The sun crept below the tree line on East Okoboji Lake as the boat slipped off the trailer and into the 50 degree water. While most lake shore residents were finishing up a nice warm supper, Jonathan Meerbeek and Jon Christensen were just heading out in search of walleyes on a crisp late October night.
Meerbeek, natural lakes research biologist with the Iowa Department of Natural Resources Fisheries Bureau, and Christensen, his research technician, were looking for walleyes that were spawned this year and more specifically, walleyes that were reared at the Lake Rathbun hatchery and transported 290 miles to the Iowa Great Lakes.
The Lake Rathbun hatchery can grow walleyes to 10 inches by October of their first year moving them out of danger from being eaten by most other fish. But, 10-inch walleye fingerlings do not come cheap. It costs $1.14 per walleye to reach that size so those advanced growth fingerlings are primarily stocked in the lakes that are the source for walleye eggs.
The project began in 2004, when West Okoboji Lake was stocked with advanced growth fingerlings but those fish had not been seen in the creel. The fish management staff were concerned that those Rathbun fingerlings did not survive.
“We work closely with the fish management side and they were worried about survival after transportation, so we started looking at them in more detail,” Meerbeek said.
The goal of the project was to identify what happened to those fish. Did they survive the six hour trip on the truck? Or, was the stress too much for them to handle?
The fish Meerbeek and Christensen are searching for were stocked two weeks earlier. The plan is simple: spend the evening shocking five standard sites on the lake to maintain consistency from year to year and net as many of the small walleyes as possible for the study.
Each walleye will be visually inspected for fin erosion (common to fish raised in a concrete hatchery raceway), measured, and have a spine and scales removed for analysis, then released back into the lake. It takes 20 to 45 minutes to cover each site.
The boat’s headlights snapped on and the onboard generator began its hypnotic humming. Two booms reach out in front of the boat like zombie arms with electrodes for fingers dipping into the lake. Meerbeek stepped on to the roughly 4 foot by 4 foot rubber mat at the front of the heavy aluminum boat, the generator surges sending electricity to the electrodes and into the water. Presto, fish began to float: carp, northern pike, yellow bass, freshwater drum, crappies, yellow perch and, of course, walleyes.
Only the large contingent of American coot swimming on the surface successfully avoids the electric current.
Late October is preferred because most of the docks ringing the lake have been removed for the year and the water temperature is above 50 degrees. Christensen noses the boat in and out of the shoreline, skirting the few remaining docks.
Young walleye will move close to shore in the evening looking for places to hide from larger predators in search of a meal. The electricity only stuns the fish making them easier to net. Once the current passes, they regain control and swim away.
On this night, the crew battled wind with gusts up to 30 miles per hour and netted fewer than 70 fish under not-so-ideal circumstances. The information will be added to the existing data and used in a couple of different projects, Meerbeek said. But on that night, he was a little disappointed in the numbers.
“We are interested in the return on those (Rathbun) fish to the fishery,” he said. “If they are not surviving and making an impact, we will have to look at doing something else.”
Heading back to the East Okoboji Beach ramp the clock ticks closer to midnight. The two researchers trailer the boat and head back to the hatchery with the information they collected. Another late night spent on the water gathering data to improve fishing in Iowa.
For more information contact Jonathon Meerbeek, Fisheries Research Biologist, Iowa Department of Natural Resources, 712-336-1840.