Wyoming Wildlife - July 2023

Double Duty

Walleye (top) and Rainbow Trout (bottom)

Trout and walleye in the same body of water can be challenging for biologists, but it can provide a quality fishery if managed properly.

Art by Zack Even
7/1/2023 12:00:05 AM

The quest to catch trout in Wyoming is tough to beat. These colorful fish are found throughout the Cowboy State, and can be caught a variety of different ways throughout the year. Also, the pursuit of walleye is growing in popularity in Wyoming. These toothy, predatory fish provide a good test for anglers, and their mild-tasting meat is, in a word, delicious.

Rainbow trout is a common and popular species for angler throughout Wyoming. (Photo by Patrick Clayton)

However, these two fish can mean trouble if they share the same body of water. Walleye eat small trout and will cause a quality trout fishery to decline rapidly. When food becomes scarce for walleye, they don’t grow and the result is a population of stunted fish with not enough to eat.
There are a handful of waters around Wyoming with trout and walleye. In all cases, those waters were managed by the Wyoming Game and Fish Department for trout. Walleye were illegally introduced in some waters, and Mother Nature aided their spread into others.
Today, Game and Fish manages these waters for trout and walleye to coexist, and in some cases other species of fish. Those bodies of water provide options for anglers, yet it takes a lot of effort, research and time to make it work.

Walleye angling in Wyoming continues to grow in popularity, but these predatory fish can harm trout populations if not managed properly. (Photo by Patrick Clayton/Eric Engbretson Underwater Photography)

This term is used when cold-water fish like trout and cool-water fish like walleye exist in the same body of water. The primary two-story fisheries in Wyoming are Alcova, Pathfinder and Seminoe reservoirs along the North Platte River in the Casper Region, Boysen Reservoir in the Lander Region and Lake DeSmet near Buffalo in the Sheridan Region.

Boysen Reservoir, located in Boysen State Park in central Wyoming, is managed for trout and walleye fishing. The state park provides many recreation and fishing opportunities. (Photo by Patrick Owen/WGFD)

Matt Hahn, Game and Fish fisheries supervisor in the Casper Region, said a big reason for two-story fishery management is demand for both species. He said trout fishing provides decent action for winter ice fishing, and in the spring and fall for shore anglers. Anglers with boats and the right equipment also do well with rainbow trout, especially during the summer when trout seek deeper, cooler water.
The best time to fish for walleye is in the summer when the surface water temperature warms up to about 70 degrees. Hahn said there isn't a large forage base for walleye in Alcova, Pathfinder and Seminoe so growth rates are slower compared to other walleye waters around the country.

Anglers at Boysen Reservoir can enjoy fishing for a variety of fish species including trout and walleye. (Photo by Patrick Owen/WGFD)

Hahn said walleye were first caught by anglers in Seminoe in 1961, and they got there presumably from illegal stocking. When sampling was conducted, it was discovered there were multiple size classes of walleye in the reservoir.
A big water year in 1973 saw water spilled out of Seminoe into Pathfinder, and with it came walleye. The same thing happened in 1985 when water from Pathfinder spilled and entered Alcova.
When those events occurred, the trout fishery in all three reservoirs declined rapidly.
“Back then those trout fisheries were managed by stocking fingerling trout,” Hahn said. “Given the forage limitations, those walleye wiped the trout out. In Seminoe, walleye became the most common species and all were stunted because there was not much food for them and the rainbow trout fishery crashed. We started stocking bigger and bigger rainbows to figure out how the trout could survive.”
The dam at Boysen was rebuilt in the 1950s and when the reservoir was filled, walleye and small trout were stocked. Through the years fish managers learned trout survival was inconsistent and poor.
Joe Deromedi, Game and Fish fisheries supervisor in the Lander Region, said it took until the 1990s to hone in on the right management strategy for rainbow trout and walleye to coexist in Boysen. Along with stocking larger rainbows, Deromedi said stocking trout in the fall worked better than the spring because as the water cools, walleye metabolism slows and they don’t eat as much.
Today and for quite some time, Game and Fish does not stock walleye in Boysen or in any of its other two-story fisheries.
Walleye were discovered in Lake DeSmet in the late 1980s and were illegally stocked. Paul Mavrakis, Game and Fish fisheries supervisor in the Sheridan Region, said walleye numbers remained low until the early to mid-1990s. Small, stocked trout saw similar fates from walleye and larger trout were stocked.
Walleye remain in DeSmet, but Mavrakis said they are not a hot commodity among anglers.
“Very few anglers catch walleye in the lake,” he said. “It is extremely clear. We can see a gill net in 30-40 feet of water. Since walleye are sight predators they are spooky in that clear water.”

Dalton Bonds, fisheries technician for the Wyoming Game and Fish Department, holds a walleye caught during gill netting at Seminoe Reservoir in June. (Photo by Janet Milek/WGFD)

The limited food base for walleye in two-story fisheries is where management of the two species gets specialized, and sometimes complicated.
Walleye will target trout for food, especially small, fingerling trout ranging from 3-4 inches long. Game and Fish often stocks waters with fingerling-sized trout because its hatchery system can raise more small fish in less space. It also costs more to feed and house fish that have to grow bigger before being stocked. And, Game and Fish can stock more small fish in a body of water at a given time. But if the walleye eat the small trout, then it's an exercise in futility.
The solution is to stock larger trout where there are walleye, larger meaning catchable-size fish that average about 8-9 inches long.
“The trade off there is there’s a finite amount of fish that size the hatcheries can produce,” Hahn said. “We continually sample and evaluate the survival of trout in trying to adjust our stocking numbers.”
Hahn added as a rule of thumb, a 7-inch stocked trout is susceptible to being eaten by a 14-inch walleye, an 8-inch trout by a 16-inch walleye, etc.
“There are typically a lot of 14-inch walleye in Alcova, Pathfinder and Seminoe and that can impact trout survival,” Hahn said.
Travis Trimble, Game and Fish assistant fish culture supervisor, said last year Game and Fish stocked 147,000 catchable-size trout in Seminoe, 136,000 in Pathfinder, 132,000 in Boysen and 67,000 in Alcova. Mavrakis said trout stocking at DeSmet went from several hundred thousand per year of fingerling-size fish to about 100,000 each year with bigger fish.
The juggling act also spills over to Game and Fish’s hatchery system to balance raising small fish and catchable-size fish for not only the needs for two-story fisheries but also around the state.
“Our hatcheries are currently running as efficiently as possible,” Trimble said. “We could raise more catchable-size fish, but some of the smaller fish requested would get cut out of the mix.”

Whitney Peters, fisheries technician for the Wyoming Game and Fish Department, sets upa gill net to survey fish in Seminoe Reservoir. (Photo by Janet Milek/WGFD).

Rainbow trout is the primary trout species in Wyoming's two-story fisheries. However, Lake DeSmet also has cutthroat and brown trout. Some reservoirs recently stocked kokanee salmon, but more data is needed to determine if that species will successfully coexist with other trout and walleye.
Kokanee were first stocked in Lake DeSmet in 2019, and early signs are positive that the salmon and walleye can coexist. The first kokanee stocked were 3-4 inches long, and Mavrakis said he didn’t expect to see those fish again.
“But they’re doing great,” he said. “The shorelines are red in the fall when those fish come in to spawn, and those fish are 3-4 years old and 16 to 20 inches long when that occurs. So they are fairly invulnerable to walleye predation.”
Marvakis also said adult kokanee “are better athletes” than walleye because of their swimming speed and ability to evade predators.
Game and Fish stocked the three reservoirs in the Casper Region with Bear River cutthroat trout, also known as Bonneville cutthroat, which is a native trout species in Wyoming.
Hahn said walleye are littoral, meaning they generally stay near shore and are oriented with the shore line. They don’t frequent deeper water in the middle of lakes and reservoirs. Bear River cutthroat when they are stocked — similar to kokanee — go to deep water and often stay there until they are about 5 years old.
“This means the Bear River cutthroat are not susceptible to predation to walleye because they’re not available in large numbers,” Hahn said. “When they move back into walleye habitat as adults, they’re too big to be eaten by walleye.
“We’ve seen some really good success there versus the rainbows. The rainbows that cruise around in the littoral area don’t make it very long.”
Hahn said of the three Casper Region reservoirs, Alcova was the first to be stocked with Bear River cutthroats about seven years ago. Based on the success there, stocking followed at Pathfinder and Seminoe and evaluations of how the cutthroat are doing in those waters is ongoing. Fish managers will look into the possibility of stocking smaller Bear River cutthroats compared to rainbow trout in these two-story fisheries.

Hahn said Alcova is in good shape right now for trout and walleye, and there are liberal walleye limits in place for anglers to keep those numbers in check.
“We had some real challenges and there were times the trout fishery suffered, but if we could hit the pause button and keep it where it is now, I think we would,” he said. “There is a nice balance of trout and walleye, and a good size structure across the board.”
Hahn said Pathfinder and Seminoe have a lot of smaller walleye that take time to grow due to a lack of food.
Deromedi said the balance of the trout and walleye fishery at Boysen is good.
“We have one of the highest abundance of walleye that we’ve had in many years, which provides a good opportunity for walleye anglers, and we’re able to say the trout fishing is excellent,” he said. “We’ve seen some of the higher catch rates in a long time.”
That includes rainbow trout 20 inches and longer, Deromedi said.
“Our trout fishery is in one of the best shapes we’ve seen in a long time,” he said. “We’re sitting on a fishery that has a lot of walleye of good size and a lot of rainbows of good size. That is a result of a lot of work from our culture section to provide the trout we need to manage the fishery in a way that benefits anglers.”
Mavrakis said walleye numbers at DeSmet fluctuate over time, but has been on a lower trend lately in terms of numbers and size. He added DeSmet is a trout fishery, but isn’t sure if walleye will ever go away.

Walleye may not be the most popular fish sought by anglers at DeSmet in the Sheridan Region, but some good-sized fish have been sampled there. (WGFD photo)

Fish management is a constant juggling act no matter the species, but that is ratcheted up a couple of notches with two-story fisheries, especially when one of those species can wipe out the other.
Game and Fish has found a good balance in managing its trout-walleye waters, although the work isn’t done — and likely never will be done.
“It is much more complex than having a single species, or just managing trout with no predator species,” Hahn said. “You can make a management change, but it takes multiple years of data collection to determine what that management change did. In the meantime, the walleye population can change. Then you tweak things again and the cycle starts all over. From that standpoint, it's far more challenging.”
— Robert Gagliardi is the associate editor of Wyoming Wildlife.


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