Moving Native Trout to Baker Lake, Postponed

A Bonneville cutthroat trout caught during a stream survey in the park. NPS photo / Jack Clark.

This page draws on an article by biological science technician Jack Clark in The Midden, the newsletter of Great Basin National Park (Winter 2023).

Bringing back a native fish

Bonneville cutthroat trout (BCT) is the only native trout in east-central Nevada. At one time it was thought that no genetically pure populations survived anywhere. Over the past four decades, conservation work has found a few pure populations isolated in small mountain streams in Nevada and neighboring states and has slowly been returning them to their native habitat.

In Great Basin National Park, BCT now occupy an estimated 50% of their historic range. Five streams in the park hold pure BCT, but none of its alpine lakes has a well-established population. The park is working to create self-sustaining populations in Johnson Lake, which has had a first transplant, and Baker Lake.

Clearing the way

Before native trout can go into Baker Lake, non-native brook trout introduced there must be removed. Park staff and partners treated the lake in September 2021 and August 2022. But a final check before the move suggested brook trout might still be present.

What the DNA showed

The park uses environmental DNA (eDNA) — DNA present in water samples — to see which fish live in a water body. Five samples were sent to the Rocky Mountain Research Station and each was tested three times. One gave a weak positive for brook trout; a retest of that sample came back completely negative for trout DNA.

It is unclear whether invasive trout remain, whether the first result was a false positive, or whether DNA from a fish that died two years earlier survived in Baker Lake's cold water and silt. Most DNA breaks down within 24 to 72 hours in sunlight or water, but it can last much longer in the right conditions — less a mosquito in amber than a few buried fish scales.

Baker Lake, waiting for its new residents. NPS photo / Jack Clark.

Next steps

• The park will keep monitoring with snorkel surveys, gill nets to catch any fish still moving in the lake, and more eDNA sampling.
• The move was postponed until the following summer. If a non-native fish is confirmed, the lake may be treated again and surveyed before any BCT are moved.
• When the lake is confirmed free of invasive trout, mature BCT will be carried up the mountain in large containers, with help from the Backcountry Horsemen of Nevada – High Desert Chapter. Fish will come from several pure populations in the Snake Range, to avoid stressing any single population and to give the new one broad genetic diversity.

The hope is that Baker Lake's new population will thrive and become a source for future conservation work.

Sources

• National Park Service, Great Basin National Park: "Fish Move Postponed," by Jack Clark, The Midden 23(2), Winter 2023.