Yellowstone biologists are concerned that nonnative smallmouth bass might reach the park's waters/USFWS

Yellowstone National Park, already grappling with an invasion of nonnative lake trout, could soon see another aquatic invader, as smallmouth bass have been detected in waters not too far downstream of the park.

“Smallmouth bass are an invasive predatory species that will threaten our wild and native trout populations if they become established in the upper Yellowstone River," Todd Koel, the park's lead fisheries biologist, said this week. "Since anglers are highly effective at suppressing invasive fish in waters where they coexist with native species such as cutthroat trout, they will be required to kill and report any smallmouth bass caught in Yellowstone National Park when the fishing season opens Memorial Day weekend.

"Additionally, Yellowstone National Park and USGS biologists will be sampling the Gardner and Yellowstone rivers, upstream of where the invasive smallmouth bass was caught," he added. "Over the next few weeks, biologists will monitor these rivers closely to gauge the possible extent of the invasion. Our goal is to protect native fish populations and natural ecosystems. We will do everything in our power to prevent the establishment of smallmouth bass in the park and prevent them from preying on and displacing trout and other native fish.”

While a 40-pound lake trout can offer a big, juicy meal, they typically swim too deeply in the 136-square-mile lake for bears and other predators to reach. That leaves them free to feast on the much smaller Yellowstone cutthroat trout, the prized species native to the lake. From osprey and river otters to maybe even elk, the long-running lake trout invasion of Yellowstone Lake has had far-reaching and surprising impacts on the ecosystem below and above the lake's surface.

Yellowstone biologists say an adult lake trout "can eat up to 41 cutthroat trout per year and can consume cutthroat trout up to 55 percent their own size." At the same time, a 12-pound female lake trout can produce roughly 9,000 eggs per year, they add.

Exactly how lake trout found their way to Yellowstone Lake isn't known, though it's been suspected that an angler hoping to boost the lake's catch dropped some in back in the 1980s and 1990s, with the first confirmed catch of one in 1994.

Today, the park pays contractors who use hydraulic lifts on fleets to hoist 6,000 miles of gillnets filled with lake trout from the lake. More than 3.4 million lake trout have been removed, but crews might never entirely wipe out the population. The gillnet operation costs about $2 million annually, and lake trout removal expenses are expected to continue in perpetuity.