Studies of odontocete population structure in Hawaiian waters: results of a survey through the main Hawaiian Islands in May and June 2003

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Citation

Baird, R.W., D.J. McSweeney, D.L. Webster, A.M. Gorgone and A.D. Ligon. 2003. Studies of odontocete population structure in Hawaiian waters: results of a survey through the main Hawaiian Islands in May and June 2003. Report prepared under Contract No. AB133F-02-CN-0106 from the National Oceanic and Atmospheric Administration, Western Administrative Support Center, 7600 Sand Point Way N.E., Seattle, WA 98115 USA

Summary

We undertook a survey of the main (windward) Hawaiian Islands during May and June 2003 to examine odontocete population structure. Our goals were: 1) to collect genetic samples to be used for examination of inter- and intra-Hawaiian population structure; 2) to collect photoidentification data to examine movements of individuals between islands and as a basis for population assessment; and 3) to examine habitat use in relation to potential deep-water barriers to movement. A total of 521 hours were spent on-effort using two vessels, and 8,461 km of trackline were covered from Kaua’i and Ni’ihau east to Hawai’i in water depths to over 4,000 m. There were 140 sightings of 14 species of odontocetes. Species most commonly seen were bottlenose dolphins (41 groups), pantropical spotted dolphins (25 groups), spinner dolphins (19 groups), short-finned pilot whales (17 groups), rough-toothed dolphins (13 groups), and dwarf sperm whales (8 groups). A total of 116 bottlenose dolphins were photo-identified, and photographic identifications were compared to a catalog of bottlenose dolphins from 2000-2002 obtained from the islands of Hawai‛i, Maui/Lana’i, and O’ahu. There were 13 between-year resightings, all to the area in which the individuals were first documented. The between-year resighting rate for bottlenose dolphins off Maui and Lana’i was approximately 70%. Using this rate of re-sightings, if movements between island areas were freely occurring, 70 of the 101 individuals documented off Kaua’i/Ni’ihau, O’ahu, and Hawai’i, should have been previously sighted off Maui/Lana’i. With no inter-island movements documented, it is clear that movements between island areas are rare, if not completely absent. While rough-toothed dolphins were the fifth-most common species overall, off Kaua’i/Ni’ihau they were the second-most encountered species (11 groups). Photo-identification efforts resulted in documentation of 94 distinctive individuals, with only eight individuals being re-sighted, suggesting a total population size much greater than 94. Other species sighted during this survey included dense-beaked whales (5 groups), melon-headed whales (3 groups), false killer whales (1 group), killer whales (1 group), pygmy sperm whales (1 group), pygmy killer whales (1 group), striped dolphins (1 group), and a single sperm whale. Genetic sampling resulted in a total of 346 samples from nine species. Combined with previously available samples this should allow for intra-Hawai’i assessment of genetic differentiation of four species, and assessment between Hawai’i and elsewhere of at least seven species. 
 

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