Basking Habits of Aquatic Turtles in Lake Marburg David Batchelor Department of Biology, York College of PA Painted Red Eared Slider Red Bellied Hypotheses H1: Turtles stop basking in the Fall because there are fewer desirable basking locations available. H2: Although still active, turtles avoid basking to maintain a low metabolism in preparation for hibernation H3: Due to the plentiful resources in Lake Marburg, it is unnecessary for the turtles to re-emerge from estivation in the Fall. Introduction Lake Marburg is a manmade lake in Hanover, Pennsylvania that has a dam controlled by the Glatfelter paper company. Throughout the warmer months, Glatfelter Company lowers the water level of the lake, possibly affecting local turtles species, including Red Eared Sliders (Trachemys scripta elegans), Painted Turtles (Chrysemys picta), and the threatened Red- Bellied Turtles (Pseudemys rubriventris). Body temperature in ectotherms affects digestion, locomotion speed, ability to catch prey, and response to predators. Many ectotherms regulate their temperature through their behavior, which is mainly done by atmospheric basking (Edwards and Blouin- Demers 2007). A turtle’s basking site must have specific parameters to balance their heat gain with the risk of predation. Turtles that are disturbed when basking will quickly dive into the water to escape predators. Therefore, basking on the shoreline or on shallow platforms may pose a greater risk to the turtle than deeper platforms (Cadi and Joly 2003). Throughout the summer months, Lake Marburg’s water levels consistently drop and existing basking locations become less desirable. Previous research has shown that when the lake was low, later in the year, there was much less turtle activity (Axe 2011, Rice 2012). My objective was to determine if providing deeper platforms would benefit turtles that may prefer to bask late in the season and in particular, Red-Bellied turtles that the park is trying to protect. Results Conclusions Deeper platforms worked as a place for turtles to bask when water levels got too low around existing platforms. Despite the new platforms, few large turtles were observed basking late in the season suggesting that other factors may be at play. Based on this preliminary data, Red-Bellied Turtles are not likely to benefit if the Codorus Park provided deeper platforms, as they were never observed in the Fall. References Axe, J A study of the population and distribution of the red-eared slider, Trachemys scripta elegans, in Lake Marburg, York County, PA. Cadi, A. & Joly, P. (2003). Competition for basking places between the endangered European pond turtle (Emysorbicularis galloitalica) and the introduced red-eared slider (Trachemys scripta elegans). Canadian Journal of Zoology. 81: 1392–1398. doi: /Z Edwards, A. L., & Blouin-Demers, G. G. (2007). Thermoregulation as a function of thermal quality in a northern population of painted turtles, Chrysemys picta. Canadian Journal Of Zoology, 85(4), Rice, S Movement of red-bellied turtles (Pseudemys rubriventris) throughout Lake Marburg at Codorus State Park, Hanover, PA. Acknowledgements I thank Dr. Nolan for her constant help through encouragement and positive criticism as my mentor. I also would like to thank Dr. Hagerty for her help with statistics and poster design. A special thanks to Codorus State Park and the Pennsylvania Boat and Fish Commission for allowing me to do research at Lake Marburg. Future Studies Test other 2 hypotheses Complications due to other species that likely effected the number of turtle observations: -Geese were seen resting on the platforms during many visits to the lake. -Muskrats built their nest on the platforms late in the year. Methods Sampling was done at Lake Marburg in Hanover, PA three times per month from April until October in Two basking platforms were built that were 3x3 feet and placed in the water at a depth of around 300 cm in April. Total number and type of turtles present on each basking platform was recorded throughout the experiment. Also Measured: Water Depth (cm) Water Temperature (°C) Oxygen (mg/L) % Vegetation Cover Chlorophyll (mg/m 3 ) Turbidity Sailboat Dub’s Chapel : Shallow : Deep Sailboat Water temperature was lower than air temperature until late summer; then water temperature exceeds the air temperature into the fall. There is less of a need for basking when water temperature is warmer than air temperature. The basking platforms all decrease in depth throughout the season. Water decreased by about 200 cm over course of a season. Turtles appeared to bask less on the shallow platforms as the lake receded. They then basked on the deeper platforms more often, later in the season. Fewer large turtles were observed in the latter part of the season. Small turtles were observed on a more consistent basis throughout the season. Map of Lake Marburg Circled areas are zoomed in below with general locations of platforms on maps. aptism_trip_2006/turtles_basking_in_the_sun.jpg