Predators as population control: FWP using fish as management tool

Jenny Gessaman
A long fish with a hooked mouth is sandwiched between text reading, "Attention anglers, tiger muskie are present in this waterbody."

Part of the FWP sign that explains the presence of tiger muskie to fishermen, such as those at Ackley Lake.

Graphic courtesy of Montana Fish, Wildlife and Parks

The tigers in Ackley Lake State Park may swim instead of walk, but they still have stripes, sharp teeth and a predatory eye. That’s good, because Montana Fish, Wildlife and Parks is hoping these hybrids will hunt down the park’s overpopulation of sucker fish.

Ackley: A sucker for the native fish
The state park’s problem comes from its origins and its primary purpose: irrigation. According to previous News-Argus reporting, Ackley Lake was built in the 1930s as a water storage project. It is an earthen dam, 51 feet tall, and draws its water reserves from the Judith River. That water is where FWP Fisheries Biologist Clint Smith said the problem comes from.

The Judith River brings in sucker fish, and that leads to a problem he commonly sees in reservoirs connected to flowing water where suckers are present.

“They are notorious for becoming overpopulated with suckers,” Smith said.

The fish family is native to Montana, but the biologist reported fishermen label them undesirable and inedible.

“They get a bad rap,” Smith said. “It’s like a dunce fish of the world: They have their mouth on the bottom of their heads, and most people call them a ‘trash’ fish.”

Although he admits recreation is the lake’s secondary purpose, fishing draws many park visitors. Popular game fish are stocked in the sucker-laden waters, but the reservoir and its resources can only support so many animals.

“Suckers end up competing with our more popular game fish, like rainbow trout, that we stock,” Smith said.

Leveling the playing field
As a fisheries biologist, Smith is familiar with several kinds of management tools, some of which have been used at Ackley Lake. One method is mechanical, or physical, controls.

In the mid-2000s, Smith said FWP tried netting the sucker population. The agency caught about eight tons of suckers, and measured consequential improvements in the game fish, both in number of fish caught and in fish measurements.

“Those efforts led to a very short-term improvement in the trout fishery in terms of their [the trout’s] body condition,” he said.

The positive effects disappeared after two years, according to Smith.

He said FWP also uses biological controls, or tools that manipulate the biology of an area to produce the desired outcome. The controls often come in the form of animals, and sometimes with their own problems.

“In the past, fishery managers haven’t had great options because what we’d introduce would take over,” Smith explained.

He said the tiger muskie has been recognized in the last two decades as a solution. The fish is the sterile result of a cross between highly predatory species, the northern pike and the muskie, and is spawned in out-of-state fisheries.

“Tiger muskie eat anything they can fit down their gullets,” Smith said. “They are swimming mouths.”

Although they are known to go after birds and amphibians, the goal is sucker fish. The biologist admitted they would also go after the fishermen’s catch.

“Yes, most definitely, tiger muskie are going to eat the trout,” he said.

Smith pointed to the stocked nature of Ackley’s popular fish and the tiger muskie’s inability to reproduce, saying the two factors made populations easy to cull or expand.

“That’s the beauty of a stocked fishery: If we start to see impacts to the trout side, we can modify our stocking routines to mitigate any impacts from the tiger muskie,” he said.

Waiting for results
Ackley Lake State Park harbored its first official tiger muskies last year: 2,000 fry, or baby fish, were stocked in April, and 3,000 fingerlings, or 5-7 inch fish, were added later in the year.

Tiger muskie may be in the lake, but FWP regulations limit fishermen to one a day, provided it is over 40 inches. Smith explained the strict rule comes from the fish’s role as a management tool.

He stated it would be several years before anyone takes home a tiger muskie, and several years before the fish creates any large-scale effects.

“It’s going to take a few years to prey on the bulk of the sucker population,” Smith said.

That wait, and the use of the tiger muskie, is something Mike Getman understands. While Getman is a member of the FWP Region Four Citizen Advisory Committee (members of the public who provide feedback and ideas to the agency) his understanding comes from being a fisherman.

Getman has fished Ackley Lake since 1989, and has seen the sucker infestation firsthand.

“When I fished out in the ’90s at Ackley, the suckers were quite abundant and it was a challenge getting a rainbow,” he said.

A sportsman’s drive motivated Getman’s research into the tiger muskie. He acknowledged the concerns of the fish preying on rainbow trout, but said the FWP’s environmental assessment showed the species feeds close to the bottom. He also pointed to the current success of Deadman’s Basin Reservoir with tiger muskie as a management tool.

“You know, the whole goal is to have the tiger muskies prey upon the suckers, which in turn will allow the rainbows to grow and be healthier,” he said.

Getman thought the fish could even add another draw to Ackley Lake.

“They’re a beautiful fish, and I’m sure after a few years people will go out there and specifically attempt to catch them,” he said.



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