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

AUGUST 2005 FINAL REPORT
Acoustics and Hearing—Recordings in the presence of minke whales have included both high- and
low-frequency sounds (Beamish and Mitchell 1973; Winn and Perkins 1976; Mellinger et al. 2000).
Mellinger et al. (2000) described two basic forms of pulse trains that were attributed to minke whales:
a “speed up” pulse train with energy in the 200 to 400 Hz band, with individual pulses lasting 40 to 60
msec, and a less-common “slow-down” pulse train characterized by a decelerating series of pulses
with energy in the 250 to 350 Hz band.
Recorded vocalizations from minke whales have dominant frequencies of 60 to greater than 12,000
Hz, depending on vocalization type (Thomson and Richardson 1995). Recorded source levels,
depending on vocalization type, range from 151 to 175 dB re 1 µPa-m (Ketten 1998). Gedamke et al.
(2001) recorded a complex and stereotyped sound sequence (“star-wars vocalization”) in the
Southern Hemisphere that spanned a frequency range of 50 Hz to 9.4 kHz. Broadband source levels
between 150 and 165 dB re 1 µPa-m were calculated. “Boings” recorded in the North Pacific have
many striking similarities to the star-wars vocalization, in both structure and acoustic behavior.
“Boings”, recently confirmed to be produced by minke whales and suggested to be a breeding call,
consist of a brief pulse at 1.3 kHz, followed by an amplitude-modulated call with greatest energy at
1.4 kHz, with slight frequency modulation over a duration of 2.5 sec (Rankin and Barlow 2003). While
no data on hearing ability for this species are available, Ketten (1997) hypothesized that mysticetes
have acute infrasonic hearing.
♦ Bryde’s Whale (Balaenoptera edeni/brydei)
Description—Bryde’s whales can be easily confused with sei whales. Bryde’s whales usually have
three prominent ridges on the rostrum (other rorquals generally have only one) (Jefferson et al. 1993).
The Bryde’s whale’s dorsal fin is tall and falcate and generally rises abruptly out of the back. Adults
can be up to 15.5 m in length (Jefferson et al. 1993), but there is a smaller species that rarely reaches
over 10 m in length (Jefferson personal communication).
It is not clear how many species of Bryde’s whales there are, but genetic analyses suggest the
existence of at least two species (Rice 1998; Kato 2002). The taxonomy of the baleen whale group
formerly known as sei and Bryde’s whales is currently confused and highly controversial (see Reeves
et al. 2004 for a recent review). It is clear that there are at least three species in this group, the
antitropically-distributed sei whale, the tropically-distributed standard form Bryde’s whale (probably
referable to Balaenoptera brydei), and the “dwarf Bryde’s whale” (probably referable to Balaenoptera
edeni), which inhabits tropical waters of the Indo-Pacific (Yoshida and Kato 1999). However, the
nomenclature is not resolved, due to questions about the affinities of the type specimens of
Balaenoptera brydei and Balaenoptera edeni.
Status—The IWC recognizes three management stocks of Bryde’s whales in the North Pacific:
Western North Pacific, Eastern North Pacific, and East China Sea (Donovan 1991). The Bryde’s
whale is designated as data deficient on the IUCN Red List (Reeves et al. 2003). This “species” is
expected to be the most common baleen whale species in the Mariana Islands (Jefferson personal
communication).
Clearly, the standard-form Bryde’s whale occurs in the area of the Mariana Islands, and the sei whale
may also occur there, at least extralimitally. It is possible that the dwarf Bryde’s whale may also occur
there, although current data suggest a more equatorial distribution for most of the records.
Habitat Preferences—Bryde’s whales are found both offshore and near the coasts in many regions.
Off eastern Venezuela, Bryde’s whales are often sighted in the shallow waters between Isla Margarita
and Peninsula de Araya, as well as into waters where there is a steep slope, such as the Cariaco
Trench (Notarbartolo di Sciara 1982). Along the Brazilian coast, distribution and seasonal movements
of the Bryde’s whale appear to be influenced by the behavior, distribution, and abundance of Brazilian
sardine (Sardinella brasiliensis) schools that approach the coast to spawn in shallow waters (Zerbini
et al. 1997). In the Gulf of Mexico, all Bryde’s whale sightings have been near the shelf break in
DeSoto Canyon (Davis and Fargion 1996; Jefferson and Schiro 1997; Davis et al. 2000). Whaling
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