Two populations or stocks of false killer whales have recently been recognized within the Hawaiian Exclusive Economic Zone (EEZ) (Carretta et al. 2011). An insular, or island-associated, population is found around the main Hawaiian Islands, and a pelagic, or open-ocean, population, has been documented in offshore waters (Chivers et al. 2007, 2010; Baird et al. 2008,
2010). Based on movements of satellite-tagged individuals, the range of the Hawaiian insular population extends throughout the main Hawaiian Islands from Ni‘ihau in the west to Hawai‘i Island in the east, and movements out to 122 km from shore have been documented (Baird et al. 2010, 2011). Individuals can be attributed to one or the other population based on genetics (i.e., mitochondrial haplotypes; Chivers et al. 2007, 2010), or on photo-identification matches of distinctive individuals. While the number of distinctive individuals from the pelagic population that have been photographically documented is small (29 noted in Baird 2009) and no resightings of individuals have been documented to date, the majority of individuals in the insular population have been photographically documented multiple times (Baird et al. 2008; Baird 2009). The insular population is relatively small (estimated at about 150 individuals, see Oleson et al. 2010), and Baird et al. (2008) noted that, on average, within a group of insular individuals, 75% of distinctive individuals photographed have been previously documented, thus assigning individuals to one or the other population based on photo-identification can be done with some certainty if more than a few distinctive individuals from any group are photo-identified.
Baird (2009) noted that of all the distinctive individuals documented within 40 km of shore of the main Hawaiian Islands (524 identifications of >100 individuals) only 13 identifications did not link by association to the insular social network. Four of these 13 individuals were documented off the island of Hawai‘i, in three encounters where only single individuals (two encounters) or a pair of individuals were identified, thus the likelihood of finding matches with the Hawai‘i insular population is small. Nine identifications were available from the island of Kaua‘i, including seven from one encounter in July 2008, but none matched to the insular social network (Baird 2009). Baird (2009) noted that, given the small sample size, it was unclear whether these individuals photo-identified off Kaua‘i were part of the insular population, part of the pelagic population, or members of a third, as yet un-described, population.
Citation:
Baird, R.W., E.M. Oleson, J. Barlow, A.D. Ligon, A.M. Gorgone, and S.D. Mahaffy. 2011. Photo-Identification and Satellite Tagging of False Killer Whales during HICEAS II: Evidence of an Island-Associated Population in the Papahānaumokuākea Marine National Monument. Document PSRG-2011-16 presented to the Pacific Scientific Review Group, Seattle, November 2011.
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