INFORMING RECOVERY OF THE ENDANGERED SONORAN TIGER SALAMANDER: 10-YEAR TRENDS IN OCCUPANCY OF SALAMANDERS, INVASIVE PREDATORS, AND THEIR CO-OCCURRENCE

Abstract/Summary

The Sonoran Tiger Salamander (Ambystoma mavortium stebbinsi) occurs in a single valley that spans the USA-Mexico border and was listed as federally-endangered in 1997. The listing was driven by a variety of threats, including small geographic range and threats from invasive predators. The recovery plan for this subspecies requires scientifically-credible estimates of changes in occurrence of the Sonoran Tiger Salamander and invasive predators before further evaluation of the listing status. The recent completion of a 10-year (2004–2013) monitoring program, coordinated by the Arizona Game and Fish Department and the U.S. Fish and Wildlife Service, generated data sufficient to estimate (1) trends in breeding site occupancy by the Sonoran Tiger Salamander, (2) trends in occupancy of introduced predators, and (3) probability of co-occurrence between Sonoran Tiger Salamanders and invasive predators. We used Bayesian hierarchical models to estimate annual probabilities of occupancy and co-occurrence, after adjusting for imperfect detection. Our analyses showed that pond-level occupancy of Sonoran Tiger Salamanders increased by an estimated 2.2% (95% credible interval [CI] = 0.4%–3.8%) per year. Occupancy of invasive predators decreased by an estimated 0.7% (95% CI = −2.4%–0.7%) per year. In ponds with water, presence of invasive predators reduced salamander occupancy by 23.01% (95% CI = 8.72–43.73) across the 10-yr monitoring program. These results will assist in evaluating the status of the Sonoran Tiger Salamander and prioritizing management actions that are supported by defensible estimates.

Publication details