunlight and will be undetectable a couple weeks after application.

Each of these reservoirs will be closed to boat traffic on the day of Rotenone application and marked with barricades across boat ramps. Anglers are advised to contact local fisheries biologists for status of the renovations before making any trips this winter.

For more information on the partial renovation projects, contact fisheries biologist Ben Neely at (620) 342-0658 or ben.neely@ks.gov.