Hatcheries

This scene may look like a blend of a chemistry laboratory and a craft brewery. In fact, it is a Minnesota Department of Natural Resources fish hatchery where eggs like those seen in these tubular canisters will be hatched and later stocked as minute “fry,” about the size of a grain of rice.

Photos courtesy of Minnesota DNR

Minnesota’s hatcheries

By Mike Rahn

help balance fish supply with angler demand

Economics is not likely to be in an angler’s thoughts as he boots up his fishfinding and boat control electronics, and lowers his electric motor for the first trolling pass of the day.

But in a very real way, a central concept of economics - supply and demand - might play a role in his angling success.

A fish that appears as an arc-shaped digital signature on his LCD screen could be as much a product of science and technology as the angler’s state-of-the-art devices.

A walleye down below suspended over a submerged rock pile might have been born in the protected nursery environment of a hatchery, rather than on a gravel shoal in six feet of water on the angler’s favorite lake.

In a purist’s perfect angling world, a fish that inhales a plastic worm or smashes a spoon or stick-bait would have emerged from an egg in the natural environment of a lake or river. But that perfect angling world is not a reality everywhere.

Today, fisheries managers often give nature a helping hand to broaden angling opportunities and increase an angler’s chances of a tangible reward on the end of his line.

Boosting fish populations through hatchery propagation and stocking meets a definite need. Despite widespread angler acceptance of a catch-and-release ethic, this admirable practice does not ensure selfsustaining fish populations everywhere.

Supply-side fisheries economics

A number of factors influence fish numbers and the balance of supply and demand. Some fish will end up as fillets sizzling in an old black frying pan, a perfectly legitimate outcome, within reason.

Others may become casualties of postrelease mortality, despite the best angler

“Where we take those walleye eggs depends on the year. But historically it’s been at Cut Foot Sioux or Lake Winnibigoshish in Cass County, and more recently the Pine River-Whitefish Chain. Musky eggs are taken at Lake Rebecca in Hennepin County, a brood stock lake.”

Marc Bacigalupi DNR Area Fisheries Supervisor

intentions and handling care. Estimates of post-release mortality range from 7% or 8% over the course of a year, rising to as high as 20% during midsummer high temperature conditions.

Live bait-caught fish, more often hooked deeply, generally have higher post-release mortality than do fish caught on artificial lures.

Other fish - of trophy size, typically - may end up above a fireplace mantel, or on a den or office wall, as taxidermy testimony to an angler’s success.

Of course, there is an alternative to this, in the form of lifelike resin replicas created from angler-recorded measurements and photos of that special fish, a substitute that serves the purpose well for many anglers.

Simple angling pressure is also a factor in the supply and demand equation. While participation in some forms of hunting has been measurably declining, that has not been the case with angling.

Not only are there some 1.4 million licensed Minnesota anglers, but our state is a popular destination for nonresidents, as well. Pressure is not divided equally among the state’s lakes, rivers and streams. Some popular and readily accessible waters are subject to significantly greater than average fishing pressure; sometimes more than nature can accommodate.

Habitat productivity is another variable. Some lakes may have a good forage base of microorganisms, aquatic insects and forage fish, but are deficient in good spawning habitat.

Walleyes and trout are good examples of angler-preferred species that would be found in fewer Minnesota waters if not for the stocking of hatchery-raised fish.

In some cases stocking supplements natural reproduction to boost fish numbers. Central Minnesota’s Gull Lake is an example of a lake with limited natural walleye reproduction, and is heavily stocked annually to boost numbers to balance its walleye population with fishing pressure on this popular lake.

In other waters, stocking creates a fishery that would not otherwise exist. This is true of former open pit mines of the Cuyuna Iron Range, near Crosby and Ironton in Crow Wing County. Here, trout of several varieties are stocked in the cavernous pits that once echoed the sounds of steam shovels and ore cars.

Following the end of mining, these pits filled with water to become deep lakes, their shorelines and mining waste piles gradually reclaimed and regrown to second-growth forest. They now provide a fishery where one previously did not exist.

For all these reasons, stocking has become an important fisheries management tool for the Minnesota Department of Natural Resources and fisheries professionals elsewhere.

Where it begins

In a state where walleye is king - it’s Minnesota’s state fish, after all - the majority of stocking is understandably devoted to this species.

“There are 11 hatcheries around the state that incubate and hatch walleye eggs,” said DNR Area Fisheries Supervisor Marc Bacigalupi, who is based in Brainerd. “Some of these hatcheries also have outdoor ponds that raise fish to larger size

Walleye eggs destined for hatchery propagation and stocking are commonly taken from wild fish that are captured on one of several popular Minnesota lakes. The eggs are fertilized with “milt” from male walleyes, then hatch and grow within the hatchery environment. 2022 Love of the Lakes | 29

throughout the summer, to be drained and their fish stocked in the fall.”

Raising fish to larger sizes before stocking is costly, so most walleye stocking consists of just-hatched “fry,” which are the size of a mosquito or a grain of rice. Every year about 200 million walleye fry are stocked in Minnesota waters, compared to only about 2.5 million walleye fingerlings.

Fingerlings are sub-adult fish that may be 4 to 6 inches, sometimes as large as 6 to 8 inches. The survival odds for any individual walleye fry are far lower than for a fingerling. But only a small percentage of the multitudes of fry stocked need to grow to catchable size to make the fry stocking strategy pay off, Bacigalupi said.

Three of these 11 hatcheries - called cool water hatcheries, to distinguish them from the DNR’s cold water hatcheries, where trout are raised - also raise other species. These are primarily muskellunge, or muskies.

Musky anglers are a vocal and dedicated group, and - perhaps due in part to their lobbying efforts - have seen the range of their favorite fish expand markedly through stocking. Unlike walleyes, most of which are stocked as tiny fry, “muskies are stocked at about 6 months old, when they are about 10-12 inches in length,” Bacigalupi said.

Muskies are considered native only to 44 lakes and eight river systems in Minnesota. The DNR has introduced them into an additional 48 lakes. Not without some controversy, however.

Some Minnesotans oppose expanding the musky’s range through DNR stocking, fearing this apex predator will reduce walleye numbers. DNR fisheries managers contend that this is not supported by data.

Most walleye lakes already harbor a closely related, top-of-the-food-chain predator - the northern pike. Nevertheless, there have been efforts in the Minnesota Legislature - so far unsuccessful - to place a moratorium on the stocking of muskies in any new waters.

Eggs obtained for hatchery rearing of walleyes and muskies are stripped from females netted in the waters where they live.

“Where we take those walleye eggs depends on the year,” Bacigalupi said. “But historically it’s been at Cut Foot Sioux or Lake Winnibigoshish in Cass County, and more recently the Pine River-Whitefish Chain. Musky eggs are taken at Lake Rebecca in Hennepin County, a brood stock lake.”

These muskies are of what fish geneticists call the Leech Lake strain, the strain native to Minnesota.

On the other hand, most trout raised in the DNR’s four cold water hatcheries are descended from adult brood stock that are kept in the hatcheries to supply eggs for rearing. Some are destined for put-andtake fisheries.

“In central Minnesota’s mine pit lakes, rainbow trout are stocked as keeper-size yearling fish, intended to be caught and harvested each year,” Bacigalupi said.

Another strategy is put-and-grow. In some of these mine pit lakes, “fingerling lake trout are stocked in the hope that they will grow and become large, quality fish. As a result, a special regulation is in place to restrict the harvest of lakers under 20 inches.”

Another passionate Minnesota angler group is steelhead fishermen. Steelhead are migratory rainbow trout that historically have been born in Lake Superior tributary streams. In Minnesota these streams are along Superior’s North Shore.

As juveniles, they migrate out into the big lake to grow and become sexually mature before returning to these streams to spawn, sometimes reaching 30 inches in length. Most spawn in spring, though some migrate into the streams in fall.

While many angler-caught steelhead are the result of natural reproduction, some are

“Water quality is very important. The rates of all metabolic processes, including hatching, growth and reproduction, are temperature dependent.”

Paula Phelps DNR fish production supervisor

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“But losses of fish in the DNR’s hatchery program due to infectious disease are very uncommon, due to the agency’s following risk assessment, surveillance and biosecurity practices”

Isaiah Tolo DNR Pathology Laboratory Supervisor

hatchery-raised, identifiable by a clipped adipose fin just ahead of their tail. Hatcheryraised steelhead provide a limited angler harvest opportunity, because wild fish are presently catch-and-release only under a DNR management plan intended to increase wild steelhead numbers.

Most of the roughly 120,000 4- to 7-inch yearling steelhead stocked in North Shore streams each year are born in the DNR’s Crystal Springs hatchery, near the Whitewater River in southeast Minnesota. They come principally from brood stock that reside in this hatchery.

But each year eggs from 30 to 50 pairs of wild steelhead are trapped at the DNR’s French River station on the North Shore and added to the program, said Cory Goldsworthy, the DNR’s Lake Superior Fisheries supervisor.

“The purpose of this is to maintain genetic diversity,” Goldsworthy said.

This is intended to ensure that those hatcheryraised fish available for angler harvest will maintain the traits of wild-born steelhead.

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Emphasis on native species

Fish stocking philosophy has shifted significantly over recent decades. The current approach emphasizes not just angler opportunity, but suitability of a fish to the aquatic environment where it is stocked.

In the mid-1970s, for example, fisheries management took some daring turns, introducing species very much foreign to waters where they were stocked. Lake Superior provides a case in point.

Species native to the Pacific Ocean, like chinook - or king - salmon, as well as coho salmon were stocked over a period spanning several decades.

“This has ended,” Goldsworthy said.

He pointed out that the emphasis now is on restoring Lake Superior’s native lake trout, once depleted by the invasive sea lamprey, as well as lake-run brook trout - called “coasters” because they grow and mature in Lake Superior, entering North Shore coastal streams in fall to spawn.

Broadening angler opportunity

There are other, lower profile, DNR fish stocking initiatives. They include limited stocking of largemouth bass, bluegills and crappies, sometimes done to repopulate a lake that has experienced winter-kill, Bacigalupi said, and in other places to provide an opportunity in neighborhood ponds that increases angler access, including for under-served and less experienced anglers.

“These fish are usually adult brood stock,” he said, and because these species are so prolific, just two to five pairs per acre are usually enough to restore or create a viable population.

Stocking as science

The angler who reels in a walleye or rainbow trout that began life as an egg hatched and reared in a hatchery is likely unaware of the science behind his results. Propagating fish in a hatchery is a far cry from raising goldfish in a bowl or tropical fish in an aquarium.

After the stripping of eggs from females in the wild, or in the hatchery, and fertilizing them with “milt” from males comes the hatching and growth phases. It’s vital to control environmental variables in a hatchery.

Some are general while others are linked to a specific fish species.

“Water quality is very important,” said Paula Phelps, DNR fish production

supervisor. “The rates of all metabolic processes, including hatching, growth and reproduction, are temperature dependent.”

Water temperature needs differ by species. For example, trout species require colder water temperatures than walleyes, muskies or bass. Equally important is dissolved oxygen.

“This is critical for cell respiration, and ultimately growth and survival,” Phelps said.

Dissolved nitrogen - the same gas that in excess amounts can give divers “the bends” - can be as toxic to fish as to humans and must be controlled as well. Also monitored are dissolved carbon dioxide - a product of respiration in fish, humans and all other life on earth - and other potentially toxic dissolved gases.

Important, too, are hatchery water acidity or alkalinity, control of dissolved solids that could smother eggs or clog hatchery apparatus, and alertness to the potential for pesticides that nearby agricultural chemical use can introduce into the groundwater supply a hatchery uses.

No less important is maintaining diseasefree hatchery conditions. With so many fish confined in close quarters, disease can spread rapidly, leading to shutdown of a hatchery and potentially the loss of all its immature fish.

Avoiding the introduction of disease into the wild via stocking is also important. While fish are susceptible to certain bacterial infections - especially when other stresses are present - “the pathogens that have the potential to cause the most serious losses to hatchery stocks are viruses,” said the DNR’s Pathology Laboratory Supervisor Isaiah Tolo. “Viruses like viral hemorrhagic disease are capable of causing devastating outbreaks in hatchery populations.

“But losses of fish in the DNR’s hatchery program due to infectious disease are very uncommon, due to the agency’s following risk assessment, surveillance and biosecurity practices,” Tolo said.

Maintaining ideal hatchery conditions is clearly no small feat.

The production- recreation equation

A parallel might be drawn between propagating and stocking fish for anglers, and the animal husbandry of farmers and ranchers who raise poultry and cattle for human consumption. It’s an imperfect comparison, because providing recreation is at the heart of fish propagation and stocking.

The consumption aspect of angling varies greatly from angler to angler. It can even vary for the same angler from one outing to the next, or by the fish being sought.

For example, an angler who would release every musky he catches might have no qualms about keeping and eating walleyes or bluegills.

But if putting food on the table were the sole objective, this could certainly be done more efficiently by a visit to a grocery store or market. To one degree or another, most anglers are driven by “the chase.”

For some, this is entirely so. There can be as much pleasure in angling’s anticipation, preparation and pursuit as there is in tangible success.

Unseen by most anglers, hatchery propagation that augments natural production of our most sought-after fish is not only a complex science, but a boon and a benefit to Minnesota anglers.

MIKE RAHN writes Inside the Outdoors, an outdoor column published in area publications, including the Pineandlakes Echo Journal.