ENMU Student Studies Habitat Characteristics of the Rio Grande Cooter

By Marcus Gay, NM WRRI Student Program Coordinator

The Rio Grande Cooter (Pseudemys gorzugi) is a freshwater turtle native to the Rio Grande and the Pecos River in New Mexico, Texas, and northeastern Mexico. The species is currently listed as threatened in New Mexico and Mexico, and is a species of greatest conservation need in Texas. In recent years, the species has been studied in tributaries of the Pecos River in New Mexico and Texas, but the Pecos River itself has not been surveyed for turtles in over a decade.

The Pecos River originates in the mountains of northern New Mexico and runs 926 miles through the Chihuahuan Desert before flowing into the Rio Grande on the Texas-Mexico border. One of the river’s historic attributes is salinity caused by natural saline groundwater. Reduced flood frequency and diminished flows have caused an increase in salinity and a decrease in water quality. The river’s water quality can also be affected by dam construction, channelization, agriculture practices, etc. In addition to being arguably one of the most anthropogenically altered river systems in the southwest United States, the Pecos River continues to be a major water source and habitat for wildlife.

There is a gap in knowledge about how these environmental changes on the Pecos can impact freshwater turtle populations like P. gorzugi. NM WRRI has awarded Laramie Mahan, a graduate student at Eastern New Mexico University (ENMU), a Student Water Research Grant to address this knowledge gap. The study, titled Occupancy and detection of Rio Grande Cooter (Pseudemys gorzugi) on the Pecos River, aims to 1) determine the current distribution of P. gorzugi along the Pecos River, and 2) determine which environmental and habitat characteristics contribute to the presence or absence of the species by utilizing a single-season, single-species occupancy modeling framework.

Under the guidance of Dr. Ivana Mali, Mahan conducted surveys across 32 sites on the Pecos River during the summer months of 2020 and 2021. Each site was visited for three survey occasions within the summer season. At each site, 45 hoopnet traps were placed in the water for 48 hours at a time. Each turtle captured was measured and marked. For each site, the team recorded water quality parameters and river characteristics predicted to affect the presence or absence of P. gorzugi. Water quality parameters included pH, conductivity, nitrates, dissolved oxygen, and temperature. River characteristics included width, depth, vegetation, and evidence of anthropogenic activity (fishing, trash, agriculture, etc.). Currently, Mahan is utilizing a single-season, single-species occupancy model, which will elaborate on which conditions best explain the occupancy and detection probabilities for the species.

This project aims to shed light on the current distribution of P. gorzugi on the Pecos River. The results obtained from this study could potentially inform the decision-making process for the species and Pecos River water management. According to Mahan, this research is significant because “turtles are important parts of their ecosystems and evolutionary history in general, yet they are amongst the most threatened groups of vertebrates. There is alarmingly little research done on many freshwater turtle species, especially studies conducted that estimate factors contributing to their occurrence and detection. Statistical techniques such as occupancy modeling can aid in pinpointing how site-specific characteristics of water quality, surrounding habitats, and river vegetation, etc., may alter the presence or absence of freshwater turtle species.” Mahan has presented her work at The Wildlife Society Annual Conference and the 66th Annual New Mexico Water Conference.

Originally from Arizona, Mahan plans to graduate with a Master of Science in Biology in 2022 from ENMU. Mahan obtained her Bachelor of Science in Wildlife and Fisheries Sciences from ENMU where she began to work with Dr. Mali on P. gorzugi research. After graduation Mahan plans to continue her work studying freshwater turtles and their role in their respective ecosystems by attending Texas State University to work towards a PhD in Aquatic Resources and Integrated Biology.