Lahontan Cutthroat Trout

Oncorhynchus clarki henshawi

Description

The Lahontan cutthroat trout, Oncorhynchus clarki henshawi, a subspecies of the cutthroat trout, can be distinguished by its relatively larger size. This trout ranges from 10-15 in (25-38 cm) in length and usually has a bright red stripe, or "cutthroat" mark, under each side of the lower jaw. The body is elon-gated and compressed with a relatively long head. The back is green to greenish blue. The head, fins, and sides may be yellowy, and the belly is silvery. Some biologists consider the Lahontan a separate subspecies only because of its geographic isolation from other cutthroat trout.

The species was originally listed as Endangered in 1970, and reclassified as Threatened in 1975 to facilitate management and allow regulated angling. There is no designated critical habitat for the species.

Behavior

The life history of the Lahontan cutthroat is similar to that of other cutthroat trout, which feed on aquatic insects and spawn from the middle of April to late May. The eggs hatch in six to eight weeks.

Habitat

This species inhabits lakes and streams and requires cool, well-oxygenated water during all its life stages. Flowing water with clean gravel substrates is necessary for spawning. The Lahontan subspecies is adapted to the highly mineralized waters found in many of the region's lakes.

Distribution

The Lahontan cutthroat trout is endemic to the enclosed Lahontan basin of west-central Nevada and adjacent portions of California. It once inhabited Winnemucca Lake, which is now dry, and was eliminated from Lake Tahoe by competing species.

In Nevada, the Lahontan cutthroat trout exists in about 155 streams and six lakes and reservoirs in Nevada, California, Oregon, and Utah. The species has been introduced outside its native range, primarily for sport fishing purposes. As of 1995, the fish occupied approximately 0.4 % of its former lake habitat and 10.7% of its former stream habitat within native range. Independence and Summit Lakes support the only remaining reproducing lacustrine form of Lahontan cutthroat trout within native range. Many of the fluvial populations occupy isolated stream segments of larger river systems with no opportunity for natural recolonization. No current population estimates have been made.

A captive population of the Lahontan trout, used to replenish stocks in Pyramid Lake, is maintained at the Verdi Hatchery, Nevada. The California Department of Fish and Game has established a captive population at its Kernville Hatchery.

Threats

The Lahontan cutthroat trout declined throughout its range because of damage to its spawning beds caused by timber harvesting, forest fires, and grazing livestock. Streams have been dammed and water diverted for irrigation or municipal uses. Construction of the Marble Bluff Dam closed off spawning grounds in the headwaters of the Truckee River until recent construction of a fish ladder there. Water pollution, particularly downstream from Reno and Carson City, has also been a limiting factor.

Conservation and Recovery

In 1986 U.S. Fish and Wildlife Service (FWS) personnel assisted more than 1,400 Lahontan cutthroat trout over the Marble Bluff Dam, the largest trout run in the fish facility's history. These spawning trout were expected to contribute to the recovering natural population in the Truckee River.

In 1987 FWS personnel conducted an emergency operation to salvage some 200 Lahontan cutthroats from drought-depleted sections of By-Day Creek in Mono County, California. These fish were transferred to a headwater stream in the East Walker River basin, then used to restock Slinkard Creek the following year.

With planned recovery activities nearly 50 percent complete, the FWS accelerated its stream rehabilitation efforts in 1989, spurred by successes in artificial propagation at the Kernville Hatchery. According to the 1995 Recovery Plan, the species will be considered for delisting when management has been instituted to enhance and protect habitat required to sustain appropriate numbers of viable, self-sustaining populations. Recovery objectives protect all existing populations until research and analysis can validate population requirements by basin.

Because fluvial and lacustrine adapted forms of the Lahontan cutthroat have different behavior, ecology, and habitat use, recovery criteria necessary to delist the species may be modified after population viability anaysis has been conducted. The ecological and genetic importance of Pyramid and Walker Lakes in recovery of the lacustrine form will be determined after research has been conducted.

Actions needed to recover the species include the identification and coordination of interagency activities to secure, manage and improve habitat for all existing populations; the revision of the Recovery Plan based on genetic, population viability and other research; and the development and implementation of reintroduction plans. Lahontan cutthroat trout harvests should also be regulated to maintain viable populations. Self-sustaining populations existing outside of native range should be managed until their need is completed.

Contact

U.S. Fish and Wildlife Service
Division of Endangered Species
Eastside Federal Complex
911 N.E. 11th Ave.
Portland, Oregon 97232
http://pacific.fws.gov/

References

Behnke, R. J. 1980. Monograph of the Native Trouts of the Genus Oncorhynchus of Western North America. U.S. Fish and Wildlife Service, Denver.

Moyle, P. B. 1976. Inland Fishes of California. University of California Press, Berkeley.