Population status of native and non-native turtles along the effluent-dependent Santa Cruz River in Pima County, AZ

Authors: Michael Bogan, Miguel Grageda, Woods Nystedt, Isabel Ross, Sydney Ingham, Conor Handley

Year: 2024

Abstract

Historically, the Santa Cruz River was home to a diverse aquatic fauna in Pima County, Arizona, including the Sonoran mud turtle (Kinosternon sonoriense). However, those historic populations were lost when the river dried up early in the 20th century. Since the 1950’s, treated wastewater has been used to restore flow in portions of the river, and since 2013 that water has been high quality, but no systematic surveys for freshwater turtles have been done in the river. In the summers of 2022, 2023, and 2024, we surveyed for turtles at six reaches of the river to document the status of native and non-native species and examine how habitat factors (e.g. flow velocity, water depth) affect their populations. We found native Sonoran mud turtles at five of the six survey reaches, but in very low numbers and we have only found older adults. In contrast, non-native spiny softshells (Apalone spinifera) were abundant at five of the six survey reaches, and occasionally present in small numbers at the sixth reach. Non-native pond sliders (Trachemys scripta) were uncommon but present at most reaches, reaching their highest abundances in the northernmost reaches of the river. Spiny softshells were most abundant in deeper water with slower velocities, but abundances of mud turtles and pond sliders weren’t high enough to draw conclusions about their habitat preferences. Finally, in August 2023, we translocated six Sonora mud turtles to our study reach at the Santa Cruz River Heritage Project in downtown Tucson– which has mainly shallow water conditions that native turtles are adapted for– and we tracked their survival and movement for one year. All translocated turtles remained within 300 meters of the release site and survived the full year after translocation. We will continue turtle surveys in summer 2025 and hope to create a management plan to ensure the survival of native turtles in the Santa Cruz River into the future.