“Our hope is to ‘reset’ food webs in the four listed state fishing lakes,” KDWPT fisheries biologist Ben Neely said. “This starts by getting rid of as many gizzard shad as possible and culminates with balance between the bluegill and largemouth bass populations. When this balance is achieved, both bluegill and largemouth bass should exhibit more rapid growth and support increased angling opportunities.”
Neely said the department believes the move will be beneficial moving forward.
During partial renovations such as this, the release says, the fish population isn’t completely eliminated as it is during a full renovation. Water levels will be lowered in late October by about 3 feet below normal lake elevation. When weather permits in November or December, a fish toxicant called Rotenone will be applied at a relatively low rate to target gizzard shad without affecting sport fish. Some unintended fish mortality may occur in a small portion of the population, the agency said, but the lakes will be restocked following treatment if larger-than-expected loss occurs.
“Lowering the water level creates a phenomenon called trophic upsurge,” Neely said. “Essentially, the lowered water level through fall, winter and spring allows nutrients in the soil to convert to terrestrial vegetation. When that vegetation is submerged as the lake refills, the nutrients are redistributed in the water. This boost in nutrients, coupled with the decreased number of gizzard shad mouths to feed, creates a ‘boom’ situation for remaining fish where there is abundant food available.
“We expect this to result in a big year class of bluegill and bass in 2019 that will simulate a stocking. In other words, we expect a big pulse in the number of bluegill and bass in the lakes.”
Aside from boosting bluegill and bass classes, the move also would be of benefit to crappie populations in the lakes. Shawnee State Fishing Lake has had trouble in the past getting crappie populations to take off and grow to full size. This move, Neely said, could help with that by supplying crappie with more of their natural diet.
“Crappie tend to be a ‘bonus’ species in many state fishing lakes that are notoriously difficult to manage for a few different reasons,” Neely said. “However, reducing or extirpating gizzard shad should help the populations. Gizzard shad grow rapidly and are too big for crappie to eat when the shad are just a few months old. Reducing their numbers will open up lower trophic levels for native stream species like red shiner, fathead minnow and bluntnose minnow that never get too big for crappie to eat.”
Gizzard shad present a challenge to managing small impoundments, which are designed to provide close-to-home fishing opportunities, the agency said in a news release announcing the moves. While gizzard shad are known as a food source for many sport fish, especially larger catfish species like blue catfish, this mostly applies to large reservoirs where open-water fish such as walleye and wipers prey on shad. In smaller impoundments such as Shawnee SFL, open-water predators are rare or nonexistent 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,” the agency said in its release. “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.”
Neely said no new species would be introduced in Shawnee SFL or the other impoundments, but said “we will intensively monitor each lake for several years following and make adjustments as needed.”
The fisheries will be closed to boat traffic on the day of the application of the toxin 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.
The state says Rotenone is a plant-based compound used primarily as an insecticide or piscicide and doesn’t harm humans, birds or other air-breathing animals, instead being toxic only to gill-breathing animals. It says Rotenone will not affect any animals that consume exposed fish. The state said no salvage order will be issued and sport fishing equipment and harvest regulations will remain in effect. Anglers will, however, be permitted to collect dead gizzard shad from the shoreline following treatments, for personal use only.
The KDWPT also announced recently it is planning a $1.6 million spillway repair project at Clark State Fishing Lake, located about 9 miles south of Kingsdown, that will begin in December and will take about six months to complete.
The project will require temporarily lowering the lake levels by 20 to 25 feet to relieve the hydraulic pressure of water in the soil pushing against the underside of the spillway floor and side walls. The KDWPT says biologists don’t anticipate a significant impact to the fishery because of the drawdown.
Boat ramps will be unusable during the drawdown. Shoreline access will be available, but the KDWPT cautions anglers that the bottom sediment may be too soft to walk on until it dries. The lake will refill naturally upon project completion. Additional habitat for fish also will be implemented in the form of 130 “Georgia Cube” PVC pipe structures, plus rock and brush piles. Boat ramps and rip-rapped fishing jetties also will be enhanced, the state says.