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IF 10 Central Region The central region of the Interbasin area contains twelve (12) valleys within which five (5) native species are currently distributed. Table 2- shows specific localities of these species and the following narrative follows the order in which they appear. Crenichthys nevadae: Railroad Valley Springfish This species has historically been confined to two thermal spring sys- tems, Duckwater 1 and 2 and the system collectively known as Lockes Ranch Springs. The latter is composed of five individual springs. In 1978, personnel from the Bureau of Land Management and the Nevada Department of Wildlife transplanted several animals into Chimney Springs approximately 6 miles south of the Lockes Ranch complex. This population has now established itself and is maintaining good numbers in this habitat. The populations of C. nevadae at Lockes Ranch are currently in excellent condi- tion, and this system supports over 3000 individuals. The presence of Gambusia affinis in the headwaters of Duckwater #1 Spring was confirmed on November 17, 1979• Springfish numbers were apparently reduced since my last visit in early October 1979. Close monitoring of this habitat should be initiated to document population fluctuations, as this is the first recorded exotic introduction into C. nevadae habitat. The population in Duckwater #2 is at this time in good condition. Systematic surveys of Railroad Valley in October of 1979 failed to produce any new locations for this species. The continued development of the existing oil field and the proposed MX missile development in this valley, as well as the recent exotic fish introduction, are the primary concerns for this species. Empetrichthys latos latos: Pahrump killifish This is the only surviving species of this genus, of which one other, E; merriami, has become extinct from the adjacent drainage in Ash Meadows, Nye County, Nevada. Two other described subspecies of E. latos known from Pahrump Valley, E.I. pahrump and E.I. concavus, were extirpated in the 1950's by destruction of their spring habitats. E.I. latos was transplanted into ponds at Corn Creek on the Desert Wildlife Refuge, Las Vegas Valley, Nevada, on August 12, 1971,when it became evident that ground water pumping would cause the springs on Manse Ranch to fail. The native population of killifish at Manse Ranch spring was extirpated due to spring failure in August of 1975• Several other transplants were attempted with this species, but only one other (on August 31, 1975, into Shoshone ponds in Spring Valley, Nevada) was successful. Current population estimates in October of 1979 show that the killifish population at Corn Creek is maintaining about 2500 individuals after peak reproduction. The population at Shoshone ponds as of October, 1979, also shows population estimates near 2500. Proposed deployment of the MX missile in eastern Nevada could pose threats to the Shoshone ponds population, and an unusually high number of Rana catesbeiana at Corn Creek should be monitored to determine possible adverse effects. The listing of this species as endangered in 1967 has helped in preservation efforts; but the maintenance of the animal in totally artificial habitats is less than ideal, and efforts to reestablish it in its native waters should be a top priority in the management of this species.