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

AUGUST 2005 FINAL REPORT
Acoustics and Hearing—Infrasonic, pattern sounds have been documented for fin whales (Watkins
et al. 1987). Fin whales produce a variety of sounds with a frequency range up to 750 Hz. The long,
patterned 15 to 30 Hz vocal sequence is most typically recorded; only males are known to produce
these (Croll et al. 2002). The most typical fin whale sound is a 20 Hz infrasonic pulse (actually an FM
sweep from about 23 to 18 Hz) with durations of about 1 sec and can reach source levels of 184 to
186 dB re 1 µPa-m (maximum up to 200) (Thomson and Richardson 1995; Charif et al. 2002). Croll et
al. (2002) recently suggested that these long, patterned vocalizations might function as male breeding
displays, much like those that male humpback whales sing. While no data on hearing ability for this
species are available, Ketten (1997) hypothesized that mysticetes have acute infrasonic hearing.
♦ Blue Whale (Balaenoptera musculus)
Description—Blue whales are the largest living animals. Blue whale adults in the northern
hemisphere reach 22.9 to 28 m in length (Jefferson et al. 1993). The rostrum of a blue whale is broad
and U-shaped, with a single prominent ridge down the center (Jefferson et al. 1993). The tiny dorsal
fin is set far back on the body and appears well after the blowholes when the whale surfaces (Reeves
et al. 2002). This species is blue-gray with light (or sometimes dark) mottling.
Status—Blue whales are classified as endangered under the ESA and endangered by the IUCN Red
List (Reeves et al. 2003). The blue whale was severely depleted by commercial whaling in the
twentieth century (NMFS 1998b). There is no designated critical habitat for this species in the North
Pacific. The stock structure of blue whales in the North Pacific is uncertain (NMFS 1998b). There
might be as many as five populations of blue whales in the North Pacific (NMFS 1998b).
Habitat Preferences—Blue whales inhabit both coastal and oceanic waters in temperate and tropical
areas (Yochem and Leatherwood 1985). Feeding grounds have been identified in coastal upwelling
zones off the coast of California (Croll et al. 1998; Fiedler et al. 1998; Burtenshaw et al. 2004), Baja
California (Reilly and Thayer 1990), and off southern Australia (Gill 2002). Blue whales also feed in
cool, offshore, upwelling-modified waters in the eastern tropical and equatorial Pacific (Reilly and
Thayer 1990; Palacios 1999). Moore et al. (2002) determined that blue whale call locations in the
western North Pacific were associated with relatively cold, productive waters and fronts.
Distribution—Blue whales are distributed from the ice edges to the tropics in both hemispheres
(Jefferson et al. 1993). Blue whales as a species are thought to summer in high latitudes and move
into the subtropics and tropics during the winter (Yochem and Leatherwood 1985). Data from both the
Pacific and Indian Oceans, however, indicate that some individuals may remain in low latitudes yearround,
such as over the Costa Rican Dome (Wade and Friedrichsen 1979; Reilly and Thayer 1990).
The productivity of the Costa Rican Dome may allow blue whales to feed during their winter
calving/breeding season and not fast, like humpback whales (Mate et al. 1999).
The range of the blue whale is known to encompass much of the North Pacific Ocean, from
Kamchatka (Russia) to southern Japan in the west, and from the Gulf of Alaska south to at least
Costa Rica in the east (NMFS 1998). The only (presumably) reliable sighting report of this species in
the central North Pacific was a sighting made from a scientific research vessel about 400 km
northeast of Hawai’i in January 1964 (NMFS 1998). Blue whale call locations in the western North
Pacific suggest that there is an association between whale distribution and the Emperor Seamounts,
the steep continental slope off the Kamchatka Peninsula, and the Aleutian Island chain (Moore et al.
2002). Moore et al. (2002) noted a seasonal progression of call-location concentrations over the
seamounts in winter, the Kamchatka Peninsula and seamounts in spring, the Kamchatka Peninsula
and waters between the seamounts and Aleutian Islands in summer, and the seamounts again in fall.
Blue whale calls have been recorded off Midway and O’ahu (Northrop et al. 1971; Thompson and
Friedl 1982; McDonald and Fox 1999); these provide evidence of blue whales occurring within
several hundred kilometers of these islands (NMFS 1998b). The recordings made off O’ahu showed
bimodal peaks throughout the year, suggesting that the animals were migrating into the area during
summer and winter (Thompson and Friedl 1982; McDonald and Fox 1999). Evidence of blue whales
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