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8 <br />and Thom Hardy, University of Nevada, Las Vegas, are initiating thorough <br />studies into the habitat preferences of native fishes in the Moapa River <br />system, and completing an investigation funded by the U. S. Fish and Wildlife <br />Service into habitat preferences of the Pahranagat roundtail chub. <br />The native fishes of the region are presented with ever-increasing <br />activities which threaten their livelihood. The following discussion is <br />offered as a summary of these fishes that are most seriously threatened. <br />Habitats and populations of the Railroad Valley springfish are being <br />influenced by diversion activities for agriculture, water depletion possibly <br />caused by nearby oil field development, and introduced fishes. The largest <br />of the habitats occupied by the species, Big Warm Spring on the Duckwater <br />Indian Reservation, is scheduled for dramatic alteration authorized by the <br />Tribe. The Bureau of Indian Affairs is sponsoring a program to capture the <br />north spring outflow in a concrete pipe to make irrigation delivery to <br />nearby pasture lands more efficient. This pipe will eliminate all but 1,100 <br />feet of springfish habitat in this outflow. Plans have also been approved <br />for David Koch to eliminate most of the habitat in the south outflow by <br />constructing an aquiculture facility to produce catfish Ictaluris punctatus). <br />These anticipated projects, in addition to recent springfish population <br />declines in this spring that are attributed to the introduction of guppies <br />Poecilia reticulata), leave little hope for the continued existence of this <br />population. The populations in Little Warm Spring on the Duckwater Indian <br />Reservation and on Locke's Ranch are doing well at this time. The introduced <br />population in Chimney Spring, however, was extripated during a partial failure <br />of the spring which occurred during August. The introduced population at <br />Sodaville is doing well in a habitat that is becoming increasingly stabilized. <br />Several fishes endemic to the pluvial White River system are doing poorly <br />because of agricultural diversion and competition and predation by exotic <br />fishes. The White River spinedace has not been recently collected in Preston <br />Big Spring and is in low numbers in its remaining habitats. Reasons for its <br />scarcity are obsecure but are attributed to spring outflow capture for <br />diversion, as these activities are the only influences that have altered the <br />habitats from what existed historically. The desert sucker endemic to this <br />drainage is also doing poorly in the habitats occupied by this spinedace; <br />agricultural diversion is again believed to be the cause. The Hiko White <br />River springfish has been extripated from Hiko Springs because of introduced <br />largemouth bass (Micropterus salmoides) and habitat alteration and is now <br />found in low numbers only in Crystal Spring where it is threatened by a variety <br />of introduced fishes. The sole population of White River springfish in Ash <br />Spring is similarily affected by introduced fishes. It is maintaining itself <br />in extremely low numbers. <br />Recent studies of the Pahranagat roundtail chub by Thom Hardy and Jim <br />Deacon show the species exists as adults only in a 10 meter length of the <br />outflow from Ash Spring. Thirty-seven individuals have been counted in this <br />population, granting this chub the dubious distinction as the Nevada fish <br />presently closest to extinction. Continued studies are necessary to determine <br />how this species can be recovered. <br />The creation of pristine aquatic habitat on the Moapa National Wildlife <br />Refuge is proceeding with development of an aquatic habitat management plan