Tearing the web: Invasive trout disrupt Glacier park's lakes


Susan Guynn, The Frederick News-Post, Md.
Sat, December 4, 2021

Dec. 4—GLACIER NATIONAL PARK, Mont. — In civilization, invaders change the language, diet and customs of the places they conquer. Invasive fish don't ride on chariots or tanks, but their disruption leaves almost warlike marks on the ecology.

That contest plays out right now between Montana's native bull trout and invasive lake trout in the Flathead River Basin. New research indicates that while the lakers have run like Genghis Khan, the bulls might hang on if they get help.

A new study from the University of Montana's Flathead Lake Biological Station shows just how big and permanent an impact invasive species have had on regional waterways.

"Once we get to a tipping point, things go bad quickly for bull trout," said Shawn Devlin, an aquatic ecologist at the Flathead Biological Station and co-author of the study.

"This work has showed if you give bulls a chance before that tipping point — before they're in a spiral they'll never come back from — they can be managed for conservation," he added. "And the good news is, these lakes were invaded a lot longer than anyone realized but it took longer than expected for the effects to take hold. It was a neat finding. That gives hope to managers, that there's more time below that tipping point than we realized."

Bull trout in lakes play the same ecological role as grizzly bears on land — the No. 1 predator in their native habitat. They eat other fish, grow large and reproduce slowly.

Lake trout fill a similar niche in their home waters of the Great Lakes and Midwest rivers. But they have a crucial spawning advantage.

Bull trout live a salmon-like life cycle of hatching in small creeks before reaching maturity in big rivers and lakes and then returning to spawn in that same creek they were born in. That makes them vulnerable to lots of other predators when young, as well as human threats like river dams, irrigation systems, and sedimentation from logging or road-building.

Lake trout spawn on deep-water rock outcrops. While grizzlies and eagles can harry bull trout in their shallow spawning streams, few competitors reach the lake trout egg deposits. And when they grow up, the lakers eat the same fish bull trout target.

Since they were artificially introduced into Flathead Lake in the early 20th century, lake trout have become a popular game fish because of their capacity to reach lunker size. Then a separate effort to enhance Swan Lake's artificial Kokanee salmon population by adding mysis shrimp had an unintended consequence. The tiny shrimp flowed down the Swan River into Flathead Lake, where they became a new food source for the lake trout. The laker population quickly expanded, sending ripples through the ecology of every other fish species in the system.

Such transformations are called "trophic cascades." In Flathead Lake's case, young lake trout outcompeted the Kokanee for zooplankton and other tiny organisms, while mature lakers ate the schools of Kokanee out of existence. They also preyed on the native cutthroat and bull trout, depleting both their populations and their food supplies.

And then the lake trout started spreading through the Flathead River network, invading the bull trout strongholds of Glacier National Park's west and south sides. Hungry Horse Dam prevented them from getting far into the Bob Marshall Wilderness Complex to the south. But McDonald, Logging, Quartz, Bowman and Kintla lakes all saw their bull trout populations crash.

Study lead author Charles Wainright of the U.S. Geological Survey spent 49 days prowling 10 remote Montana lakes. That included Glacier Park battlegrounds like Quartz and Logging and Arrow lakes, as well as sites in the Bob Marshall Wilderness Complex that still have undamaged bull trout habitat, such as Big Salmon Lake.

The bodies of water in the park comprise almost a third of the entire bull trout habitat in the Lower 48 States. Bull trout have "threatened" status under the federal Endangered Species Act.

"If we lose bull trout out of these lakes, the system will never shift back to what it looked like," Devlin said. What the study found was that one species doesn't just over-eat the other. Everything around them gets affected.

"The whole lake is important, not just the traditional food path of small things to big things," Devlin said. "Bull trout are not good at finding other food. When they can't get the large fish they used to eat in the middle of the lake, they're forced into the shallows and littoral zones with sub-optimal food. Then their growth rate gets stifled. Meanwhile, lake trout are growing like gangbusters."

That change also affects everything around the two trout species: the phytoplankton, insects, frogs, spiders and everything else that feeds from the lake or falls into it. As bull trout shift from eating other fish to eating bugs, that affects bug populations as well as other trout like cutthroat and rainbow that hunt bugs. The entire food web gets frazzled, and can fray apart.

Which brings up the other important finding of the study: the time factor.

By looking at both the ratios of invader fish to native fish, and what everything was eating, the study gave ways to gauge how far along — how close to permanent — an invasion had become. And it turned out, the process takes longer than most researchers expected.

That gives wildlife managers more options. Late-stage interventions might have to be as complicated as Glacier Park's effort to create bull trout sanctuaries while gillnetting infested lakes. An early invasion might fall to simple fishing regulations, like no-limit takes on lake trout in protected waters. Flathead Lake has passed that point.

'Rock snot' reaches Michigan's Lower Peninsula. Why it could be bad news for trout

Keith Matheny, Detroit Free Press
Mon, December 6, 2021, 

It's not as slimy as it sounds, but it could mean trouble for Michigan's prized trout fishery.

The Michigan departments of Environment, Great Lakes and Energy and Natural Resources on Monday announced the detection of "rock snot" — didymo, a freshwater alga — in the Lower Peninsula for the first time.

A person holds hands full of didymo alga, or rock snot, during a major bloom on the Duval River in Quebec, Canada in this 2013 photo.

The course, woolly textured alga was found in a portion of the Upper Manistee River in Kalkaska County. It has plagued streams in the western and eastern U.S., forming thick mats that cover river and stream bottoms, reducing the habitat for macroinvertebrates, the tiny organisms at the bottom of the food chain upon which small fish feed. Those small fish in turn provide food for Michigan's prized sports fish, such as trout.

Extensive mats of didymo were found on the Michigan side of the St. Marys River near Sault Ste. Marie in the Upper Peninsula in 2015.

"Didymo has potential to be a nasty nuisance species in Michigan’s cold-water fisheries," said Samuel Day, a water quality biologist with the Little Traverse Bay Bands of Odawa Indians. "Unlike the harmful algal blooms that plague areas of the Great Lakes due to warm temperatures and excess nutrients, didymo blooms form in cold, low-nutrient streams that most folks would generally consider pristine and great habitat for trout."

Fishermen play a role in the alga's spread — and can play a role in keeping it contained, said Bill Keiper, an aquatic biologist with EGLE’s Water Resources Division.

"Didymo can attach to fishing equipment, wading gear and other hard surfaces and be moved to new waterways," he said. "With each new detection, it becomes more important for people who fish, wade or boat to clean boats and equipment, including waders, after each use."

According to Michigan State University Extension, didymo is thought to be native to Lake Superior, parts of Canada and Northern Europe. Its invasive character was only recorded beginning in the late 1990s. It’s not known what conditions cause didymo to alter its native, non-invasive character and form dense invasive mats, but some speculate that climate change could be playing a role.

Didymo was found east of the Mississippi in 2005 in Tennessee, and west of the Mississippi in Montana, Utah, Colorado and South Dakota in 2004. It was even documented in New Zealand the same year.