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INTRODUCTION
Two sub-species of blue whale are found in the Southern
Ocean, the Antarctic blue whale, Balaenoptera musculus
intermedia, and the pygmy blue whale, B.m. brevicauda.
There appears to be a general geographic segregation of the
sub-species in the austral mid-summer, with pygmy blue
whales occurring primarily north of 60°S and Antarctic blue
whales south of this latitude (Kato et al., 1995). Sub-species
discrimination in the field is problematic because it relies on
experienced observers noting relative body proportions and
details of the head shape. Population research related to the
conservation of large baleen whales requires accurate
species identification (IWC, 1995). Recent studies indicate
that monitoring of blue whale vocalisations may provide a
means of determining sub-species in the field (Ljungblad et
al., 1997; 1998; Stafford et al., 1999; 2001).
Sounds recorded in the presence of blue whales can be
divided into two categories: short-duration or long-duration
(Thompson and Cummings, 1996; Norris and Barlow,
2000). The short-duration vocalisations consist of individual
pulses and frequency-modulated (FM, typically downswept)
sounds of less than five seconds duration. These
vocalisations vary in frequency and duration and have been
recorded in the presence of blue whales in many locations
(Thompson and Cummings, 1996; Ljungblad et al., 1997;
Stafford et al., 2001). Short-duration sounds appear to be
common; however, they are underrepresented in the
literature.
Long-duration vocalisations are composed of one or more
units that are FM or amplitude-modulated (AM) sounds and
longer than five seconds (McDonald et al., Submitted). An
individual unit is defined as a continuous sound having
consistent characteristics; these vocalisation units are often
repeated in patterned sequences, or songs (Payne and
McVay, 1971; McDonald et al., Submitted). These song
units have been shown to vary geographically (Cummings
and Thompson, 1971; Edds, 1982; Thompson and Friedl,
1982; Alling et al., 1991; Thompson and Cummings, 1996;
Stafford et al., 1999; 2001). Preliminary examination of
sounds recorded in the presence of Antarctic blue whales
and pygmy blue whales in the Southern Hemisphere
indicate a similar geographic distribution of long-duration,
low-frequency song units (Clark and Fowler, 2001;
Ljungblad et al., 1997).
Recordings of pygmy blue whales off Madagascar show
repetitive sequences of 10-20s tonal sounds in the 25-45Hz
band (Ljungblad et al., 1998). Pygmy blue whale
vocalisations recorded off Australia consist of three separate
long tonal units in the 18-26Hz band (McCauley et al.,
2000). The long-duration sounds recorded in the presence of
Antarctic blue whales in the Antarctic consist of patterned
sequences of tonal sounds composed of three distinct units.
The first tone is centred at 28-29Hz with a duration of 8-12s.
A short 2s downsweep from 28-20Hz connects the first tonal
unit to the third, a slightly modulated tone (20-18Hz), that is
approximately 8-12s in duration (Ljungblad et al., 1998).
The three-unit vocalisation, or phrase, is usually repeated
J. CETACEAN RES. MANAGE. 7(1):13–20, 2005
13
Vocalisations of Antarctic blue whales, Balaenoptera musculus
intermedia, recorded during the 2001/2002 and 2002/2003
IWC/SOWER circumpolar cruises, Area V, Antarctica
SHANNON RANKIN
*
, DON LJUNGBLAD
+
, CHRIS CLARK
#
AND HIDEHIRO KATO
++
Contact e-mail: Shannon.Rankin@noaa.gov
ABSTRACT
Blue whale vocalisations recorded during the 2001/2002 and 2002/2003 International Whaling Commission-Southern Ocean Whale and
Ecosystem Research (IWC/SOWER) cruises were analysed to determine the feasibility of using acoustic recordings for sub-species
identification of the Antarctic blue whale (Balaenoptera musculus intermedia) and the pygmy blue whale (B.m. brevicauda). The research
was conducted in IWC Area V, from latitude 60°S to the ice edge and between longitudes 130°E and 150°E on the Shonan Maru
(2001/2002), and between 150°E and 170°W on the Shonan Maru No.2 (2002/2003). Data including 15 groups consisting of 42 animals,
as well as opportunistic recordings of an unknown number of animals during evening sonobuoy stations were examined for this study.
Vocalisations included long-duration 28Hz tonal sounds and relatively short-duration frequency-modulated sounds. The short-duration calls
were similar to vocalisations recorded in the presence of blue whales in other locations worldwide. Not all recordings contained the long-
duration 28Hz call, considered to be a species-specific vocalisation of Antarctic blue whales. None of the sounds that have previously been
attributed to pygmy blue whales were detected. The long-duration 28Hz tonal vocalisations included 3-unit calls, considered to be song
phrases, as well as simple 28Hz sounds and 28Hz sounds followed by a downsweep. The centre and peak frequencies of the 28Hz tone for
these three sound types were stable regardless of signal strength; however, for the 3-unit vocalisation, the presence and characteristics of
their 2
nd
and 3
rd
units were variable. Examination of two distinct groups of simultaneously vocalising blue whales showed no evidence of
temporally repeated patterns of vocalisations (song phrases). The results of this study suggest that the peak frequency of the 28Hz
vocalisations may be used as a diagnostic feature to aid in discriminating between Antarctic blue whales and pygmy blue whales in the field;
however, examination of vocalisations in relation to group size and behaviour are necessary to understand the circumstances in which the
28Hz vocalisations are produced.
KEYWORDS: BLUE WHALE; COMMUNICATION; VOCALISATION; ANTARCTIC; MANAGEMENT PROCEDURE; SURVEY-
ACOUSTIC; POPULATION ASSESSMENT; ACOUSTICS; DISTRIBUTION; SOWER
*
Southwest Fisheries Science Center, NOAA, US National Marine Fisheries Service, 8604 La Jolla Shores Drive, La Jolla, CA 92038, USA.
+
Ljungblad Associates, PO Box 6, Elk Mountain, WY 82324, USA.
#
Bioacoustics Research Program, Cornell Laboratory of Ornithology, Cornell University, 159 Sapsucker Woods Rd, Ithaca, NY 14850, USA.
++
Large Cetacean Section, National Research Institute of Far Seas Fisheries, 5-7-1 Orido, Shimizu, Japan.
every 70-80s, at intervals between 40-50s (Ljungblad et al.,
1998). There is a high degree of variability in the presence
and intensity of the three individual units, and therefore we
use the terms ‘3-unit vocalisation’ to describe vocalisations
with all three units intact, ‘28Hz downsweep’ to describe
vocalisations with the first two units intact, and ‘28Hz tone’
to describe vocalisations where only the first unit is intact.
In addition to studying the distinct variation in
vocalisations of the two sub-species of blue whale for
accurate species identification in the field, knowledge of the
behavioural contexts of these sounds is needed for long-
term vocal and population studies. The blue whale
component of the International Whaling Commission’s
SOWER (Southern Ocean Whale and Ecosystem Research)
programme obtains videos, photographs, biopsies and
acoustic recordings of blue whales in the field. This study
examines recordings and behavioural information obtained
in the presence of blue whales during two seasons of
SOWER cruises to provide a preliminary examination of the
variability associated with the 3-unit vocalisation, and its
effect on blue whale population studies in the Southern
Ocean.
METHODS
Data collected by the authors during the 2001/2002 SOWER
cruise from the vessel Shonan Maru and the 2002/2003
SOWER cruise from the vessel Shonan Maru No.2 were
used for this study. The research area surveyed was in IWC
Area V
1
between 130°E-150°E (2001/2002) and 150°E-
170°W (2002/2003), and extending from 60°S to the ice
edge (Fig. 1). Line-transect visual observations of cetaceans
were conducted between 06:00 and 18:00 local time,
weather permitting, using a visual observation team
consisting of three tiers of experienced observers
(Anonymous, 2002b). Summaries of the methods are given
in Ensor et al. (2002 and 2003). Briefly, the visual
observation team was responsible for sighting and positively
identifying whales, estimating group sizes and obtaining
biopsy samples, video tapes, and photo-identification
photographs. An acoustician was responsible for obtaining
recordings in the vicinity of blue whales and collecting
opportunistic evening recordings.
The primary acoustic recording method used expendable
DIFAR (Direction Finding and Ranging) AN/SSQ 53B
sonobuoys. These were deployed in close proximity to
sighted blue whales and monitored for as long as time
permitted for a minimum of 30 minutes. Opportunistic
recordings were also made while drifting in the evenings.
The sonobuoy radio signal was received via the ship
antenna, which was coupled to an ICOM IC-R100 single
channel receiver. This output was connected to a Sony DAT
TCD-D7 recorder (flat frequency response from 5Hz to
24kHz) or a Sony mini-disk MZ-R700 recorder (frequency
response 20Hz-20kHz ± 3dB). Recordings were later
digitised to a Sony PCG-FX120 computer (sample rate
48kHz) using the software program ISHMAEL (Mellinger,
2001) and analysis was performed using Spectra-Plus
software. All vocalisations attributed to blue whales with a
strong signal-to-noise ratio (SNR) from the 2001/2002
season were measured (44.1kHz sample rate, 32768 point
FFT size, 90% overlap, Hamming window). Only long-
duration calls with a strong SNR from the 2002/2003 season
were measured (5512Hz sample rate, 8192 point FFT size,
90% overlap, Hanning window).
All high-quality vocalisations attributed to blue whales
were categorised according to their frequency and duration
characteristics. The short-duration FM calls included
amplitude-modulated downsweeps, high-frequency
downsweeps, low-frequency downsweeps, high-frequency
upsweeps, low-frequency upsweeps and complex calls. The
long-duration sounds included the 3-unit vocalisations,
28Hz downsweeps and 28Hz tonal vocalisations.
Measurements were made of lowest frequency, highest
frequency, centre frequency (for tonal sounds), start
frequency, end frequency, frequency shift, peak frequency,
and duration for all vocalisations and vocalisation units.
Measurement of the time between the deployment of the
sonobuoy and detection of the first 3-unit vocalisation was
made to examine feasibility of using these vocalisations for
in situ species identification.
Temporal patterns of vocalisations were examined for a
series of recordings (10.5 hours total) associated with blue
whale sightings on 23 January 2003. All times are given as
local times at sea. Bearings to each vocalisation were
obtained using DIFAR signal processing. This was
performed using an automatic MATLAB function within
Ishmael that executes a series of commands for de-
multiplexing the DIFAR signal (software developed by
Greenridge Sciences, Inc.), and determines the bearing to a
sound source (software designed by M. McDonald).
Bearings of individual vocalisations allowed the detection
of distinct groups of vocalising whales, so that patterns of
vocalisations could be examined within and between
groups. It was not possible to use DIFAR to distinguish
individuals within groups due to the close association and
variable movement patterns of animals. The paucity of
recording tapes available during the 2001/2002 season
necessitated recording at the lowest possible sampling rate
to maximise the recording time (with a sample rate of
32kHz, the frequency response of the Sony TCD-D7 was 20-
14,500Hz ± 1dB). This eliminated the multiplexed DIFAR
signal and so bearings could not be obtained for these data.
RESULTS
Recordings were made in the vicinity of 12 blue whale
groups (31 animals total) during the 2001/2002 season and
in the vicinity of three blue whale groups (11 animals total)
for the 2002/2003 season (Table 1). Blue whale sounds were
detected during 14 of these 15 groups.
Blue whale encounters
2001/2002
Between 6 and 8 January 2002, a total of nine sightings of
blue whales were observed within an area bounded by
64°18’S and 64°29’S and 136°29’E and 137°24’E, near the
northern margin of belts of the pack ice. Seven of the groups
(totalling 14 animals) were determined to be Antarctic blue
whales; photo and/or video and biopsy attempts were made
for these groups (Table 1). The eighth was a group of three
animals observed at night that was not approached and was
classified as undetermined blue whales. A distant group of
two animals determined to be ‘like’ blue whales were
sighted outside of a larger congregation of blue whales, but
these animals were not approached. During all encounters,
sounds attributed to Antarctic blue whales were recorded,
although for most encounters these sounds were not
detected within the first hour of recording (Table 1).
From 21-31 January 2002, three groups of Antarctic blue
whales (totalling 12 animals) and three groups of
unidentified blue whales (six animals total) were sighted.
14 RANKIN
et al.:
VOCALISATIONS OF ANTARCTIC BLUE WHALES
1
For a description of IWC Areas, see Donovan (1991).
Photos and/or video and acoustic recordings were obtained
for all but the undetermined groups of whales, and biopsy
attempts were made for the groups identified on 29 and 31
January (Table 1). Very few vocalisations were recorded
during these encounters.
2002/2003
On 23 January 2003, two groups of Antarctic blue whales
(totalling 8 animals) were sighted in the outer margin of the
pack ice, in the vicinity of 67°07’S and 166°54’E (Table 1).
All animals appeared to be feeding on krill patches.
Photography, biopsy attempts and acoustic recordings were
undertaken during this sighting. Acoustic recordings began
at 17:10 and continued throughout the night in the location
of the scattered blue whale sightings. An additional sighting
of three animals was detected in the middle of the night (24
January) and confirmed the continued presence of blue
whales in the area. A detailed examination of DIFAR
processing of the acoustic behaviour of these groups is
described below.
Characteristics of blue whale vocalisations
A total of 85 hours of recordings were made from the
Shonan Maru during the 2001/2002 cruise, with over 33
hours of recordings in areas of blue whale sightings. All
recordings were monitored for the presence of sounds that
could be attributed to blue whales, and over 42 hours of
recordings contained blue whale vocalisations. A total of
193 short FM vocalisations and 261 long-duration tonal
vocalisations (including 3-unit, 28Hz downsweep and 28Hz
tonal vocalisations) were measured from the recordings for
this survey.
J. CETACEAN RES. MANAGE. 7(1):13–20, 2005
15
Fig. 1. Locations of acoustic detections of blue whales within the study area. The open squares represent recordings from blue
whale sightings; the closed circles represent opportunistic evening sonobuoy stations with blue whale acoustic detections.
A total of 38.7 hours of recordings were made from the
Shonan Maru No.2 during the 2002/2003 survey, including
11 hours in the vicinity of blue whale sightings. Sounds that
could be attributed to blue whales were detected in nearly 26
hours of recordings, however only recordings associated
with sightings were examined. A total of 92 long-duration
tonal vocalisations with high SNRs were measured from this
survey; short FM vocalisations were recorded, but not
measured.
The most common short-duration FM vocalisation was
the simple high-frequency downsweep from 76.3-40.0Hz,
with a mean signal duration of 2.7 seconds (n=132, Table 2,
Fig. 2(a)). The amplitude-modulation found in the pulsed
downsweep appeared to be caused by propagation, and the
basic frequency and duration characteristics closely
resemble those of the high-frequency downsweep (Fig.
2(b)). The low-frequency downsweep (n=4), low-frequency
upsweep (n=7) and high-frequency upsweep sounds (n=4)
were relatively uncommon compared to the high-frequency
downsweep vocalisations (Table 2).
Although the complex sounds were variable in nature,
several similar types were frequently observed. The most
common complex vocalisations were variations on the high-
frequency downsweep, with one or more inflection points
(Fig. 2(c)). Other less common complex vocalisations are
short, high-frequency downsweeps, variable FM sounds and
‘concave’ sounds (Fig. 3).
The long-duration calls were divided into three categories
as described in the Introduction: the 3-unit vocalisation; the
28Hz downsweep; and the 28Hz tone (Fig. 4). The 3-unit
vocalisation consisted of a tone at 27.7Hz lasting an average
of 8.3 seconds, occasionally followed by a brief downsweep
of variable duration, to a typically FM moan from 19.5-
19.1Hz with an average duration of 6.9 seconds (Table 3).
The 28Hz downsweep consisted of a moan at 27.7Hz of a
variable duration followed by a downsweep to
approximately 19.1Hz. Measurements of the entire sample
of vocalisations (‘All’) were compared with a sub-sample of
high-quality vocalisations (‘Best’); the centre and peak
frequency of the 28Hz tone varied little, regardless of the
vocalisation type or signal quality. For vocal animals, at
least 30 minutes elapsed between sonobuoy deployment and
initial detection of vocalisations associated with the
Antarctic blue whales (defined as the acoustic identification
time) (Table 1).
DIFAR analyses of vocalisations
DIFAR analyses of recordings from 23 January 2003
allowed differentiation between the calls from several
groups of blue whales (sightings 11 and 12; Fig. 5).
Determination of the bearing angles to the sound source
using DIFAR analysis was performed on 1,069 vocalisations
(208 long-duration, 861 short-duration) during the 11 hours
of recordings. Close association of several animals within a
group prevented identification of the vocalising animal in
most cases; sound source for all sightings is for the group
and not an individual animal (where group size >1). The
similar DIFAR bearing angles of the blue whales (160°) and
the ship (167°) at 17:45 indicate that animals biopsied at this
time were vocalising (Fig. 5(a)). The discontinuity in the
ship’s course at 18:15 (Fig. 5(b)) occurred as the ship
returned to course and speed after biopsy sampling;
Fig. 2. Spectrogram of the most common short-duration FM
vocalisations (5kHz sample rate, 2048 point FFT): (a) high-
frequency downsweep; (b) amplitude-modulated downsweep; and
(c) a complex variation of the high-frequency downsweep.
16 RANKIN
et al.:
VOCALISATIONS OF ANTARCTIC BLUE WHALES
Fig. 3. Spectrogram of uncommon short-duration FM vocalisations
(5kHz sample rate, 2048 point FFT): (a) high frequency upsweep;
(b) short high frequency downsweep; (c) variable high frequency
downsweep; and (d) concave vocalisation.
excessive noise during this manoeuvre temporarily
precluded DIFAR processing. At 18:15 the ship’s true
course of 5° closely matched that determined by the
sonobuoy. At 18:45 the ship’s course crossed 0° in front of
the sonobuoy.
Movement of the ship and the subsequent loss of the
sonobuoy signal led to a gap in the recordings from 19:00
until 23:00. Recordings continued while the vessel was
drifting for the remainder of the night, and DIFAR bearing
angles suggest that a large congregation of vocalising blue
whales separated into two distinct groups at about 00:30
(Fig. 6(a)). At 01:20 on 24 January a group of three blue
whales (Fig. 6(b), 350°) were seen feeding next to the ship.
DIFAR angles show that this group may have produced
occasional short-duration FM vocalisations, but was not a
part of either consistently vocalising group (40° and 150°).
Between 00:39 and 02:49 the sounds from the two
simultaneously vocalising blue whale groups (denoted A
and B) had a high SNR and well-defined DIFAR bearing
angles. Both short-duration FM and long-duration tonal
vocalisations from the two groups were plotted over time to
identify patterns in temporal variation (Fig. 7). However,
there was no apparent temporal pattern for the short-
duration or long-duration 28Hz vocalisations. An expanded
view of the common high-frequency downsweeps (HFDN)
does not suggest countercalling between groups Aand B.
DISCUSSION
This study shows that the 3-unit vocalisation is a
geographically distinct call associated with Antarctic blue
whales in the Southern Ocean south of 60°S. The 3-unit
vocalisations recorded during 2001/2002 are consistent with
previous results for sounds attributed to Antarctic blue
whales in the Antarctic (Anonymous, 2002a; Clark and
Fowler, 2001; Ljungblad et al., 1998). The dataset presented
here represents the largest analysis to date of these calls.
None of the characteristic sounds attributed to pygmy blue
whales in Madagascar (Ljungblad et al., 1998) or Chile
(Cummings and Thompson, 1971) were detected in the 247
hours of recordings. During the two cruises, all whales
visually identified at the sub-species level were considered
to be Antarctic blue whales. Genetic analysis of biopsies
obtained on these cruises is underway and will hopefully
confirm that these sounds were indeed produced by
Antarctic blue whales. The association of specific calls
exclusively to Antarctic blue whales provides a step towards
in situ acoustic sub-species identification. As noted earlier,
real-time identification currently relies on visual inspection
by experienced observers. However, whales do not vocalise
continuously, which limits the value of the technique. In
addition, should time be limited, identifications in real-time
may not be feasible due to the processing time required for
a single identification. Nonetheless, the technique is a
valuable tool, particularly when used in conjunction with
genetic analysis and visual identification methods.
To use vocalisation for species identification one must be
able to positively detect the call. There appears to be
variability in the presence and characteristics of the 2
nd
(inter-tone downsweep) and 3
rd
(19Hz tone) unit of this
vocalisation (Table 3). It is clear that blue whales produce
both 28Hz tonal and 28Hz downsweep vocalisations, in
addition to the 3-unit calls previously examined. Even with
a high SNR, an overlap of the multi-path signals of long-
J. CETACEAN RES. MANAGE. 7(1):13–20, 2005
17
Fig. 4. Spectrogram of three long-duration blue whale vocalisations
associated with different Antarctic blue whales (48kHz sample rate,
decimation ratio 4:1, 32768 point FFT): (a) 3-unit vocalisation
including 28Hz tone followed by an inter-tone interval and a 19Hz
tone; (b) 28Hz tone plus downsweep; and (c) a 28Hz tone. All were
sufficiently intense to suggest detection of the entire signal.
Fig. 5. DIFAR bearings for blue whales during biopsy attempts for sighting number 11 on 23 January 2003. Two distinct groups could
be identified, one at 260° and the other at 160°. All magnetic bearing angles were converted to true angles for comparison.
duration calls can make it difficult to determine the
characteristics of individual sounds. With increasingly faint
vocalisations, it may be difficult to distinguish the 3-unit
vocalisations from the 28Hz tonal and 28Hz downsweeps.
The primary consistent feature is the tone centred at 27.7Hz;
peak frequency varies little among these three vocalisations
regardless of the signal intensity. If all three long-duration
28Hz vocalisations can be positively, and exclusively, linked
to Antarctic blue whales, then this research suggests that it
may be possible to attribute any long (6-12s) 28Hz tonal
vocalisation south of 60°S to Antarctic blue whales.
Research to date suggests this to be the case. Sub-species
identification based on detection of the 28Hz tonal
vocalisation is feasible for most groups of Antarctic blue
whales, assuming a minimum one hour recording time.
Future efforts should include deployment of sonobuoy
arrays to localise calling animals so that comparisons with
visual detection and genetic sampling of individual calling
animals can be conducted.
Previous studies suggested that the long-duration, low-
frequency sounds produced by blue whales are songs
(Anonymous, 2002a), or patterned series of repeated
vocalisations. The 2.5 hour sample of two vocalising groups
within the larger congregation of scattered blue whales,
recorded on 23 January 2003, does not suggest that the
vocalisations were repeated in patterned series within a
given group, or between the two groups (Fig. 7). The
comparisons of vocalisations with the various blue whale
18 RANKIN
et al.:
VOCALISATIONS OF ANTARCTIC BLUE WHALES
Fig. 6. DIFAR bearings for blue whales during evening recording in location of sighting numbers 11 and 12 for 23 January 2003 and
sighting number 1 on 24 January 2003. All magnetic bearing angles were converted to true angles for comparison. The discontinuities
in the ships’ bearing angle are associated with repositioning.
Fig. 7. Temporal variation of vocalisation types for the two blue whale groups from 00:30 until 3:00, 24 January 2003. An expanded
view of HF DN vocalisations is provided for clarity. HF=high frequency; LF=low frequency; DN=downsweep; UP=upsweep.
sightings (Table 3) suggest that there is considerable
variation in the vocal behaviour of different groups. The
sightings in the 2001/2002 study differed in group size,
behaviour and habitat. Unfortunately, the locations of
vocalising animals in relation to the sonobuoy could not be
determined due to problems in recording the DIFAR signal.
This severely limited our ability to examine temporal
patterns, or the presence of song during the 2001/2002
cruise. Further research combining visual and acoustic
studies (with functional DIFAR) on different blue whale
groups is necessary to understand the circumstances in
which the temporal patterns considered to be ‘song’ are
produced.
Successful use of bottom-mounted hydrophones to
monitor whale song in the Pacific (McDonald et al., 1995;
Stafford et al., 1999) and Atlantic Oceans (Clark, 1995) led
to deployment of similar hydrophones in the Southern
Ocean to monitor the blue whale population year-round
(Sirovic et al., 2004). Minimum abundance can be estimated
through noting the ranges of individual singing whales;
however, our results suggest that only a small proportion of
the blue whale population may be singing. The ability to
relate geographically distinct vocalisations (song units) to
an index of abundance relies heavily on their behavioural
contexts. These concerns are essentially the same as those
for using acoustics as a method for species identification.
The short FM vocalisations recorded here are similar to
sounds associated with blue whales in other regions. With
the exception of the high-frequency downsweep, most short
FM vocalisations are uncommon. Groups of vocalising
whales were noted to produce both short-duration FM and
long-duration 28Hz vocalisations. During extended biopsy
attempts during the 2001/2002 survey there was an apparent
overall increase in vocalisations. The inability to confirm
the vocalising group using DIFAR software limits this to a
simple speculation. This should be examined for other close
approaches, as this may influence the ability of acoustics to
determine species identification.
Clearly there is great variation in the vocal behaviour of
different blue whale groups; however, we cannot yet explain
these differences. The structure of the 3-unit vocalisation
appears to be highly variable, but 27.7Hz peak frequency is
stable even over great distances. The 3-unit vocalisations,
and the other 28Hz vocalisations do not always occur in
patterned series or ‘songs’, and some whale groups are not
vocal. More information must be gathered on the variations
in vocalisations by age, sex, season, time of day, group
composition and behaviour. These data can only be obtained
by integrated in situ studies of blue whales.
The IWC has stated that there is a need for a dedicated
blue whale study in the Southern Ocean to combine visual
and acoustics surveys with biopsy, photo-identification and
J. CETACEAN RES. MANAGE. 7(1):13–20, 2005
19
satellite tagging of individuals in order to determine the
winter breeding grounds. Blue whales have been known to
frequent the ice edge between 150°E and 165°E (Kato et al.,
1995). The relatively high populations of blue whales in this
area during the 2001/2002 and 2002/2003 confirm that this
is an ideal location for deployment of a series of bottom-
mounted hydrophones for recording of vocalisations,
coinciding with future shipboard populations surveys.
ACKNOWLEDGMENTS
This work could not have been accomplished without the
hard work and dedication of the captain and crews of the
Shonan Maru and the Shonan Maru No.2. George Murphy
and the US Navy provided surplus sonobuoys for use in this
project. Financial support was provided by the International
Whaling Commission, The Office of Naval Research and
the US Navy. Special thanks to Jay Barlow, Robert
Brownell, Kathy Kane, Steve Rankin and the Southwest
Fisheries Science Center for their continued support and
Paul Ensor, Jay Barlow, Erin Oleson, Kate Stafford and
Mark McDonald for their comments on earlier versions of
this manuscript, and Richard Cosgrove for assistance with
the graphics. This work could not have been accomplished
without the dedication and guidance of Paul Ensor with
whom it was an honour to work.
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20 RANKIN
et al.:
VOCALISATIONS OF ANTARCTIC BLUE WHALES
