M. B. Hanson

Short Note: Open-Ocean Movements of a Satellite-Tagged Blainville’s Beaked Whale (Mesoplodon densirostris): Evidence for an Offshore Population in Hawai‘i?

Abstract : In Hawaiian waters, a single stock of Blainville s beaked whale (Mesoplodon densirostris) is recognized, extending throughout the U.S. Exclusive Economic Zone (EEZ) surrounding the archipelago and into adjacent international waters (Carretta et al., 2011). Abundance within the entire EEZ around Hawai i was estimated at 2,872 individuals based on a large vessel sighting survey (Barlow, 2006), with a single on-effort sighting near the western boundary of the EEZ (Hamilton et al., 2009). There is, however, considerable uncertainty associated with this estimate (CV = 1.17; Barlow, 2006), and there is recent evidence that individuals documented around the main Hawaiian Islands may not be part of an open-ocean population (McSweeney et al., 2007; Schorr et al., 2009). Individual Blainville s beaked whales instrumented with satellite tags off the island of Hawai i have remained strongly associated with the island, primarily using slope habitats for the entire duration of satellite tag transmissions (up to 71 d; Schorr et al., 2009). Schorr et al. (2009) noted a mean distance from shore of 16.9 km (range 4.4 to 27.7 km) and a mean depth of 1,156 m (range 880 to 1,455 m) for six satellite tagged individuals, over periods ranging from 15 to 71 d (median = 43 d), with from 26 to 405 locations per individual (median = 195 locations/ individual). Although these individuals moved a cumulative distance of at least 8,000 km over the duration of their tag attachments, median distances of locations from the tagging location for the different individuals ranged from 19.9 to 91.8 km, and the maximum distance any individual moved from where it was tagged was only 139 km (Schorr et al., 2009). Combined with long-term resightings of distinctive individuals off the island (McSweeney et al., 2007), such results suggest the existence of an island-resident population.