As summer approaches, fishery employees in Yellowstone National Park anticipate a busy season removing lake trout from Yellowstone Lake.
Ever since the species’ introduction in the mid-1990s, lake trout have steadily displaced the native cutthroat trout, a favorite catch of anglers and Yellowstone wildlife like eagles and bears.
Indeed, lake trout feed on cutthroats too—they practically feast on them. According to fish biologist Phil Doepke (a 14-year veteran of cutthroat trout conservation efforts), an adult lake trout will eat approximately 42 cutthroats a year.
In years past, Yellowstone’s fishery has ramped up efforts to remove lake trout and reintroduce fish like cutthroat and Arctic grayling to Yellowstone’s waterways. Besides catching and killing, according to the Cody Enterprise, crews use increasingly sophisticated methods to try and eradicate lake trout from Yellowstone Lake, along with other invasive trout:
Gillnetting, electroshocking, angling and trying new programs have gradually helped tip the balance somewhat back to the cutthroat, a fish integral to the Yellowstone ecosystem.
“We’re not saying, ‘Yea! Victory!’ yet,” Doepke said. “Hopefully, in the future.”
Cutthroat are an important element in the food chain for eagles, bears, pelicans and other species.
“Lake trout are not a replacement,” Doepke said.
The effort is being funded by Yellowstone Forever ($1 million annually) and from Park fees ($1 million annually).
The Park Service and its contractors put out 5,600 miles of net last year and used scientific techniques to chart the whereabouts of fish and 14 lake trout spawning beds that could be target for elimination.
“From here to Italy,” Doepke said of the length of the nets combined.
“We are anticipating the same amount of gillnetting in 2018 as last year.”
Efforts against lake trout aren’t limited to NPS employees. It’s also written into Yellowstone’s fishing regulations. Unlike other species (like cutthroat and grayling), there is no catch limit on lake trout—and any lake trout caught must be killed, no matter what.
Last year, we reported “inroads” were being made against lake trout, with over 400,000 lake trout removed from Yellowstone Lake. Nonetheless, park fish biologists caution that it’s likely impossible to eradicate lake trout entirely. Rather, crews are working to restore cutthroat trout from the brink and ensure that lake trout don’t pose such a dire threat again.
According to the Enterprise, the fate of the program depends on its funding. Currently, Yellowstone Forever pledges $1 million a year in a three-year cycle. Todd Koel, Yellowstone fisheries supervisor, says the funding is not currently in danger of being cut off, although that may not always be the case.
Koel added that gillnetting is by far the most effective tool fishery employees have to remove lake trout from Yellowstone Lake.
As mentioned, fishery employees have employed numerous means to cut down on lake trout—including targeting spawning beds. From the Enterprise:
Those trying to reduce the lake trout population regularly try new things to wipe out large groups at once at the most efficient rate for the least amount of money.
One way is plucking out the lake trout caught in the nets, killing them, cutting open the bellies and then sinking the carcasses onto spawning beds to suffocate the eggs. Also tried: shredding the carcasses first and then dropping them overboard on a spawning bed.
Shocking, Doepke said, “was effective, but not on a large scale.”
The carcass tactic was successful, he said, but at five spawning beds in shallow water, bears were attracted to the dead fish and pounced on the carcasses. That was not an issue at nine deeper water spawning beds.
Some investigation is taking place about the possibility of using a poison pill to kill lake trout; a pellet with ingredients that will harm the fish.
Scientists are also exploring the value of producing fish with YY chromosomes that if introduced could over the long term affect a localized population.
“Everything’s on the table,” Doepke said.
In addition to restoration efforts in Yellowstone Lake, crews have also been working to restore cutthroat trout and Arctic grayling to streams in the Madison and Gallatin River watersheds. There, the main methods are creating barriers to keep invasive species out and treating portions of Yellowstone’s waterways with Rotenone, a piscicide.