Desert Fishes Council, Cuatro Cienegas, Coahuila, November 2005.
Analyzing translocation success from sporadic monitoring data using survival analysis: lessons from the Gila topminnow (Poeciliopsis occidentalis).
F.J. Sheller, W.F. Fagan & P.J. Unmack
Translocation, the intentional release of captive-propagated and/or wild-caught animals into the wild in an attempt to establish, reestablish, or augment a population, is one of the most commonly used approaches to species conservation. Despite their frequent use and prominence in many species recovery plans, translocations have demonstrated limited success in the creation of sustainable populations. To improve the effectiveness of translocation efforts, it is essential to identify what differentiates translocations that succeed from those that fail. This study analyzed a unique database consisting of records for 148 translocations of the endangered Gila topminnow (Poeciliopsis occidentalis) to identify characteristics associated with the translocated populations and stocking environments that have significantly influenced translocation success. Using records from the United States Fish and Wildlife Service and the Arizona Game and Fish Department, we quantified translocation success as the "persistence time" of the translocated populations and analyzed the resulting dataset using survival analysis. We found that several factors, including the season in which the fish were translocated, the habitat type of the translocation site, and the genetic origin of the fish stocked significantly affected persistence times of translocated populations. For the Gila topminnow, our findings suggest that future translocations should 1) be undertaken in late summer or fall (not early summer), 2) occur into pond like habitats (not streams, wells, or tanks), and 3) should utilize individuals from genetic lineages other than Monkey Spring. With regard to the general practice of translocation as a conservation technique, our results imply that particular factors associated with stocking, the population stocked, and the site of translocation can significantly affect the persistence of translocated populations and thus increase the probability of translocation success.