7994

• UCREFRP Catalog Number: 7994
• Author: Duff, D. A., Tech. Ed.
• Title: Conservation Assessment For Inland Cutthroat Trout, Distribution, Status and Habitat Management Implications.
• USFW Year: 1996.
• USFW - Doc Type: \
• Copyright Material: NO

separately for ease of reporting and because each State considered their populations as separate
entities. In sub-basins outside Utah but within the Bonneville basin, the BCT historically occurred in
80% of Nevada sub-basins, and 100% of sub-basins in Idaho and Wyoming.

In recent times, since major settlement by European man in the mid-1800's, massive destruction of
stream ecosystems and increased fragmentation of habitats occupied by the BCT has occurred.
Primary causal agents of this destruction were stream water depletion and loss from irrigation
diversions, dams, logging, mining, livestock grazing, roading, overharvest of fish, and massive
basin-wide introductions of exotic (non-native) fish species (Popov and Low 1950, Behnke 1960,
1992, Sigler and Sigler 1986,1987). Millions of trout were stocked basin-wide from the late 1800's to
1950's by state and federal managers. The Forest Service (FS) was a willing partner in this stocking
effort and in 1930 alone some 34.6 million trout were stocked by intermountain States on National
Forests, with the FS stocking an additional 15.6 million that same year (USDA FS 1984). This
indiscriminate and wide-spread stocking of exotic trout, especially rainbow trout since 1883, into
virtually every habitable water body of the Bonneville Basin and their subsequent hybridization with
indigenous BCT, coupled with habitat loss, was the primary cause for the almost complete elimination
of pure BCT populations.

Habitat fragmentation and isolation in smaller headwater reaches of sub-basins contributed to the
extirpation, over time, of BCT populations. As BCT populations became more isolated, through
habitat loss, hybridization, and competition with introduced exotics, entire watershed and sub-basin
metapopulations declined and finally were extirpated. Habitat fragmentation, loss of stream connec-
tivity and disruption of aquatic ecosystems has been shown in other studies of trouts to increasingly
isolate populations as well as isolate or eliminate unique life-history forms (Reiman & Mcintyre, 1995).
As a result of man's collective and cumulative activities BCT populations have been extirpated in 50%
of the Bonneville Basin's sub-basins in Utah, 75% in Nevada sub-basins, 33% in Idaho sub-basins,
and 50% in Wyoming sub-basins (Table 1).

The historic occurrence of BCT populations, by major basin and sub-basin, population, and by
specific national forest and state is shown in Tables 2,3,4, and 5. The BCT has been extirpated in
67% of the total sub-basins of the Bonneville Basin on nine NF's. In Utah, the BCT has been extirpated
in 76% of sub-basins on NFS lands of six NF's, and 43% of sub-basins on two Idaho NF's. Both
Nevada and Wyoming NF's (Humboldt and Bridger-Teton) have BCT populations in each of their one
sub-basins with NFS lands. Three NF's (Sawtooth, Uinta, and Manti-La Sal) have 100% extirpation
of BCT in all thirteen sub-basins on NFS lands (Table 3).

This current assessment indicates (Tables 6, 6a-d) that approximately 5,131 perennial stream miles
occurred in the Bonneville Basin, most of which may have been occupied by BCT populations.
Current occupancy on NFS lands account for 67 pure BCT populations (includes 4 lake populations)
in 190 stream miles. The total pure BCT populations within the basin, including all other lands,
consists of 81 populations occupying a total estimated 234 stream miles. This total is based on
estimates obtained from state and federal fisheries biologists. National Forest waters account for 81 %
of the known BCT occupied stream mileage habitat and 83% of BCT populations.

Historic NF stream miles account for 32% of the basin's total historic stream miles. Current occupancy
by BCT on NF stream miles is only 3.7% of the basins total historic stream miles and only 11.5%
occupancy of the total NF historic stream miles. It should be noted that most BCT occupancy is in
fragmented habitats, in watersheds of marginal condition. Lost is connectivity to other populations
which historically could have been present through metapopulation exchange in the basin. BCT
populations are estimated to be 96% extirpated in Bonneville Basin historic waters and 87% extirpated
in historic waters on NF's. These massive losses in BCT populations in previously occupied habitat,

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