Diving behavior of a false killer whale, Pseudorca crassidens, in the Kuroshio—Oyashio transition region and the Kuroshio front region of the western North Pacific

摘要

False killer whales, Pseudorca crassidens, are mid-sized toothed whales reaching about 6.1 m in body length (Odell and McGlune 1999). They are found primarily in deep water and offshore areas in all tropical and temperate oceans and usually travel ingroups of 20-100 individuals (Odell and McGlune 1999, Baird 2002). In Japan, they appear to be relatively common in coastal waters (Odell and McGlune 1999) and have been target species of drive fisheries. We studied their diving behavior related to foraging in waters of the western North Pacific Ocean. Here, the confluence of the transition waters of the western North Pacific, where the Kuroshio current (a strong subtropical western boundary current in the western North Pacific, flowing in a westerly direction) and the Oyashio current (a cold subarctic ocean current that flows south and circulates counterclockwise in the western North Pacific Ocean) produce a complex environment affecting vertical distribution patterns of various marine organisms (Watanabe etal. 1999, 2006). This is the first report concerning false killer whale diving behavior associated with oceanographic environments and the first to analyze time-serial depth data recorded by a pop-up archival transmitting (PAT) tag.