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

AUGUST 2005 FINAL REPORT
MacLeod et al. (2004) reported that Blainville’s beaked whales are found in shallower waters than
Cuvier’s beaked whales in the Hawaiian Islands and the Bahamas, respectively.
Distribution—The Blainville’s beaked whale occurs in temperate and tropical waters of all oceans
(Jefferson et al. 1993). The distribution of Mesoplodon species in the western North Atlantic may
relate to water temperature (Mead 1989; MacLeod 2000), with Blainville's beaked whale generally
occurring in warmer southern waters (MacLeod 2000). In the eastern Pacific, where there are about a
half-dozen Mesoplodon species known, the Blainville’s beaked whale is second only to the pygmy
beaked whale (Mesoplodon peruvianus) in abundance in tropical waters (Wade and Gerrodette
1993). In waters of the western Pacific, where the pygmy beaked whale is not considered to be
present, the Blainville’s beaked whale is probably the most common and abundance tropical species
of Mesoplodon (Jefferson personal communication).
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
range for this species. Beaked whales may be expected to occur in the area including and
seaward of the shelf break (Figure B-11). There is a low or unknown occurrence of beaked
whales on the shelf between the 50 m isobath and the shelf break, which takes into account that
deep waters come very close to the shore in this area. In some locales, beaked whales can be
found in waters over the shelf, so it is possible that beaked whales have similar habitat
preferences here. Occurrence patterns are expected to be the same throughout the year.
Behavior and Life History—Observed group sizes for the Blainville’s beaked whale are generally
small, with single individuals or pairs being the most common (Jefferson et al. 1993). In the northern
Bahamas, groups of one to seven individuals have been reported; groups in this area contain a
number of adult female and juveniles, and it is rare for more than one adult male to be present
(MacLeod et al. 2004). Most sightings are brief; these whales are often difficult to approach and they
actively avoid aircraft and vessels (Würsig et al. 1998). Life history data for the Blainville’s beaked
whale are extremely limited. All species of beaked whales probably feed at or close to the bottom in
deep oceanic waters, taking whatever suitable prey they encounter or feeding on whatever species
are locally abundant (MacLeod et al. 2003). Analysis of stomach contents from captured and
stranded individuals suggests that beaked whales are deep-diving animals, feeding by suction
predominantly on mesopelagic fish and squid or deepwater benthic invertebrates (Mead 1989;
Heyning and Mead 1996; Santos et al. 2001; MacLeod et al. 2003). Mesoplodon species feed on
small cephalopods (Mead 1989; MacLeod et al. 2003). Dives exceeding 45 min and longer have been
documented for Blainville's beaked whales (Jefferson et al. 1993). Tagged Blainville’s beaked whales
have been recorded to dive to depths as great as 975 m (Baird et al. 2004; Johnson et al. 2004).
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. Recently, an acoustic recording tag was attached to two Blainville’s
beaked whales in the Ligurian Sea (Johnson et al. 2004). This species was found to be highly vocal,
producing high-frequency echolocation clicks with no significant energy below 20 kHz (Johnson et al.
2004). The source level of these clicks ranged from 200 to 220 dB re 1 µPa-m (Johnson et al. 2004).
Madsen et al. (2005) reported interclick intervals of 300 to 400 ms.
There is no direct information available on the actual 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 direct evidence
to support this idea (MacLeod 1999).
♦ Ginkgo-toothed Whale (Mesoplodon ginkgodens)
Description—The maximum known sizes for ginkgo-toothed whales are 4.9 m for females and 4.8 m
for males (Jefferson et al. 1993). All Mesoplodon species have a relatively small head, large thorax
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