January 4, 2011
Principal Investigator: Karen Martien, Marine Mammal Genetics Group
There is currently a single recognized stock of melon-headed whales (MHWs; Peponocephala electra) in U.S. territorial waters - the Hawaiian stock, which encompasses the entire Hawaiian EEZ. However, recent photo-identification work suggests the presence of at least two populations around the main Hawaiian Islands that may warrant protection as separate stocks (Aschettino 2010). The Main Hawaiian Islands population is a large population (N=5794, CV=0.20) that ranges through the main Hawaiian Island chain, while the Hawaiæi Resident population is restricted to a small, shallow-water region off the northwest coast of the island of Hawaiæi and is estimated to contain only 447 (CV=0.12) individuals (Aschettino 2010). MHWs are also known to inhabit the waters around the Palmyra and Johnston Atolls. Even less is known about these animals than the Hawaiian animals, and they are not currently included in the U.S. Pacific Marine Mammal Stock Assessment Reports.
Preliminary analyses of mtDNA sequence data from 115 MHWs suggest significant differentiation between Hawaiæi, Palmyra, and Johnston. We also detected significant differentiation between the Main Hawaiian Islands population and the Hawaiæi Resident population, despite the small sample size (n=10) for the latter. In 2011, we are planning to expand this project through the addition of more samples and the use of nuclear markers.
Aschettino, J. 2010. Population size and structure of melon-headed whales (Peponocephala electra) around the main Hawaiian Islands: evidence of multiple populations based on photographic data. M.Sc. thesis, Hawaiæi Pacific University. 125pp.
Brownell, R.L., K. Ralls, S. Baumann-Pickering, and M.M. Poole. 2009. Behavior of melon-headed whales, Peponocephala electra, near oceanic islands. Marine Mammal Science 25:639-658.