Rarely, if ever, has a dam been considered a savior for fish. Typically the structures block natural fish migration and forever alter the habitat, harming native species. But Lima Reservoir dam in southwestern Montana may be an exception.
Above the reservoir is Upper and Lower Red Rock lakes, two shallow water bodies in the 51,300-acre Red Rock Lakes National Wildlife Refuge. Located in the beautiful Centennial Valley, the lakes are home to “one of the last known endemic populations of adfluvial (lake-dwelling) Arctic grayling in the contiguous United States,” according to the U.S. Fish and Wildlife Service, which manages the refuge.
“That’s the only place they’ve held on, and the only reason is because of Lima Reservoir, which blocked brown trout,” said Jim Mogen, a senior field biologist for the USFWS in Bozeman.
Brown trout are non-natives and eat other fish, like lake- and river-dwelling grayling. In Montana, grayling are considered a species of concern. The Fish and Wildlife Service has been petitioned to consider the fish for listing as a threatened or endangered species. A decision is expected in September 2015.
This spring and last, the Fish and Wildlife Service and Montana Fish Wildlife and Parks have been trapping grayling as they travel up two Red Rock lakes feeder streams — Odell and Red Rock creeks. The fish are then milked of their eggs and milt to fertilize eggs for planting in other refuge streams where the fish have not survived. It’s part of a five-year study to see if the Arctic grayling population can be boosted.
Consider all of the Missouri River tributaries upstream from Great Falls: well-known trout fisheries like the Jefferson, Madison and Gallatin and all of their feeder creeks spread like veins across the Rocky Mountains in southwestern Montana.
Yet, among all of these there are only two natural lakes: Ennis and the Red Rock lakes. That’s important because as far as biologists can discern, those are the only two places in the state where lake-dwelling arctic grayling lived.
Historic records indicate that adfluvial grayling spawned in the tributary streams of Upper and Lower Red Rock, tributaries to the Red Rock River below Lower Red Rock Lake, and in streams entering nearby Elk Lake, according to the refuge’s conservation plan. “More recent surveys determined that adfluvial grayling spawning use is currently limited to Red Rock and Odell creeks,” the plan stated.
One of the interesting differences between fluvial and adfluvial grayling is that although the river-dwelling fluvial grayling can live in lakes, adfluvial grayling when planted in streams always move downstream in search of a lake, Mogen said.
To boost grayling populations on Red Rocks refuge, USFWS decided to establish spawning runs in other streams and create a brood stock to preserve the fish’s genetics against any catastrophic occurrence. Improvements are also being made to the habitat by reducing grazing, working with surrounding landowners to rotate their grazing on feeder streams, improving spawning habitat in the streams and reducing irrigation diversions.
Back when Mogen conducted his first study of the Red Rock grayling in the early 1990s as a graduate student, he found as few as 85 grayling with a peak of 250 and a bunch of Yellowstone cutthroat trout.
Yellowstone cutthroat are another rare species. It has been estimated that pure Yellowstone cutthroat trout occupy only about 10 percent of the streams where they were originally found in Montana. Yet they were not native to the Red Rock lakes area, which historically would have been westslope cutthroat trout habitat. But, back when fisheries biologists thought all cutthroat were the same, some Yellowstone cutthroat trout were planted in the area within the past 60 years and have thrived.
Now, as part of the study on boosting the adfluvial grayling population, Yellowstone cutthroat trout are being removed from the creeks that feed Red Rock lakes. It’s an unusual situation considering the scarcity of cutthroat habitat in Montana.
“It’s doubtful we could ever get rid of the Yellowstone cutthroat, but we can control their population,” said Andrew Gilham, USFWS biological technician, who has been working at Red Rock lakes.
Last year, about 2,700 cutthroat trout were removed from the refuge system via traps and with help from anglers. The traps are set in the feeder streams to capture cutthroat as they travel upstream in the spring to spawn. FWP also increased the cutthroat trout limit to 20 fish. In Montana's other western streams and lakes, only three cutthroat can be kept by anglers. According to an angler survey, fishermen took about 700 cutthroats out of the system last year. Cutthroat have also been captured and moved to a nearby pond.
The traps also capture grayling as they move upstream to spawn, allowing USFWS and FWP personnel to strip the fish of eggs and milt. The eggs are then fertilized and put in remote site incubators that are placed in the tributary creeks. After the fish hatch, the crews will place seine nets in the creeks to capture the fry to try to estimate the fish’s survival rate.
“They have a good estimate of how many eye up and fry, but we haven’t looked at survival,” Gilham said.
Grayling differ from cutthroat and other trout in how they spawn.
“The cutthroat spawn first and they really dig up the gravel,” Mogen said. “They tear the place apart.”
The grayling come in after the cutthroat and broadcast their more numerous but smaller eggs atop the gravel. A female grayling may release 100,000 eggs. When cutthroat eggs hatch and the fish emerge, they look like inch-long trout. But when grayling hatch they are half-inch-long larvae that more closely resemble a sperm than a fish, Mogen said.
The grayling fry tumble downstream until they can find a slow eddy to hold in. Consequently, the fish seem to reproduce better when streamflows are lower.
“The toughest time for them is when they emerge from the gravel,” Mogen said. “Grayling produce a lot more eggs knowing that they’re not going to survive.”
Once the fish pass through the first few weeks of growth, though, they seem to be a hardy species. Mogen noted that they survive in pools left after the irrigation water is shut off to the Sunny Slope Canal near Choteau while other species die. In Alaska the fish are found swimming in borrow ditches alongside roads.
That’s important because the Red Rock lakes are shallow — only about 5 feet deep.
“Essentially they’re swamps,” Mogen said. “And they may be getting shallower over time.”
In the summer, such shallow water heats up. Hotter water means less oxygen for fish. In the winter the high mountain lakes are locked in ice. When vegetation dies under the ice it can also rob fish of oxygen. Yet somehow grayling have been able to survive in these difficult conditions.
“Where they’ve survived is where the non-natives couldn’t hold on,” Mogen said.
On the mend
It’s too early to say whether the work stocking grayling and removing Yellowstone cutthroat trout is having its desired effect. But even before the work started, grayling populations had climbed, now estimated at more than 2,500 fish. About 1,000 were captured and tagged last year. The cutthroat trout population is estimated at 4,500.
“The numbers are as high as they’ve been in the last several decades,” Mogen said.
Some of the grayling are big.
“Outside of Alaska and Canada, they’re probably as big as they get,” Gilham said, up to about 2 pounds. “It’s one of the only places you can go and catch an 18-inch grayling.”
But the survival of fish compared to the amount of eggs that reach fry stage is still minimal. So the question the fisheries biologists are trying to figure out is whether the small grayling fry are being eaten by other fish, such as non-native brook trout that were stocked in the 1940s, or if it’s a habitat problem.
“It’s just a test right now,” Mogen said. “We’ll remove the cutthroat and see if the grayling respond.”
For now, both species seem to be doing well in the Red Rocks refuge, cut off by the Lima Reservoir dam from most other non-native fish that would otherwise compete with them.
“There’s so much food and those systems are so productive that regardless of what’s in there, it would be big,” Mogen said.