Study Tracks Walleye Population at Iowa Great Lakes
Posted: 02/07/2012
SPIRIT LAKE, Iowa – For the past 21 years, every walleye caught during the April gillnetting season at the Iowa Great Lakes received a unique alpha numeric tag, gave up a spine and was measured before heading back to the cool water from which they came.

That information has been feeding a database now stretching 24,000 walleyes strong and is being used to keep track of the health of one of the most important populations used for Iowa’s fish culture program.

The Iowa Great Lakes walleye population supports the Spirit Lake hatchery with eggs to produce more than 67 million fry that are eventually stocked into lakes and streams across the state.  The database tracks annual abundance, survival and growth rates of those walleyes and is used to support additional research projects aimed at improving walleye fisheries across the state.

Jonathan Meerbeek, natural lakes research biologist for the Iowa Department of Natural Resources, took over the study in 2010. 

“We can learn a lot about walleye population dynamics by tagging and recapturing uniquely identified fish,” Meerbeek said. “For example, we can look at annual growth rates and what influenced a good growth year, like a large class of young of the year yellow perch. That data can also help us with our stocking strategies and with our regulations.  If we are seeing the numbers go down we can adjust something to correct the trend. We’re really interested in abundance, keeping a healthy population for our anglers and for our fish hatchery.”

The 2011 brood stock collection allowed researchers to mark 2,792 new walleyes 15 inches and longer and to update the information on 260 previously tagged walleyes. The observed annual growth data on 1,700 walleyes caught in consecutive years shows a correlation between walleye growth rates and the abundance of young of the year yellow perch. As in many other natural lakes, successful spawns and growth by yellow perch impacts the walleye population.

Meerbeek said the DNR bases management decisions, like regulations or stocking rates, on several years of data to correct for natural variables, say a down turn in the yellow perch population. He said research and management work hand in hand and when the walleye population veers off course they can step in and get it back on track.

“Usually when fishing is poor, we hear about it from the angler,” Meerbeek said. “But we try to avoid those situations by correcting the problem before it is perceived as a problem. That’s where continuous monitoring of a population becomes a useful management tool.”

One example of getting the population back on course is the 17 to 22-inch protected slot limit.
The protected slot limit focuses harvest on smaller fish that allows for better growth rates and helps remaining walleyes reach the slot more quickly, increasing the brood stock population and the abundance of fish in that range.  The slot limit is a tool to improve the valuable brood stock population and will continue to be evaluated.

Population studies are also going at Clear Lake and Storm Lake.  Similar population characteristics are estimated from these studies that help researchers calculate walleye abundance, evaluate impacts of special length limits, and observe changes in growth rates.

Did you catch a tagged walleye?
Turn the fish upside down and look the clear skin below the lower jaw.  If there is a tag, it will be small and colored, like a piece of confetti. If releasing the fish, write the number down and note the color of the tag (or in this modern age, take a photo with your cell phone). Measure the fish and send it to Meerbeek (Spirit Lake Hatchery, 122 252nd Ave., Spirit Lake, IA 51360) along with where and when it was caught.  If harvesting the fish, do the same or remove the tag with the tip of a knife and send it in with the other details.

The database can provide anglers with a unique capture history of their walleye, including the number of times and locations the fish was captured, the estimated age of the fish and observed changes in growth.

Frequent Netters
A number of walleyes have made multiple trips in to the hatchery creating a biography of sorts for these fish including four that have been netted seven times.

Other walleyes with unique stories include MY4 that was a 19 year old male caught five times before being harvested by an angler at 10 p.m., May 1, 2004, near Village West on West Okoboji Lake, during opening day of the walleye season. He measured 21-1/2 inches.

X66 was a walleye from Spirit Lake that was captured seven different times in gillnets and was 18 years old in 2004.

XC0 was captured in a gillnet four times including twice in 2003.

Who is catching these fish?
One angler from Pocahontas reported 27 tagged walleyes between 1994 and 2004. One Spirit Lake family has reported 29 tags

A tagged walleye was caught and released at the North Grade on Spirit Lake by retired fisheries employee Ed Thelen. The same tagged fish was caught by a different angler from the same location the following week and was harvested.