ABSTRACT
Sharks are important living resources to human societies globally in cultural, economic, health, biodiversity, and conservation contexts. They can play a key role in the functioning of marine ecosystems and may provide higher trophic-level indication of ocean ecosystem state (Sims and Quayle 1998; Myers et al. 2007). However, rapid declines in some large pelagic sharks are occurring on a worldwide scale due to overfishing (Baum et al. 2003; Myers et al. 2007). There is particular concern that target and by-catch fisheries that have been well developed for at least the past century in the Atlantic Ocean, for example, are depleting shark populations below sustainable levels where recovery may not be possible, or at best may be very slow, even if fishing pressure is removed (Pauly et al. 2002; Clarke et al. 2006). Although some fisheries assessments indicate less pronounced declines for large pelagic (Sibert et al. 2006) and coastal sharks (Burgess et al. 2005), undoubtedly they are particularly susceptible to overharvesting on account of slow growth rates, late age at sexual maturity, and relatively low fecundity. During the twentieth century some large skate species were eliminated from areas where they were once very common and have not returned (Brander 1981; Casey and Myers 1998), suggesting large sharks, having at least some similarities in life history to skates, are also likely to be at risk of regional extinction (Chapter 17). Many pelagic sharks are now redlisted by the International Union for Conservation of Nature (IUCN), with some now at a fraction of their historical biomass (Dulvy et al. 2008). In the face of these apparently dramatic declines and the need for prompt action aimed at securing the future of species and populations, biologists have developed over the last 30 years or so numerous techniques for tracking and analyzing the movements of individual sharks in the natural environment. But how is this linked to broader issues in understanding animal ecology, and how can this help in applied settings, such as in shark fisheries management and species conservation?
