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

AUGUST 2005 FINAL REPORT
Acoustics and Hearing—MacLeod (1999) suggested that beaked whales use frequencies of
between 300 Hz and 129 kHz for echolocation, and between 2 and 10 kHz, and possibly up to 16
kHz, for social communication. Vocalizations recorded from two juvenile Hubbs’ beaked whales
consisted of low and high frequency click trains ranging in frequency from 300 Hz to 80 kHz and
whistles with a frequency range of 2.6 to 10.7 kHz and duration of 156 to 450 msec (Lynn and Reiss
1992; Marten 2000).
There is no direct information available on the exact hearing abilities of beaked whales (MacLeod
1999). Beaked whale ears are predominantly adapted to hear ultrasonic frequencies (MacLeod
1999). Based on the anatomy of the ears of beaked whales, these species may be more sensitive
than other cetaceans to low frequency sounds; however, as noted earlier, there is no empirical
evidence to support this idea (MacLeod 1999). There are no hearing data available for the Hubbs’
beaked whale.
♦ Longman’s Beaked Whale (Indopacetus pacificus)
Description—This species was often referred to as the “tropical bottlenose whale” in the past. This
was due to the fact that whales now known to be of this species had been sighted in various locations
in the tropical/subtropical Indo-Pacific but not identified to species (Pitman et al. 1999). At the time,
this species was known only from a handful of skulls, and the external appearance of the species was
undescribed. Until several stranded specimens were identified as Longman’s beaked whales based
on skull morphology and genetics (Dalebout et al. 2003), the sighted whales were thought to be
members of the Hyperoodon genus (either far-ranging southern bottlenose whales or possibly an
undescribed tropical species). We now know these animals to be Longman’s beaked whales. The
Longman’s beaked whale looks very much like the southern bottlenose whale (Hyperoodon
planifrons) in general shape and coloration, though is more slender (Pitman et al. 1999; Dalebout et
al. 2003). The estimated adult length is 7 to 8 m (Pitman et al. 1999). The tall, falcate dorsal fin is set
far back on the body (Pitman et al. 1999; Dalebout et al. 2003). The head has a well-rounded melon
in profile and the beak length is variable, suggesting developmental changes in beak size (Pitman et
al. 1999; Dalebout et al. 2003). This species has a single pair of teeth that are set close to the tip of
the lower jaw; it is suspected that, like most other beaked whales species, only adult males will have
erupted teeth (Dalebout et al. 2003). The body color has been described as variable but is dominated
by tan to grayish-brown tones (Pitman et al. 1999). Young animals are distinctively patterned; they
are darker gray-brown above with a conspicuous pale melon and white sides (Pitman et al. 1999).
The light area on the head extends only as far back as the blowhole.
Status—Longman’s beaked whale is considered to be a relatively rare beaked whale species
(Pitman et al. 1999; Dalebout et al. 2003). There is no designation for this species on the IUCN Red
List. There are no abundance estimates for this species in this area.
Habitat Preferences—Beaked whale abundance off the eastern U.S. may be highest in association
with the Gulf Stream and associated warm-core rings (Waring et al. 1992). In summer, beaked
whales use the shelf edge region off the northeast U.S. as primary habitat (Waring et al. 2001).
Ferguson et al. (2001) noted that offshore waters beyond the continental slope are not often identified
as beaked whale habitat, yet this may be a function of lack of survey effort rather than a reflection of
the animals’ true habitat. Longman’s beaked whale appears to have a preference for warm tropical
water, with most sightings occurring in waters with a SST warmer than 26ºC (Pitman et al. 1999).
Distribution—Beaked whales normally inhabit deep ocean waters (>2,000 m) or continental slopes
(200 to 2,000 m), and only rarely stray over the continental shelf (Pitman 2002). Longman’s beaked
whale is known from tropical waters of the Pacific and Indian Oceans (Pitman et al. 1999; Dalebout et
al. 2003). Ferguson and Barlow (2001) reported that all Longman’s beaked whale sightings were
south of 25ºN.
Information Specific to the Marianas MRA Study Area—There are no occurrence records for this
species in the Marianas study area and vicinity, but this area is within the known distribution
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