Age estimation in juvenile green turtle Chelonia mydas at Uruguayan coast

CABRERA, MARIO R.; ESTRADES, ANDRES; FALLABRINO, ALEJANDRO; VELEZ RUBIO, GABRIELA; JOAQUIN, LEILA

Las Vegas

Simposio; 2017 International Sea Turtle Symposium; 2017

The Uruguayan coast is an important feeding and development area for green turtles (Chelonia mydas) during the juvenile neritic stage of their life cycle in the South Western Atlantic Ocean. The present study seeks to contribute with basic data on the demographic structure of the green turtle aggregation that use those coastal waters. Since 2001 the NGO Karumbé conducts seasonally beach surveys along the Atlantic coast of Uruguay, looking for live and dead stranded turtles to record different biometric data and collect tissue samples. The objective of this study is to obtain an age estimation of the C. mydas individuals according to turtle size at Uruguayan feeding grounds, using skeletochronology method.The fieldwork was carried out along the Uruguayan coast including the Departments of Canelones, Maldonado and Rocha. Right humeri of dead stranded turtles were removed using a scalpel. After that, the bones were cleaned and macerated in water, washed and dried outdoors. For this study, 86 humeri were collected during different surveys from 2002 to 2013 of the dead stranded turtles founded in different decomposition stages. They present a mean Curved Carapace Length (CCL) of 38.3 +-4.9 cm (range 27.7 to 51.0 cm), with the most frequent size range between 36.0 and 42.4 cm. Using an electric saw, a 5 to 8 mm thick cross-section was obtained, applying them histological technique for permanent preparations with hematoxylin and eosin staining. Nine cuts were discarded as they lacked clarity under the microscope caused by breakage or technical defect. The remaining 77 specimens presented 0 to 5 lines of arrested growth (LAGs). If each LAG represents a one year-period we can infer that the turtles were between one to five years. Most of turtle present only one or two years old. The LAGs could be visualized only on those turtles that reached at least a size of 29.9 cm of CCL, on which the first growth mark was verified. This data ascertain an exploratory analysis of the growth data that could help us to infer the recruitment age of C.mydas to Uruguayan neritic grounds. Also help us to understand the distribution of the species in their earlier stages in the western South Atlantic.