There are two populations of false killer whales within the Hawaiian Exclusive Economic Zone, an insular population around the main Hawaiian Islands and an offshore population. In
order to assess the degree of overlap of individuals from these populations, surveys offshore of the island of Hawai‘i were undertaken in 2008, using a medium-sized charter vessel to survey further from shore than has been undertaken in previous small-boat surveys. In 10 days of survey effort 1,850 km of trackline were covered, with more than 60% of the effort in depths >4,000 m, and survey coverage out to 129 km from shore. Forty sightings of nine species of odontocetes were documented, with high sighting rates of species typically seen in very deep waters in Hawai‘i, including rough-toothed dolphins (n = 11 sightings), striped dolphins (n = 5 sightings), and Risso’s dolphins (n = 3 sightings). Three sightings of false killer whales were documented from 106-124 km offshore, all on Jaggar Seamount. A comparison of photographs of 13 distinctive/very distinctive individuals to a catalog of 152 distinctive/very distinctive individuals photo-identified around the main Hawaiian Islands revealed no matches, suggesting the individuals documented were part of the offshore population. Genetic analyses of three biopsy samples collected from two of the groups encountered confirmed these individuals were part of the offshore population.
Citation:
Baird, R.W., G.S. Schorr, D.L. Webster, D.J. McSweeney, A.M. Gorgone, and S.J. Chivers. 2008. A Survey to Assess Overlap of Insular and Offshore False Killer Whales (Pseudorca crassidens) off the Island of Hawai‘i. Report prepared under Order No. AB133F07SE4484 for the Protected Species Division, Pacific Islands Fisheries Science Center, National Marine Fisheries Service, Honolulu, HI.
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