Experts predict that trout will recover in the upper Madison River following sudden drop in flows

Hebgen dam trout Madison River
Adam Jolivette, from Livingston, releases trout and other fish into the upper Madison River after they were removed from a drying channel of the river on Wednesday, Dec. 1, 2021. A malfunction at Hebgen Dam caused flows in the upper Madison River to drop suddenly Tuesday morning, leaving parts of the river dry and prompting state officials to order a full fishing closure for the upper river.Samuel Wilson/Chronicle/Report for America

Fisheries experts are cautiously optimistic that trout populations along the upper Madison River will rebound after a Hebgen Dam malfunction reduced streamflows drastically earlier this week.

Travis Horton, regional fisheries manager for Montana Fish, Wildlife and Parks, said the department’s staff won’t know the extent to which Tuesday morning’s sudden drop in flows impacted the fishery until annual sampling next fall.

Much depends on whether brown trout redds, or the spawning beds where the fish lay their eggs, stayed moist and didn’t freeze overnight, Horton said. Luckily, overnight temperatures on Tuesday and Wednesday were mild, the public rallied to move fish back into the main channel, and wild trout are resilient.

Brown trout typically spawn sometime between early October and late November, depending on the area. Females will find suitable habitat with fairly consistent flows and depths. They’ll dig a redd in the gravel, they’ll spawn and the eggs will sit there until they hatch early in the spring.

“Had it been 20 below zero, the effect on redds that had been dewatered would have been far more dramatic,” Horton said. “Part of the beauty of wild trout is you’ve got a lot of resiliency built into the system. There’s excessive recruitment on an annual basis.”

Horton compared wild trout survival to a game of musical chairs. There are only so many chairs — or suitable habitat and available food — to go around. Typically, there are more fish than can fill the chairs, and some fish die when the music stops in the winter.

In the case of the upper Madison, Horton predicts that the unforeseen drop in flows will result in fewer trout competing for food and habitat, which will cause the rate of mortality to decrease.

“At the end of the day, my guess is that when the music stops, we will still have most of the chairs filled, if not all of them,” he said.

A broken gate component on Hebgen Dam caused a massive dip in flows on the upper Madison in the wee hours of Tuesday morning. A U.S. Geological Survey gauge showed that flows in the portion of the river below the dam dropped from about 650 to around 200 cubic feet per second.

Redds along portions of the river were exposed as the water dried up, and fish lay stranded, primarily in the stretch between Hebgen and Earthquake lakes. A large fleet of volunteers raced to the area to scoop stranded fish and return them to the main channel on Tuesday and Wednesday.

Horton said that trout can’t survive out of the water for very long, but they can swim quickly. Water levels dropped instantly right below the dam, but the dip was more gradual farther down the river. He’s hopeful that many fish were able to detect the drop and swim out of the shallows in time.

Whether crews of volunteers were able to get enough fish back into the main channel in time is a wild card, and it probably will have a significant impact on their overall survival, Horton said.

“The public did a great thing,” he said. “We’ll never know how many fish were moved by the public that way because there was such a tremendous response from people.”

NorthWestern Energy fixed the gate and restored flows to the river just before midnight on Thursday.

In addition to the brown trout, rainbow trout, mountain whitefish, sculpins and a few brook trout occupy the impacted stretch of the Madison River. However, Horton is most concerned about the event’s impacts on the river’s brown trout population.

Brown trout have been declining in most southwest Montana rivers over the past decade, though populations haven’t decreased much in the portion of the river between Hebgen Lake and Ennis Reservoir, according to Horton.

That’s largely because water releases from Hebgen Dam make flows consistent year-round and keep water temperatures cool, he said. Other southwest Montana rivers, such as the Big Hole, don’t have that luxury.

Brown trout populations in the Big Hole, Beaverhead, Ruby, Boulder, upper Yellowstone, Shields, upper Stillwater and lower Madison rivers have declined.

Robert Al-Chokhachy, a research fisheries biologist for USGS, said that in general, habitat and water temperatures are good on the stretch where the sudden drop in flows occurred. He predicts that trout populations will rebound in the long term.

“Short-term, what we’ll see are probably some reduced macroinvertebrates …. Some adults are going to die and some redds will be compromised,” he said. However, there is a source population of fish downstream and the food-base will rebound.

The one caveat, Al-Chokhachy said, is that recovery could take longer if the region continues to experience drought in the coming years. Reduced flows caused by drought conditions increase water temperatures and decrease drifts, he said.

Brain Neilsen, chair of Montana Trout Unlimited, said he’s primarily concerned about how many of the exposed redds will hatch in the spring, but he praised the volunteers who scooped trout and rallied around a river that’s in the public spotlight.

“This is going to be another shock to the system on the lack of brown trout if those redds don’t make it,” Neilsen said.