Population dynamics of spikedace, Meda fulgida, and loach minnow, Tiaroga cobitis, in the upper Gila River, NM 2008-2013: populations in peril

Authors: James E. Whitney, Keith B. Gido

Year: 2013 (xlv)

Abstract

On March 26, 2012 the spikedace, Meda fulgida, and loach minnow, Tiaroga cobitis, were officially uplisted from the status of threatened to endangered under the Endangered Species Act of 1973. As part of this uplisting 1,146 km were designated as critical habitat for the two species, of which 259 km (23%) are located in the Gila River Subbasin in Catron, Grant, and Hidalgo counties of southwestern New Mexico. The objective of our research was to describe current (2008-2013) population dynamics of the loach minnow and spikedace throughout the Gila River Subbasin, and identify potential causes of spatiotemporal variation in density. These objectives were accomplished by sampling loach minnow and spikedace three times annually across six longitudinally-positioned sites during June 2008 to June 2013. We also measured nonnative biomass, physical habitat characteristics, discharge, and chlorophyll a concentration. Differences in density and potential drivers were assessed using analysis of variance. Spikedace were found at all six sites, and occurred in more than half of the collections at four sites. Loach minnow were collected at five of the six sites, and occurred in more than half of the collections at three of the sites. Densities of spikedace and loach minnow were significantly greater at the two most-downstream sites, which had greater chlorophyll a concentrations and water velocity, and lower nonnative piscivore biomass. Of the four sites where spikedace were common, a significant temporal decrease in density was observed at one, and extirpations were observed at two others. Loach minnow densities were more stable at the locations where they were common, exhibiting no temporal trend at two sites, but extirpation at the third. Recent temporal decreases in density appear to be related to long-term drought, whereas recent extirpations occurred after ash flows from the Miller and Whitewater-Baldy Complex fires of 2011 and 2012, respectively. Our results indicate that spikedace are now absent from two of the five streams designated as occupied in the 2012 uplisting ruling, whereas loach minnow are now absent from three of six streams designated as occupied at the time of ruling. Conservation of these imperiled species may require restocking efforts at locations where they have been extirpated.