Laboratory evaluations of stocking strategies for Gila topminnow (Poeciliopsis occidentalis occidentalis) and desert pupfish Cyprinodon macularius)

Authors: David L. Ward, Anthony T. Robinson

Year: 2009 (xli)

Abstract

Gila topminnow (Poeciliopsis occidentalis occidentalis) and desert pupfish (Cyprinodon macularius) inhabit similar environments and are often stocked into the same waters as part of conservation programs. Success of these stocking efforts varies widely. We conducted laboratory tests in 10, 2.4-m diameter recirculating tanks to evaluate differences in topminnow and pupfish numbers over a 2-month period using the following stocking strategies: 1) stock only pupfish, 2) stock only topminnow, 3) stock pupfish first, and then stock topminnow one month later, 4) stock topminnow first, and then stock pupfish one month later 5) stock both topminnow and pupfish simultaneously. Pupfish appear to do best when stocked alone and had an average increase in numbers of 11%, whereas when topminnow were stocked first, pupfish showed an average decrease in numbers of 27%. Pupfish stocked concurrently with topminnow had an average decrease of 7%. Topminnow recruitment appears low when pupfish are stocked first and showed an average increase of only 157% compared to increases over 1200%, when topminnow were either stocked first or concurrently with pupfish. Although these two species commonly co-exist stocking them simultaneously during reintroduction efforts may not be the best strategy for establishing these species.