Although considerable information is available on residency patterns and spatial use of odontocetes in the eastern half of the Hawai‘i Range Complex (HRC), much less is known about odontocetes in the western half of the HRC. In the first year of a three-year effort we undertook surveys off O‘ahu (in October 2010) and Kaua‘i (in February 2011) to examine spatial use and residency patterns using satellite tags, as well as obtaining individual identification photographs and biopsy samples for assessment of population identity and structure. In 18 days of combined effort we encountered 43 groups of 10 species of odontocetes, deployed 15 satellite tags on three species, obtained over 23,000 photographs for contribution to photo-identification catalogs, and obtained 39 genetic samples of six species. Location data were obtained from satellite tags for periods from 7.2 to 223 days (median = 36.8 days). Tags deployed on three Hawaiian insular false killer whales provided the most detailed dive data yet available for this species and movement data will be contributed to studies of critical habitat for this species. Satellite tags were deployed on individuals in two groups of pygmy killer whales, one of the least known species of delphinids world-wide and a rare species in Hawaiian waters. Habitat use of the two groups differed substantially, and may be related to the residency of groups as evident from photo-identification data. Most individuals in one group had been previously photo-identified off O‘ahu (12 of 15), some in up to three previous years, and the group spent the 30 days post-tagging along the south and west shores of O‘ahu and off the western end of Penguin Bank, remaining primarily in water depths of less than 1,000 m (median depth = 576 m). Although 17 individuals in the other group were photo-identified, none had not been previously photographed off O‘ahu, although one had been previously documented off each of Lana‘i and Hawai‘i. The tagged individual from this group moved repeatedly from less than 1,000 m depth to over 3,000 m depth off O‘ahu, spending most of its time over the 7 days of tracking in water depths greater than 1,000 m (median depth = 2,487 m). Short-finned pilot whales were tagged both off O‘ahu (six individuals) and Kaua‘i (three individuals). As with the pygmy killer whales, considerable variation in movement patterns and habitat use were apparent with tagged short-finned pilot whales, with some groups remaining close to the area of tagging, suggesting residency, and others moving over very wide ranges and using a broad range in depths, illustrating different ranging patterns that may have implications for exposure and responses to Navy exercises. Combined these studies provide the most detailed information yet available on spatial use and ranging patterns of both pygmy killer whales and short-finned pilot whales in the western half of the HRC.
Citation:
Baird, R.W., G.S. Schorr, D.L. Webster, S.D. Mahaffy, J.M. Aschettino, and T. Cullins. 2011. Movements and Spatial Use of Satellite-Tagged Odontocetes in the Western Main Hawaiian Islands: Results of Field Work Undertaken off O‘ahu in October 2010 and Kaua‘i in February 2011. Annual progress report under Grant No. N00244-10-1-0048 from the Naval Postgraduate School.
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