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. .,. ... -- .. ( 1 \ I . .1 1 t I j ~ HOLDEN, ET AL.: THREATENED FISHES OF UTAH 58 Factors Influencing Decline: Loss ofbabitat in the Gila River system through irrigation demands and in the main Colorado River and lower Virgin by reservoir construction. appear to be major decimating factors for woundfin. Virgin River populations remain strong, although recent con- struction oflnterstate Highway 15 through Virgin River Canyon (Arizona) may have a negative effect on populations there. Lepidomeda mollispinis mollispinis- Virgin River Spinedace Status: Threatened species Description: A member of the cyprinid tRDe Plagopterini, the Virgin River spinedace has two weakly developed doual spines, is very silvery, and usually has random dark speckles over its bOdy (Figure 4). Dorsal fin rays usually 9, anal fin rays 8-10 (9), lateral line scales 77-91, and pharyngeal teeth 2, 54, 2. Small amounts of reddish1JJange or pink are found at the axils of the paired fins and the base of the anal fm. It is distinguished from the woundfin (Plagopterus argentissimus)by a lack of barbels and evident scales. Documentation: Endemic to the Virgin River system of Utah, Arizona, and Nevada, the Virgin River spinedace is:a tributary form associated with cool, clear water. In Utah it is found in the Santa Clara River system, Leeds Creek, Ash Creek, and North Fork of Virgin River. It is found in the main Virgin River only near the mouth of one of the above tributaries and usually at low periods of flow and turbidity (Cross and Deacon, 1973). It isalsa found in Beaver Dam Creek, Arizona_It was reported from the Paria River of Utah (Utah Division of Wildlife Resources), but 1974 sampling in Arizona failed to recover the species. Spinedace were abundant in the Santa Clara River system until just recently. Introduced redside shiner (Richardson ius balteatus) populations have increased there, and a marked decrease in spinedace was noticed in 1972aod 1973 (Behnke, 1973). Also, largemouth bass (Micropterus salmoides) iatroduced into Gunlock Reser- voir on the Santa Clara have moved upstream and spinedace populations have dropped markedly (Cross and Deacon. 1973). This very sharp popula- tion decline in the spinedace's best habitat has promoted the threatened status. Factors Influencing Decline: Introductioo of redside shiner and large- mouth bass into spinedace habitat appear to be the primary decimating factors. Recent Studies Inventory studies of all rare Virgin Riva fishes are currently under way by the University of Nevada, Las Vegas,iacluding a life history study of 7,",= - . .. . -10 .I' . ~