Eddies as offshore foraging grounds for melon‐headed whales ( Peponocephala electra )

: Movements of upper trophic level predators in an open ocean environment should be driven, in part, by the distribution, density, and movements of their prey. Surveys have shown that cetacean densities are higher closer to shore around the main Hawaiian Islands than in offshore waters (Barlow 2006), presumably reflecting increased productivity or spatial and temporal predictability of prey associated with island effects (Baird et al. 2008a). A number of high trophic level pelagic species have been shown to concentrate around and/or use mesoscale eddies as foraging habitat (e.g., Davis et al. 2002, Seki et al. 2002, Bakun 2006, Polovina et al. 2006, Yen et al. 2006). The islands, and their interaction with winds and currents, create a complex system of eddies that may also concentrate some prey types farther offshore (Seki et al. 2002), but whether island-associated cetacean populations use these offshore eddy systems for foraging habitat is unknown. Melon-headed whales (Peponocephala electra) are a tropical delphinid that primarily inhabits open-ocean waters and is known to feed on mesopelagic squid and fish (Best and Shaughnessy 1981, Clarke and Young 1998). In Hawaiian waters, these whales are encountered relatively infrequently. Around the main Hawaiian Islands, two populations have been identified: a main Hawaiian Islands population and a population resident to the island of Hawai i (Aschettino et al. 2011). As part of a multispecies study examining movements and habitat use of cetaceans around the main Hawaiian Islands (e.g., Schorr et al. 2009, Baird et al. 2010), individual melonheaded whales from the main Hawaiian Islands population have been instrumented with satellite tags for various purposes (e.g., Baird et al. 2008b), including to assess their movements in relation to mesoscale eddies, to determine whether they use offshore eddy systems as foraging habitat.