Interactions between Desert Pupfish and Gila Topminnow Can Affect Reintroduction Success

Abstract

In fisheries, recovery actions for species of concern sometimes involve reintroductions of multiple species. As an example, desert pupfish Cyprinodon macularius and Gila topminnow Poeciliopsis occidentalis historically had sympatric distributions and inhabited similar environments, and they are often reintroduced into the same waters. Success of these stockings has varied greatly, and a hypothesis developed among conservationists that desert pupfish populations were more likely to establish and persist if they were stocked first and allowed to establish before Gila topminnow were stocked. We examined historical records of desert pupfish reintroductions and conducted laboratory experiments to evaluate this hypothesis. For the reintroductions, we evaluated 29 ponds where four general stocking strategies (treatments) were implemented: (1) only desert pupfish were stocked, (2) desert pupfish were stocked first and allowed to establish and then Gila topminnow were stocked, (3) both desert pupfish and Gila topminnow were stocked simultaneously, and (4) Gila topminnow were stocked first and allowed to establish before desert pupfish were stocked. Desert pupfish established populations and persisted in 100% of desert pupfish-only and desert pupfish-first ponds and 57% of simultaneous-stocking and Gila topminnow-first ponds. In laboratory experiments utilizing 2.4-m-diameter tanks, the same four treatments plus one additional treatment (in which only Gila topminnow were stocked) were implemented; each treatment was replicated four times. Desert pupfish abundance increased in 75% of the desert pupfish-only trials and 50% of the desert pupfish-first trials but decreased in 75% of simultaneous-stocking trials and 100% of Gila topminnow-first trials. Gila topminnow increased in abundance in all treatments and trials but increased the least when desert pupfish were stocked first. Our results support the original hypothesis and emphasize the need to evaluate species interactions in multiple-species reintroductions. To increase success, desert pupfish should be stocked in isolation or stocked first and allowed to establish before Gila topminnow are stocked.

Received July 12, 2011; accepted August 30, 2011

ACKNOWLEDGMENTS

Funding for our research was provided by the U.S. Bureau of Reclamation Central Arizona Project via the Gila River Basin Native Fishes Conservation Program directed by the U.S. Fish and Wildlife Service. The desert pupfish and Gila topminnow used in the laboratory experiments were acquired from Dexter National Fish Hatchery, Dexter, New Mexico. Various Arizona Game and Fish Department personnel helped with the laboratory experiments, including J. Walters, D. Boyarski, C. Crowder, A. Medina, and S. Prager. Thanks to David Boyarski for creating the map of the study sites. Doug Duncan (U.S. Fish and Wildlife Service, Ecological Services Field Office, Tucson) reviewed the manuscript and provided valuable suggestions for improvement. Ross Timmons (Arizona Game and Fish Department) provided valuable ideas for the research as it progressed.