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

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. A Cormack-Jolly-Seber method within program MARK was used to: compare survival and recapture probabilities among age and sex classes of turtles; and estimate survival and recapture rates for male and female adults and sub-adults from 665 capture-mark-recapture profiles of E. imbricata. 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). 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. 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. © 2012 John Wiley & Sons, Ltd.