High survivorship of an annually decreasing aggregation of hawksbill turtles, Eretmochelys imbricata, found foraging in the northern Great Barrier Reef


I. Bell, School of Tropical and Marine Biology, James Cook University, Townsville QLD 4814, Australia. E-mail: ian.bell@my.jcu.edu.au


  1. An 8-year study of the foraging abundance of an Eretmochelys imbricata aggregation, found on 13 reefs (Howick Group) within the northern section of the Great Barrier Reef Marine Park was undertaken.
  2. A Cormack–Jolly–Seber method within program MARK was used to: (1) compare survival and recapture probabilities among age and sex classes of turtles; and (2) estimate survival and recapture rates for male and female adults and sub-adults from 665 capture–mark–recapture profiles of E. imbricata.
  3. Mean annual population density estimates were consistently greater for adult female E. imbricata (n = 333.7; SD = 135.6; R = 221–581) than for adult males (n = 32.4; SD = 33.4; R = 8–98), with both adult males and females displaying high survivorship rates (71.1%; 92.2%, respectively). This was also apparent in immature age-classes, with male and female turtles showing similarly high survivorship likelihoods (78.0%; 93.0%, respectively).
  4. Both sexes exhibited a similar overall trend with a peak population density being displayed in the first two years of the study, followed by a general decline in the female stock and stable male population.
  5. These are the only reliable long-term abundance time-series data for a population that includes all age-classes of E. imbricata in the western Pacific and provide good baseline data for the detection of possible climate change induced trends.

Copyright © 2012 John Wiley & Sons, Ltd.