Serum testosterone and estradiol-17ß levels during the peak period in a year-round Hawksbill Turtle Eretmochelys imbricata L. nesting population

Abstract

Serum testosterone (T) and estradiol-17ß (E2 ) concentrations were determined for 95 Hawksbill Turtles Eretmochelys imbricate nesting at Milman Island, northern Great Barrier Reef, Australia. This information describes gonadal hormone concentration during the Austral summer months for peak nesting in an E. imbricata population that nest year-round. A total of 173 samples was collected from 95 turtles, with 39 turtles sampled sequentially within their nesting cycle (n = 117 samples) and the remainder sampled at random. E2 -levels were measured from seven turtles sampled sequentially within their nesting cycle (n = 31 samples). T-Ievels ranged from 0 to 7 520 pg/ml; E2-Ieveis varied between 0.0 and 119.0 pg/ml. Peak T-Ievels in turtles sampled sequentially within their nesting cycle occurred after laying clutch number two or three while E2-levels peaked after clutch number one or two; levels of both hormones decreased thereafter. T- and E2-levels decreased monthly (December to March) within a nesting season. Based on T-Ievels, the greatest proportion (58%) of turtles began their nesting cycle in December. Turtles in the middle of their nesting cycle were found in equal proportions (27?35%) throughout the Austral summer months. Turtles at the end of their nesting cycle were most frequent (61%) in March. The implications of these results for future research and for managing access to islands with year-round marine turtle nesting are discussed.