Population status of the Sonoyta Mud Turtle (Kinosternon sonoriense longifemorale) in the Sonoyta River, Sonora, Mexico

Authors: Miguel Garcia, Michael Bogan

Year: 2019

Abstract

The endangered Sonoyta Mud Turtle, Kinosternon sonoriense longifemorale, is a subspecies endemic to a small portion of the Sonoyta River in Sonora, Mexico and Quitobaquito Springs in Arizona. Human development in the region and economic activities, such as agriculture, livestock production and mining, have caused overdraft of the Sonoyta aquifer and reduced flow in the river. This situation has led to a decrease in the habitat available for the Sonoyta mud turtle. Localities with Sonoyta Mud Turtles have been reduced from seven sites in 2003 to three natural and two transplanted sites in 2019, one of which is a sewage treatment lagoon. The largest natural population occurs in the Agua Dulce reach of the Sonoyta River, a roughly 2 km long reach that contracts to only pools during the dry season. From 2017-2019, we estimated the mud turtle population size of the Agua Dulce reach using the capture-recapture sampling method. Additionally, we quantified mud turtle movements based on ten individuals (5 males and 5 females) that were radio-tagged in 2017 and 2018. Thus, we estimated mud turtle seasonal home ranges by calculating the Minimum Convex Polygon (MCP) based on all locations where tagged individuals were recorded. Using the Schumacher-Eschmeyer model, we estimated a population size of 209 turtles, with a 95% confidence interval. Radio-tagged individuals had a mean seasonal home range size of 0.09 ha and travel paths with a mean length of 173 m. Females had larger mean seasonal home ranges than males (0.12 ha vs 0.04 ha) and longer mean travel paths (239 m vs 91 m). Despite their ability to survive in degraded wetlands and tolerate periodic loss of flow in the river, decreasing dry season habitat poses a serious conservation concern. If wetted areas keep decreasing in the study site due to water withdrawals and a change in the precipitation requency, then the Sonoyta River may not support a healthy turtle population in the future.