Davis creek culvert

The Custer Gallatin National Forest plans to start work on replacing this perched, undersized culvert along Davis Creek in June. Replacing this culvert and another located along Eagle Creek will help restore populations of Yellowstone cutthroat trout to the upper watershed.

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To help conserve cutthroat trout, officials from the Gardiner Ranger District and Custer Gallatin National Forest are planning to replace two culverts on Yellowstone River tributaries this summer.

The culverts that will be replaced are approximately three miles up Eagle Creek Road outside of Gardiner. Since the current culverts are undersized and perched, they prevent native Yellowstone cutthroat trout from traveling up Eagle and Davis creeks, two Yellowstone River tributaries.

“We are thrilled to have this project happening on the ground this summer,” said Mike Thom, Gardiner District ranger, in a news release. “This is a wonderful opportunity to conserve Yellowstone cutthroat trout and further build sustainable populations through partnership efforts.”

Clint Sestrich, fisheries biologist for the Custer Gallatin National Forest, said culverts that are too steep or small can increase the velocity of the water flowing through, eroding the stream bed below. Over time, the erosion can cause the culverts to become perched above the stream, preventing fish from swimming uphill.

Fragmented Yellowstone cutthroat trout populations then face inbreeding and become more susceptible to wildfires. Fires and inbreeding can kill upstream populations that have limited habitat, Sestrich said. By connecting cutthroat trout habitat below and above the culverts, there is a greater chance populations will persist.

According to a news release, the project will more than double the length of secure cutthroat trout habitat from around two miles to nearly five miles.

Thom said Eagle Creek is geographically important for conserving Yellowstone cutthroat trout populations, as the trout in its headwaters don’t face competition from brook trout or hybridization with rainbow trout — two nonnative species. Eagle Creek is among just four Yellowstone River tributaries like this in the Gardiner Basin.

Sestrich said workers will replace the existing culverts with “sunken aquatic organism passage culverts.” They will add sand and other materials to the base of the culvert to improve surface flow, and they will place boulders inside to create pools for fish.

The U.S. Fish and Wildlife Service, Montana Fish, Wildlife and Parks and region one of the Forest Service all helped pay for the project, which will cost approximately $175,000.

Sestrich, who will be monitoring the project, said it’s a big investment. He expects monitoring will last as long as five years.

“If we’re spending that amount of money, we need to make sure it’s a good investment,” he said.

That means cutthroat trout don’t just need to be able to pass through the culvert — they need to thrive in the habitat above it.

To make sure that happens, 200 trout below the culverts will be tagged and two antennas will be placed on each culvert, Sestrich said. Biologists will use the antennas and tags to track which direction fish are moving to see whether they are inhabiting areas upstream.

FWP and Yellowstone National Park have been working with the Custer Gallatin National Forest to conserve Yellowstone cutthroat trout in the upper drainage of the Yellowstone River since 2013.

Impassable culverts are unfortunately common in the U.S., and can cause entire populations of fish above culverts to go extinct, Sestrich said.

Work on the culverts along Eagle and Davis creeks will begin July 13 and continue until around mid-August, according to the news release. The Gardiner Ranger District anticipates Eagle Creek Road will be closed for two approximately 10-day periods.

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Helena Dore can be reached at hdore@dailychronicle.com or at 582-2628.

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