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Bonneville Cutthroat Trout

Oncorhynchus clarkii utah

Rev. 2.1 - 3/2010

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Species Summary

Once thought to be extinct, Bonneville cutthroat trout (BCT) were rediscovered in recent decades and relatively pure populations continue to persist along the periphery of the Bonneville Basin in Utah, Idaho, Wyoming, and Nevada. BCT evolved in ancient Lake Bonneville and its tributaries during the Pleistocene period, after the Bear River was diverted from the Snake River drainage into the Great Basin by a massive lava flow. The subspecies now occupies only a portion of its historic range and was unsuccessfully petitioned for listing under the ESA in 1998. BCT is currently considered a species of special management concern in all of the states where it is found.

Like Lahontan cutthroat trout, BCT have adapted to survive in relatively warm water and marginal habitats, and migratory life forms historically grew to be quite large in lakes and large rivers. Some populations within the Bear River drainage in southern Idaho and northern Utah continue to exhibit the species’ impressive range of life history strategies and habitat requirements, migrating seasonally between turbid, lower elevation mainstem rivers and cold, clear, high elevation tributary streams. These adaptations, along with their unique ability to persist in the presence of non-native salmonids, make the conservation and restoration of this species a priority.

Key CSI Findings

  • Life history diversity and habitat and population connectivity are greatest in the upper Bear and Weber River drainages
  • BCT populations are vulnerable to future climate change
  • General conservation priorities are protection in higher elevation northern subwatersheds, restoration in lower elevation northern subwatersheds, and reintroduction in southern subwatersheds
Historic Range Relief Map

Bonneville Cutthroat Historic Range Relief Map
Bonneville Cutthroat Trout Underwater

According to the Range-Wide Status Assessment for BCT the subspecies occupies only about 35% of its historic range in the Bonneville Basin. However, 97% of occupied subwatersheds scored in the top two categories for CSI Range-Wide Conditions, suggesting that BCT populations are well distributed within the subwatersheds where they remain. Total CSI scores for BCT were moderate to high, with 90% of occupied subwatersheds scoring in the top three categories but only 13% scoring in the top category (80-100 out of 100). Scores and distribution maps reflect a pattern of range constriction towards higher elevations and northern latitudes that has been relatively common among cutthroat trout subspecies across the West. Most of the historically occupied subwatersheds in the southern range of BCT no longer support extant populations.

Population and Habitat Integrity scores are highest for subwatersheds in the upper Weber and Bear River drainages, largely due to the presence of connected habitats and life history diversity in those two systems. Life history diversity, in fact, appears to be the greatest limiting factor in the overall Population Integrity scores for the subspecies, with a median score of 1 out of 5 across occupied subwatersheds. The greatest limiting factor for BCT habitat is land stewardship. The median score for land stewardship in occupied subwatersheds is 1, reflecting the fact that most BCT populations are located on unprotected public and private lands.

Future Security scores across subwatersheds suggest that the greatest future threat to BCT might be climate change, as the subspecies is somewhat isolated in a desert basin and will have limited access to higher elevation refugia if lower elevation habitats warm up or dry out. As such, conservation actions should focus on protecting connected habitats and life history diversity in the northern range, and restoring connectivity and reintroducing BCT populations in lower elevation habitats and throughout the southern range.

Prepared by Warren T. Colyer, TU, 11/29/06

Conservation Strategies Map

(click to enlarge)
Conservation Strategies Map