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Pahranagat roundtail chub (Gila robusta)
Pahranagat roundtail chub (Gila robusta jordani) is one of three endemic fishes federally listed as endangered in the Pahranagat Valley in Lincoln County, Nevada. This species was once thought to have inhabited all major waters in the Pahranagat Valley. Currently, the chub inhabit approximately 3.5 km of the remaining 20 km of the Pahranagat River and to a lesser extent the upper 2.5 km of a 14.2 km irrigation ditch (Pahranagat Ditch) just downstream of the Pahranagat River. Chub can also be found in the upper portion (approximately 1 km) of a 5.6 km intermittent drain (Pahranagat Drain), located in the old river channel. The decline of these species has been attributed to habitat destruction and the introduction of exotic fishes.
Pahranagat roundtail chub are often found in habitat with hard cobble substrate and can be found in pools below a riffle, deeper pools, closer to the stream bottom, and in faster water. Habitat differs among the three locations. The Pahranagat River has a dense riparian corridor of ash and willows bordering most of the stream. Substrate varies depending on the reach and is comprised of cobble, gravel, sand, silt, and clay. The Pahranagat Ditch is a concrete channel with no riparian corridor. Sections of the Pahranagat Ditch have broken concrete creating artificial pools that provide refugium for the chub from high flows that occur in other sections of the Pahranagat Ditch. The Pahranagat Drain has an intermittent riparian corridor composed of ash and willow. The substrate is primarily sand and silt. The Pahranagat Drain has been considered as a sink for the species due to chub becoming stranded when the Pahranagat Drain dries up during the summer. In addition, it has been hypothesized that chub that travel too far downstream in the Pahranagat Ditch may not be able to get back upstream due to high flows and little structure. If stranding does occur the Pahranagat Ditch may also reduce the survival of the chub.
In collaboration with the U.S. Fish and Wildlife Service, we examined seasonal movements and site preferences of Pahranagat roundtail chub (Gila robusta) in the Pahranagat River, NV. We remotely tracked movement of PIT tagged chub with 10 custom antennas. We determined that recent declines in the populations are more likely due to mortality than emigration from the last 7 km of known habitat.