When Leo Rosenthal learned that a team of professional net fishermen had plucked a pair of walleye from Swan Lake, his heart sank like a downrigger lure.
The Montana Fish, Wildlife and Parks’ Swan Lake fisheries biologist knew the agency had caught more than it bargained for, and the consequences could be devastating to the aquatic system’s native fish populations.
“It is always very disappointing when we discover another illegal introduction,” Rosenthal said. “Of course, we don’t know if these fish have become established yet, so in that regard there are a lot of unknowns about whether this is going to be a problem.”
But the agency already has more problems than it can handle, and the Swan Lake discovery is just the latest in a string of outlaw fish plantings commonly known as “bucket biology” – the illegal act of moving live fish from one body of water to another. It’s a practice adopted by rogue anglers looking for new fishing opportunities, and it has damaged fisheries across Montana, particularly in this corner of the state.
“Illegal introduction issues are a huge problem in the Flathead and all over western Montana,” Mark Deleray, FWP’s regional fisheries manager in Kalispell, said. “I don’t know how many people are involved, but it is a problem widely affecting numerous fish communities. So we need to try and get our hands around it.”
Deleray estimated nearly 600 illegal introductions have occurred in 250 bodies of waters in the state, and roughly half of those incidents were in Northwest Montana. “Bucket biologists” have cost FWP hundreds of thousands of dollars in its attempts to remove the invasive predators and preserve the existing fish populations.
Illegal fish introductions displace existing fish by squeezing out established populations, resulting in a loss of fishing opportunity, as well as irreversible damage to the fishery. In the case of a highly predacious fish species like walleye, or the introduction of northern pike in the Clark Fork River, the impacts on native bull trout and kokanee salmon have been immense.
Perhaps not surprisingly, the walleye discovery in Swan Lake occurred during an effort to capture another invasive fish species, lake trout, which is part of an ongoing campaign to protect populations of bull trout and kokanee salmon.
More than 20 years ago, another illegal fish introduction toppled the kokanee population in Lake Mary Ronan in Lake County. In 1992, net surveys revealed that the fish composition of Lake Mary Ronan consisted of 77 percent kokanee salmon, 5 percent westslope cutthroat, 9 percent bass and sunfish, and 9 percent rainbow trout.
That same year, an angler dumped a bucketful of perch into Lake Mary Ronan, and the population exploded like a time bomb. By 1998, perch had overwhelmed the system, and net surveys revealed that 93 percent of the fish in Lake Mary Ronan were perch, while cutthroat and bass accounted for just 1 percent, rainbow trout made up 2 percent and kokanee 3 percent.
“Perch really took over Lake Mary Ronan and fundamentally altered that fishery,” Rosenthal said.
In the ongoing struggle over how to manage existing nonnative fish populations, Montana FWP sees each new illegal introduction as a setback in its efforts to maintain the delicate aquatic balance between predator and prey in the state’s lake and streams, and further evidence that many anglers don’t understand the gravity of the ecological upset.
Rosenthal and Deleray won’t know whether the recently caught walleyes in Swan Lake evince a larger problem until laboratory analysis of the fish’s ear bones, or otoliths, is complete. Otoliths contain a unique fingerprint of the water chemistry where the fish swims on a given day, and can be used to map the entire life history of a fish within a lake or river network.
If the analysis on the recently caught walleye identifies Swan Lake as their natal water, it means they came from a breeding population.
“There are a still a lot of unknowns, but these are very complicated aquatic systems and when you add a new species into that mix it makes it even more complex,” Deleray said. “We don’t know what effect walleye will have on this system but potentially it will be a game changer.”
In Canyon Ferry, where walleye were illegally introduced, walleyes eat more than 750,000 pounds of perch each year, or about 4 pounds of perch per walleye.
Penalties of illegal introductions can range from fines of $2,000 to $10,000, loss of fishing, hunting, and trapping privileges, and liability for the costs to eliminate or mitigate the effects of the introduction, but the laws are extremely difficult to enforce.
Last year, the Fish and Wildlife Commission strengthened FWP’s policy for dealing with illegal introductions, and as the agency moves forward with its investigation to determine whether walleye have established a population in Swan Lake, it’s offering up to $15,000 to anyone who comes forward with information that leads to a successful conviction.
Angler groups like Montana Trout Unlimited became involved after FWP discovered that someone had planted smallmouth bass in Seeley Lake, about 50 miles south of Swan Lake. The group offered a $10,000 reward for convictions, but it’s difficult for FWP to cite someone for an illegal introduction without evidence, so many illegal introductions go unpunished
“If we are going to flesh someone out the reward is going to have to be substantial,” Deleray said, praising the angler groups that have stepped up to increase the value of awards.
Bob Gilbert, executive director and lobbyist for Walleyes Unlimited of Montana, said his group is adamantly opposed to illegal introductions, and has offered a cash reward for information on illegal introductions for the last decade.
“In those 10 years no one has been arrested and convicted,” Gilbert said. “It’s about the most difficult crime to investigate because you have to either go out in the middle of the night and catch someone with a bucket-load of fish or someone rats out their buddy.”
Fortunately, not all introductions are successful, but that doesn’t diminish Deleray’s frustration over having to launch yet another investigation into an illegal introduction.
“What’s frustrating is that these introductions are not short in duration, and they have huge potential to change the foreseeable future as far as what that aquatic community is and can be,” Deleray said.