Mother Nature throws a curve at interstate walleye sampling project in newly surveyed river system

When it comes to stocking fisheries, it’s vital to match the right fish with the right habitat. But that means more than merely matching trout to stream. Two populations of the same species can develop differences over thousands of years that suit them to one environment over another. And although breeding between strains is common, fishery managers still treasure those strains that have remained relatively pure throughout the centuries.

A cooperative project between Wisconsin and Michigan fisheries targeted one such strain of Lake Michigan walleye that has managed to avoid the widespread hybridization occurring in nearby waters. The project aimed to kill two birds with one stone, as collection efforts were tied to a routine survey in the Brule River, the home of the pristine walleye strain.

Prior to the survey, the Brule River was a largely unexplored system, according to Mike Vogelsang, north district fisheries supervisor with the Wisconsin Department of Natural Resources. A new fisheries station located in Florence opened up new opportunities for the DNR’s research.

“We’re getting surveys done on a lot of water that didn’t previously get a lot of attention,” Vogelsang said. “Among everything else, we’d been looking for a source for the Lake Michigan walleye eggs. Genetically, they’re all a little bit different, so we just want to make sure we’re stocking the properly strained fish in each basin.”

The Wisconsin DNR had worked with the Michigan DNR on other projects, so they invited their neighbors to join them in surveying the Brule’s under-charted waters. Together, the crew of researchers and hatchery workers sought to collect between a dozen and 20 spawning female walleye and at least as many males. The average adult female walleye can carry between 70,000 and 80,000 eggs, so only a handful would be necessary to stock a fishery. After a weigh-in, the crew would harvest eggs and milt from the walleye before returning them to the river.

Fishery managers place special value on walleye belonging to less hybridized strains. (Credit: Wisconsin DNR)

However, lack of information on the Brule River posed more of a challenge than the team had anticipated.

“Once we got in there and gathered initial data at the walleye fishery, we didn’t catch enough females and males to make it work out,” Vogelsang said. “But it’s one of those things you don’t really know until you get there.”

There were several factors that contributed to the project’s failure, all illustrating the complicated nature of fisheries work. The river system’s large size made the walleye nets less efficient. Additionally, ice coverage on a major flowage in the Brule system may have driven walleye further downstream and over an impoundment where they were less accessible, Vogelsang suggested. That same ice coverage also made it difficult for the team to navigate their boat.

Luckily, the team was able to gather its eggs from the nearby Butternut Lake. Vogelsang says there are no existing plans to continue egg collection at Brule River, but another survey should be expected in five to 10 years.

While Vogelsang says he’s disappointed that the project didn’t go through, he’s not altogether surprised.

“Typically, when we’re gathering our walleye eggs, we’re going to known spots where we have a 100 percent chance of getting the eggs,” he said. “It’s pretty difficult in those riverine systems to sample walleyes.”

Most of that difficulty tends to arise from the river’s’ morphology and current, rather than lack of fish, Vogelsang said. The Wisconsin DNR doesn’t stock the state’s river systems “because they do so well on their own.”

“It would have been a nice opportunity to cooperate and coordinate with Michigan on this project,” Vogelsang said. “Unfortunately, Mother Nature threw us a curve.”