Flooding likely affects Gila Topminnow population establishment in Fossil Creek, Arizona

Authors: Drewyer Pearson, Anthony T. Robinson, Clayton D. Crowder

Year: 2012 (xliv)

Abstract

Between 2007 and 2011 the Arizona Game and Fish Department’s Gila River Basin Native Fishes Conservation Program and its partners stocked Gila topminnow Poeciliopsis o. occidentalis annually into Fossil Creek as part of the second phase of the native fish restoration project with the goal of establishing self-sustaining populations therein. Even though 2,000 to 12,600 topminnow were stocked each year, few or none were detected during monitoring each year. Possible reasons why topminnow seem so rare include: insufficient effort to detect rare species, negative interactions with other species, unsuitable habitat, or environmental events such as flooding. Of these, flooding was hypothesized to have the greatest impact on population establishment. For example, shortly after 3,000 topminnow were stocked in 2007, Fossil Creek experienced a flood likely exceeding 10,000 ft3/s; base flow in the creek is about 43 ft3/s. During post-stocking monitoring in 2008, no topminnow were detected. It may be that the population had not increased enough to withstand and recover from large-scale flooding. No large-scale flooding occurred during the winter of 2008-2009, and topminnow were detected during monitoring in spring 2009. An even more massive flood, likely exceeding 14,000 ft3/s occurred in January 2010, and no topminnow were detected during monitoring in summer of that year. However, no large-scale flooding occurred during the winters of 2010-2011 or 2011-2012, and topminnow were detected during monitoring in both 2011 and 2012. Both adult and post-partum topminnow were detected in 2011 and 2012, and topminnow were widely distributed in 2012. Gila topminnow may have increased in abundance enough that the population can persist past the next major flood event given that complex habitat that likely provides refuge during floods is moderately abundant in Fossil Creek.