Spirit Lake serves as the primary source of walleyes for the Spirit Lake Fish Hatchery’s annual egg collection that provides half of all walleye fry and 25 percent of the fingerlings stocked statewide.
To maintain that level of production, the Iowa Department of Natural Resources (DNR) placed a special 17-22 inch protected slot limit on walleyes in 2007. This slot limit was chosen because it showed the potential for highest catch rates for anglers while maintaining a population of walleyes most coveted by the hatchery.
Once in place, fishing was initially excellent, but gradually the number of fish caught outside of the slot decreased. Although some anglers preferred the quality of fish provided by the slot; others suggested a change to the regulation.
DNR researchers predict even a slight change in the regulation could lead to undesirable consequences. In fact, allowing anglers to harvest one walleye in the current slot-limit as part of their daily bag limit would reduce the brood stock population by 50 percent in just one year.
So what happened to the keepers?
“As the abundance of adult walleyes increases, recruitment may actually decrease due to competition for food,” said Jonathan Meerbeek, natural lakes research biologist for the Iowa DNR. “The boom and bust year class cycles that used to drive the fishery with high harvest periods that follow, are not as common and a more moderate cycle of recruitment occurs.”
The number of largemouth and smallmouth bass, northern pike and muskies in Spirit Lake increased as well, placing more pressure on the primary food source – yellow perch.
Perch numbers fluctuate annually and while reproduction has been steady, adult yellow perch numbers have decreased considerably since 2010. The 2012 perch harvest was the lowest since 1957. Adult walleye abundance is partially responsible for the imbalance, but simply put, there are a lot of teeth out there and they all eat yellow perch.
“The walleye population in Spirit Lake is the most studied of any fish in any Iowa lake,” Meerbeek said. “We will continue to monitor it and make changes when necessary.”