Clover Valley Speckled Dace

Rhinichthys osculus oligoporus

Description

Clover Valley speckled dace, Rhinichthys osculus oligoporus, is a small minnow that grows to 4 in (10.2 cm). It has an olive-green back, silver or gold abdomen, and a random pattern of black spots. It is distinguished from other speckled dace by its less developed lateral stripe, the location of its pectoral fins, and the number of pectoral fin rays.

Behavior

The speckled dace is an adaptable species, able to occupy a variety of habitats, from cold streams and rivers with rocky bottoms to thermal springs with silt bottoms. This adaptability has enabled it to survive in environments too harsh for other species. The isolation of populations has led to a large number of forms that are recognized as sub-species. They feed primarily on insects and are presumed to spawn in mid-summer.

Habitat

Clover Valley speckled dace are found primarily in reservoirs and outflows of the three spring systems: Clover Valley Warm Springs, Wright Ranch Spring, and Bradish Spring. There do not appear to be any associated marshes with these springs, only the outflows that have been heavily modified. The introduction of rainbow trout appears to have affected the speckled dace in the past. Because access to the properties for conducting studies has not been permitted, details of Clover Valley speckled dace seasonal habitat requirements, population size, distribution over time, reproductive potential, and available habitat are unknown.

Ground water in Clover Valley is derived principally from precipitation on the east slope of the East Humboldt Range and to a lesser extent from the north side of Spruce Mountain and the west slope of the Chase Spring Mountains. Gravity-fed springs and seeps issue from the lower alluvial slopes along the west side of the valley and are used primarily for supplemental irrigation of meadows. The three spring systems in the valley currently inhabited by the Clover Valley speckled dace are Clover Valley Warm Springs, Wright Ranch Spring, and Bradish Spring. All of these springs are privately owned and have been modified to provide water for agricultural purposes.

Clover Valley Warm Spring is impounded immediately downstream of the springhead into a small reservoir approximately 10 ft (3 m) wide and 2 ft (0.6 m) deep. Temperatures recorded in the spring system have ranged from 65 to 67°F (18.3 and 19.4°C) to and seem to change accordingly with ambient air temperature further downstream.

There are two outflows from the reservoir. The riparian areas in the first are composed primarily of sedges and grasses, while rush and hard-stem bul-rush are common. Several types of mesic forbs were found only occasionally in the riparian zone. Aquatic vegetation was mostly watercress and algae. Surveys found this section to be relatively rich in aquatic insects. Leeches, scuds (amphipod crustaceans, such as beach fleas), caddis flies, and native snails were all abundant in the channel. While dragon fly larvae were common, non-native snails were found occasionally, and giant water bugs were rarely encountered.

The second section of the original channel has been divided with irrigation ditches. The irrigated section shows signs of heavy livestock use, resulting in compaction. The aquatic plants and insects are in lower abundance than in the first section. In the past, irrigation practices completely dewatered the natural stream channel.

Distribution

In October 1995, the Nevada Division of Wildlife surveyed the Clover Valley Warm Springs area and the two outflows for distribution and population numbers of Clover Valley speckled dace. There are two outflows for this spring: presumably the original channel and an irrigation ditch. The resulting population estimates were 13,500 for the first section and 10,440 for the second. The Wright Spring population was estimated at 1,500 individuals occupying the pond and 12,500 inhabiting the out-flows. The Brandish Spring population could not be surveyed because permission to access the property could not be obtained.

Threats

Initial surveys for Clover Valley speckled dace in 1934 indicated that springs occupied by the speckled dace had been altered at a much earlier date. Outflows from the springs had been impounded into reservoirs before being distributed to various irrigation ditches. The habitat below the reservoirs was periodically dewatered on the irrigation schedule. At the time of listing, the irrigation usage continued, and speckled dace populations were restricted to habitats within the reservoirs and seasonally in the outflows. In the most recent survey of 1995, populations of speckled dace were present at both the Clover Valley Warm Springs and Wright Ranch Spring areas. The out-flows that were the most stable or had the greatest flow of water also had the largest number of speckled dace.

Conservation and Recovery

This dace is threatened by its limited distribution, diversion of the spring water, and predation by introduced fish species. These springs have long been impounded for irrigation purposes, limiting the dace to the outflow and certain sections of the reservoir. Often the reservoirs are stocked with sport fish, such as rainbow trout (Salmo gairdneri ), largemouth bass (Micropterus salmoides ), and blue-gill (Lepomis machrochirus ), which feed on the dace, forcing it to retreat to areas safe from the predatory species.

So far the owners of the springs have not been willing to sign agreements to conserve the species. One has indicated an intention to increase the use of a spring for irrigation, while another plans to introduce game fish into a reservoir, despite the danger to the Clover Valley speckled dace. The U. S. Fish and Wildlife Service hopes that it will be able to obtain conservation easements and manage the springs to protect the dace.

Contacts

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
(503) 231-6121
http://pacific.fws.gov/

U. S. Fish and Wildlife Service
4600 Kietzke Lane, Building C
Reno, Nevada 89502

References

Hubbs, C. L., R. R. Miller, and L. C. Hubbs. 1974.Hydrographic History and Relict Fishes of the North Central Great Basin. Memoirs of the California Academy of Sciences. Volume 7.

McNatt, R. M. 1988. "Field Trip Report on Investigation of Three Speckled Dace Sites in Clover Valley, Nevada." U. S. Fish and Wildlife Service, Great Basin Complex, Reno, Nevada.

Minckley, W. L., and J. E. Deacon. 1968. "South-western Fishes and the Enigma of Endangered Species.'" Science 159: 1424-1432.

Vinyard, G. L. 1984. "A Status Report about the independence Valley Speckled Dace (Rhinichthys osculus lethoporus ), Independence Valley Tui Chub (Gila bicolor isolata ), and Clover Valley Speckled Dace (Rhinichthys osculus oligoporus ); Three Fishes Restricted to the Northeastern Portion of Nevada." U. S. Fish and Wildlife Service, Reno, Nevada.