SREL Reprint #2242

Estimation of age for Trachemys scripta and Deirochelys reticularia by counting annual growth layers in claws

R. Brent Thomas1, Daniel W. Beckman2, Kip Thompson3, Kurt A. Buhlmann4, J. Whitfield Gibbons4, and Don L. Moll2

1Department of Biological Sciences, Mississippi State University, Mississippi State, Mississippi 39762
2Department of Biology, Southwest Missouri State University, Springfield, Missouri 65804
3Department of Marines Sciences, University of South Alabama, Dauphin Island Sea Lab,
Dauphin Island, Alabama 36528
4University of Georgia, Savannah River Ecology Laboratory, Aiken, South Carolina 29802

Introduction: The need for accurate methods of age determination in life-history studies is well recognized. Techniques used to estimate the age of turtles include analysis of body size (Balazs, 1982; Frazer and Ehrhart, 1985; Frazer and Ladner, 1986), weighing eye lenses (J. Frazier, J. Ballon, and S. Salas, unpubl.), counting growth zones on plastral scutes (Cagle, 1946; Sexton, 1959; Gibbons, 1983), and skeletochronology (Mattox, 1935; Zug, 1990; Klinger and Musick, 1992). Each technique has its disadvantages, and finding a technique that is accurate and can be applied objectively has been difficult (Zug, 1991). An ideal age estimation technique would not cause stress or mortality to the individual being aged, would be valid for all age/size classes, would be based on a clearly recognizable structure that is permanent throughout the life of the individual, and would not require subjective judgment. The use of claws could potentially satisfy three of these requirements for turtle age estimation. Zug (1991) suggested that because claws grow continuously throughout the life of a turtle and because growth is aftected by environmental factors, the formation of seasonal growth layers might be expected. The objective of our study was to determine whether annual layers could be observed in sections of claws from Trachemys scripta and Deirochelys reticularia and whether counts based on such layering could provide reliable data for age estimation.

SREL Reprint #2242

Thomas, R.B., D.W. Beckman, K. Thompson, K.A. Buhlmann, J.W. Gibbons, and D.L. Moll. 1997. Estimation of age for Trachemys scripta and Deirochelys reticularia by counting annual growth layers in claws. Copeia 4:842-845.

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