A Study of the Population and Distribution of the Red-eared Slider, Trachemys scripta elegans,

in Lake Marburg, York County, PAJoshua Axe

Department of Biological Sciences, York College of Pennsylvania

Introduction•The red-eared slider’s native home range is within states of the Mississippi Valley. Through the pet trade, it has become an invasive species worldwide (Ernst et al. 1989) including Lake Marburg located in southwestern York County, Pa.

•Red-eared sliders have been found to compete with native turtle species, such as the European pond turtle and Spanish terrapin, for resources including nesting and basking sites (Cadi & Joly 2003, Polo-Cavia et al. 2010). Of importance in Lake Marburg is the native red-bellied turtle which is a threatened species due to pollution and industrial/residential development (Ernst et al. 1994, Swarth 2003). It is unknown if the red-eared slider and red-bellied turtle compete, but if they have overlapping home ranges this could increase the possibility of competition.

•Of the 14 red-eared sliders caught in Lake Marburg during summer of 2009 and 2010 (Haneschlager 2011, Harbin 2009), none were recaptured. Researchers hypothesized they were not recaptured because they moved throughout the entire lake. A home range that encompasses the whole lake would give red-eared sliders more access to food, nesting locations, and basking sites.

•A home range should include an undisturbed nesting location, an area to feed, an area to bask in colder months, and a cooler area to estivate in hotter months (Bonin et al. 2006).

•Understanding the movement and home ranges of the red-eared slider is critical in determining whether they are competing with native species of turtles. In order to determine the home ranges of this species within Lake Marburg, I used radio-telemetry to track movement of four red-eared sliders.

Objectives

•To estimate the population of red-eared sliders within Lake Marburg.

•To monitor the movement of red-eared sliders and to determine their home ranges.

Hypotheses

H1: I hypothesize that red-eared sliders have large home ranges and move throughout the whole lake.

H2: I hypothesize that red-eared sliders move to the center of the lake as summer progresses to estivate.

Methods•Basking and baited traps were placed at three locations near permanent basking platforms.

•Traps were checked daily during an approximate one week period each month.

•Once captured, the following measurements were taken on each turtle: weight and carapace length, width, and height.

•For future identification, marginal scutes were notched using a file.

•Population estimates were made using the Schnabel Method (Schnabel, 1934).

•Two adult male and two adult females were tagged with Wildlife Materials transmitters at frequencies in the 172.000 MHz range.

•Locations were taken at least once a week from May to September with a Field Marshall 1000 digital tracking receiver.

•Home range sizes were estimated using the minimum convex polygon method (Mohr, 1947).

Literature Cited

•Bonin F, Devaux B, Dupré A. 2006. Turtles of the world. John Hopkins University Press., Baltimore, Md. •Cadi, A., and Joly, P. 2003. Competition for basking places between the endangered European pond turtle (Emys orbicularisgallotindica) and the introduces red-eared slider (Trachemys scripta elegans). Canadian Journal of Zoology. 81(8): 1392-1398. •Ernst, C. H., Lovich J. E., and Barbour R. W. 1994. Turtles of the United States and Canada. Washington, D.C. Smithsonian Institution Press.•Ernst, C. H., Barbour R. W. 1989. Turtles of the World. Washington, D.C. Smithsonian Institution Press.•Haneschlager, L. 2011. Study of the red-bellied (Pseudemys rubriventris) population in Lake Marburg located in Codorus Park, PA.•Harbin, R. 2009. A study of the red-bellied turtle population, Pseudemys rubriventris, at Codorus State Park.•Mohr, C. O. 1947. Table of equivalent populations in North American small mammals. The American Midland Naturalist. 37: 223-249.•Polo-Cavia, Nuria, and Pilar Lopez, and Jose Martin. "Competitive Interactions during Basking between Native and Invasive Freshwater Turtle Species.” Biological Invasions. 12.7 (2010): 2141-152.•Schnabel, Z.E. 1938. The estimation of the total fish population of a lake. American. Mathematical Monthly . 45:348-352•Swarth, C.W. 1999. Natural History and Reproductive Biology of the Red-Bellied Turtle (Pseudemys rubriventris). P73-83 In: Swarth, C.W., Roosenburg, W.M. and Kiviat, E. (eds.). Conservation and Ecology of Turtles of the Mid-Atlantic Region: A Symposium. Bibliomania! Publishing Co., Salt Lake City, Ut. •http://blogs.ncmls.org/keepers/2011/09/05/dont-let-them-go/

Results Discussion•There was no change in number of turtles caught per month. In May, it was easier to net the turtles as colder temperatures caused the turtles to move slowly.

•Males were found to remain in one large cove or move between two smaller adjacent coves. Females were found to have a similar pattern but had a larger home range and moved more often.

•At the beginning of August all turtles stopped moving. One male remained within the cove, whereas the other male and female moved to the edge of their cove. No turtles moved to deepest part of the lake as hypothesized.

•Over the summer, red-eared sliders were observed throughout the lake. Given their small home ranges, the population estimate for the lake is likely underestimated. Therefore, a population estimate was made for each home range and an estimate of total number of possible home ranges within the lake was made. Given this, I believe the population estimate for the lake is closer to 700 turtles.

Future Research•A larger sample size needs to be tagged in order to verify determined home ranges and over a larger number of coves in the lake

•Tag females to locate possible nesting sites and estimate clutch size

Acknowledgments

A special thanks to Dr. Nolan for all her help and guidance. Also to Codorus State Park, DCNR, and PA Fish and Boat for issuing permits and allowing me to perform my research.

Conclusions•Based on home range sizes found in this study, all the resources needed to survive appear to be within one or two coves, allowing them to remain there year round.

•The population estimate for the lake was 188 but is believed to be underestimated due to turtles having a limited range.

•Given the limited range of the red-eared slider I believe the competition for resources with the red-bellied turtle, based on home range size, is not as significant as previously assumed.

Figure 7. Home range of male red-eared sliders represented by black polygons. Circle size represents number of weeks spent at the location.

Figure 8. Home range of female red-eared sliders represented by black polygons. Circle size represents number of weeks spent at the location. The female in chapel cove disappeared two weeks into June. Her shell was found later in the summer and appeared to have been hit by a propeller blade.

Location Population95% Confidence Interval

Upper Lower

Whole Lake 188 1254 67

Dubs Cove 69 367 4Chapel Cove 74 394 4

Table 1. Population Estimates and 95% Confidence Intervals of the Red-Eared Slider within Lake Marburg. Estimates were made for individual coves due to turtles limited home range.

Figure 1. Basking trap

Figure 2. Dr. Nolan using the Field Marshall 1000 digital tracking receiver

Figure 3. Baited trap

Figure 4. Vertical view of male red-eared slider with transmitter attached

Figure 5. Horizontal view of male red-eared slider with transmitter attached