If you’ve ever had the pleasure of catching a walleye or musky or pretty much any fish in Wisconsin, you might want to thank someone from the Wisconsin Department of Natural Resources (WDNR). They’re the folks tasked with stocking our lakes with fish, keeping an eye on fish populations and setting bag and size limits. About a week before last Saturday’s fishing season opener here in the southern half of the state, I went out with WDNR fisheries biologist, Dan Oele and his crew as they wrapped up the second year of a two-year study of game fish on Madison’s lakes.
The study looked at several species, from bluegill to yellow perch to northern pike, but it’s muskellunge and walleye that really seem to get anglers’ attention. While Madison’s lakes are well-known as great spots to fish for those two species, Oele explained as we motored out to check the first net of the day, that’s only because we put so many of them in the lake to fish for.
Musky aren’t even native to the Yahara chain of lakes and walleye, although native, wouldn’t be able to reproduce in numbers large enough to compensate for the intense angling pressure they get year-round.
The problem, Oele says, is that, during spawning season, musky and walleye (among many other fishes) “really need that complex habitat where there are big fields of cobble [small rocks] or brush and there’s lots of interstitial spaces for the eggs to fall into and kind of be protected.” In the Yahara chain of lakes, however, most of the shoreline is developed and, even where there is good fish-spawning habitat like nearshore woods or wetlands, we regulate water levels to prevent flooding. While that’s good news for homeowners’ basements, it also means, that “we don’t have a spring pulse of water that inundates complex habitat for that key period in the spring when fish are spawning,” Oele says.
There’s also another human-induced wrinkle to this fish tale – while the lakes here in Madison might not be great for growing fish populations, they are excellent at growing individual fish. The influx of nutrients carried in from the lakes’ predominantly agricultural watershed makes the Yahara lakes “eutrophic,” or, basically, super productive. Those nutrients feed tons of algae and phytoplankton, which in turn feed tons of aquatic insects and zooplankton, which in turn feed tons of smaller fishes, which in turn, well, you get the point – popular game fish grow big and they grow big quickly in our lakes, which is one reason why they’re so popular to anglers.
Using a net called a Fyke net, which traps fish in a sort of “holding cell” Oele and his team were able to check fish like walleye and musky for tags or fin clips which would indicate what hatchery they’d initially come from and when they had been stocked by the DNR.
The tags also let his crew measure how much each fish had grown since it had last been caught and reported by an angler or pulled out of the water in a DNR survey. The fish are then returned to the water, where they go back about their business unharmed – a decided advantage over other kinds of nets used in fisheries science.
All that information helps “Inform regulations, bag limits, and size limits,” Oele says. “It also lets us tweak the stocking if we need to, and keep an eye on harvest rates and all of these things are key pieces of information to maintain and sustain the fishery, given the high profile and heavy angling pressure that these lakes get.”
While he hasn’t crunched all of the data yet, Oele says that early numbers look good. Musky,.for example, show “good size structure.” Oele reports that his crew was finding lots of musky in the 35 to 44 inch range and plenty over 48.
So, happy fishing and, if you see those DNR boats on a Madison lake, give them a wave – they likely had a hand in your prize catch.
Enjoy some other shots from my day on the lake below: