Declining Turtles Use Different Habitats than Co-Occurring Introduced Turtles in an Urban Creek

Overview

Species inhabiting urban waterways face numerous threats including water pollution, invasive species, and habitat alteration. While virtually all water bodies are at risk of significant human modification, urban waterways are subject to a unique set of human modification practices to reduce flood risk. The vast amount of impervious surface in urbanized areas can dramatically increase storm runoff and the risk of catastrophic flooding. As a result, management agencies often implement flood and erosion control measures such as creation of drop structures, riprapping, deadwood removal, and manual modification to streamline watercourses and expedite the flow of water away from urban areas. These efforts can reduce the habitat quality for native species. The added effects of other urban habitat alterations, such as invasive species introduction, could further exacerbate any negative effects associated with an already physically altered habitat. Aquatic turtles can be especially prone to such disruptions due to their reliance on many microhabitats to survive. We conducted 32 surveys over the course of approximately six months investigating basking behavior and basking substrate usage by native Southwestern Pond Turtles (Emys pallida) and non-native Red-Eared Sliders (Trachemys scripta elegans) in an urban creek in Orange County, California. We compare usage of basking site substrates between these two species. Noise level, another factor associated with urban areas, is also analyzed. Results are interpreted in context of urban stream management, and the effects both heavy human modification of a creek system and introduced species can have individually, and together, on Southwestern Pond Turtles. We also recommend management practices that may benefit declining Southwestern Pond Turtles based on the results obtained herein.