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6 Death Valley Region The portion of this region within Nevada comprises some 2593 square miles along the extreme southwestern margin of the state. The principal drainage pattern is that of the Amargosa River which is an intermittent tributary to Pluvial Lake Manly in Death Valley, California. The native fish fauna is represented by Rhinichthys osculus nevadensis in the intermittent reaches near Springdale and Beatty. This species as well as Cyprinodon diabolis, C. nevadensis mionectes and C.n. pectoralis inhabit spring systems in the Ash Meadows area south of Beatty. Empetrichthys latos latos is the single surviving species of that genus in the adjacent area of Pahrump Valley but is extinct in its natural habitat. Specific species accounts are given in the order they appear in Table 1. Cyprinodon diabolis: Devils Hole Pupfish The Devils Hole pupfish continues to respond to increased water levels and is maintaining winter populations of over 200 individuals. Severe scour- ing from floods has reduced the total amount of algae on the shelf this fall (1979), and primary productivity estimates are below normal. Consideration is being given to turning on the artificial lights to increase the algae. The proposed transplants into the Amargosa pupfish station are progressing, and contingency plans are being drawn up to establish monthly monitoring at the site. Concern has been raised over the continued development of the Ash Meadows area for domestic use, as the water rights established by the Supreme Court do not appear to govern domestic wells. Cyrpinodon nevadensis mionectes: Ash Meadows pupfish Comprehensive surveys and population estimates were conducted over the entire range of this subspecies in May of 1979, and these data are presented for each spring as it occurs in Table 1. Big Spring: The pupfish population in Big Spring is in very good shape with as many as 1000 fish utilizing the main pool. Reproduction is evident as many small fish were observed in the shallow waters. The Poecilia population in the spring pool is well. above that of the pupfish and is easily the most common fish in the spring. Bullfrogs and tadpoles are present in high numbers and were evident throughout all levels of the habitat. The outflow areas contained fair numbers of pupfish in the quieter water and support a good population of dace. The dace in the pool habitat were observed mostly on the bottom of the pool and did not integrate with the other fish. The entire system has at least 2000 pupfish and several hundred dace. Bradford 1,2,3: This spring system contains the highest concentration of mollies observed in the Ash Meadows area. The pupfish population is estimated at approximately 500 for this area, and only larger adults were obtained. The presence of dace in small numbers, and only adults, suggests that the molly population is restricting the reproductive effort of the native fishes in this system.