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

AUGUST 2005 FINAL REPORT
in the Micronesia region is almost entirely lacking, except for near the Solomon Islands (Reeves et al.
1999).
Information Specific to the Marianas MRA Study Area—There are no occurrence records for the
blue whale in the Marianas study area and vicinity, but this area is within the known distribution
range for this species. There is a low or unknown occurrence of the blue whale seaward of the 50
m isobath. This takes into consideration the endangered status of this species, the probability of
encountering this species in both coastal and oceanic waters, and the unknown possibility that
this species might occur in this area (Figure B-6). Occurrence patterns are expected to be the
same throughout the year, reflecting our lack of knowledge and the possibility of year-round
residents, but with a higher probability during winter and the adjacent months from November to
May (Jefferson personal communication).
Behavior and Life History—Blue whales are found singly or in groups of two or three (Yochem and
Leatherwood 1985). As noted by Wade and Friedrichsen (1979), apparently solitary whales are likely
part of a large dispersed group. Blue whales, like other rorquals, feed by “gulping” (Pivorunas 1979)
almost exclusively on krill (Nemoto and Kawamura 1977). Female blue whales reach sexual maturity
at 5 to 15 years of age (Yochem and Leatherwood 1985). There is usually a two-year interval
between calves. Calving occurs primarily during the winter (Yochem and Leatherwood 1985).
The usual duration of blue whale dives is 3 to 20 min (Wynne and Schwartz 1999). Croll et al. (2001)
determined that blue whales dived to an average of 140.0 m (+S.D. 46.01) and for 7.8 (+S.D. 1.89)
min when foraging and to 67.6 m (+S.D. 51.46) and for 4.9 (+S.D. 2.53) min when not foraging.
Calambokidis et al. (2003) deployed tags on blue whales and collected data on dives as deep as 300
m.
Acoustics and Hearing—Blue whale vocalizations are long, patterned low-frequency sounds with
durations up to 36 sec (Thomson and Richardson 1995) repeated every 1 to 2 min (Mellinger and
Clark 2003). Their frequency range is 12 to 400 Hz, with dominant energy in the infrasonic range at
12 to 25 Hz (Ketten 1998; Mellinger and Clark 2003). Source levels are up to 188 dB re 1 µPa-m
(Ketten 1998; McDonald et al. 2001). During the Magellan II Sea Test (at-sea exercises designed to
test systems for antisubmarine warfare), off the coast of California in 1994, blue whale vocalization
source levels at 17 Hz were estimated in the range of 195 dB re 1 µPa-m (Aburto et al. 1997).
Vocalizations of blue whales appear to vary among geographic areas (Rivers 1997), with clear
differences in call structure suggestive of separate populations for the western and eastern regions of
the North Pacific (Stafford et al. 2001). While no data on hearing ability for this species are available,
Ketten (1997) hypothesized that mysticetes have acute infrasonic hearing.
♦ Sperm Whale (Physeter macrocephalus)
Description—The sperm whale is the largest toothed whale species. Adult females can reach 12 m
in length, while adult males measure as much as 18 m in length (Jefferson et al. 1993). The head is
large (comprising about one-third of the body length) and squarish. The lower jaw is narrow and
underslung. The blowhole is located at the front of the head and is offset to the left (Rice 1989).
Sperm whales are brownish gray to black in color with white areas around the mouth and often on the
belly. The flippers are relatively short, wide, and paddle-shaped. There is a low rounded dorsal hump
and a series of bumps on the dorsal ridge of the tailstock (Rice 1989). The surface of the body behind
the head tends to be wrinkled (Rice 1989).
Status—Sperm whales are classified as endangered under the ESA and are designated as
vulnerable by the IUCN Red List (Reeves et al. 2003). There is no designated critical habitat for this
species in the North Pacific. For management purposes, the IWC has divided the North Pacific into
two management regions defined by a zig-zag line which starts at 150°W at the equator, is at 160°W
between 40° to 50°N, and ends up at 180°W north of 50°N (Donovan 1991).
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