The chemical rotenone has been applied at Wehrspann Lake by the NE Game and Parks Commission in order to remove gizzard shad. Wehrspann is managed by the Papio-Missouri River NRD and the district relies on the NE Game and Parks Commission to manage the fishery.
Gizzard shad are susceptible to a low dose of rotenone while fish such as largemouth bass, bluegill, channel catfish and crappie are less affected. Low dosages of rotenone are done at low water temperatures to increase its effectiveness on shad and lower impacts on nontarget species.
“Gizzard shad are targeted for removal because they are a detrimental species in small reservoirs such as Wehrspann,” said Daryl Bauer, fisheries outreach program manager with the Nebraska Game and Parks Commission. “With their high reproductive capability, gizzard shad compete for the same food used by young sport fish such as bluegill, crappie and largemouth bass. The presence of gizzard shad in a small reservoir often results in reduced natural recruitment, growth and body conditions of sport fish.”
Rotenone, derived from the roots of plants that grow in South America, inhibits the uptake of oxygen at the cellular level. It only affects gill-breathing organisms.
Next spring, additional 4-inch largemouth bass will be stocked in Wehrspann.
“Those small bass should have good survival once the gizzard shad have been removed, and they will provide extra predation on any remaining shad,” Bauer said. “Anglers can expect to have good fishing at Wehrspann next spring. We have had very positive results on other waters where it has been done and we expect a great future for the Wehrspann fishery,”