Paiute cutthroat trout

Paiute cutthroat trout
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Salmoniformes
Family:	Salmonidae
Genus:	Oncorhynchus
Species:	O. clarki
Subspecies:	O. c. seleniris
Trinomial name
Oncorhynchus clarki seleniris John O. Snyder, 1933

Main article: Cutthroat trout

Paiute cutthroat trout (Oncorhynchus clarki seleniris) is a subspecies of cutthroat trout native only to Silver King Creek, a headwater tributary of the Carson River in the Sierra Nevada Mountains of California, U.S.A. The Carson River lies within the Great Basin interior drainage system, within the historic range of Lahontan cutthroat trout (O. c. henshawi). The subspecies is named after the native Paiute people.

Natural history

It is believed that a sub-population of Lahontan cutthroats became isolated in Silver King Creek above Silver King Canyon Gorge after erosion made the gorge impassible to trout swimming upstream, probably between 5,000 and 8,000 years ago. The upstream population then adapted to local conditions independent of the larger population below that had evolved in pluvial Lake Lahontan during the Pleistocene. Although Lahontan cutthroats are heavily spotted, the isolated sub-population lost virtually all spotting, perhaps because spots made fish more visible and susceptible to predation in the ultra-clear and shallow mountain stream. Paiute cutthroats are also notable for a purple coloration, whereas Lahontan cutthroats have bronze coloration. The Paiute strain must have adapted to a diet mainly of insects and become less migratory since juvenile fish swimming downstream in search of larger waters would have passed below downstream barriers and left the isolated gene pool.

Conservation

Basque sheepherders began grazing sheep along upper Silver King Creek in the 1800s. They noticed the unusual trout and by 1912 had transplanted them above Llewellyn Falls which had originally been the upper limit. This is fortunate because by 1924 hybrids with ordinary Lahontan cutthroat and introduced rainbow trout (cutbows) were found below Llewellyn Falls, either due to ill-considered stocking or barriers in the gorge washing out.

Since the finite and localized population of Paiute cutthroats was vulnerable to forest fire and angling as well as hybridization, relatively unhybridized Paiute cutthroats from upstream were transplanted into virtually all available tributaries of Silver King Creek above the gorge, into Stairway and Sharktooth Creeks to the south in the Sierra Nevada, and into Cottonwood Creek and Cabin Creek in the White Mountains.

The subspecies was listed as an endangered species in 1967. In 1975 it was upgraded to threatened status.

Subsequent studies have found some degree of hybridization in virtually all populations of Paiute cutthroats. This was initially addressed by poisoning stream segments with higher levels of hybridization and transplanting fish from other stream segments thought to be less hybridized. In the 1980s the focus shifted somewhat to electrofishing, which temporarily stuns fish so they can be captured and examined. Fish showing more evidence of hybridization are removed to other drainages, while relatively pure Paiute cutthroats are returned to the water unharmed.

Angling is prohibited in most streams where Paiute cutthroats predominate, however future plans include downstream expansion of Paiute cutthroat range by removing other trout and installing barriers. When populations are sufficient, the subspecies may be de-listed and limited angling may be permitted.

References

• U.S. Fish & Wildlife Service description
• EPA recovery plan
• Jeff Delong, "Plan to poison stream to save trout revived", Las Vegas Review-Journal, Jun 25, 2006.