Factors related to the persistence or extirpation of populations of Little Colorado Spinedace ( Lepidomeda vittata ) and Bluehead Suckers ( Pantosteus discobolus ) in the Little Colorado River basin of Arizona and New Mexico

Habitats of extant populations of Little Colorado Spinedace (Lepidomeda vittata) and Bluehead Suckers (Pantosteus discobolus) were compared to habitat areas from which historical populations were extirpated in the Little Colorado River basin above Grand Falls, a natural barrier to upstream migration, to evaluate factors associated with population persistence versus extirpation. Populations of Little Colorado Spinedace have persisted or been successfully reintroduced in stream segments representing 23% of the cumulative length of historically occupied stream segments, while Bluehead Suckers fared somewhat better at 40%. Thirteen of 14 extant populations of spinedace inhabit areas lacking large dams and major diversions, whereas 25 of 34 extirpated populations occurred where streams have been impounded or have highly altered flow or seasonally dewatered channels due to large upstream dams, major diversions, or a combination of both. Bluehead Sucker populations exhibited a similar pattern, with 20 of 23 extant populations occupying areas with natural flow and 35 of 40 areas where extirpations occurred having streams that are impounded, have diminished flow, or experience seasonal dewatering due to dams or diversions. Among both species, areas in which populations were extirpated had significantly more nonnative fish species than areas where populations persisted, and negative associations were documented with Channel Catfish (Ictalurus punctatus), Common Carp (Cyprinus carpio), Green Sunfish (Lepomis cyanellus), and Largemouth Bass (Micropterus salmoides). The best geographic predictor of population persistence for spinedace and Bluehead Suckers was relatively high-gradient stream channels, reflecting a shift toward isolation in headwater streams. Spinedace populations were also associated with streams trending in a more northerly direction than streams in areas from which populations were extirpated. Multiple extirpations occurring in 2002 or later were attributable to drought-related losses of core perennial habitats.