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

AUGUST 2005 FINAL REPORT
Information Specific to the Marianas MRA Study Area—Beaked whales may be expected to occur
in the area mostly 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—Life history data on beaked whale species are extremely limited for the
Cuvier’s beaked whale. 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). Analyses of stomach contents from captured and stranded
individuals suggest that beaked whales are deep-diving animals, feeding by suction (Heyning 1989;
Heyning and Mead 1996; Santos et al. 2001; MacLeod et al. 2003). Stomach contents of Cuvier’s
beaked whales primarily contain cephalopods, and rarely, fish (MacLeod et al. 2003). Dives
exceeding 45 min and longer have been documented for Cuvier's beaked whales (Jefferson et al.
1993); Baird et al. (2004) documented a dive up to 87 min in duration for a tagged individual. Johnson
et al. (2004) recorded dives as deep as 1,267 m.
Acoustics and Hearing—Very little information is available on characteristics of sound produced by
beaked whales. 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. Click pulses of Cuvier’s beaked whales recorded by Frantzis et al. (2002) had a peak
frequency between 13 and 17 kHz.
There is no direct information available on the 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).
♦ Blainville’s Beaked Whale (Mesoplodon densirostris)
Description—Blainville's beaked whales appear to reach a maximum of around 4.7 m in length and
weights up to 1,033 kg (Jefferson et al. 1993). Adults are blue-gray on their dorsal side and white
below (Jefferson et al. 1993). All Mesplodon species have a relatively small head, large thorax and
abdomen, and short tail. Mesoplodon species all have a pair of throat grooves on the ventral side of
the head on the lower jaw. Beaked whales in the genus Mesoplodon are characterized by the
presence of a single pair of sexually dimorphic tusks, which erupt only in adult males. The lower jaw
of the Blainville’s beaked whale is highly arched and massive flattened tusks extend above the upper
jaw in adult males (Jefferson et al. 1993).
Status—There are no abundance estimates for the Blainville’s beaked whale in this area. The
Blainville’s beaked whale is designated as data deficient on the IUCN Red List (Reeves et al. 2003).
Habitat Preferences—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). Most of the
ecological information regarding this species comes from the northern Bahamas (MacLeod et al.
2004; MacLeod and Zuur 2005). The Blainville’s beaked whale in the northern Bahamas was most
often sighted in waters with a bottom depth of 200 to 1,000 m (MacLeod and Zuur 2005); the majority
of its time was spent along the canyon wall, where water depth is less than 800 m (Claridge 2003;
MacLeod et al. 2004; MacLeod and Zuur 2005). In the Society Islands, Blainville’s beaked whales
were observed in waters with a bottom depth of 300 to 1,400 m (Gannier 2000). Ritter and Brederlau
(1999) reported sightings of this species in waters with a bottom depth less than 500 m, and as
shallow as 100 m, off the island of La Gomera in the Canary Islands. Both Baird et al. (2004) and
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