Lower Virgin River native fish monitoring: Population dynamics and response to high flows

Authors: Ronald B. Kegerries, Brandon Albrecht

Year: 2012 (xliv)

Abstract

Since 1996, BIO-WEST, has sampled several reaches of the lower Virgin River to monitor general fish community dynamics, with an emphasis on woundfin (Plagopterus argentissimus) and Virgin River chub (Gila seminuda) populations in the lower Virgin River. A river-wide, long-term perspective of endemic, endangered, and native fish trends from 1998-2011 depicts a seemingly stochastic pattern of native fish catch rates throughout years and between biannual sampling events. Since large flood events were thought to impact the native fish community within the lower Virgin River, comparisons were made in native fish catch rates both before and after the large floods experienced in both 2005 and 2010. Spring 2005 native fish catch rates were reduced; however, there appeared to be increases in native fish catch rates through 2008 (post flood). Similar increases in catch rates of native fishes were found after the 2010 flood event; though, this increase occurred much sooner after flooding in 2010 than in 2005. Comparisons of nonnative fish catch rates reveal drastic declines in catch per unit effort during the spring 2005, as well as the spring 2011, post-flood sampling trips. Based on this data, native fish populations appear to show a positive response following high flow events, but we hypothesize that the fish community response is dependent on the timing, duration, and/or amplitude of flood events. Finally, we conclude that the impacts of low stream flow continue to hinder the success of native fishes in the lower Virgin River, but may not be the only limiting factor associated with the recovery of these unique species.

Resumen

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