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Given a clean place to live, protection from enemies, plentiful food and good company, almost any population could sustain itself. Fish are no different. And fisheries experts increasingly aim to create the right conditions so fish will naturally reproduce and keep their population growing.
Unfortunately, a lot can go awry in the watery world. Pollution seeps in, nutrients cause plants to grow too quickly and exotic organisms that eat eggs or uproot habitat can invade. Hungry predators cruise the waters, and human anglers have a taste for fish. Small wonder that in many cases natural reproduction of fish can't keep pace with "consumer demand."
To give anglers a greater chance of catching fish, Wisconsin has stocked state waters for more than 100 years. Walleye have been stocked since 1876, when the Nevin Hatchery was established in the Madison countryside that became Fitchburg.
Then and now, we primarily stock fish to provide angling opportunities for the public, explains Al Kaas, the statewide fish propagation coordinator. We raise fish in hatcheries to protect them during their most vulnerable life stages, then we release them to grow to adulthood back in wild waters.
Fish stocking quotas fluctuate somewhat annually and today, DNR operates 14 state hatcheries and three spawning facilities.
Fish may be stocked when they are fry (newly hatched), fingerlings (up to one year old), yearlings (12 to 23 months old) and as adults. Wisconsin annually stocks around 11 million fingerlings and yearling fish, but much larger quantities of the smaller fry are released. Twenty to 40 million fry are stocked – trout and salmon fry, fingerlings and yearlings in the Great Lakes; trout, walleye, muskellunge, northern pike and largemouth bass fry, fingerlings and yearlings on inland lakes, rivers and streams.
While that sounds like a lot of fish, stocking actually is not necessary in most Wisconsin waters.
"Most state waters support excellent fish populations and do not require stocking," Kaas says. "Introducing fish to lakes that already support excellent fish populations could upset the genetic balance in those waters and go beyond the biological carrying capacity of the lake.
Frank Pratt, a fisheries manager in Hayward, says stocking can be a valuable tool when a lake or stream has a smaller fish population than it should support because spawning habitat has been destroyed, cover for young fish is weak, food supplies have dropped off or there's a problem with predation.
Lake surveys and past experience determine if a lake should be stocked, what species should be stocked and what size the fish need to be to survive in the water, Pratt says. Fisheries biologists consider harvest regulations, catch records and demand in figuring how many fish should be stocked and which waters would most benefit from supplemental fish.
It's a balancing act.
Take the muskellunge, Wisconsin's most sought trophy game fish, as an example. Every year, small musky are transferred from hatchery rearing ponds and stocked in more than 200 musky waters statewide. Musky populations are low in some waters due in part to competition with northern pike, and declines in habitat and spawning grounds.
The bulk of musky fingerlings are wild stock reared at the Gov. Tommy G. Thompson Hatchery at Spooner, the newest and most modern coolwater hatchery, and at the recently renovated Art Oehmcke Hatchery at Woodruff and West Central Region rearing ponds. Mature fish are captured during spring spawning. Their abdomens are then rubbed to expel roe (eggs) and milt (sperm). In the wild, less than 0.1 percent of the eggs deposited would hatch and survive, in the hatchery, 60 to 95 percent of the incubated eggs make it.
Stocking is the culmination of weeks, sometimes months or years of care, says Rod Patrick, the South Central Region operations manager who oversees the Lake Mills and Nevin hatcheries.
Last year, the Nevin Hatchery provided wild fish for 169 trout streams. The hatchery leads the state in raising wild trout that remain wary after stocking. The wild trout program started five years ago when state fisheries biologists found that domesticated trout strains didn't fare as well as wild trout raised with less human interaction.
While all the hatcheries raise fish, not all hatcheries hatch eggs. Some, called "rearing stations," raise fish that are hatched and transferred from other facilities. In true hatcheries, after eggs are mixed with milt and left to firm up or "water harden" for a while, the fertilized eggs are collected and placed in hatching jars supplied with oxygen rich water at a specific temperature. Newly hatched fish (fry) are raised indoors in tanks. As they grow, they are transferred to outdoor raceways and ponds.
Some hatcheries also are taking part in research projects such as tracking conditions that cause hatchery-raised chinook salmon to contract Bacterial Kidney Disease as adults.
Aside from special projects and the day-to-day intricate art of raising fish, the state hatchery/stocking program faces longer-term challenges. One of the most significant is keeping the facilities in working order. Some hatcheries are 50 years old or more and need upgrading to meet compliance standards for water supply issues.
At some hatcheries old windows need to be replaced, black topping is needed, buildings need to be insulated, and raceways need upgrading.
Stan Johannes, a Northern Region operations manager in Spooner, says more environmentally friendly chemicals are being explored and used in state fish hatcheries and new technologies are being explored to prevent fish diseases. Over the past few years there also has been a shift from manual hands-on control of feeding, water volume and temperature to automated (computer-controlled) systems.
Ultimately, Johannes says, the greatest shift has been a shift from producing numbers of fish to producing quality fish that survive better in the wild.
"Fish culture has changed a lot over the past 100 years," Kaas says. "But we are working throughout the state to ensure that the fish we are stocking will continue to grow to legal size and in coming years provide a healthy fishery and good fishing opportunities."
Natasha Kassulke is the associate editor of Wisconsin Natural Resources magazine.