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

AUGUST 2005 FINAL REPORT
♦ Hubbs’ Beaked Whale (Mesoplodon carlhubbsi)
Description—The body and head shape of the Hubbs’ beaked whale is typical of other Mesoplodon
species. All Mesoplodon species have a relatively small head, large thorax and abdomen, and short
tail. The Hubbs’ beaked whale is medium-sized, reaching a maximum length of about 5.3 m and a
weight of approximately 1,500 kg (Mead et al. 1982). The body coloration is medium to dark gray,
with the underside of the flukes lighter than the dorsal side (Mead et al. 1982). The most prominent
external feature of this species is the pigmentation of the head, particularly in the adult male, which
has a white rostrum and a white “skull cap” or “beanie” in the melon in front of and around the
blowhole (Mead et al. 1982). 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 male
Hubbs’ beaked whale has a massive flattened tusk in the middle of each side of the lower jaw, which
protrudes above the level of the upper jaw (Heyning 1984).
Status—There are no abundance estimates available for the Hubbs’ beaked whale in this area. The
Hubbs’ 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). Along the
Pacific Coast of the North America, the distribution of this species corresponds with the dilute and
upwelling domains on the surface and with the confluence of the subarctic current and the California
Current systems at depth (Mead et al. 1982).
Distribution—The Hubbs’ beaked whale appears to be restricted to the North Pacific Ocean (Mead
et al. 1982; Houston 1990; MacLeod et al. in press). Nearly all records to date have been strandings
along the west coast of North America and in Japan. However, there have also been several
sightings in relatively nearshore waters of the Pacific Northwest, and MacLeod et al. (in press)
speculated that the distribution might actually be continuous across the North Pacific between about
30° and 45°N. This, however, remains to be confirmed.
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. The
range of the Hubbs’ beaked whale is not well-known. While it is possible that this species could
occur in the Marianas MRA study area and vicinity, its apparent preference for colder waters
suggests that any occurrence would be extralimital.
Behavior and Life History—Life history data for the Hubbs’ beaked whale are extremely limited.
Calving in this species most probably takes place in summer (Mead et al. 1982; Willis and Baird
1998b).
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). Stomach contents of a stranded Hubbs’ beaked whale consisted of squid
beaks, fish otoliths, and fish bones (Mead et al. 1982).
3-35