Generation length is defined as the age to maturity plus one half the reproductive longevity (Pianka 1974). Hawksbills mature very slowly, taking 20 to 40 years, and so are long-lived (Chaloupka and Musick 1997). In the Caribbean and
Data on reproductive longevity in Hawksbills are limited, but becoming available with increasing numbers of intensively monitored, long-term projects on protected beaches. During the last decade, numerous individual
Given estimated ages to maturity of 25 years in the Caribbean and 35 years in the Indo-Pacific, with half of reproductive longevity estimated at 10 years, a conservative generation length of 35 years (25 + 10 years) is calculated for the Caribbean and Western Atlantic, and 45 years (35 + 10 years) in the Indo-Pacific. In analyzing the data, declines over three generations are therefore measured for up to 105 years in the Caribbean and
Nesting Population Size and Fecundity
Sea turtle population trends are best diagnosed using in-water abundance estimates coupled with estimates of demographic parameters such as survival and recruitment possibilities (Chaloupka and Limpus 2001, Bjorndal et al. 2005). However, these data rarely exist for sea turtle populations and so most assessments are based on evaluating nesting trends, which assumes a close correlation between population trends and nesting activity (Bjorndal et al. 2005).
For this assessment the size of a nesting population is defined as the average number of individual females nesting per year. In some cases, population numbers can be determined by saturation tagging of nesting females or by recording the total number of slaughtered nesters. More often, however, population estimates need to be derived from records of the total number of egg clutches laid during a season. Saturation tagging of nesting females indicates that at most sites the average female Hawksbill lays between three and five egg clutches during a single nesting season (Richardson et al. 1999, Mortimer and Bresson 1999), with indications that newly recruited females lay fewer egg clutches (Mortimer and Bresson 1999, Beggs et al. 2006), and possibly fewer clutches in the Arabian/Persian Gulf (Pilcher 1999). Following the pattern of earlier status reviews, the present assessment calculates the annual number of nesting females by dividing the total number of egg clutches recorded, by three to five to produce a bracketed population estimate.
Population Trends and Conclusions
In many parts of the world, Hawksbill populations have continued to decline since the publication of the previous Red List Assessment (Meylan and Donnelly 1999). Continuing losses in
In 2001 the IUCN Red List Standards and Petitions Subcommittee upheld the Critically Endangered listing of the Hawksbill, based on ongoing and long-term declines in excess of 80% within the time frame of three generations and ongoing exploitation (IUCN 2001b). The Subcommittee review cited “convincing evidence of reductions in excess of 80% over the last three generations at many, if not most of the important breeding sites throughout the global range of the species”. Not surprisingly, those declines reflect the intensity of the tortoiseshell trade in the 20th Century. Although some relatively large populations still exist, especially in
The current assessment clearly demonstrates the importance of protection in both terrestrial and marine habitats. With protection, some populations have stabilized, and others are now increasing, most notably in the