Geographic and seasonal variation of blue whale calls in the North Pacific

The call characteristics and distribution of blue whales in the North Pacific were examined by use acoustic surveys. Two distinct vocalisation types have been previously attributed to from limited regions (cf. Thompson Friedl, 1982; Rivers, 1997). Hydrophone data sixteen sites for these whale vocalisations. There geographic seasonal differences between occurrence two types. hydrophones that more westerly recorded ‘northwestern’ vocalisation, those eastern ‘northeastern’ central both Northeastern vocalisations July-December northeast February-May tropical Pacific. Northwestern most often July-December, essentially absent March-May northwestern These results suggest different may represent at least groups