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

AUGUST 2005 FINAL REPORT
sightings that could occur just inshore of the shelf break, since deep water is very close to shore
at these islands. Occurrence patterns are assumed to be the same throughout the year.
Behavior and Life History—Almost nothing is known about the reproductive biology and social
organization of this species. This species usually forms relatively small groups (Ross and
Leatherwood 1994). Pygmy killer whales eat mostly fish and squid, and sometimes attack other
dolphins (Perryman and Foster 1980; Ross and Leatherwood 1994). They occur in small to moderate
herds of most often less than 50 to 60 individuals. There is no information available on diving
behavior of this species.
Acoustics and Hearing—The pygmy killer whale emits short duration, broadband signals similar to a
large number of other delphinid species (Madsen et al. 2004). Clicks produced by pygmy killer whales
have centroid frequencies between 70 and 85 kHz; there are bimodal peak frequencies between 45
and 117 kHz; the estimated source levels are between 197 and 223 dB re 1 µPa-m (Madsen et al.
2004). These clicks possess characteristics of echolocation clicks (Madsen et al. 2004). There are no
hearing data available for this species.
♦ False Killer Whale (Pseudorca crassidens)
Description—The false killer whale is a large, dark gray to black dolphin with a faint gray patch on
the chest, and sometimes light gray areas on the head (Jefferson et al. 1993). The false killer whale
has a long slender body, a rounded overhanging forehead, and little or no beak (Jefferson et al.
1993). The dorsal fin is falcate and slender. The flippers have a characteristic hump on the leading
edge—this is perhaps the best characteristic for distinguishing this species from the other “blackfish”
(pygmy killer, melon-headed, and pilot whales) (Jefferson et al. 1993). Individuals reach maximum
lengths of 6.1 m (Jefferson et al. 1993).
Status—This species is designated as least concern on the IUCN Red List (Reeves et al. 2003).
Nothing is known of the stock structure of false killer whales in the North Pacific Ocean. There are
estimated to be about 6,000 false killer whales in the area surrounding (mostly north of) the Mariana
Islands (Miyashita 1993).
Habitat Preferences—This species is found primarily in oceanic and offshore areas, though they do
approach close to shore at oceanic islands (Baird 2002). False killer whales have been known to
approach very close to shore in such areas as the inshore waters of Washington and British
Columbia (Baird et al. 1989), the coast and estuaries of China (Zhou et al. 1982), the Marquesas
Islands of French Polynesia (Gannier 2002), and Lembata Island of the Indonesian archipelago
(Rudolph et al. 1997). Inshore movements are occasionally associated with movements of prey and
shoreward flooding of warm ocean currents (Stacey et al. 1994).
Distribution—False killer whales are found in tropical and temperate waters, generally between 50ºS
and 50ºN latitude with a few records north of 50ºN in the Pacific and the Atlantic (Odell and McClune
1999). Seasonal movements in the western North Pacific may be related to prey distribution (Odell
and McClune 1999). Baird et al. (2005a) noted considerable inter-island movements of individuals in
the Hawaiian Islands.
Information Specific to the Marianas MRA Study Area—There are two unpublished sightings and
no reported strandings of the false killer whale in the Marianas study area and vicinity. The false
killer whale is an oceanic species, occurring in deep waters, and is known to occur close to shore
near oceanic islands (Baird 2002, Jefferson personal communication). The false killer whale in
the Marianas study area and vicinity is expected to occur seaward of the 50 m isobath (Figure B-
22). There is also a low or unknown occurrence from the coastline to the 50 m isobath which
would take into account any sightings that could occur closer to shore since deep water is very
close to shore at these islands. Occurrence patterns are assumed to be the same throughout the
year.
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