DENSITY DISTRIBUTION OF ANTARCTIC WHALES

Full paper

DENSITY DISTRIBUTION OF SEVERAL MAJOR
WHALE SPECIES IN THE INDO-PACIFIC REGIONOF ANTARCTIC USING JARPA AND JARPAIISIGHTING DATA OBTAINED THROUGH
1987/88 –2008/09 SEASONS
Koji MATSUOKA* and Takashi HAKAMADA
Institute of Cetacean Research, 4 – 5 Toyomi-cho, Chuo-ku, Tokyo 104 – 0055, Japan(*Corresponding author: matsuoka@cetacean.jp)

Abstract
This paper examined the geographical distribution of several whale species in the IndoPacific 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 of
35°E – 145°W, south of 60°S, between 1987/88 and 2008/09. The searching effort comprised a
total of 353,134 n.miles. The 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. Density index of whales (DIW: no. of individuals sighted/100 n.miles)
was calculated using all primary effort and sightings data and its geographical distribution plotted on maps with Lat. 1 degree × Long. 1 degree squares for each species. These maps are moredetailed compared to those of the previous maps which used 5° × 5°squares in the 1960s. The
geographical distribution was described for each whale species together with some features of
their distribution. For example, sei, dwarf minke, humpback and southern bottlenose whales
were not sighted in the Ross Sea, distribution areas of southern right whales were limited to thesector 80°E and 135°E, and high-density areas of humpback whales were observed between
80°E and 110°E. The large scale and long-term sighting data set has made a substantial contribution to understanding the geographical distribution patterns and habitat use of whales in the
Antarctic ecosystem.
Key words: Antarctic, distribution, baleen whales, toothed whales.

Introduction

One of the main sources of large scale and long-term sighting data for assessing the population
status of whale species in the Antarctic is the JARPA (Japanese Whale Research Program under Special
Permit in the Antarctic), the first phase of which was conducted between 1987/88 and 2004/05, with
its second phase, JARPAII (sighting component), conducted between 2005/06 and 2008/09. One of
the features of JARPA and JARPAII is that, unlike the IWC/IDCR (International Whaling Commission/
International Decade for Cetacean Research)-SOWER (Southern Ocean Whale and Ecosystem
Research) programmes conducted from 1978/79 to 2009/10 (Matsuoka et al., 2003a), surveys havebeen repeated in the same area and in the same months every second season over a long period. CurCetacean Population Studies (CPOPS)
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MATSUOKA AND HAKAMADA

rent distribution maps are more detailed for each Area compared to those of the IDCR/SOWER maps
which had covered the area only three times for each set of circumpolar data on whales. Therefore,
the JARPA and JARPAII surveys facilitate description of the extent of detailed local distribution ofwhales.
The sighting data collected during the JARPA and JARPAII have been used for studying the distribution patterns and estimated abundance of several large whale species (Kishino et al., 1991;
Kasamatsu et al., 2000; Matsuoka et al., 2003b, 2011; Branch et al., 2004; Murase et al., 2002, 2014).
The objective of this study was to investigate the geographical distribution patterns of large whale
species in the Indo-Pacific region of the Antarctic during the austral summer feeding season. The study
was based on sighting data collected systematically by the JARPA and JARPAII surveys.

Materials and Methods

Research area
The research area comprised the Indo-Pacific region of the Antarctic every year, specifically the IWC
Management Areas IIIE (35° – 70°E), IV (70° – 130°E), V (130°E – 170°W) and VIW (170° – 145°W),
south of 60°S (Fig. 1). Each individual survey was conducted from December to March during australsummer (Fig. 2).
These Areas were divided into two sectors (western sector and eastern sector). Each sector was also
divided into two strata (northern and southern strata), along the 60°S latitude line to the line of 45 n.miles
from the ice-edge (northern stratum), and ice-edge to 45 n.miles from the ice-edge line (southern stratum),except for the Prydz Bay and the Ross Sea regions. The Prydz Bay is defined as south of 66°S, and theRoss Sea is defined as south of 69°S. There are no stratifications for Areas IIIE and VIW in JARPA. In
JARPAII, there are stratifications for Areas IIIE and VIW which are the same as in Area IV (Fig. 3).

Fig. 1. The main research area of the JARPA and JARPAII surveys between 35°E and 145°W, south of 60°S withsearching efforts (red lines) in the period 1987/88–2008/09, including the transit sighting surveys between low
latitude and Antarctic regions with the IWC Antarctic Areas for the management of baleen whales (except
Bryde’s whale).

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DENSITY DISTRIBUTION OF ANTARCTIC WHALES

Sighting data
The collection procedures and analyses of sighting data that have been used in JARPA are very
similar to those used in IWC/IDCR-SOWER cruises. Activities aboard the ship are classified into two
principal groups: On-effort and Off-effort. On-effort activities are times when full search effort is being
executed and conditions (such as weather and sea conditions) are within acceptable parameters to
conduct research. Off-effort activities are all activities that are not On-effort. All sightings recorded
while the ship is On-effort are classified as Primary sightings. All other sightings are Secondary sightings.
Primary search effort is only conducted in acceptable weather conditions. These conditions aredefined as visibility better than 2.0 n.miles, with wind speed less than 20 knots and Beaufort sea stateless than 6. These conditions are used as guidelines; in some circumstances, less severe conditions
may still be inappropriate for search effort. The sighting procedure in JARPAII (2005/06 – 2008/09)
did not differ substantially from JARPA (Hakamada et al., 2006; Nishiwaki et al., 2014).
The research vessels (ship length averages about 70 meters) were equipped with a top barrel (almost
20 meters from the sea level), from which three men conducted sighting observations. On the upper
bridge (almost 11.5 meter from the sea level), a captain, a gunner, a helmsman and a researcher also
conducted sightings. The sighting activity was carried out from 30 minutes after sunrise to 30 minutes
before sunset. The survey ship speed averages about 11.5 knots.
When a sighting is made, the topman (or upper bridge observer) gives an estimate of the distanceand angle to the sighting and the ship turns immediately, regardless of the angle to the sighting. The
whales were approached and the species, number of animals and number of calves (if present) determined. In order to save valuable research time, closure to the sighting position of whales that can bepositively identified as long-diving species (such as sperm whales or beaked whales) may be abandoned if it is considered that the animals have dived.
In addition, using the round-trip transit sighting surveys were also conducted every season between
low latitude and Antarctic regions, although the searching effort was low compared to that south of
60°S (Fig. 1).

Fig. 2. Start and end dates of JARPA and JARPA II surveys (1989/90–
2008/09) in the research area.
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MATSUOKA AND HAKAMADA

III-E
1

1 9 8 9 /9 0

1 9 9 1 /9 2

1 9 9 3 /9 4

IV-NW IV-NE
5
2

IV-NW IV-NE
5
1

IV-NW IV-NE
5
2

IV-SW
3

IV-SW
3

IV-SW
3

IV-SE
1

IV-SE
2

1 9 9 5 /9 6

IV-SE
1

IV-NW IV-NE
3
5

III-E
1

IV-SW
2

IV-PB
4

IV-PB
4

IV-PB
4

IV-PB
4

1 9 9 7 /9 8

1 9 9 9 /0 0

2 0 0 1 /0 2

2 0 0 3 /0 4

IV-NW IV-NE
2
4

IV-NW IV-NE
2
3

IV-NW IV-NE
2
3

IV-SW
5

IV-SE
3

III-E
1

IV-SW
5

IV-PB
6

IV-SE
4

IV-PB
6

2 0 0 5 /0 6
III-NE IV-NW IV-NE V-NW
34
62
III-SE IV-SW IV-SE V-SW
3
4
6
2

V-NE
1
V-SE
1

III-E
1

IV-SW
5

IV-SE
4

IV-NW IV-NE
2
3

III-E
1

IV-SW
5

IV-PB
6

IV-PB
6

2 0 0 7 /0 8
III-NE IV-NW IV-NE V-NW
1
2
3
4
III-SE IV-SW IV-SE V-SW
12
3
4

unsurveyed

IV-PB
5

IV-SE
6

IV-SE
4

V-NE
V-SE

unsurveyed

IV-PB
unsurveyed

1 9 9 0 /9 1

1 9 9 2 /9 3

1 9 9 4 /9 5

1 9 9 6 /9 7

V-NW
2

V-NE
4

V-NW
3

V-NE
1

V-NW
2

V-NE
3

V-NW
4

V-NE
2

V-SW
1

V-SE
3

V-SW
2

V-SE
4

V-SW
1

V-SE
4

V-SW
3

V-SE
5

1 9 9 8 /9 9
V-NW
2

V-NE
1

V-SW
3

V-SE
4

2 0 0 0 /0 1
VI-W
5

V-NW
4

V-NE
2

V-SW
5

V-SE
3

2 0 0 6 /0 7

2 0 0 2 /0 3
VI-W
1

V-NW
4

V-NE
2

V-SW
5

V-SE
3

VI-W
1

2 0 0 4 /0 5
VI-W
1

V-NW
4

V-NE
2

V-SW
5

V-SE
3

VI-W
1

2 0 0 8 /0 9

V-NW
4

V-NE
2

VI-NW
1

V-SW
4

V-SE
3

VI-SW
1

V-NW
1

V-NE
4

VI-NW
2

V-SW
1

V-SE
3

VI-SW
2

Fig. 3. Survey order by strata for the period from 1989/90 to 2008/09 seasons. Key: III= Area III, IV= Area IV,
V = Area V, VI = Area VI, E = East, W = West, NW= North-West, NE= North-East, SW= South-West, SE= SouthEast, PB = Prydz Bay. A common number in a season indicates that two strata were surveyed in the same
period. V-NE, V-SE and IV-PB strata could not be surveyed at all in 2007/08 season (Hakamada and Matsuoka,
2014a).

Density index of whales and mean school size
The Density Index of Whales (DIW), i.e. the number of individual whales sighted per 100 n.miles,
was calculated for each Lat.1° × Long.1° grid square. The mean school size (Mss) in this study is thearithmetic mean (i.e. number of animals divided by number of schools).

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DENSITY DISTRIBUTION OF ANTARCTIC WHALESResults and Discussion

Searching efforts
A total of 353,134 n.miles were surveyed in Areas IIIE, IV, V and VIW, south of 60°S, between
1989/90 and 2008/09. Fig. 4 shows the distribution of the primary searching effort (n.miles). All gridsquares were searched and the research area south of 60°S was completely covered.
Distribution of whales
Tables 1a and 1b show a summary of the primary sightings of baleen and toothed whales, respec-

Fig. 4. Distribution of the primary searching effort by Lat.1° × Long.1° squares in JARPA and JARPAII
surveys in the period 1987/88 – 2008/09 seasons.
Table 1a. Summary of baleen whale species sighted in the Indo-Pacific region of the Antarctic.
No.

SeasonResearch Effort
area(n.miles)Blue whale

Fin whalesch. ind. calfsch.

Sei whale

Ant. minke whale

Dwarf minke
whale

Humpback whale

S. right whaleind.

calf sch. ind. calf

sch.

ind.

calf sch. ind. calf

sch.

ind.

calf sch. ind. calf

1

1987/88IV

8,860.6

0

0

0

3

3

0

1

1

0

237

719

0

1

2

0

35

76

0

1

1

0

2

1988/89

V

10,806.7

2

3

0

7

16

0

0

0

0

353

768

0

5

5

0

1

2

0

0

0

0

3

1989/90IV

16,423.2

5

9

0

5

20

0

0

0

0

758

1,968

0

3

3

0

121

210

11

2

2

0

4

1990/91

V

14,660.0

4

6

0

33

67

0

0

0

0

740

1,713

0

6

6

0

58

90

0

0

0

0

5

1991/92

IV

17,844.1

3

3

0

8

34

0

2

2

0

597

2,030

0

0

0

0

177

321

7

26

30

0

6

1992/93

V

13,924.9

7

9

0

15

27

1

2

4

0

1,024

3,228

0

7

7

0

28

56

5

3

4

0

7

1993/94

IV

17,957.3

5

9

0

9

26

0

0

0

0

688

1,619

0

4

4

0

133

220

1

11

14

0

8

1994/95

V

14,047.7

13

20

1

73

241

1

2

5

0

823

2,453

0

6

6

0

131

228

9

0

0

0

9

1995/96

IIIE, IV

21,466.7

9

16

0

60

214

1

0

0

0

887

2,008

0

2

2

0

325

562

10

8

8

0

10

1996/97

V, VIW

17,783.2

7

9

0

37

82

1

1

1

0

853

2,610

0

9

9

0

114

200

3

0

0

0

11

1997/98

IIIE, IV

21,594.4

16

25

0

18

57

0

0

0

0

672

1,373

0

2

2

0

577

1,122

2

34

37

0

12

1998/99

V, VIW

8,066.5

4

7

1

45

222

1

0

0

0

826

2,665

0

3

3

0

106

203

7

0

0

0

13

1999/2000

IIIE, IV

16,341.5

25

53

2

66

356

3

0

0

0

1,507

6,581

0

0

0

0

661

1,269

5

3

3

0

14

2000/01

V, VIW

20,421.3

10

18

0

114

374

0

7

13

0

1,907

4,949

0

27

27

0

191

341

3

2

2

0

15

2001/02

IIIE, IV

19,767.4

17

26

1

143

983

2

1

2

0

1,867

4,374

0

0

0

0

1,219

2,387

5

15

22

1

16

2002/03

V, VIW

18,126.2

5

10

0

52

216

0

8

14

0

2,420

6,531

0

6

6

0

145

228

4

0

0

0

17

2003/04

IIIE, IV

19,287.4

32

61

0

109

446

0

0

0

0

1,092

3,250

0

2

2

0

1,690

3,134

5

1

2

1

18

2004/05

V, VIW

18,486.7

12

16

0

49

118

1

1

1

0

1,663

4,278

0

0

0

0

197

336

2

2

2

0

19

2005/06

IIIE, IV

16,372.7

24

38

2

188

748

1

2

3

0

1,657

4,375

0

0

0

0

1,702

3,200

22

53

73

4

20

2006/07

V, VIW

11,968.8

7

12

1

37

253

0

0

0

0

969

2,169

0

1

1

0

160

283

13

0

0

0

21

2007/08

IIIE, IV

14,575.3

43

84

1

48

134

4

2

2

0

823

1,702

0

0

0

0

1,314

2,536

7

72

96

0

22

2008/09

V, VIW

14,351.4

14

28

1

109

440

2

5

7

0

1,870

4,668

0

0

0

0

339

587

8

0

0

0

-

Total

-

353,134

264 46210

1,228 5,077

18

34

55

0

24,233 66,031

0

84

85

0

9,424 17,591 129 233 296

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MATSUOKA AND HAKAMADA

Table 1b. Summary of toothed whale species sighted in the Indo-Pacific region of the Antarctic.
Research Effort
area(n.miles)S. bottlenose
whale

Sperm whale

Unid. beaked
whalesKiller whale

No.

Season

sch.

ind.

calf

sch.

ind.

calf

sch.

ind.

calf

sch.

ind.

calf

1

1987/88IV

8,860.6

6

6

0

3

5

0

87

218

0

20

194

0

2

1988/89

V

10,806.7

81

91

0

2

4

0

65

143

0

31

189

0

3

1989/90IV

16,423.2

204

215

0

23

46

0

281

514

0

69

859

0

4

1990/91

V

14,660.0

175

188

0

13

26

0

241

421

1

32

870

2

5

1991/92

IV

17,844.1

225

233

0

29

51

0

181

304

1

53

805

0

6

1992/93

V

13,924.9

105

108

0

10

19

0

202

361

0

82

1,130

0

7

1993/94

IV

17,957.3

321

336

0

145

243

0

205

337

0

56

399

1

8

1994/95

V

14,047.7

133

135

0

74

146

1

168

263

0

35

281

1

9

1995/96

IIIE, IV

21,466.7

341

352

0

137

273

1

161

284

0

109

1,282

1

10

1996/97

V, VIW

17,783.2

121

128

0

75

128

0

78

144

1

50

539

4

11

1997/98

IIIE, IV

21,594.4

295

302

0

222

409

0

197

338

0

82

931

9

12

1998/99

V, VIW

8,066.5

49

50

0

23

53

0

35

54

0

35

409

5

13

1999/2000

IIIE, IV

16,341.5

195

204

0

138

251

0

110

188

0

109

2,011

7

14

2000/01

V, VIW

20,421.3

100

106

0

72

121

0

173

272

0

72

1,471

2

15

2001/02

IIIE, IV

19,767.4

269

272

0

126

226

0

134

205

0

79

939

0

16

2002/03

V, VIW

18,126.2

128

129

0

97

168

0

113

154

0

63

953

0

17

2003/04

IIIE, IV

19,287.4

222

223

0

154

274

0

208

338

0

120

1,348

0

18

2004/05

V, VIW

18,486.7

105

108

0

44

78

0

89

159

0

78

1,472

3

19

2005/06

IIIE, IV

16,372.7

181

182

0

88

179

0

135

244

0

100

1,563

3

20

2006/07

V, VIW

11,968.8

63

63

0

51

80

0

66

88

0

44

394

0

21

2007/08

IIIE, IV

14,575.3

280

280

0

79

157

1

102

155

0

62

790

0

22

2008/09

V, VIW

14,351.4

75

76

0

32

61

0

77

140

0

38

788

14

-

Total

-

353,134

3,674 3,787

0

1,637 2,998

3

3,108 5,324

3

1,419 19,617

52

Table 2. Summary of sighting information for the whole research area in the period 1987/88-2008/09, for 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).
All Areas (IIIE, IV, V and VIW;
south of 60S, 35E-145W)

Species
Sch.

Ind.

Order
of

Dec.

Jan.

Feb.

Mar.

Calf

Mss

DIS

DIW

DIW

DIW

DIW

DIW

DIW

Blue whale

286

495

11

1.73

0.081

0.140

8

0.281

0.092

0.101

0.102

Fin whale

1,268

5,209

20

4.11

0.359

1.475

5

1.323

0.794

1.760

3.059

Sei whale

36

59

0

1.64

0.010

0.017

11

0.002

0.004

0.020

0.044

0

2.71

7.223 19.561

1

10.173 14.301 33.331 19.436

Antarctic minke whale
Dwarf minke whale

25,507 69,076

0

1.01

0.024

0.024

10

0.008

0.031

0.039

0.008

Humpback whale

10,036 18,770 137

1.87

2.842

5.315

3

3.425

4.842

7.337

6.708

Southern right whale

235

298

6

1.27

0.067

0.084

9

0.001

0.014

0.156

0.292

Sperm whale

3,810

3,926

0

1.03

1.079

1.112

6

1.500

1.272

0.992

0.292

Southern bottlenose whale

1,666

3,045

3

1.83

0.472

0.862

7

0.932

0.974

0.787

0.570

Unid. beaked whale

3,175

5,457

3

1.72

0.899

1.545

4

1.864

1.594

1.123

1.209

Killer whale

1,472

20,56959

13.97 0.417

5.825

2

1.935

5.692

9.303

6.624

20

84

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DENSITY DISTRIBUTION OF ANTARCTIC WHALES

tively for each individual survey. Table 2 shows the summary of sighting data for each species suchas the number of calves and the observed mean school size. Total DIW for each species were the total
numbers of sighted individuals divided by the total effort and multiplied by 100. Monthly DIW wereobtained similarly. Figs. 5a – 5d show the maps of the DIW for Antarctic blue (Balaenoptera musculusintermedia), fin (B. physalus) and sei (B. borealis), Antarctic minke (B. bonaerensis), dwarf minke (B.
a. subsp.), humpback (Megaptera novaeangliae), southern right (Eubalaena australis), sperm (Physeter macrocephalus), southern bottlenose (Hyperoodon planifrons), unidentified beaked (Ziphiidae) andkiller (Orcinus orca) whales, for each Lat.1° × Long.1° grid square. Figs. 6a and 6b show the longitudinal band of DIW for each species. Figs. 7a and 7b show the latitudinal band of DIW for eachspecies. Fig. 8 shows a plot with time trends of DIW for each species. Fig. 9 shows the monthly change
in DIW for most of the species.
A description of the geographical distribution of each whale species is presented and discussed
below.
Blue whale
Blue whale ranked 8th for DIW among the ten species sighted in the research area (Table 2). Blue
whales were widely distributed in the research area, not only in the northern stratum, but also in thesouthern stratum. High density values were recorded for this species in Area IIIE, particularly between
45°E and 65°E (Fig. 5a). Blue whales were rarely found in Prydz Bay, but were sighted in the Ross
Sea between 70°S and 77°S. A total of 286 schools (495 individuals), including eleven calves, weresighted south of 60°S (Table 2). Observed mean school size was 1.73 individuals. Sighting rate of amother and calf pair was 3.85% (11 out of 286 schools) which is the highest number compared to otherbaleen whale species in the Antarctic. A high-density area was observed between 35°E and 65°E (Fig.
6a). The DIW of this species was 0.140 for the whole survey period and the indices were almost
stable from December to March (Table 2; Fig. 9). Previous studies have noted that blue whales are
more common close to the ice edge than in more northerly waters (e.g. Kasamatsu et al., 2000). Thisappears to be true for 110°E eastward, although there are blue whale sightings at or around 60°S in
the region 45°E – 110°E (Figs. 6a and 7a). Similar distribution pattern was observed by Branch (2007).
Two subspecies of blue whales exist in the 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). Complete reviews of the spatial and seasonal distributions, as well as
densities and movements of blue whales has been provided by Kato et al. (1995), Branch (2007) and
Branch et al. (2007), respectively. These studies indicated that there is little evidence that pygmy blue
whales migrate to high latitudes of the Antarctic, with less than 1% of the records south of 52°S beingof this subspecies. There have been a couple of genetic studies reporting some population structure in
Antarctic blue whales (Sremba et al., 2012, Attard et al., 2016), but there is limited evidence for multiple separate populations in these papers.
The latest abundance estimate of this species (south of 60°S, 35°E – 145°W) was 1,223 whales(CV = 0.345) in the 2007/08 and 2008/09 seasons, and the abundance trend was 8.2% (95% CI: 3.9%,
12.5%) between 1995/96 and 2008/09 combined for Areas IIIE, IV, V and VIW, based on JARPA and
JARPAII data (Matsuoka and Hakamada, 2014). In this study, no formal analysis has been conducted
but it is probable that the trend of DIW is increasing (Fig. 8). There is a need for continued monitoringof the abundance and abundance trends of this species, especially because it provides an excellent
opportunity to improve our understanding of the dynamics of baleen whale populations recoveringfrom low levels.
Fin whale
Fin whales ranked 5th for 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
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was 4.11 individuals. This species was more frequently encountered in Areas V and VIW than in Areas
IIIE and IV in both northern and southern strata. High density areas were observed in Areas IIIE andIV, particularly between 55°E and 80°E, and in Area V between 163°E and 170°W (Figs. 5a and 6a).
Fin whales tended to be distributed more northerly than blue whales (Fig. 7a). The DIW of this species
was 1.475 for the whole period and the indices increased from December to March (Fig. 9).
In the summer feeding grounds in the Antarctic, fin whales occur year-round, but a higher density
is found from November to May (Kasamatsu et al., 1996; Mackintosh, 1966). These whales can befound as far south as 65 – 70°S, but most of the population seems to occur north of 60°S (Miyashita
et al., 1995). Catches occurred throughout the Antarctic, but most whales (~73%) were taken in IWC
Management Areas II and III (Kasamatsu et al., 1996). Sighting data of this study suggest that the fin
whale’s spatial distribution varies across ocean basins. In this study, no formal analysis has been conducted but it is probable that there is an increasing trend of DIW (Fig. 8). Historically more blue
whales were caught than fin whales in the earlier years of pelagic whaling, and thus fin whales arelikely less depleted than blue whales now, given their much higher sighting rates. There have been acouple of genetic studies on population structure for fin whales in the management Areas III, IV, V
and VI (e.g. Goto and Taguchi, 2019), but these studies did not find any genetic structure in the
research area.
Sei whale
The sei whale was rarely sighted in the research area. A total of 36 schools (59 individuals) weresighted south of 60°S (Table 2), with no calves observed. Observed mean school size was 1.64 individuals. Sei whales occurred more frequently in Areas V and VIW than in Areas IIIE and IV in thenorthern strata (Fig. 5a). High density areas were observed in Area VW, particularly between 150°E
and 160°E (Fig. 6a). Sei whales were tended to distribute more northerly between 40°S and 45°S
compared to fin and blue whales (Fig. 7a). The DIW of this species was 0.017 for the whole research
period.
In summer, sei whales do not venture into higher latitude waters near the Antarctic continent as muchas some other baleen whales. Most of the population occurs between 40°S and 60°S, usually north of
the Antarctic Convergence (Miyashita et al., 1995). Juveniles are found further north than matureindividuals. Occurrence in low latitude wintering grounds has been recorded from March to December,but abundance 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 the seasons progress, relatively morewhales are observed 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 of previous studies.
Antarctic minke whale
The Antarctic minke whale was the most frequently sighted species throughout the surveys. A totalof 25,507 schools (69,076 individuals) were sighted south of 60°S (Table 2). No calves were observed.
Observed mean school size was 2.71 individuals. High density areas were observed along the ice-edge,
especially between 140°E and 160°E, in the Ross Sea and the Prydz Bay (Fig. 5b). Antarctic minke
whales were widely and evenly distributed in the area south of 60°S (Figs. 6a and 7a). The DIW ofthis species for the whole research period was the highest of all recorded species (19.561). The indicesincreased from December to February and decreased in March (Fig. 9).
In the austral summer, the majority of Antarctic minke whales congregate in the Southern Ocean,with the greatest densities being close to and within the pack ice, and lower densities with increasing
distance from the ice (Kasamatsu et al., 2000; Hakamada and Matsuoka, 2014a; Herr et al., 2019),
including some north of 60°S. Antarctic minke whales are noticeably well adapted to living within theice (Ainley et al., 2007), but the exact proportion of these whales found within the pack ice, and inpolynyas, is currently a source of debate. It is possible that a large proportion of the population exists

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Fig. 5a. DIW of blue, fin and sei whales in the Indo-Pacific region of the Antarctic, based on one degreesquares (whole research period).
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MATSUOKA AND HAKAMADA

within the pack ice, out of reach of ship-based sighting surveys (Murase et al., 2005; 2014; Shimada
and Kato, 2007; Williams et al., 2014).
There have been a couple of genetic studies reporting some population structure in Antarctic minke
whales which indicated at least two stocks in the research areas: P-stock originating from breeding
grounds in the western South Pacific and I-stock originating in the Indian Ocean. The study also suggested that the two stocks overlap geographically in a wide area of the Antarctic located at 130°E–165°E,
which changes by year and sex depending on the krill availability (Pastene and Goto, 2016).
Dwarf minke whale
Distribution of dwarf minke whale was limited within the research area. There were two separate
areas of distribution between 120°E and 147°E, and between 165°E and 170°W in the northern stratum(mainly between 48°S and 63°S), south of Australia and New Zealand (Figs. 5b, 6a and 7a). The dwarf
minke whale has a white band on the flipper that distinguishes it from the Antarctic minke whale, but
it was only recently identified as separate from Antarctic minke whales (Best, 1985; Rice, 1998;
Pastene et al., 2010). Based on previous 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)
(Branch and Butterworth, 2001). Based on this, no formal analysis has been conducted but it is probable that less than 0.2% of the minke whales south of 60°S are dwarf minke whales. In this study, only
0.129 % (85 out of 66,031) of the identified sightings were dwarf minke whales south of 60°S. Katoet al. (in press) further examined this aspect by a more extended data set.
Humpback whale
The humpback whale held the 3rd rank among the ten species sighted in the research area. A totalof 10,036 schools (18,770 individuals), including 137 calves, were sighted (Table 2). Observed meanschool size was 1.87 individuals. Humpbacks were widely distributed in the research area in both
northern and southern strata. They were rarely found within Prydz Bay and no sightings occurred southof 73°S in the Ross Sea. This is a very curious difference in their distribution compared to blue whales
and Antarctic minke whales. The current distribution map of this species suggests that humpback
whales are encountered more frequently in the sector 80°E – 110°E from the ice-edge to 60°S becauseof its high productivity (Figs. 5b and 6a). A high density area was observed in the north between 58°S
and 65°S (Fig. 7a). In the 80°E – 110°E sector, large scale distribution changes and a “Shift in baleen
whale dominance” from Antarctic minke to humpback whales was observed between 85°E and 110°E(Matsuoka et al., 2011; Matsuoka and Hakamada, 2014; Murase et al., 2014; Hakamada and Matsuoka,
2014b). The DIW of this species was 5.315 for the whole survey period. Indices increased from
December to February and decreased in March (Fig. 9).
There have been a couple of genetic studies reporting some population structure of humpback
whales in the Antarctic (Pastene et al., 2019), which suggested the core distribution areas for each ofthe ‘D: western Australia stock’ and ‘E1: eastern Australia stock’ and possible mixing areas around
130°E.
IDCR/SOWER circumpolar cruises encountered humpback whales more frequently in the sectors
20°E–40°E, 80°E – 100°E and 150°E – 180° (Branch, 2011). It has been suggested that such changes
are related to changing oceanographic and krill environment conditions such as the effect of regime
shift in global sea-surface temperatures in relation to El Nino-southern oscillation events (Watanabe
et al., 2014; Naganobu et al., 2014). This suggestion should be further investigated in the future.
Southern right whale
A total of 235 schools (298 individuals), including six calves, were sighted (Table 2). Distribution
area of this species was limited at certain longitudes of the sector 80°E – 135°E, south of Western

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Fig. 5b. DIW of Antarctic minke, dwarf minke and humpback whales in the Indo-Pacific region of the
Antarctic, based on one degree squares (whole research period).
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MATSUOKA AND HAKAMADA

Australia (Figs. 5c and 6a). Sighting rate of mother and calf pairs was 2.54% (6 out of 235 schools)
which is highest number compared to other baleen whale species in the Antarctic. Southern rightwhales tended to be distributed more northerly between 40°S and 45°S and more southerly between
62°S and 65°S (Fig. 7a).
The DIW of this species was 0.084 for the whole survey period. Indices increased from December
to March (Fig. 9). In summer, southern right whales migrate south, but generally not as far south asother baleen whale species. Southern right whales appear to occur near the subtropical convergence insummer (January to March) at around 40°S – 50°S (Ohsumi and Kasamatsu, 1985), but there arerecords of these animals much further south, for example, around 60°S – 65°S, south of Australia(Bannister et al., 1999; 2008). The population estimate for the coastal area of Western 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), based on JARPAII data for the 2007/08 season (Matsuoka and Hakamada, 2014). This
indicates that southern right whales migrate and make the Antarctic region an important feeding
ground in the Austral summer.
Sperm whale
The sperm whale held 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). Of these sightings,
most were single large males (96.5%) and, consequently, the observed mean school size was 1.03.
Sperm whales were widely distributed in the research area with high density values being recorded
between 35°E and 100°E and between 170°E and 170°W, in the mouth of the Ross Sea (Figs. 5c and6b). These whales tended to be concentrated on the Antarctic continental slope, on the southern
Kerguelen Plateau, and around the mouth of the Ross Sea, where the depth was usually between 1,000
and 4,000 m. This species was rarely found within Prydz Bay or in the Ross Sea (Fig. 5c). Latitudinally,
sperm whales tended to be distributed between 40°S and 45°S and between 61°S and 73°S (Fig. 7b).
There were no sightings south of 74°S in the Ross Sea. In this study, no formal analysis has been
conducted but it is probable that the trend of DIW was stable (Fig. 8). The DIW of this species was
1.081 for the whole research period. The indices decreased from December to March (Fig. 9).
Southern bottlenose whales
The southern bottlenose whale was ranked 7th among the ten species sighted in the research area.
A total of 1,666 schools (3,045 individuals), including three calves, were sighted (Table 2). These
whales were widely distributed in the research area but were rarely sighted within Prydz Bay and in
the Ross Sea. High density values of this whale were observed between 35°E and 70°E (Figs. 5c and6b). Southern bottlenose whales were latitudinally distributed between 47°S and 70°S (Fig. 7b).
Observed mean school size was 1.83 individuals. The DIW of this species was 0.862 for the wholesurvey period. Indices decreased from December to March (Fig. 9).
Unidentified beaked whales
Unidentified beaked whales held the 4th rank among the ten species sighted in the research area. A
total of 3,175 schools (5,457 individuals), including three calves, were sighted (Table 2). The sightings
were recorded as unidentified species but confirmed as beaked whales. These ‘unidentified beaked
whales’ possibly included the southern bottlenose whale (Hyperoodon planifrons), Arnoux’s beaked
whale (Berardius arnuxii), strap-toothed whale (Mesoplodon layardii), Grey’s beaked whale (M. grayi)and Cuvier’s beaked whale (Ziphius cavirostris). The distribution pattern of the unidentified beaked
whales was consistent with that of southern bottlenose whales (Fig. 5d).
Killer whale
Killer whales held the 2nd rank among the ten species sighted in the research area. A total of 1,472

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Fig. 5c. DIW of southern right, sperm and southern bottlenose whales in the Indo-Pacific region of the
Antarctic, based on Lat.1° × Long.1° squares (whole research period).
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MATSUOKA AND HAKAMADA

Unid. beaked whale

Fig. 5d. DIW of unidentified beaked and killer whales in the Indo-Pacific region of the Antarctic, basedon Lat.1° × Long.1° squares (whole research period).

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 study period (Table 2). These
whales were widely distributed in the research area longitudinally and latitudinally (Figs. 6b and 7b),and were more frequently sighted in the southern stratum. High density areas were observed near the
ice-edge or within Prydz Bay and in the Ross Sea where the pack-ice had melted on the continental
shelf slope in February (Figs. 5d, 6b, 7b and 9). Killer whale abundance in the Antarctic was estimatedby Branch and Butterworth (2001), and appears to be far higher than in any other ocean in the world.
In this study, no formal analysis has been conducted but it is probable that the trend of DIW wasstable (Fig. 8). The large school size of killer whales considered to be fish eaters were often sighted
in the Prydz Bay and the Ross Sea. Further analyses will be required to definitively identify the killer
whale type (fish eater or marine mammal eater etc.) as part of ongoing Antarctic ecosystem research.

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Fin whale

Sei whale

Antarctic minke whale

Dwarf minke whale

Humpback whale

Southern right whale

Fig. 6a. The longitudinal band of DIW for blue, fin, sei, Antarctic minke, dwarf minke, humpback and southern
right whales in the Indo-Pacific region of the Antarctic, based on Lat.1° × Long.1° squares (whole research
period).
Sperm whale

Southern bottlenose whale

Unidentified beaked whale

Killer whale

Fig. 6b. The longitudinal band of DIW for sperm, southern bottlenose, unidentified beaked and killer whales in
the Indo-Pacific region of the Antarctic, based on Lat.1° × Long.1° squares (whole research period).
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MATSUOKA AND HAKAMADABlue whale

Fin whale

Sei whale

Antarctic minke whale

Dwarf minke whale

Humpback whale

Southern right whale

Fig. 7a. The latitudinal band of DIW for blue, fin, sei, Antarctic minke, dwarf minke, humpback and southern
right whales in the Indo-Pacific region of the Antarctic, based on Lat.1° × Long.1° squares (whole research
period).

Sperm whale

Southern bottlenose whale

Unidentified beaked whale

Killer whale

Fig. 7b. The latitudinal band of DIW for sperm, southern bottlenose, unidentified beaked and killer whales in the
Indo-Pacific region of the Antarctic, based on Lat.1° × Long.1° squares (whole research period).

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Fin whale
4.00

0.05

0.40

3.50

0.04

0.35

0.03

2.50

0.20

2.00

DIW

0.25

DIW

DIW

0.04

3.00

0.30

1.50

0.15

0.05

0.50

0.00

0.00

1987

1991

1995

1999

2003

2007

0.01
1987

1991

1995

30.00

14.00

0.07

12.00

0.02

5.00

0.01

0.00

0.00
2003

2007

1987

1991

1995

1999

2003

0.00

2007

1.80

1.40

1.60

DIW

DIW

0.00

0.00

1991

1995

1999

2003

2007

2003

2007

1.00
0.80
0.60

0.40
0.20

2007

1.20

0.80

0.05

1999

1.40

0.60

0.10

1995

S. bottlenose whale

1.60

1.00

0.15

1991

Season

1.20

1987

1987

Sperm whale

0.20

2003

2.00

S. right whale

0.25

2007

6.00

Season

0.30

2003

4.00

Season

0.35

1999

8.00

0.04

10.00

1995

10.00

0.03

1999

1991

Humpback whale

0.08

DIW

DIW

15.00

1995

1987

Season

0.05

20.00

DIW

0.00

2007

0.06

25.00

DIW

2003

Dwarf minke whale

Ant. minke whale

0.40
0.20
1987

1991

1995

1999

2003

2007

SeasonSeasonUnid. beaked whales

0.00

1987

1991

1995

1999

SeasonKiller whale

3.50

10.00
9.00

3.00

8.00

2.50

7.00
6.00

DIW

2.00
1.50

5.00
4.00
3.00

1.00

2.00

0.50
0.00

1999

Season

35.00

1991

0.02

0.01

Season

1987

0.03

0.02

1.00

0.10

DIW

Sei whale

0.45

1.00
1987

1991

1995

1999

2003

2007

Season

0.00

1987

1991

1995

1999

2003

2007

SeasonFig. 8. Plot with time trends in DIW for each species and unidentified beaked whales in the Indo-Pacific regionof the Antarctic (south of 60°S) during 1987/88 to 2008/09 seasons.

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MATSUOKA AND HAKAMADA

Fig. 9. Yearly trend in DIW for baleen (top) and toothed (bottom) whales inthe the Indo-Pacific region of the Antarctic (south of 60°S) during 1987/88
to 2008/09 seasons.

Conclusions

Importance of monitoring whale populations
Most large whales were heavily exploited during the past century and most of the stocks in theSouthern Hemisphere were substantially depleted. In the Antarctic Ocean, catches of southern right,
humpback, blue, fin and sei whales were prohibited in 1932, 1963, 1964, 1976 and 1978, respectively.
Eighty years have passed since the southern right whale has been protected, and more than 50 years
have passed since the humpback whale and blue whale have been protected. In the coastal waters ofSouth America, South Africa and along the east and west coasts of Australia, significant recovery ofsouthern right whales and humpback whales in these breeding areas has been recently reported. On
the other hand, the information on the present status of pelagic species, such as blue, fin and sei whales
was limited. The IWC/IDCR-SOWER cruises have covered the same area every year for 6 years
however this is insufficient for monitoring the ecosystem. On the other hand, JARPA and JARPAII
have been monitoring baleen whale species populations by large-scale and long-term line transect
surveys for over 30 years in Areas IV and V. However, the survey years is still not enough to detect

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precise yearly trends for whale populations. For this reason, the JASS-A (Japanese Abundance andStock structure Surveys in the Antarctic) was started from the 2019/2020 season as a successor to theJapanese Antarctic survey programs such as JARPAII and NEWREP-A (New Scientific Whale
Research Program in the Antarctic Ocean), in order to continue to provide additional information about
the recovery of whale stocks (Government of Japan, 2019).
Relationship between distribution and oceanographic conditions
There was a common pattern for several whale species to concentrate mainly in the sector
80°E–110°E, south of 60°S. This area is characterised by a large meander (rise to 61°S and slowmoving down to 63°S) of the southern boundary of the Antarctic Circumpolar Current (ACC), which
seems to be caused by large-scale upwelling with nutritious bottom waters, resulting from the bottom
shape of the southern Kerguelen Plateau (Watanabe et al., 2014; Naganobu et al., 2014). The BROKE
Australian Antarctic survey previously indicated the possibility of large-scale upwelling between 80°E
and 100°E (Bindoff et. al., 2000). In the JARPA 1999/2000 cruise, a high density of Euphausiids wasreported between 100°E and 120°E (Murase et al., 2002). Humpback, southern right, large male spermand southern bottlenose whales used this longitudinal section between 80°E and 100°E as their key
feeding area from December to March. It is necessary to further investigate the relationship between
whale distribution and oceanographic condition shifts such as the effect of regime shift in global seasurface temperatures in relation to El Nino-southern oscillation events (Matsuoka et al., 2003;
Watanabe et al., 2014; Naganobu et al., 2006; 2014).

Acknowledgements

We are grateful to all successive cruise leaders, researchers, captain and crew members for their hard
works under difficult conditions in the JARPA and JARPAII surveys from which the data used in thepresent study were collected. We also would like to express our gratitude to Drs. Seiji Ohsumi(deceased), Hiroshi Hatanaka, Hidehiro Kato, Yoshihiro Fujise and Luis Pastene of the Institute of
Cetacean Research, Dr. Tomio Miyashita, the National Research Institute of Far Seas Fisheries(Shimizu), Dr. Hiroto Murase, Tokyo University of Marine Science and Technology, for their usefulcomments on earlier versions of this paper. We also thank to Mr. Nishiwaki Shigetoshi, secretary andother members of the Institute of Cetacean Research (ICR) for their contribution for the database. All
photographs are provided by ICR. The manuscript benefited from helpful comments from threeanonymous reviewers. Finally, we are deeply grateful for the fair and constructive reviews of anonymous reviewers.

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Received: October 17, 2019
Accepted: March 31, 2020
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MATSUOKA AND HAKAMADA© ICR
Photo 1. Two surfacing Antarctic blue whales during biopsy experiment in the Antarctic.

© ICR
Photo 2. Five fin whales surfacing in the Antarctic.

© ICR
Photo 3. Surfacing sei whale.

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DENSITY DISTRIBUTION OF ANTARCTIC WHALES© ICRPhoto 4. Seven Antarctic minke whales surfacing near pack-ice.

© ICR
Photo 5. Surfaced humpback whale in the Antarctic.

© ICR
Photo 6. Surfacing southern right whale during biopsy experiment in the Antarctic.
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MATSUOKA AND HAKAMADA© ICR
Photo 7. Surfacing sperm whales near pack-ice in the Antarctic.

© ICR
Photo 8. Surfacing southern bottlenose whales in the Antarctic.

© ICR
Photo 9. Killer whales in the Antarctic.

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