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

AUGUST 2005 FINAL REPORT
tropics and subtropics around islands, over shallow banks, and along continental coasts, where
calving occurs. Most humpback whale sightings are in nearshore and continental shelf waters;
however, humpback whales frequently travel through deep water during migration (Clapham and
Mattila 1990; Calambokidis et al. 2001).
North Pacific humpback whales are distributed primarily in four more-or-less distinct wintering areas:
the Ryukyu and Ogasawara (Bonin) Islands (south of Japan), Hawai’i, the Revillagigedo Islands off
Mexico, and along the coast of mainland Mexico (Calambokidis et al. 2001). In the central North
Pacific, whales use Hawaiian waters as a major breeding ground in winter and spring (December
through March). There is known to be some interchange of whales among different wintering
grounds, and matches between Hawai’i and Japan, and Hawai’i and Mexico have been found (Salden
et al. 1999; Calambokidis et al. 2000, 2001; Figure 3-1). However, it appears that the overlap is
relatively small between the Western North Pacific humpback whale population and Central and
Eastern North Pacific populations (Darling and Mori 1993; Calambokidis et al. 2001).
There is also some trans-oceanic interchange between the North Pacific and South Pacific breeding
populations (Medrano-Gonzalez et al. 2001). Baker et al. (1993) hypothesized that the most likely
route for such interbreeding of northern and southern humpback whales is the equatorial waters of
the eastern Pacific Ocean. This apparently occurs through geographic overlap of some individuals
from both ocean basins off the Central American coast (Acevedo and Smultea 1995). However, this is
probably a relatively rare occurrence.
In addition to Japanese waters, humpbacks have been documented in recent years off Taiwan and
the Philippines (Yamaguchi et al. 2002), although it is not known if whales are breeding in these latter
areas or simply using them as stopover points. The waters of the Ogasawara (Bonin) Islands off
Japan are considered to be one of the main wintering grounds for humpback whales of the western
North Pacific population (Mori et al. 1998). Mori et al. (1998) suggested that calving might actually
take place in waters with slightly higher temperatures than the waters of the Ogasawara Islands, for
example, in the lower latitudes along the Ogasawara Islands rim, possibly extending from the Kazan
Retto to the Northern Mariana Islands. The historical winter range in the western North Pacific
included the waters around Taiwan, Hainan Island, and the Mariana and Marshall islands (Darling
and Mori 1993). Although Townsend (1935) indicated that many humpbacks were caught off the
Marianas in earlier years, preliminary surveys of Taiwan and Saipan suggest that humpback whales
are no longer common there and have not generally reinhabited this part of the range (Darling and
Mori 1993). Darling and Mori (1993) suggested that the recent humpback whale sightings off Saipan
might indicate that the range of the population is currently expanding, or alternatively, these could just
be a few wayward individuals. In addition, humpback whales have recently been observed in the
Babuyan Islands off the northern Philippines, raising the question as to whether this also may have
been part of their traditional wintering range (Yamaguchi et al. 2002).
During summer months, North Pacific humpback whales feed in a nearly continuous band from
southern California to the Aleutian Islands, Kamchatka Peninsula, and the Bering and Chukchi seas
(Calambokidis et al. 2001; Figure 3-1). There is much interchange of whales among different feeding
grounds, although some site fidelity is the rule. Whales migrate between the Mexican breeding
ground and feeding grounds along the west coast of the continental U.S., using a corridor along the
coast of Baja California (Figure 3-1). The primary feeding range of the Western North Pacific
humpback stock is not known. Mark recoveries from whaling operations suggest connections with
summering areas in the Okhotsk and Bering seas, off Kamchatka, and the Aleutian Islands (Nishiwaki
1966; Ohsumi and Masaki 1975). There are recent photo-identification matches to the Gulf of Alaska,
southeast Alaska, and the Pacific Northwest (Calambokidis et al. 2001). However, there are also
indications of genetic associations of Ogasawara humpbacks with the North American coastline
(Baker et al. 1998), and some Western North Pacific humpbacks apparently feed off British Columbia
(Darling et al. 1996; Calambokidis et al. 1997). Clearly, the picture is not a simple one. The paucity of
photo-identification data for the Aleutian Islands, Bering and Okhotsk seas, and Kamchatcka waters
may be somewhat masking the true identity of the primary feeding grounds, but this remains to be
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