Plagopterus argentissimus

Formerly more widespread in the Colorado and Gila River systems in Arizona, Nevada, and Utah, now essentially restricted to the Virgin River system; dams and water diversions have destroyed, fragmented, and degraded most of the historical habitat; declines are also associated with increases in non-native red shiner; threatened by ongoing drought and water development associated with ongoing human population growth.

The historical range of the Woundfin included the Colorado and Gila River basins in Arizona, Nevada, and Utah (USA), including at least the Colorado River from Yuma upstream into the Virgin River in Arizona, Nevada and Utah, and the Gila River from Yuma to the confluence of the Salt River. No barriers or habitat considerations would have limited the species to this specific area, so it is likely that the historical range extended farther upstream in the Verde, Salt, and Gila rivers in Arizona (USFWS 2000). In 1972, Woundfin were transplanted into four locations in the Gila River system, but populations were not established (USFWS 2008). In 1985, streams in the Gila River drainage were identified as reintroduction sites, and the Gila River drainage was designated as a nonessential experimental population. Additionally, in 1970, 200 Woundfin were stocked into the Paria River in Arizona in an attempt to establish a population (Minckley 1973).

Currently, Woundfin are found sporadically throughout the Arizona portion of the Virgin River mainstem (Mohave County). Experimental-nonessential designation in portions of the Verde, Gila, San Francisco, and Hassayampa rivers and Tonto Creek. No self-sustaining populations have been documented from releases in these localities. In Nevada, Woundfin are currently rare in river reaches downstream of Littlefield, Arizona and into the Nevada portion of the Virgin River. The current range of the Woundfin is restricted to a small segment of the Virgin River from the Arizona/Nevada border approximately 15 kilometers downstream near Riverside. A single specimen was collected from the Muddy River when the Muddy River was a tributary to the Virgin River in the 1960’s (Deacon and Bradley 1972). Historically, a single account of a Woundfin, used as bait, on the Colorado River was recorded in June of 1952 (Miller 1952).

This fish is functionally extirpated under current conditions in both the Arizona and Nevada sections of the Virgin River, and only rare occurrences are typically only found in Arizona and Nevada reaches after high flow events in the monsoon season or after stocking events in the upper Virgin River. Currently the only viable self-sustaining population of Woundfin occurs in Utah in a 26.2 km reach in the upper Virgin River between La Verkin Springs and the Washington Fields Diversion. The periodic and occasional distribution of Woundfin in the lower reaches of the Virgin River are from exceptional reproduction and recruitment years in the upper Virgin River (UDWR 2019).

This species is effectively represented by single reproducing population that occurs in a 26.2 km section of the Virgin River between La Verkin Springs and the Washington Fields Diversion in Utah.

The Woundfin inhabits one of the fastest-growing parts of Utah, and associated extensive water development are an ongoing threat (Minckley and Deacon 1991). Most habitat destruction that threatened this species occurred between 90 and 110 years ago. Historical habitat has been lost due to human impacts including habitat fragmentation, introduction of nonnative species and de-watering due to agriculture, mining and urbanization. Water conveyance systems (diversions and canals) have contributed to the disappearance of the Woundfin throughout most of its historical range and continue to impact it in the Virgin River today.

Changes to flow patterns caused by dams and diversions have facilitated movement of Red Shiner, Cyprinella lutrensis, upstream in the Virgin River (USFWS 1994). The non-native Red Shiner largely has replaced the Woundfin and has introduced the Asian tapeworm, which now parasitize many of the remaining Woundfin (Heckmann et al 1986). Maintenance of a 26-kilometer Red-Shiner-free zone above the Washington Fields Diversion (WFD) in Utah has benefited the Woundfin, providing habitat to allow successful recruitment and persistence. However, the presence of Red Shiner below the WFD continues to be the primary threat today as it was in the late 1980s when red shiners became established in the upper river (USFWS 2008).

Primary threats to Woundfin are competition and predation from nonnative species (primarily Red Shiner) in the lower basin and degraded habitat conditions (reduced flow / high temperatures) throughout the range (USFWS 2008). Currently causes for declines in Woundfin numbers are attributed to the following suite of environmental conditions: continued drought with summer temperatures exceeding behavioral thermal maximum and critical thermal maximum; altered streamflow regimes, diversions, decreased turbidity, water management events, and a decline in optimum spawning and rearing habitat (USFWS 2008 and Huizinga and Fridell 2012).