SREL Reprint #2254

Differences in body size among populations of red-eared sliders (Trachemys scripta elegans) subjected to different levels of harvesting

Lisa M. Close1,2 and Richard A. Seigel1,3

1Department of Biological Sciences, Southeastern Louisiana University , Hammond, Louisiana 70402 USA
2Garberville Redway Veterinary Group, 230 Alderpoint Road, P.O. Box 67, Garberville, California 95542 USA
3Savannah River Ecology Laboratory, University of Georgia, Drawer E, Aiken, South Carolina 29802 USA

Introduction: Although turtles have been exploited by man for hundreds or even thousands of years (Humane Society, 1994), quantitative studies of the effects of human predation on turtle populations have been conducted only recently (e.g., Crouse et al., 1987; Congdon et al., 1993, 1994). These studies showed that a critical consequence of the co-evolved life-history traits of long-lived organisms such as turtles is a high degree of susceptibility to changes in patterns of survival, especially changes in the survival rates of older juveniles and adults (Crouse et al., 1987; Congdon et al., 1993, 1994). In the absence of a substantial compensatory decrease in mortality rates among neonates or smaller juveniles, increases in human-induced harvesting of adults from the wild may result in sharp decreases in population size. For example, Congdon et al. (1994) showed that a harvest pressure as low as 10% per year could result in a 50% reduction in adult snapping turtles (Chelydra serpentina) within 15 years. Furthermore, Brooks et al. (1991) found that juvenile snapping turtles showed no compensatory response to increased adult mortality. Thus, the ability of turtle populations to withstand even moderate levels of increased mortality from humans for long periods is questionable (Kiemens and Moll, 1995).
The red-eared slider (Trachemys scripta elegans) is one of the most common freshwater turtles in North America (Ernst et al., 1994). Until 1975, large numbers of hatchlings of this species were sold as pets throughout the US, but such trade was banned by the Food and Drug Administration owing to health concerns (Williams and Heisdon, 1965; Lamm et al., 1972). However, a considerable commercial market still exists for this species in: 1) international trade in hatchlings for pets, and 2) commercial take for meat. Although interstate sales of hatchlings are illegal in the US, an estimated 26 million T. scripta were exported from the US to international markets between 1989 and 1994 (Humane Society, 1994). The vast majority these turtles are thought to be hatchlings produced by turtle ranches in southern Louisiana (M. Anderson, pers. comm.), but some are adults (C. Warwick, pers. comm.). In addition, unknown numbers of adults are collected every year by turtle ranchers to replace breeding stock. We use the term "ranch" to note that turtles are not raised to maturity to support a self-sustaining program, all offspring being sold as hatchlings. Adult red-eared sliders are also harvested for meat, both for local and national consumption and for international export (Warwick and Steedman, 1988).

SREL Reprint #2254

Close, L.M. and R.A. Seigel. 1997. Differences in body size among populations of red-eared sliders (Trachemys scripta elegans) subjected to different levels of harvesting. Chelonian Conservation and Biology 2:563-566.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).