Walking onto the campus of the Art Oehmcke fish hatchery in Woodruff is like a trip back in time, with picturesque bridges over the creek, huge trees, sturdy old wooden buildings and art work celebrating the iconic game fish of the Northwoods: walleye and musky.
After more than 100 years, the staff still use traditional methods and, increasingly, new technology to propagate the species and boost the populations of these fish, important not only to modern anglers, but predators that help keep area lake ecosystems healthy.
Even today, hatchery foreman Tom Lorenzen and crew, employees of the Wisconsin Department of Natural Resources, are subject to the ancient life cycles of the fish. It begins in early spring.
“We get out in the boats just after ice-out,” he says. “The walleye are ready first, depending on a combination of day length and water temperature. Generally, we look for 44 to 45 degrees and have only a two- or three-day window; if we miss it, that’s it.”
It’s cold work, according to Lorenzen, often windy and wet, and a crew will typically work several 8- to 12-hour days in a row. Huge nets are stretched from the shoreline out into the lake. “We know from experience where the fish will gather for spawning,” he says. “They like shallow water with a rocky bottom.”
During the off-season, one of the nets is on display, strung up under some pines just outside the hatchery building. Lorenzen gestures, showing how the fish run up against the net and are funneled into the end, where personnel are ready to scoop them out.
The lakes selected for this process fit a specific criterion. They are generally large, with healthy self-sustaining populations of game fish, and many have been used for dozens of years. “We collect brood stock from Butternut Lake for the Lake Michigan walleye strain, and Lake Tomahawk for the Mississippi Headwaters strain,” he explains.
The two-person crew carefully pulls each fish out of the net and squeezes or “milks” it for its eggs or sperm, referred to as milt. The products are mixed in containers right there in the boat and the big fish immediately released.
The fertilized eggs are then transported back to the hatchery. “The crew drops it off at the door; they don’t enter,” says Lorenzen. “At that point, this building is restricted. We take extra precautions to make sure everything is kept clean and clear of contamination.”
Outside, the crew begins to dry and clean the net, boat and equipment. “We know about any aquatic invasive species in the lakes we deal with,” Lorenzen says. “The protocols we follow ensure that everything is completely clean before we use it again. We certainly don’t want to be the ones that spread this around.”
Inside, the millions of eggs are slowly introduced to their new water. “Our water is pumped in from nearby Madeline Lake,” says Lorenzen. “We run the water through micro-filters and are careful to temper it to match the Ph level and temperature, so as not to shock the eggs.
“Then we rinse the eggs in an iodine solution to kill any viruses, bacteria or fungus that may be present,” he continues. “Our process is constantly being monitored to make sure we aren’t going to spread any pathogens.”
At this point, the hatchery staff begins using 100-year-old methods, relying on the wisdom and science of generations past. “These batteries of jars have been used for decades,” says Lorenzen. “They’re now made of plastic instead of glass, but it’s basically the same.”
The eggs are kept in the jars for several weeks with fresh water constantly flowing around them. “After about a week, you can see the eye inside the eggs,” he says. “During this time, we must constantly watch for and remove any dead eggs.”
In another week, the sack fry emerge, so called because they have a heavy yolk sack attached to their bellies. “The yolk sack weighs them down, but it’s their initial food source,” Lorenzen explains. “When it’s absorbed, we put a light above them and they swim up toward it out of the top of the jar.”
The tiny fry are deposited into a trough and drained into nearby stock tanks, ready to be moved into outdoor lined ponds after just a couple days. They are fed plankton for about another month.
At this point, the small fingerlings are 11/2 to 2 inches long, and ready to be stocked out to area lakes. Some, though, are stocked back into the hatchery ponds for the summer, feasting on minnows.
“By the time the lake temperatures cool in the fall, they are 6 to 9 inches long and ready to be stocked into area lakes as large fingerlings,” says Lorenzen. “During this time, we have to keep a close eye on them; they are quite carnivorous, and if they run out of food, they will begin to prey on each other.”
It’s not long before the small walleye are ready to be moved to the lined ponds outside. There, they eat minnows for another few weeks until they are about 2 inches long and ready to be stocked in area lakes. The hatchery also produces longer, older fingerlings.
This year was pretty typical, Lorenzen says. They processed six million walleye eggs. Out of that number, five million hatched. A total of 730,000 fry were stocked in the hatchery ponds, of which about 75 percent survived to the fingerling stage.
“Unfortunately, we don’t have the space to bring them all to maturity,” says Lorenzen. “But we make sure to include eggs from both early and late spawners. We do what we can to get a good genetic mix.”
Musky are processed similarly, he adds, with a few key differences. “They are larger and harder to handle; we typically send three people out in the boat to collect the breeding stock.”
This year, 19 female musky were captured out of Big Arbor Vitae, and about three times that many males needed to fertilize the eggs. Fortunately, according to Lorenzen, the males seem to be more plentiful.
The newly hatched musky fry do not swim as well as their walleye counterparts, and over the years a rather interesting technique has been developed to help them. “We lay spruce boughs across the top of the water in the tank,” he explains. “This allows the musky fry to attach themselves and disperse, otherwise they would all just sink to the bottom and suffocate.”
Musky are, no doubt, prized above all other fish in the Northwoods, and they are treated with great care at the hatchery. Three years ago, the DNR adopted a new protocol, installing electronic ID tags in each fish stocked back into broodstock lakes.
“Some years down the road, we’ll be able to tell just where each individual came from and when it was stocked,” Lorenzen says.
“That will help us track brood stock and determine how fast they grow. We will also make sure to only breed fish from different years, in that way avoiding crossing siblings. That will help us to ensure a better genetic legacy.”
Young musky and walleye are constantly hungry, and the staff at the hatchery has developed a relatively inexpensive way to keep them fed: they produce the food. “We breed suckers, in much the same way we do the predator fish, to use as feed during the early weeks,” says Lorenzen. “Unfortunately, we usually run out before we’re ready for stocking the fingerlings, so we have to buy minnows.”
By this time in the late summer, big tanker trucks of minnows arrive weekly. Staff members monitor the ponds closely to make sure the growing fingerlings have enough to eat until they’re ready to be shipped out to their new home in a Wisconsin lake.
Selecting lakes for stocking is the job of biologists, and in Oneida County, the decisions are made by DNR fisheries biologist John Kubisiak.
“We stock for three reasons,” he explains. “If a lake experiences winter-kill because of low oxygen, then we may go in to bring the population back up.
“If there are problems with natural reproduction, such as habitat degradation or predation of the young fish, we’ll stock as a one-time reestablishment of the species. We’ve done this with both walleye and musky in the Minocqua chain.
“Sometimes, we go into a lake to create a fishery,” Kubisiak continues. “We’ve gone into Thunder Lake to try to establish walleye in a system otherwise dominated by bass and northern pike.”
Human anglers are not the only ones to profit from a healthy population of game fish. “Predator fish do eat minnows, but their main food source is panfish like perch, blue gills and sunfish,” Kubisiak explains. “In a lake without enough predator fish, panfish become over-populated and experience reduced growth rates that we call stunting. By adding more predators, we can thin out the over-abundance of panfish.”
Kubisiak is often asked about the prospects for anglers in stocked lakes. “The best lakes, really, are the ones that don’t need to be stocked,” he says. “We do our best to create fisheries and address problems, but fishing a naturally healthy lake is best.”
He points out that catch-and-release methods, especially for musky, have lightened the burden on that species. “In the 1970s and ’80s, people generally kept any musky they caught,” he says.
“By the time that catch-and-release became very popular, about 1984, we began seeing changes: more big fish and higher populations. Musky take about 10 years to reach 40 inches, and maybe 18 years to get over 50 inches. They can live to be 20 to 30 years old.”
With modern fishing methods that include better mapping of lakes and electronic fish locators, game fishing will continue to be a popular pastime among locals and tourists alike.
The Wisconsin DNR is committed to sustaining fish populations in area lakes. Since the entire operation at the Art Oehmcke hatchery is funded by money collected through fishing licenses, the future is secure.
“Fishing is such an important part of our economy in this part of the state,” says Lorenzen, “what we do here is value returned. Together with our partners in the University of Wisconsin system and the input of our own DNR biologists, we’ll continue to make fishing better.”
Sue Schneider is a freelance writer who lives in Rhinelander. Her articles also appear in Northwoods Commerce™ and Northwoods ‘boomers and Beyond™ magazines.