Technical Reports of the Institute of Cetacean Research (2018)

pp. 20–31

Technical Report (not peer reviewed)

Geographical distribution of whales in the Indo-Paciﬁc region of the
Antarctic based on JARPA and JARPAII sighting data collected in the
period 1987/88–2008/09
Koji Matsuoka* and Takashi Hakamada
Institute of Cetacean Research, 4–5 Toyomi-cho, Chuo-ku, Tokyo 104–0055, Japan*Contact e-mail: matsuoka@cetacean.jp

ABSTRACTThis paper examined the geographical and temporal pattern of distribution of several whale species in the
Indo-Paciﬁc region of the Antarctic during the austral summer. The analyses were based on sighting data collected systematically by JARPA and JARPAII surveys in the longitudinal sector 35°E–145°W, south of 60°S, between 1987/88 and 2008/09. A total of 353,134n.miles was surveyed in these Areas. Density Index of Whales(No. of individuals sighted/100 n.miles) was calculated and its geographical distribution plotted for each individual species. Antarctic minke whale was the species most frequently sighted, followed by killer, humpback,unidentiﬁed beaked, ﬁn, sperm, southern bottlenose, blue, southern right and sei whales. The geographicalpattern of distribution was described for each whale species. The large sighting data set collected systematically by JARPA and JARPAII in the Indo-Paciﬁc region has made a substantial contribution to understanding thepattern of geographical distribution and habitat use of whales in the Antarctic ecosystem.

INTRODUCTION
One of the main sources of sighting data for assessing
the population status of whale species in the Antarctic is
the JARPA which was conducted between 1987/88 and2004/05, and its second phase JARPAII conducted between 2005/06 and 2008/09.
The sighting data collected during the JARPA have beenused for studying the distribution pattern and abundance
estimation of several large whale species (Kishino et al.,
1991; Kasamatsu et al., 2000; Matsuoka et al., 2003;
2011; Branch et al., 2004; Murase et al., 2002; 2014).

Figure 1.

20

The objective of this study was to investigate the pattern of geographical distribution of large whale species in
the Indo-Paciﬁc region of the Antarctic during the australsummer feeding season. The study was based on sighting data collected systematically by JARPA and JARPAII
surveys.

MATERIAL AND METHODS
Research area
The research area comprised the Indo-Paciﬁc regionof the Antarctic, speciﬁcally the International Whaling
Commission (IWC) Management Areas IIIE (35°E–70°E),

The IWC Antarctic Areas for the management of baleen whales (except Brydeʼs whale), and the research
Area of the JARPA and JARPAII surveys between 35°E and 145°W.

Geographical distribution of whales in the Indo-Pacific region of the Antarctic based on JARPA and JARPAII

IV (70°E–130°E), V (130°E–170°W) and VIW (170°W–
145°W), south of 60°S (Figure 1).
Sighting data
Primary sighting and eﬀort data were collected by JARPA
and JARPAII systematic surveys in the period 1987/88–
2008/09. Surveys were conducted by sighting and sampling vessels (SSV) and dedicated sighting vessels (SV).
Sighting procedure
The sighting procedure in JARPAII (2005/06–2008/09)
was not substantially changed with regard the procedures in JARPA (Nishiwaki et al., 2014). The research
vessels were equipped with top barrel, where three top
men conducted sightings. On the upper bridge, a captain,a gunner, a helmsman and a researcher also conducted
the sighting. The sighting activity was conducted under
acceptable weather conditions (see below), from 30 minutes after sunrise to 30 minutes before the sunset.
Survey modes
Searching was conducted under closing and passing
modes (Hakamada et al., 2006). These modes were used
under acceptable weather conditions (minke whale visibility of 2 n.miles or more and wind speed under 20
knots in the northern strata, and under 25 knots in thesouthern strata) (Nishiwaki et al., 2014).
Conﬁrmation of the sightings
When a sighting was made, the vessel closed to theschool immediately in order to identify the species, estimate the school size and get other biological information

Figure 2.

(number of calves, estimated body length, etc.).
Density Index of Whales
The Density Index of Whales (DIW) (the number of individual whales sighted by 100 n.miles) was calculated byeach Lat.1°× Long.1°grid squares.

RESULTS AND DISCUSSIONS
Searching eﬀorts
A total of 353,134 n.miles was surveyed in Areas IIIE, IV,
V and VIW, south of 60°S between 1989/90 and 2008/09.
Figure 2 shows the distribution of the primary searchingeﬀort.
Distribution pattern of whales
Tables 1a and 1b show a summary of primary sightings of baleen and toothed whales, respectively. Table
2 shows the number of calves, observed mean school
size and DIW, by species and month. Figures 3a–d show
the maps of the DIW for i) blue, ﬁn and sei whales; ii)
Antarctic minke, dwarf minke and humpback whales; iii)
southern right, sperm and southern bottlenose whales;
and iv) unidentiﬁed beaked (Ziphiidae) and killer whales,
respectively, by each Lat.1°× Long.1°grid squares. Figure
4 shows the monthly change in DIW for most of the species.
A description of the geographical distribution by whale
species is presented and discussed below.
Blue whale
Blue whale had the 8th rank of DIW among the ten species sighted in the research area (Table 2). They were

Searching eﬀorts (red line) by JARPA and JARPAII surveys in the period 1987/88–2008/09, including transit
sighting survey in middle latitude.
21

Technical Reports of the Institute of Cetacean Research (2018)
Table 1a
Summary of baleen whale species sighted in the Indo-Paciﬁc region of the Antarctic.
Eﬀort

Blue whale(n.miles)sch. ind. calfAnt. minke whale

Humpback whale

calf sch. ind. calf

sch.

ind.

calf

sch.

ind.

3
16

0
0

1
0

1
0

0
0

237
353

719
768

0
0

35
1

76
2

0
0

1
0

1
0

0
0

5
33
8
15
9
73
60
37
18
45
66
114
143
52
109
49

20
67
34
27
26
241
214
82
57
222
356
374
983
216
446
118

0
0
0
1
0
1
1
1
0
1
3
0
2
0
0
1

0
0
2
2
0
2
0
1
0
0
0
7
1
8
0
1

0
0
2
4
0
5
0
1
0
0
0
13
2
14
0
1

0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

758
740
597
1,024
688
823
887
853
672
826
1,507
1,907
1,867
2,420
1,092
1,663

1,968
1,713
2,030
3,228
1,619
2,453
2,008
2,610
1,373
2,665
6,581
4,949
4,374
6,531
3,250
4,278

0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0

121
58
177
28
133
131
325
114
577
106
661
191
1219
145
1690
197

210
90
321
56
220
228
562
200
1,122
203
1,269
341
2,387
228
3,134
336

11
0
7
5
1
9
10
3
2
7
5
3
5
4
5
2

2
0
26
3
11
0
8
0
34
0
3
2
15
0
1
2

2
0
30
4
14
0
8
0
37
0
3
2
22
0
2
2

0
0
0
0
0
0
0
0
0
0
0
0
1
0
1
0

188
37
48
109

748
253
134
440

1
0
4
2

2
0
2
5

3
0
2
7

0
0
0
0

1,657
969
823
1,870

4,375
2,169
1,702
4,668

0
0
0
0

1702
160
1314
339

3,200
283
2,536
587

22
13
7
8

53
0
72
0

73
0
96
0

4
0
0
0

264 462 10 1,228 5,077 18

34

55

0

24,233 66,031

1

9,424 17,591 129 233 296

6No.

Season1
2

1987/88
1988/898,860.6
10,806.7

0
2

0
3

3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18

1989/90
1990/91
1991/92
1992/93
1993/94
1994/95
1995/96
1996/97
1997/98
1998/99
1999/2000
2000/01
2001/02
2002/03
2003/04
2004/05

16,423.2
14,660.0
17,844.1
13,924.9
17,957.3
14,047.7
21,466.7
17,783.2
21,594.4
8,066.5
16,341.5
20,421.3
19,767.4
18,126.2
19,287.4
18,486.7

5
4
3
7
5
13
9
7
16
4
25
10
17
5
32
12

19
20
21
22

2005/06
2006/07
2007/08
2008/09

16,372.7
11,968.8
14,575.3
14,351.4

24
7
43
14

Total

353,134

Fin whale
sch.

ind.

0
0

3
7

9
6
3
9
9
20
16
9
25
7
53
18
26
10
61
16

0
0
0
0
0
1
0
0
0
1
2
0
1
0
0
0

38
12
84
28

2
1
1
1

Sei whale

S. right whale

calf sch. ind. calf

Table 1b
Summary of toothed whale species sighted in the Indo-Paciﬁc region of the Antarctic.
S. bottlenose whale

Unid. beaked whales(n.miles)

sch.

ind.

calf

sch.

ind.

calf

sch.

ind.

calf

sch.

ind.

calf

1987/88
1988/898,860.6
10,806.7

6
81

6
91

0
0

3
2

5
4

0
0

87
65

218
143

0
0

20
31

194
189

0
0

3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18

1989/90
1990/91
1991/92
1992/93
1993/94
1994/95
1995/96
1996/97
1997/98
1998/99
1999/2000
2000/01
2001/02
2002/03
2003/04
2004/05

16,423.2
14,660.0
17,844.1
13,924.9
17,957.3
14,047.7
21,466.7
17,783.2
21,594.4
8,066.5
16,341.5
20,421.3
19,767.4
18,126.2
19,287.4
18,486.7

204
175
225
105
321
133
341
121
295
49
195
100
269
128
222
105

215
188
233
108
336
135
352
128
302
50
204
106
272
129
223
108

0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

23
13
29
10
145
74
137
75
222
23
138
72
126
97
154
44

46
26
51
19
243
146
273
128
409
53
251
121
226
168
274
78

0
0
0
0
0
1
1
0
0
0
0
0
0
0
0
0

281
241
181
202
205
168
161
78
197
35
110
173
134
113
208
89

514
421
304
361
337
263
284
144
338
54
188
272
205
154
338
159

0
1
1
0
0
0
0
1
0
0
0
0
0
0
0
0

69
32
53
82
56
35
109
50
82
35
109
72
79
63
120
78

859
870
805
1,130
399
281
1,282
539
931
409
2,011
1,471
939
953
1,348
1,472

0
2
0
0
1
1
1
4
9
5
7
2
0
0
0
3

19
20
21
22

2005/06
2006/07
2007/08
2008/09

16,372.7
11,968.8
14,575.3
14,351.4

181
63
280
75

182
63
280
76

0
0
0
0

88
51
79
32

179
80
157
61

0
0
1
0

135
66
102
77

244
88
155
140

0
0
0
0

100
44
62
38

1,563
394
790
788

3
0
0
14

353,134.0

3,674

3,787

0

1,637

2,998

3

3,108

5,324

3

1,419

19,617

52

No.

Season

1
2

Total

22

Sperm whale

Eﬀort

Killer whale

Geographical distribution of whales in the Indo-Pacific region of the Antarctic based on JARPA and JARPAII

widely distributed in the research area in both northernand southern strata. High density values of this species
were observed in Areas IIIE, particularly between 45°E
and 65°E (Figure 3a). They were rarely found in the Prydz
Bay. Blue whales were sighted within the Ross Sea between 70°S and 77°S. A total of 286 schools (495 individuals) including eleven calves were sighted south of 60°S
(Table 2). Observed mean school size was 1.73 individuals. The DIW of this species was 0.140 for the whole period and the indices were almost stable from December
to March (Table 2 and Figure 4).
Two subspecies of blue whales exist in Southern Hemisphere: the Antarctic (or true) blue whale (Balaenoptera
musculus intermedia) and the pygmy blue whale (B.
m. brevicauda) (Mackintosh, 1966; Ichihara, 1966;
Rice, 1998). A complete review of spatial and seasonal
distribution, densities and movements of blue whales isprovided by Branch (2007) and Branch et al. (2007). Thesestudies indicated that there is little evidence that pygmy
blue whales migrate into high latitudes of the Antarctic.
Less than 1% of the records south of 52°S were of thissubspecies. There is no current evidence of population
structure in Antarctic blue whales. The latest abundance
estimate of this species (south of 60°S, 35°E–145°W) was
1,223 whales (CV=0.345) in 2007/08+2008/09 seasons,and the abundance trend was 8.2% (95% CI: 3.9%, 12.5%)
between 1995/96 and 2008/09 for combined Areas IIIE+
IV+V+VIW based on JARPAII data (Matsuoka and Hakamada, 2014). There is a need for continued monitoringof the abundance and abundance trend of this species,
especially because they provide an excellent opportunity

to improve our understanding of the dynamics of baleen
whale populations recovering from low levels.
Fin whale
Fin whale had the 5th rank of DIW among the ten species sighted in the research area. A total of 1,268 schools(5,209 individuals) including 20 calves, were sighted(Table 2). Observed mean school size was 4.11 individuals. This species was more frequently encountered in
Areas V and VIW than in Areas IIIE and IV in both northernand southern strata. High density areas were observedin Areas IIIE, particularly between 55°E and 65°E, VW,
between 140°E and 160°E and VE between 163°E and170°W (Figure 3a). The DIW of this species was 1.475 forthe whole period and the indices increased from December to March (Figure 4).
In the Antarctic feeding grounds, ﬁn whales occur yearround but higher density is found from November to May(Kasamatsu et al., 1996; Mackintosh, 1966). Whales canbe found as far south as 65°S–70°S, but the majority ofthe population seems to occur north of 60°S (Miyashita
et al., 1995). Catches occurred throughout the Antarctic,
but the majority of whales (∼73%) were taken in the IWC
Management Areas II and III. Sighting data suggest thatspatial distribution varies across ocean basins (Kasamatsu
et al., 1996).
Sei whale
Sei whale was rarely sighted in the research area. A totalof 36 schools (59 individuals) were sighted south of 60°S
(Table 2) and no calves were observed. Observed mean

Table 2
Summary of sighting information in the whole research area in the period 1987/88–2008/09, by whale species and month. Sch.:
number of primary sightings of schools; Ind.: number of primary sightings of individuals; Calf: number of calves; Mss: mean school
size (Ind./Sch.); DIS: Density Index (schools/100 n.miles); DIW: Density Index (individuals/100 n.miles).
SpeciesAll Areas(IIIE, IV, V and VIW; south of 60°S, 35°E–145°W)

Order of
DIW

Dec.
DIW

Jan.
DIW

Feb.
DIW

Mar.
DIW

Sch.

Ind.

Calf

Mss

DIS

DIW

Blue whale
Fin whale
Sei whale
Antarctic minke whale
Humpback whale
Southern right whale

286
1,268
36
25,507
10,036
235

495
5,209
59
69,076
18,770
298

11
20
0
0
137
6

1.73
4.11
1.64
2.71
1.87
1.27

0.081
0.359
0.010
7.223
2.842
0.067

0.140
1.475
0.017
19.561
5.315
0.084

8
5
10
1
3
9

0.281
1.323
0.002
10.173
3.425
0.001

0.092
0.794
0.004
14.301
4.842
0.014

0.101
1.760
0.020
33.331
7.337
0.156

0.102
3.059
0.044
19.4366.708
0.292

Sperm whale
S. bottlenose whale
Unid. beaked whale
Killer whale

3,810
1,666
3,175
1,472

3,926
3,045
5,457
20,569

0
3
3
59

1.03
1.83
1.72
13.97

1.079
0.472
0.899
0.417

1.112
0.862
1.545
5.825

6
7
4
2

1.500
0.932
1.864
1.935

1.272
0.974
1.594
5.692

0.992
0.787
1.123
9.303

0.292
0.570
1.209
6.624
23

Technical Reports of the Institute of Cetacean Research (2018)school size was 1.64 individuals. This species occurred
more frequently in Areas V and VIW than in Areas IIIE and
IV in the northern strata (Figure 3a). The DIW of this species was 0.017 for the whole period.
In summer, sei whales do not venture into higher

Figure 3a.

24latitude waters near the Antarctic continent as muchas some other baleen whales (Horwood, 1987; Miyashita et al., 1995). The majority of the population occurs
between 40°S and 60°S, usually north of the Antarctic
Convergence. Juveniles are found further north than

DIW of blue (top), ﬁn (middle) and sei (bottom) whales in the Indo-Paciﬁc region of the Antarctic, by
Lat.1°× Long.1°square (whole research period).

Geographical distribution of whales in the Indo-Pacific region of the Antarctic based on JARPA and JARPAII

mature individuals. Occurrence in low latitude wintering
grounds has been recorded from March to December, butabundance peaks from June/July to August/September(Horwood, 1987). In late spring and summer, abundance
peaks in November between 30°S and 50°S. As theseason progresses relatively more whales are observed

Figure 3b.

south of 40°S and abundance between 50°S and 60°S
increases consistently until March (Horwood, 1987). The
results in the present study are consistent with those ofprevious studies.

DIW of Antarctic minke (top), dwarf minke (middle) and humpback (bottom) whales in the Indo-Paciﬁcregion of the Antarctic, by Lat.1°× Long.1°square (whole research period).
25

Technical Reports of the Institute of Cetacean Research (2018)

Antarctic minke whale
This was the most frequently sighted species throughout
the surveys. A total of 25,507 schools (69,076 individuals) were sighted south of 60°S (Table 2). No calves wereobserved. Observed mean school size was 2.71 individuals. High density areas were observed along the ice-edge,
especially the Ross Sea and Prydz Bay (Figure 3b). The
DIW of this species for the whole period was the highest(19.561). The indices increased from December to February and decreased in March (Figure 4).
In the austral summer the majority of Antarctic minke
whales congregate in the Southern Ocean, with greatest densities close to and within the pack ice, and lower
densities with increasing distance from the ice (Kasamatsu et al., 2000; Hakamada and Matsuoka, 2014a),
including some north of 60°S. Antarctic minke whales are
noticeably well adapted to living within the ice (Ainley
et al., 2007), but the exact proportion of Antarctic minke
whales found within the pack ice, and in polynyas, is currently a source of debate. It is possible that a large proportion of the population is found within the pack ice, outof reach of vessel-based sighting surveys (Murase et al.,2005; 2014; Shimada and Kato, 2007).

found within the Prydz Bay and the Ross Sea and no sighting occurred south of 73°S. High density values of thisspecies were observed between 85°E and 110°E (Figure3b). The DIW of this species was 5.315 for the whole period. Indices increased from December to February anddecreased in March (Figure 4).
IDCR/SOWER circumpolar surveys encountered humpback whales more frequently in the sectors 20–40°E,
80°E–100°E and 150°E–180°E (Branch, 2011). The current
distribution map of this species suggests that humpback
whales are encountered more frequently in the sector
80°E–100°E because of its high productivity. In the sector 80°E and 100°E, large scale distribution changes wereobserved (Matsuoka et al., 2011; Murase et al., 2014;
Hakamada and Matsuoka, 2014b). It has been suggested
that such changes are related to changing oceanographic
conditions such as the eﬀect of the regime shift in the
global sea-surface temperatures in relation to El Ninosouthern oscillation events (Watanabe et al., 2014; Naganobu et al., 2014). This should be further investigatedin the future.

Dwarf minke whale
Distribution of this species was limited within the research area. There are two separated areas of distribution, between 120°E and 147°E, and between 165°E and170°W in the northern stratum (mainly between 60°S and
63°S), south of Australia and New Zealand (Figure 3b). The
dwarf minke whale has a white band on the ﬂipper that
distinguishes it from the Antarctic minke whale, but was
only fairly recently identiﬁed as separate from Antarctic
minke whales (Best, 1985). On available information,
only a small percentage of minke whales in the Antarctic(south of 60°S) are dwarf minke whales. For example, in
the IDCR/SOWER surveys from 1993/94–1997/98 only
0.2% of the identiﬁed sightings were dwarf minke whales(2 out of 906). No formal analysis has been conducted
but it is probable that less than 1% of the minke whales
south of 60°S are dwarf minke whales (Branch and Butterworth, 2001).

Southern right whale
A total of 235 schools (298 individuals) involving six
calves were sighted (Table 2). Distribution area of thisspecies was limited to the sector 80°E and 135°E, southof Western Australia (Figure 3c). The DIW of this species was 0.084 for the whole period. Indices increased
from December to March (Figure 4). In summer southern right whales migrate south but generally not as
far south as other baleen whale species. They appear
to occur near the subtropical convergence in summer(January to March) at around 40°S–50°S (Ohsumi andKasamatsu, 1985), but there are records of animals muchfurther south (e.g. around 60°S–65°S south of Australia(Bannister et al., 1999; 2008). The present distribution
map of this species is consistent with these previous
studies. The population estimate for the coastal area ofWestern Australia was 2,400 in 2006 (Bannister, 2008).
A current estimate in Area IV south of 60°S is 1,557 individuals (95% CI: 871–2,783) in the 2007/08 season basedon JARPAII data (Matsuoka and Hakamada, 2014).

Humpback whale
Humpback whale had the 3rd rank among the ten species
sighted in the research area. A total of 10,036 schools(18,770 individuals) including 137 calves were sighted(Table 2). Observed mean school size was 1.87 individuals. They were widely distributed in the research area
in both northern and southern strata. They were rarely

Sperm whale
Sperm whale had the 6th rank among the ten species
sighted in the research area. A total of 3,810 schools(3,926 individuals) were sighted. No calves were observed (Table 2). Single large males were mainly sighted(96.5%) and consequently the observed mean school size
was 1.03. They were widely distributed in the research

26

Geographical distribution of whales in the Indo-Pacific region of the Antarctic based on JARPA and JARPAII

Figure 3c.

DIW of southern right (top), sperm (middle) and southern bottlenose (bottom) whales in the Indo-Paciﬁcregion of the Antarctic, by Lat.1°× Long.1°square (whole research period).

area. High density values of sperm whales were observedin Area IV (between 70°E and 100°E) and Area V (between
170°E and 170°W, in the mouth of the Ross Sea (Figure3c). They tended to be concentrated on the Antarctic
continental slope, on the southern Kerguelen Plateau,

and around the mouth of the Ross Sea, where most frequently the depth was between 1,000 m and 4,000 m.
They were rarely found within the Prydz Bay and the Ross
Sea (Figure 3c). There were no sightings south of 74°S in
the Ross Sea. The DIW of this species was 1.081 for the27Technical Reports of the Institute of Cetacean Research (2018)

whole period. The indices decreased from December toMarch (Figure 4).
Southern bottlenose whale
Southern bottlenose whale had the 7th rank among theten species sighted in the research area. A total of 1,666
schools (3,045 individuals) including three calves weresighted (Table 2). They were widely distributed in the
research area but were rarely sighted within the Prydz
Bay and the Ross Sea. High density values of this whale
were observed between 85°E and 130°E (Figure 3c). Observed mean school size was 1.83 individuals. The DIWof this species was 0.862 for the whole period. Indicesdecreased from December to March (Figure 4).
Unidentiﬁed beaked whales
Unidentiﬁed beaked whales had the 4th rank among theten species sighted in the research area. A total of 3,175
schools (5,457 individuals) including three calves were

Figure 3d.

28sighted (Table 2). The sightings were recorded as unidentiﬁed species of beaked whales. This ʻunidentiﬁed beaked
whalesʼ possibly included southern bottlenose whale (Hyperoodon planifrons), Arnouxʼs beaked whale (Berardius
arnuxii), strap-toothed whale (Mesoplodon layardii) andGreyʼs beaked whale (M. grayi). Distribution pattern of
the unidentiﬁed beaked whales was consistent with thatof southern bottlenose whales (Figure 3d).
Killer whale
Killer whale had the 2nd rank among the ten species
sighted in the research area. A total of 1,472 schools(20,569 individuals) including 59 calves were sighted(Table 2). Observed mean school size was 13.97 individuals. The DIW of this species was 5.825 for the whole period (Table 2). They were widely distributed in the researcharea and were more frequently sighted in the southern
stratum. High density areas were observed within the
Prydz Bay and the Ross Sea (Figure 3d).

DIW of unidentiﬁed beaked (top) and killer (bottom) whales in the Indo-Paciﬁc region of the Antarctic, by
Lat.1°× Long.1°square (whole research period).

Geographical distribution of whales in the Indo-Pacific region of the Antarctic based on JARPA and JARPAII

to March. It is necessary to further investigate the relationship between whale distribution and oceanographic
condition shifts such as the eﬀect of the regime shift
in the global sea-surface temperatures in relation to El
Nino-southern oscillation events (Matsuoka et al., 2003;
Watanabe et al. 2014; Naganobu et al., 2006; 2014).

ACKNOWLEDGEMENTS
We thank all researchers, captains, oﬃcers and crew
members that participated in the JARPA and JARPAII surveys from which the data used in the present study werecollected. We also thank S. Suzuki for help in drawing
some of the ﬁgures.

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Figure 4.

Monthly change of DIW for baleen (top) and toothed(bottom) whales in the whole research area andperiod.

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