It’s already been a busy spring for South Dakota Game, Fish and Parks Department fisheries workers as they’ve been collecting walleye and yellow perch eggs from various water bodies for incubation at Blue Dog Lake State Fish Hatchery.
On the northwest shore of Blue Dog Lake near Waubay, S.D., it is one of four fish hatcheries operated by the state, but it’s the only warm-water hatchery and is largely responsible for the state’s stocking efforts concerning walleye and yellow perch.
“We’re done bringing eggs in this year, and the eggs that we have, overall, are looking pretty good,” said Ryan Rasmus, fisheries resource biologist at the hatchery. “The first eggs came in April 8, and the last ones came in April 23.”
Rasmus said the hatchery took in 101 million walleye eggs. He said 45 million were collected from the northeastern part of South Dakota, 36 million came from the southeastern part of the state and 20 million came from Lake Oahe near Mobridge.
“Every year is different, but it was a nice, steady spawn for us,” he said. “We shoot for a 50 percent hatch on those eggs, and some walleye eggs are just starting to hatch for us.”
Rasmus also said the hatchery received 10.5 million yellow perch eggs, all of which were collected from bodies of water in the southeastern part of the state.
While Blue Dog produces walleye fry and fingerlings for stocking, yellow perch are a different story.
“Yellow perch are actually stocked before they hatch as eyed-eggs, and most of our perch stocking is done in the southeastern part of the state,” Rasmus said. “We have them here in a controlled environment for a majority of their incubation, but we generally ship them out a week or so before they hatch.”
Collecting millions of eggs is no small task, and Rasmus said there’s a cooperative effort each spring to ensure the state’s stocking goals are met.
“This is a statewide effort to get the eggs,” he said. “There was staff from the Sioux Falls, Mobridge, Watertown and Webster offices who helped, and we even had help from the Black Hills staff who would come over and help with the walleye spawn. It’s definitely a big effort on everyone’s part.”
To collect walleye eggs, Rasmus said GFP workers generally set trap nets where a panel of mesh called a lead is set perpendicular to shore in known spawning areas.
“Fish follow that lead, and it funnels them into a series of frames, which are kind of like boxes,” he said. “They’re funneled through these frames until they get to a section we call the throat, which funnels them even more into the catch pocket where they’re basically trapped.”
The pocket on each net is marked with an anchored buoy, and workers can pull up in a boat and begin taking in trapped walleyes for spawning.
“Once we take fish out of the pocket, we generally have big water tanks where we place the male and female walleyes,” he said. “Once they’re full, we sort them into different groups.”
Rasmus said female walleyes are separated into three classes: females considered “ripe” are ready to be spawned that day, females that aren’t quite ready are called “green,” and females that have already spawned are classified as “spent.”
“We can hold green females up to three days,” he said. “If they don’t ripen, we release them back into the lake.”
To collect the eggs, fisheries staffers gently press or squeeze on the bellies of ripe females and catch the eggs in shallow pans. The same process is used to extract sperm from male walleyes.
“We want the fish dry and don’t want any water in the pan, so we’ll wipe them off and, depending on their size, take one to three females and place their eggs into one pan,” he said. “Then we’ll actually grab two to three males and fertilize the eggs by adding sperm to the pan.
“The interesting part is that we’ll actually add 2 cups of water to the mixture of eggs and sperm. The water activates the sperm, which is only good for one minute, so that’s why early in the process we want to keep the eggs and sperm dry. We want to have as much control over that part of the process as we can.”
After water is added, Rasmus said the mixture is then stirred for about two minutes in hopes most of the eggs in the pan are fertilized.
“Naturally, those eggs have an adhesiveness to them, so they’re sticky,” he said. “We don’t won’t want them sticky when they come to the hatchery because that means some eggs wouldn’t get as much fresh water. Basically, we use a mud mixture of diatomaceous earth and pour that into the fertilized eggs and stir it for another two minutes.”
Rasmus said the mud mixture removes the eggs’ adhesive qualities and helps them separate so they can each get an equal amount of fresh water during incubation.
To estimate the number of eggs, Rasmus said GFP uses a known egg-per-milliliter ratio.
“We measure by liters, basically, as they’re brought to us,” he said. “We’re measuring walleye eggs 1,000 milliliters at a time, and that’s how we get our number.”
Once walleye eggs have been collected, fertilized and separated, they’re placed into thick plastic bags with water, transported to the hatchery and placed in incubation jars.
“Incubation typically lasts 21 days for walleye eggs,” Rasmus said. “We’re able to incubate our eggs on well water, which is a constant 50 degrees. We have a water heating system we turn on May 3, which should increase the water temp to 56 degrees and should get them hatching.”
In addition to promoting development and growth, warming the water in the incubation jars mimics what’s going on naturally in lakes and streams across the state.
“Whatever the lake temps are, we try to mimic that,” Rasmus said. “That way we don’t have to temper or acclimate the fry to the body of water where they’re being stocked.”
Once the walleye fry hatch, they swim out of the jars into a gravity-fed water trough that leads to catch tanks where walleye fry are collected.
“When they first hatch they’re about the size of a mosquito, and those catch tanks have real fine mesh screens to keep them in there so we don’t lose them,” he said. “Also, it’s fairly dark where the catch tanks are located, and there’s one light over each tank. The fry are attracted to that light and (that) makes it easier for us to catch them.”
The number of walleye fry is estimated by volume using water displacement.
“We’ll actually catch the walleye fry, drain the water off of them and dump them into a beaker filled with 200 milliliters of water,” Rasmus said. “As that volume increases we get a known amount, because we have an estimate that’s based on how many fry per milliliter of water displaced.”
Most fry leave the facility soon after hatching, Rasmus said, as walleye fry feed on their yolk sac, which provides them with nutrients for their first three days of life.
“Because there is no food here for them, we have to get them out of the catch tanks as soon as possible and get them into ponds,” he said. “Some fry stay on site, as we have 36 rearing ponds here, and right now we’re filling those ponds.”
Rasmus said the hatchery plans to keep enough fry to produce 1.3 million walleye fingerlings.
“We’ll start stocking our ponds this weekend, and it’ll be around the second week of June when we’ll harvest those ponds,” he said. “They’ll be small fingerlings, approximately an inch-and-a-half long by then, that we’ll also use for stocking.”
All the other walleye fry will soon be shipped statewide, from West River reservoirs to East River lakes, Rasmus said. If the hatchery meets its 50 percent hatch-rate goal, that means roughly 50 million walleye fry and fingerlings will soon be headed to new homes.
— Follow @OutdoorForumMag on Twitter.
Blue Dog Lake State Fish Hatchery quick facts:
• Each year the hatchery incubates 100 million walleye eggs and produces 60 million fish for stocking across South Dakota.
• The hatchery has 36 rearing ponds totaling 53 surface acres of water.
• A complex water supply system equipped with filtration allows lake or well water to be used for fish production, and a water heating system allows yellow perch and largemouth bass to be grown during winter months.
• The best time to view walleye eggs and newly hatched fry is the second week of May. The hatchery is open Monday through Friday from 8:30 a.m. to 4 p.m. Reservations for large groups are recommended.
• Address: 44437 139A Street, Waubay, SD 57273
• Phone: 605-947-4657
Source: South Dakota Department of Game, Fish and Parks