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

AUGUST 2005 FINAL REPORT
Information Specific to the Marianas MRA Study Area—The expected occurrence for endangered marine
mammals is based primarily on the occurrence of the sperm whale but the humpback whale’s occurrence
patterns were also considered. Throughout the year, endangered marine mammals in the Marianas MRA
study area are expected to occur seaward of the shelf break into open ocean waters (Figure B-2). This is
based on expected occurrence of the sperm whale in this area. There is a low or unknown occurrence of
endangered marine mammals from the coastline (excluding harbors and coastlines) to the shelf break,
except during June through September when there is no possible occurrence of endangered marine
mammals (specifically, the humpback whale) in lagoons (Figure B-2).
♦ North Pacific Right Whale (Eubalaena japonica)
Description—Until recently, right whales in the North Atlantic and North Pacific were classified
together as a single species, referred to as the “northern right whale.” Genetic data indicate that these
two populations represent separate species: the North Atlantic right whale (Eubalaena glacialis) and
the North Pacific right whale (Eubalaena japonica) (Rosenbaum et al. 2000).
Right whales have a robust body shape; overall body color is black, although many individuals also
have irregular white patches on their undersides (Reeves and Kenney 2003). There is no dorsal fin
on the broad back. The largest recorded North Pacific right whales are an 18.3 m female and a 16.4
m male (Omura et al. 1969); North Pacific right whales are larger than their North Atlantic
counterparts (Reeves and Kenney 2003). The head is nearly one-third of the total body length. The
jawline is arched and the upper jaw is very narrow in dorsal view. The head is covered with irregular
whitish patches called “callosities,” which have whale lice attached.
Status—The North Pacific right whale is perhaps the world’s most endangered large whale species
(Perry et al. 1999; IWC 2001). North Pacific right whales are classified as endangered both under the
ESA and on the IUCN Red List (Reeves et al. 2003). There are insufficient genetic or resighting data
to address whether there is support for the traditional separation into eastern and western stocks
(Brownell et al. 2001); however, Clapham et al. (2004) noted that north-south migratory movements
support the hypothesis of two largely discrete populations of right whales in the eastern and western
North Pacific. No reliable population estimate presently exists for this species; the population in the
eastern North Pacific is considered to be very small, perhaps only in the tens of animals (NMFS 2002;
Clapham et al. 2004), while in the western North Pacific, the population may number at least in the
low hundreds (Brownell et al. 2001; Clapham et al. 2004). There is no designated critical habitat for
the North Pacific right whale (NMFS 2002).
Habitat Preferences—Feeding habitat for right whales is defined by the presence of sufficiently high
densities of prey, especially calanoid copepods (Reeves and Kenney 2003). Development of those
patches is essentially a function of oceanic conditions, such as SST, stratification, bottom topography,
and currents, which concentrate zooplankton, and concentration is probably enhanced by the
behavior of the organisms themselves (Beardsley et al. 1996; Tynan et al. 2001). The shift in Bering
Sea right whale occurrences from deep waters in the mid-twentieth century to the mid-shelf region in
the late 1900s was attributed to changes in the availability of optimal zooplankton patches, possibility
relating to climatic forcing (variability in oceanic conditions caused by changes in atmospheric
patterns) (Tynan et al. 2001). Sightings in the Bering Sea are clustered in relatively shallow water
(waters with a bottom depth of 50 to 80 m) (Tynan et al. 2001). However, North Pacific right whales
also have been sighted in waters with bottom depths as deep as 1,700 m (Carretta et al. 1994). The
IWC (2001) noted a surprising absence of evidence for coastal calving grounds, since right whales in
the North Atlantic and in the Southern Hemisphere have calving grounds located in shallow bays,
lagoons, or in waters over the continental shelf.
Distribution—Right whales occur in sub-polar to temperate waters. The North Pacific right whale
historically occurred across the Pacific Ocean north of 35°N, with concentrations in the Gulf of Alaska,
eastern Aleutian Islands, south-central Bering Sea, Sea of Okhotsk, and the Sea of Japan (Omura et
al. 1969; Scarff 1986; Clapham et al. 2004). Presently, sightings are extremely rare, occurring
primarily in the Okhotsk Sea and the eastern Bering Sea (Brownell et al. 2001). Prior to 1996, right
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