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

AUGUST 2005 FINAL REPORT
catches also have shown that the Bryde’s whale is not always a coastal species (Ohsumi 1977). The
Bryde’s whale appears to have a preference for water temperatures between approximately 15° and
20°C (Yoshida and Kato 1999).
Distribution—The Bryde’s whale is found in tropical and subtropical waters, generally not moving
poleward of 40° in either hemisphere (Jefferson et al. 1993). Long migrations are not typical of
Bryde’s whales, though limited shifts in distribution toward and away from the equator, in winter and
summer, respectively, have been observed (Cummings 1985). The Bryde’s whales’ large wintering
grounds may extend from the western North Pacific to the central North Pacific, with 20°N perhaps
being the northernmost boundary (Ohizumi et al. 2002). During the winter, Bryde’s whales are
distributed in the western North Pacific around the Mariana, Ogasawara, Kazan, and Phillippine
Islands, as well as near New Guinea (Ohizumi et al. 2002). Tagging data suggests that Bryde’s
whales undertake considerable east-west migrations, and that the stock in the western and central
North Pacific does the same (Kishiro 1996). In summer, the distribution of Bryde’s whales in the
western North Pacific extends as far north as 40°N, but many individuals remain in lower latitudes, as
far south as about 5°N. Data also suggest that winter and summer grounds partially overlap in the
central North Pacific (Kishiro 1996; Ohizumi et al. 2002). Bryde’s whales are also distributed in the
central North Pacific in summer; the southernmost summer distribution of Bryde’s whales inhabiting
the central North Pacific is about 20°N (Kishiro 1996). By November, Bryde’s whales are usually
absent from their central North Pacific summering area (Miyashita et al. 1995); in the western North
Pacific, they migrate as far south as the equator in winter (Kishiro 1996; Miyashita et al. 1996). In
March, Bryde’s whales are found at high densities in several areas of the central Pacific, from
approximately 175°E to 150°W and 15°N to 5°S (Miyashita et al. 1995). Some whales remain in
higher latitudes (around 25°N) in both winter and summer (Kishiro 1996).
Information Specific to the Marianas MRA Study Area—Bryde’s whales are seen year-round
throughout tropical and subtropical waters (Kato 2002). They have been reported to occur in both
deep and shallow waters globally. The Bryde’s whale is expected to occur from the 50 m isobath
to seaward of the Marianas study area and vicinity (Figure B-9). There is also a low or unknown
occurrence from the coastline, including lagoons, to the 50 m isobath. Bryde’s whales are
sometimes seen very close to shore and even inside enclosed bays (Best et al. 1984). There was
one sighting in July 1999, approximately 9.3 to 18.5 km west of FDM. Additionally, there was a
sighting 195 km southeast of Guam made during December 1996, which was reported to the
NOAA Fisheries for their Platforms of Opportunity Program (Figure B-9). There is one reported
stranding for this area that occurred in August 1978 (Eldredge 1991, 2003). Occurrence patterns
are expected to be the same throughout the year.
Behavior and Life History—This species is generally seen alone or in pairs (Tershy 1992), although
they can be seen in groups of up to 10 individuals (Miyazaki and Wada 1978). The Bryde’s whale
does not have a well-defined breeding season in most areas. There is a 2-year reproductive cycle
composed of 11 to 12 months gestation, 6 months of lactation, and 6 months resting (Kato 2002).
Bryde’s whales are lunge-feeders, feeding on fish and krill (Nemoto and Kawamura 1977). Cummings
(1985) reported that Bryde’s whales may dive as long as 20 min.
Acoustics and Hearing—Bryde’s whales produce low frequency tonal and swept calls similar to
those of other rorquals (Oleson et al. 2003). Calls vary regionally, yet all but one of the call types
have a fundamental frequency below 60 Hz; they last from one-quarter of a second to several
seconds; and they are produced in extended sequences (Oleson et al. 2003). While no data on
hearing ability for this species are available, Ketten (1997) hypothesized that mysticetes have acute
infrasonic hearing.
♦ Pygmy and Dwarf Sperm Whales (Kogia breviceps and Kogia sima, respectively)
Description—Pygmy sperm whales have a shark-like head with a narrow underslung lower jaw
(Jefferson et al. 1993). The flippers are set high on the sides near the head. The small falcate dorsal
fin of the pygmy sperm whale is usually set well behind the midpoint of the back (Jefferson et al.
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