Snake River Finespotted Cutthroat Trout

Oncorhynchus clarkii behnkei

The Snake River finespotted cutthroat (SRFCT) is one of two cutthroat trout subspecies native to the upper Snake River in Wyoming and Idaho. The Yellowstone cutthroat, a large-spotted trout, also occurs in the Snake River and Yellowstone River drainages and is treated separately in the CSI and by most fishery management agencies.

The SRFCT are thought to have evolved from the Yellowstone cutthroat and highlight the difficulty in delineating between closely related yet distinct subspecies. Despite differences in spotting pattern, both subspecies occur in the Snake River drainage and may occasionally hybridize.

Historic Range Relief Map

The SRFCT occurs from Jackson Lake and the Gros Ventre River drainage southward in the Snake River system to the South Fork of the Snake downstream of Palisades Reservoir. The finespotted subspecies also occurs in headwaters of the Bighorn River according to data provided by May et al. in a 2003 in an assessment utilized in our CSI analysis.

Compared to other subspecies of cutthroat trout, the conservation status of the SRFCT is very good, especially in the upper Snake River drainage where most subwatersheds scored in the highest CSI category. Of all the intermountain cutthroat subspecies, only the SRFCT continues to dominate their native range in the face of introduced salmonids.

Within the Bighorn River system, the distribution of SRFCT is more patchy with apparent extirpations in many tributaries and mainstem of the Wind River.

We have little data on lake populations although there are indications that many lake-dwelling subspecies of cutthroat have declined. Jackson Lake has a long history of stocking with lake trout, for example, which has clouded our knowledge of the historic diversity of SRFCT in that lake basin although it is clear that substantial declines in native cutthroat populations have occurred. Other lake populations in Grand Teton National Park have similarly declined as a result of non-native lake trout stockings

Population Integrity and Habitat Integrity scores are relatively high for nearly all subwatersheds in the upper Snake River drainage and the Greybull River (Bighorn drainage). Lowest scores for Population Integrity are in the Wind River drainage, where populations are more isolated and in need of restorative work. Another highly isolated population occurs in the Nowood River drainage, where most historic populations are believed to be extirpated.

Key CSI Findings

• Much of the historic habitat in the Snake River drainage ranks high integrity
• Nearly half (49%) of historic range is occupied as measured by subwatersheds
• Total CSI scores are relatively high: 80% of range-wide subwatersheds with current populations score 81/100 or higher
• Only 3% of occupied subwatersheds have total CSI scores less than 70/100
• Introduction of non-native trouts is the greatest remaining threat to many populations

Despite recent assessments, our CSI reveals many important gaps in our understanding of the SRFCT, including genetic and taxonomic relationships with the Yellowstone cutthroat. Lake populations appear more threatened than stream forms but data on lake populations are scarce.

Prepared by Jack E. Williams, TU, 12/1/2006

Conservation Strategies Map

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