Date of Graduation

Fall 2023

Degree

Master of Science in Biology

Department

Biology

Committee Chair

Day Ligon

Abstract

The Central American River Turtle (Dermatemys mawii) is native to southern Mexico, eastern Guatemala, and Belize and is primarily restricted to watersheds that drain into the Gulf of Mexico and Caribbean Sea. Hunting, both for personal consumption and market meat, has been the primary driver of declines, and the species is now classified as critically endangered. Results from past studies that have used netting and visual surveys to detect D. mawii suggest that the species is chiefly nocturnal. However, it is unclear to what extent the perception of nocturnality has been biased by the timing of survey efforts (e.g., animals may appear to be nocturnal if efforts to detect them are restricted to nighttime surveys). A more detailed understanding of activity patterns is important, in part because it informs many other aspects of the species’ biology (foraging patterns, environmental effects, etc.), but also because understanding when individuals are most likely to be moving can help to inform hunting regulations and research efforts. Therefore, to quantify the daily and seasonal activity patterns of D. mawii in a natural river system in Belize, I equipped 8 males, 8 females, and 8 juveniles with archival dataloggers to record acceleration (movement), temperature, and pressure (water depth), and sonic transmitters to aid in relocating and recapturing turtles. Over the course of five sampling trips, from June 2021 to July 2022, I recaptured and downloaded data from 18 of the 24 tagged individuals, resulting in intervals of consecutive data for each turtle ranging from 1–13 months. Surprisingly, and contrary to previous assertions that the D. mawii are chiefly nocturnal, my results indicate that this species exhibits a crepuscular activity pattern, with lowest rates of activity occurring at night. Overall, males were more active than juveniles, which were more active than females. Additionally, I observed a distinct seasonal pattern in activity for males and females, with higher levels of nocturnal activity in the rainy season and higher levels of diurnal activity during the dry season. Temperature negatively correlated with activity, and depth was positively correlated with activity, suggesting D. mawii are more active at greater depths and cooler temperatures. Additionally, females spend more time at greater depths than males or juveniles, and all three demographic groups go deeper during the dry season.

Keywords

activity, accelerometer, conservation, Dermatemys, diel

Subject Categories

Behavior and Ethology | Other Ecology and Evolutionary Biology | Terrestrial and Aquatic Ecology

Copyright

© Cora Dyslin

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