Re-establishment of a population of Virgin spinedace, Lepidomeda mollispinis mollispinis, in upper Beaver Dam Wash, Nevada

Authors: Mark Beckstrand, Jon C. Sjoberg, Jim Heinrich, Cory Anderson

Year: 2008 (xl)

Abstract

The Virgin spinedace Lepidomeda mollispinis mollispinis is a plagopterine minnow endemic to tributary streams of the Virgin River system in Utah, Arizona and Nevada. Virgin spinedace were historically present in upper Beaver Dam Wash, Nevada but were extirpated from this stream reach after approximately 1963, corresponding with the construction of Schroeder Dam and Reservoir to develop sport fishing opportunities in Beaver Dam State Park. Efforts to re-establish spinedace in Beaver Dam Wash in Nevada by the Nevada Department of Wildlife began in 1995 but met with limited success until after spring 2005, when extreme high flow events in excess of 8,000 cfs led to the overtopping and breaching of Schroeder Dam and the removal of Schroeder Reservoir as a main stem impoundment in Beaver Dam Wash. Prior to 2005 spinedace were released in tributary and main stem stream habitats below the dam using fish translocated from lower Beaver Dam Wash with the assistance of Utah Division of Wildlife Resources and the Arizona Game and Fish Department, and showed limited evidence of reproduction and recruitment. After the 2005 flow events which scoured riparian habitats to pre-impoundment conditions and re-created access into additional habitat in and above the former reservoir impoundment, and coupled with the translocation of additional adult spinedace from lower Beaver Dam Wash in Utah and Arizona, spinedace have expanded adult presence into areas above the former reservoir and show increasing evidence of successful reproduction and recruitment into adult age classes. Although the 2005 flow events may have had a role in ‘re-setting’ habitat conditions, Schroeder Dam and Reservoir may have had additional impacts to habitat suitability for spinedace beyond restricting access to upstream suitable habitats including thermal effects on downstream habitat suitability during typical summer low-flow conditions and interception of periodic maintenance flows essential to maintain aquatic habitat quality.