Hawksbill sea turtles: can phylogenetics inform harvesting?

In their recent articles, Mortimer et al. (2007) and Bowen et al. (2007) imply that historical declines in hawksbill sea turtle (Eretmochelys imbricata) populations in the Caribbean together with new phylogenetic data provide solid evidence that hawksbills cannot be harvested on a sustainable level. We suggest that broad inferences on the impacts of harvesting based on phylogenetic data alone are insufficient as an argument against sustainable use of sea turtles. Rather, we recommend that the merits of harvesting schemes should be assessed on a case-by-case basis, which should enable beneficial and sustainable projects to proceed and also discourage unsustainable ones. As reported by Mortimer et al. (2007), recent data on mtDNA haplotype diversity show that rookeries and foraging areas in the Caribbean are connected, with juveniles moving across national boundaries from natal beaches to foraging grounds, and back again to natal beaches as adults (Bowen et al. 2007). Based on these associations, Bowen et al. (2007) suggest that 'harvest [of hawksbills] in the Caribbean foraging areas will deplete nesting populations across multiple jurisdictions', while Mortimer et al. (2007) state that any harvest on nesting beaches or feeding grounds could negatively impact hawksbill populations throughout the Caribbean region. We suggest that these claims are not necessarily true in all situations. A case in point is the current harvesting of hawksbills in Cuban waters (Carrillo et al. 1999) and the ongoing increase of the nearby nesting population of hawksbills in the Yucatán Peninsula (Garduño-Andrade et al. 1999). Published phylogenetic studies have reported that a significant source rookery for turtles harvested in Cuba is the Yucátan Peninsula (Díaz-Fernández et al. 1999; Bowen et al. 2007). A second example is the hawksbill rookery in Antigua. Phylogenetic data show that hawksbills from Antigua contribute significantly to foraging grounds in Cuba (Bass 1999; Díaz-Fernández et al. 1999; Bowen et al. 2007). And yet, numbers of nesting females in Antigua have been increasing over the last decade, despite the ongoing harvest of hawksbills in Cuba (Richardson et al. 2006a). Clearly, the situation regarding harvesting and its impacts on regional nesting populations is more complex than presented in Mortimer et al. (2007) and Bowen et al. (2007). A primary principle of wildlife management is that a target population can be kept at a level below its carrying capacity, through harvesting or culling, without causing a decline in the population, due to density-dependent rates of growth (Getz & Haight …