Dewatering: A possible alternative to chemical renovation, and the attempted removal of nonnative Western mosquitofish, Gambusia affinis, from Sharp Spring, Arizona.

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

Year: 2013 (xlv)

Abstract

Many methods have been developed to remove nonnative species from systems, so native fish populations can be restored. Chemical renovations in particular, can effectively eradicate nonnative fishes in complex lotic systems. However, the general public often holds firm and deep rooted concerns about public health and safety issues associated with the use of piscicides. Mechanical removal in complex lotic systems is challenging and typically does not result in complete eradication. Water draw-down, a type of environmental alteration, can be used to eradicate fish in some situations. Sharp Spring, a complex series of cienega-like springs in the San Rafael Valley in Santa Cruz County, Arizona, is an historic Gila topminnow, Poeciliopsis occidentalis, site that was invaded by nonnative Western mosquitofish, Gambusia affinis, in 1979. The mosquitofish replaced the Gila topminnow, which have not been observed since 1999. In 2013, Arizona Game and Fish Department devised a plan to dewater Sharp Spring long enough to eliminate surface water, and thereby eradicate mosquitofish from Sharp Spring, after which Gila topminnow could be repatriated. During a low water period in June, gas and diesel powered water pumps, hand tools, and manual labor were used to draw down the water in several of the Sharp Spring pools. The uppermost pool was successfully dewatered, but water could not be completely removed from the other pools, so mosquitofish were not eradicated from those. Nonetheless, as a result of this project, factors that hindered success were identified and new ideas were developed that might be effectively implemented to remove nonnative fish in complex lotic systems similar to Sharp Spring.