A new, natural population of an endangered fish in southern Arizona?

Authors: Duncan, Douglas K.*1, Timmons, Ross2, Paulus, Sheridan2

Year: 2015 (xlvii)

Abstract

Department). In September 2015, we received a credible report that Gila Topminnow Poeciliopsis occidentalis had been seen in Parker Canyon, Santa Cruz County, Arizona. The report was made by a retired U.S. Forest Service wildlife biologist, who had seen Gila Topminnow in the wild before. Timmons and Paulus surveyed the location on 30 September and observed and captured numerous poeciliids. When processing captured fish, Timmons identified topminnow, subsequently confirmed by Paulus. Duncan and others have since confirmed that identification. Western mosquitofish Gambusia affinis were also present. Parker Canyon is in the San Rafael Valley, which had three naturally occurring Gila topminnow sites; Santa Cruz River, Sharp Spring, and Sheehy Spring. The San Rafael Valley is also the headwaters for the Santa Cruz River. Parker Canyon is a major drainage on the east side of the valley largely on the Coronado National Forest, and contains Parker Canyon Lake. The surveyed site is on the National Forest, and downstream of Parker Canyon Lake. Parker Canyon Lake is the likely source of the Western Mosquitofish and other nonnative fish that have historically occurred in Parker Canyon below the lake. Parker Canyon empties into the Rio Santa Cruz in Mexico, about 2.5 km south of the International Border. In June 2006, we found three stream reaches of the Rio Santa Cruz in Mexico with water and fishes. Opportunistic surveys at the upstream-most site, 13 km below the border and 10 km below the confluence with Parker Canyon, found only western mosquitofish. The second watered section was 17 km below the border and preliminary surveys here we found all size classes of Gila Topminnow, and no Western Mosquitofish. The third site was another six kilometers downstream and our preliminary surveys found all size classes of Gila Topminnow, and no Western Mosquitofish. We need to have a genetic analysis of these topminnow to determine if they are a remnant, historical population, immigrants from Mexico, or may have been transported by humans. If this is a naturally occurring population, it is an incredibly important find, and of great conservation importance. The presence of nonnative fishes, especially Western Mosquitofish, at this site is of great concern. We will further discuss our findings, conservation implications, and plans for these Gila topminnow.