Spatiotemporal variation of Virgin River chub and Moapa speckled dace abundances in the Muddy River, NV

Authors: Zachary Shattuck, Ronald B. Kegerries, Brandon Albrecht, Ronald Rogers

Year: 2012 (xliv)

Abstract

From 2007 to 2012, the Southern Nevada Water Authority (SNWA) contracted BIO-WEST, Inc. (BIO-WEST) to sample the Muddy River to determine the distribution and abundance of nonnative and native fishes, including Virgin River chub Gila seminuda and Moapa speckled dace Rhinichthys osculus moapae. For the past six years, sampling has been conducted from the Overton Wildlife Management Area upstream to the Bureau of Land Management (BLM) fish barrier twice annually (i.e., spring [April-May] and fall [September]). In sampling, a total of 968 Virgin River chub and 565 Moapa speckled dace have been captured in hoop nets, minnow traps, and/or seines; while nonnatives in aggregate combine for a total of 17,768 individuals in the same gears. Virgin River chub and Moapa speckled dace are the only two native fishes that are typically captured in these portions of the Muddy River, with the majority of these individuals found upstream of the Wells Siding Diversion. Seasonal variation in abundance has been observed for both Virgin River chub and Moapa speckled dace with well documented spatial variation, generally increasing from downstream to upstream reaches. Since 2010, Virgin River chub have been marked with passive integrated transponder (PIT) tags as part of a mark-recapture study to develop a population estimate comparable to estimates created by Scoppettone and others during the 1990s. Recaptured individuals moved as much as 5.6 km, increasing previously recorded maximum movement by more than 4.6 km. In the section of Muddy River from the Wells Siding diversion upstream to the Paiute diversion, a modified Lincoln-Peterson closed-model calculated in the program MARK estimated there to be a total of 270 Virgin River chub with confidence limits of 187 and 425. Continued long-term monitoring of Virgin River chub and Moapa speckled dace in the Muddy River will allow a better understanding of the relationships between abundance and habitat; while also allowing for the continued evaluation of the impact and threat of nonnative fishes.