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

AUGUST 2005 FINAL REPORT
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. Adult male ginkgo-toothed whales appear to be dark gray over the
entire body with a faint light patch on the anterior half of the rostrum and lower jaw, while females are
apparently lighter in color (Mead 1989). They are not as heavily scarred as are other Mesoplodon
spp. 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. In the ginkgo-toothed beaked whale, the
tusks of males are wide and flattened with a small denticle at their apex (Mead 1989).
Status—There are no abundance estimates for the ginkgo-toothed beaked whale in this area. The
ginkgo-toothed 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). Palacios
(1996) suggested based on stranding records in the eastern Pacific Ocean, that this species may
select relatively cool, upwelling-modified habitats, such as those found in the California and Perú
Currents and along the equatorial front.
Distribution—The ginkgo-toothed whale is known only from strandings (there are no confirmed
sightings) in temperate and tropical waters of the Pacific and Indian Oceans (Mead 1989; Palacios
1996).
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. Very
little is known about the distribution of this species. What is known of its range suggests any
records in the Marianas MRA study area and vicinity would be rare (Jefferson personal
communication).
Behavior and Life History—Little life history data is available for the ginkgo-toothed whale.
Durations of long dives for Mesoplodon species are over 20 min (Barlow 1999; Baird et al. 2004). 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).
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. There is no information available for ginkgo-toothed whale
vocalizations.
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 empirical
evidence to support this idea (MacLeod 1999).
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