used to detect individual variance in growth rates (Vaughan, 2009). A greater effort needs to be made to archive humeri from sea-turtle carcasses of known size, sex, location, and date for age and growth studies.
Length-frequency analyses, which rely on maximum-likelihood algorithms to detect ageclass modes in size distributions, have been used widely in fisheries and successfully in sea turtles (Bjorndal et al., 1995, 2000b, 2001). A disadvantage of the technique is that, with currently available software, only von Bertalanffy growth models can be used. Greater overlap of body lengths in older ageclasses may limit the use of the technique. Its main advantage is that it requires only data on size distributions.
Two other techniques for measuring growth of sea turtles have been investigated. Hays and Marsh (1997) estimated growth rates of the very early stages by analyzing drift times to remote locations and the size of small turtles at those locations. And the use of RNA and DNA ratios, which have been used extensively in studies of fish growth, has been tested in sea turtles with some success (Roark et al., 2009b). Both techniques deserve further evaluation.
Age at sexual maturity is a critical demographic parameter. Estimating age at maturity on the basis of somatic growth rates is problematic because, for all Atlantic populations, few data are available on growth rates of large subadult turtles (i.e., above 70 cm in carapace [upper shell] length in green turtles). A high priority might be to determine growth rates of large subadults so that estimates of age at sexual maturity can be based on a stronger foundation.
Because sea turtles exhibit environmental sex determination, primary sex ratios are determined by environmental factors, as described above (see the section “Fecundity”). Variation in secondary sex ratios (i.e., the odds of a hatchling will be male) on foraging grounds may result from variation in primary sex ratios, sex-specific mortality, or sex-specific dispersal. Data on secondary sex ratios of immature and adult sea turtles are needed to develop sex-specific population models and to evaluate “optimal” sex ratios (i.e., ratios at which reproductive output is maximized in a population). If it becomes necessary because of global warming, the latter will be critical for programs to manipulate primary sex ratios at nesting beaches (Mrosovsky and Godfrey, 1995).
Rates in a population are said to be density dependent if they vary with the abundance or density of the population. For example, in the