Reading the Genes of Nevada's Bonneville Cutthroat Trout

By Joseph Danielson, biological science technician. From The Midden (Great Basin National Park), Vol. 22, No. 2, Winter 2022.

A Bonneville cutthroat trout in one of the park's small streams. NPS photo / Joey Danielson.

Great Basin National Park and Brigham Young University (BYU) are working to learn how genetically varied — and how pure — Nevada's Bonneville cutthroat trout (BCT) populations are.

A trout with a long history

The BCT is a subspecies of cutthroat trout that lived throughout the Bonneville Basin — Lake Bonneville (now the Great Salt Lake) and its tributaries — at the end of the last ice age.

• Rediscovered: once thought extinct, genetically pure populations have been found in recent decades in Utah, Idaho, Wyoming and Nevada.
• The only native: it is the only trout native to the park and to east-central Nevada.
• Still at risk: careful management has kept it off the endangered species list, but development, non-native trout, more severe fires and worsening drought threaten it, especially at the edges of its range.

Why genetics

Nevada's BCT live in small, isolated populations, shrinking further in recent droughts. That invites inbreeding and genetic drift, which erode diversity. The analysis will show:

• which populations are genetically diminished;
• whether moving fish between streams could help;
• which populations can supply fish for reintroductions, starting with Baker Lake.

Park biologists collect a fin clip. NPS photo / Joey Danielson.

Refuges in high lakes

The park's fisheries crew restores habitat and protects BCT in local streams. But fires recently wiped out several populations, so the park started a high-elevation lake refuge project, moving BCT into Baker and Johnson lakes to add populations in Nevada. A good source population needs enough fish and enough genetic diversity.

Sampling: the crew clips a small piece of the tail (caudal) fin from at least 30 fish per stream. So far, about 500 fish from 15 of the 16 Nevada streams where the species lives.

What BYU will look for

• Variation within and between Nevada's BCT streams.
• Hybridization with non-native trout. After white European settlement, other trout were stocked haphazardly and BCT were outcompeted or hybridized in many places. Rainbow trout, which produce fertile hybrids with BCT, are the main local worry and have done so in park streams before.
• Lineages: Nevada's populations were restored from a few local sources, which the results should reflect. They were not considered bottlenecked, but their small size could make genetic diversity a problem later.

The results will guide introducing BCT into Baker Lake in 2023 and managing all of Nevada's isolated populations.

Sources

Based on "Genetic Analysis of West Desert Bonneville Cutthroat Trout," by Joseph Danielson, The Midden, Great Basin National Park, National Park Service; a work of the United States government in the public domain.