Marine Resources Assessment for the Marianas Operating ... - SPREP

AUGUST 2005 FINAL REPORT
Behavior and Life History—This species may occur in large groups (group sizes as large as 300
have been reported) (Brown et al. 1966). The known maximum dive depth is about 500 m (Odell and
McClune 1999). No seasonality in reproduction is known for the false killer whale (Jefferson et al.
1993). False killer whales primarily eat deep-sea cephalopods and fish (Odell and McClune 1999),
but they have been known to attack other cetaceans, including dolphins (Perryman and Foster 1980;
Stacey and Baird 1991), sperm whales (Palacios and Mate 1996), and baleen whales (Jefferson
personal communication). False killer whales in many different regions are known to take tuna from
longlines (Mitchell 1975; Nitta and Henderson 1993).
Acoustics and Hearing—The dominant frequencies of false killer whale whistles are 4 to 9.5 kHz;
those of their clicks are 25 to 30 kHz and 95 to 130 kHz (Thomas et al. 1990b; Thomson and
Richardson 1995). The source level is 220 to 228 dB re 1 µPa-m (Ketten 1998). Best hearing
sensitivity measured for a false killer whale was around 16 to 64 kHz (Thomas et al. 1988, 1990b).
♦ Killer Whale (Orcinus orca)
Description—This is probably the most instantly-recognizable of all the cetaceans. The black-andwhite
color pattern of the killer whale is striking, as is the tall, erect dorsal fin of the adult male 1.0 to
1.8 m in height). The white oval eye patch and variably-shaped saddle patch, in conjunction with the
shape and notches in the dorsal fin, help in identifying individuals. The killer whale has a blunt head
with a stubby, poorly-defined beak, and large, oval flippers. Females may reach 7.7 m in length and
males 9.0 m (Dahlheim and Heyning 1999). The killer whale is the largest member of the dolphin
family.
Status—This species is designated as lower risk on the IUCN Red List (Reeves et al. 2003). There
are no abundance estimates available for the killer whale in this area. Little is known of stock
structure of killer whales in the North Pacific, with the exception of the northeastern Pacific where
resident, transient, and offshore stocks have been described for coastal waters of Alaska, British
Columbia, and Washington to California (Carretta et al. 2004).
Habitat Preferences—Killer whales can be found in the open sea, as well as in coastal areas
(Dahlheim and Heyning 1999). Offshore concentrations of killer whales in the eastern tropical Pacific
occur within the divergence zones of the NEC and the Equatorial Counter Current (Dahlheim et al.
1982). Killer whales have the most ubiquitous distribution of any species of cetacean, and they have
been observed in virtually every marine habitat, from the tropics to the poles, and from shallow,
inshore waters (and even rivers) to deep, oceanic regions (Dahlheim and Heyning 1999). Although
they are not common in most of these habitat types, there is a possibility of seeing killer whales just
about anywhere in the marine environment.
Distribution—This is a cosmopolitan species found throughout all oceans and contiguous seas, from
equatorial regions to the polar pack-ice zones. This species has sporadic occurrence in most regions
(Ford 2002), including the Micronesia region (Reeves et al. 1999). Though found in tropical waters
and the open ocean, killer whales as a species are most numerous in coastal waters and at higher
latitudes (Mitchell 1975; Miyazaki and Wada 1978; Dahlheim et al. 1982).
Sightings in most tropical waters, although not common, are widespread (Visser and Bonoccorso
2003). Japanese tuna longline fishermen and Japanese whaling or whale sighting vessels reported
killer whale presence in Pacific equatorial waters (Iwashita et al. 1963; Miyashita et al. 1995), though
Reeves et al. (1999) noted that records from fishermen have reliability issues, since they are often not
sufficiently well-documented. Observations from Japanese whaling or whale sighting vessels are
more credible (Miyashita et al. 1995) and indicate concentrations of killer whales north of the Northern
Mariana Islands.
Information Specific to the Marianas MRA Study Area—Killer whales in general are uncommon in
most tropical areas (Jefferson personal communication). The distinctiveness of this species would
lead it to be reported more than any other member of the dolphin family, if it occurs in a certain
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