干旱区生态环境知识资源中心

In order to better determine the current status of desert pupfish populations ( Cyprinodon macularius macularius) in the Lower Colorado River Basin of Mexico, bimonthly fish sampling and habitat evaluations were carried out from September 1996 to August 1997 in six localities of Baja California and Sonora. Desert pupfish were collected using minnow seines and traps. Four sampling sites are in Sonora, in shallow marginal habitats of the Cienega Santa Clara ( Hunters' Camp, Outlet of the Welton-Mohawk channel, El Doctor and Flor del Desierto) and two are in Baja California (Cerro Prieto and streams south of Cerro Prieto). The most abundant fish species sampled was native desert pupfish ( C. macularius, 59%) followed by sailfin molly ( Poecilia latipinna, 19%), redbelly tilapia ( Tilapia cf. zilli, 10%) and western mosquito fish ( Gambusia affinis, 7%). Significant temporal fluctuations in distribution and abundance of desert pupfish populations, as previously reported for these populations, was again documented. The main anthropogenic factors affecting distribution and abundance of desert pupfish populations in the Mexican portion of the Lower Colorado River Basin are progressive alteration of aquatic and riparian habitats, as well as presence of exotic fishes that have caused the displacement or elimination of native fish populations. Both habitat and presence of the desert pupfish populations in the study area are controlled by the periodicity, quality and volume of discharges into the Mexican portion of the basin from the United States.