As anglers across the state ready their gear and fantasize about this weekend’s fishing opener, scientists on a west metro lake Wednesday were creating some of Minnesota’s future trophy fish.
Department of Natural Resources fisheries specialist B.J. Bauer was half-standing in a johnboat with a 42-inch female muskie across his lap. He firmly stroked its plump white belly from front to back, while an assistant holding a plastic bowl caught thousands of dark, mustard-yellow fish eggs oozing from its vent.
The three-day “egg take” happens annually at 254-acre Lake Rebecca. It is Minnesota’s main source of muskies-to-be each year, the origin of wild eggs that go to hatcheries and yield fish for stocking programs statewide. Large muskies are popular as a sport fish, and especially for their trophy value.
“We try to keep conditions as close to natural as possible,” said Bauer, as he continued the fish massage for about five minutes.
Natural conditions mean that timing is critical. Bauer has been waiting for the water temperature to reach 52 degrees, which is when male and female fish become “ripe” for spawning. Normally, that happens in the second or third week of April, he said, but this year it was May 6.
Natural conditions also mean setting nets in shallow water, where muskies would be searching for places to lay eggs.
Bauer said Lake Rebecca is an excellent place for DNR’s brooding stock of the fish, but it doesn’t have the right aquatic plant beds and other conditions for their egg-laying to succeed.
But that doesn’t stop them from trying, he said. “They’re fish. By instinct they’ll go through the motions of spawning, even if the habitat isn’t that good for success,” Bauer said.
Pulling the nets
The first step in the process is to set trap nets around the lake, anchored to shore. Each morning Bauer and fisheries specialist Kristan Maccaroni motor from net to net to see what they’ve caught. At each stop they haul in a mix of snapping and painted turtles, crappies, bluegills and the occasional bass or carp, all of them dwarfed by the 12- to 15-pound adult muskies.
“Pulling the nets is my favorite part. It’s a surprise every time,” said Maccaroni.
The muskies are transferred to an aerated 180-gallon galvanized stock tank on the boat, until enough are collected to bring ashore for the egg take. Wednesday morning the two-person crew collected five females and three males from half of the 14 nets spaced around the perimeter of the lake.
Beached on shore, the boat became a lab. Bauer and Maccaroni sedated two male fish and massaged milky white sperm from them into test tubes. They added a chemical extender to keep the semen inactive. Then they sedated the female, stroked her for eggs, and mixed in the sperm.
“At this point sperm are active only for about a minute, so we have to work fast,” Bauer said.
Maccaroni stirred the mixture gently with a turkey feather as Bauer added lake water and packaged the now-fertilized egg slurry in a plastic-foam shipping container for transport to the hatchery. The fish were released, and then it was on to the next batch.
Bauer said Lake Rebecca has been used for muskie brood stock since 1987. It’s an excellent choice, he said, because its ice melts earlier than northern lakes, the lake is surrounded by Three Rivers Park District land, and only electric motors are allowed on the water.
“Anglers know we use the lake for brood stock,” he said, and they respect that by not overharvesting the fish.
Bauer and Maccaroni will harvest and fertilize about 900,000 fish eggs in a three-day period. The eggs will go to hatcheries in St. Paul, Waterville and New London for incubation and hatching, and will then move to rearing ponds for the summer. About 30,000 will survive and grow large enough to be stocked in lakes around the state this fall, he said, including Lake Rebecca.
Maccaroni said that a large female can produce about 50,000 to 80,000 eggs, or about a quart. To reach the state muskie egg quota, she and Bauer will need to net 60 to 75 of the adult muskies, including about 20 females.
“It’s really satisfying to get a lot of eggs,” she said. “It makes it seem like all the hard work is worthwhile.”