ON THE BALEEN FILTER AREA IN THE SOUTH
PACIFIC BRYDE'S WHALESAKITO KAWAMURA
Faculty of Fisheries, Hokkaido University, Hakodate

ABSTRACTThe baleen filter area of the South Pacific Bryde's whale was examined,
and found that the total filter area in terms of square meters was 1.43-1.99(Av. 1.75) in male, 1.19-2.40 (Av. 1.95) in female, while it was 1.04-1.92(Av. 1.64) in male, 1.10-2.44 (Av. 2.02) in female in the North Pacific animals. The averaged filter area per unit body length (m2 /m body length) of
being combined both sexes was 0.136 in the South Pacific animals while it was0.145 in the North Pacific animals. It was indicated that the South Pacificanimals are smallest in the filter area of Bryde's whale ever examined, andthey are possibly separated from the North Pacific populations occurring inboth northern pelagic and coastal waters.
INTRODUCTION

It has been known that Bryde's whales in the North Pacific show a polymorphic,a considerable variety on both the whole structure and shape of filtering apparatus, and details of baleen plates (Kawamura and Satake, 1976; Omura, 1977).
Although Kawamura and Satake (1976) did not find any conclusive morphologicaldifferences among a possible localized populations except one supposition that there
seems to exist two or three characteristic groups of animals in the North Pacificregion. The differences which made them be separated were the shape of baleen
plates such as the width versus length quotient and the total filter area, which may
roughly correspond to those ' offshore ' and ' inshore ' types found in the South
African waters (Best, 1977). Two of them possibly mingle with each other in thewaters off Sanriku, northern Japan. The baleen plates of the Bryde's whales occurring in the pelagic waters of the North Pacific are relatively slender with finer bristles
than the animals usually occur in the waters around Bonin Islands and in the East
China Sea region, i.e., the filtering apparatus in the former animal is structured
more alike to that of sei whale while the latter two are more alike a 'traditional'
Bryde's whale treated in the previous reports (Omura et al. 1952; Kawamura andSatake, 1976, Figs 8, 10 and Table 8). Since filtering apparatus in baleen whales is
supposed to be an organ closely related to feeding strategies by an inter- and/orintra-specific relationships under various state of feeding environments (e.g. Kawamura, 1974), possible morphological changes acquired through the adapation for
the existence might be found. It seems, therefore, to be an interest to examineand compare the filter area of Bryde's whales came from various localities with aSci. Rep. Whales Res. Inst.,

No. 30, 1978, 291-300.

292

KAWAMURA

hope to find characteristics by each local population since there exist very few
information concerning the identity of Bryde's whale populations throughout thewarmer waters over the world.
MATERIAL AND METHOD
The material dealt with in this report was obtained from the animals caught under
the scheme of special permission in the tropical South Pacific between New Zealandand Fiji Islands during 1976/77 season (Ohsumi, 1977) (Fig. 1). Their food wasconsisted exclusively of euphausiids, Euphausia diomedae, E. recurva and Thysanoessa
gregaria, and the general feeding habits have been reported previously (Kawamura,1977), where he discussed considerable nutritional availability for baleen whales.

0;,\OLQMON
10~

IS.

.

~,

.

FIJI IS .

"'CALEDONIA,..
20 .NEW

3040s. '.
to~

E 160

I

N~NO-.-

170

...

.
.
.

.
.

.
.
.
180
170 w

Fig. I. Sea area of catch for the Bryde's whales, 30 October-5 November, 1976.

even in the tropical seas. The filtering apparatus and some related measurements
for a total of 22 out of 113 animals caught by the Yonan Maru No. 2 operation in thewaters mentioned above were measured by the ship's personnel. The measurements
obtained were: 1) length of a row of baleen plates along both palatal ridge andgum level, 2) spread of baleen rows between both sides at their widest position,3) distance from anterior end of baleen row to the largest baleen plates, and 4)
length of baleen plates including minor plates along the meshed filter surface by aninterval of every 30 cm so as to be calculated the whole inside filter area by reappearing the unfold filter shape. The particulars of measurements concerned were
given in Appendix Table 1 along with the proportions against body length. Dataand figures for the North Pacific Bryde's whales used in this report were quoted
Sci. Rep. Whales Res. Inst.,
No. 30, 1978.

293

BALEEN FILTER AREA

from Kawamura and Satake (1976) .
. RESULT AND DISCUSSION
In order to examine the shape of oral cavity in horizontal plane two dimensions werefigured (Fig. 2). The length of a row of baleen plates along gum level keeps fairly
constant and proportional growth with the length of palatal ridge. As far as thesefigures are concerned, there found no significant differences in this relationships
between the North Pacific and South Pacific animals. However, when we see thequotient for maximum spread between both sides of baleen rows versus length ofpalatal ridge, it is observed on the whole that the South Pacific animals show atrend of more prominent oval shaped oral cavity or more larger hunging angle inbaleen row (Fig. 3). The hanging angle (8) for the North Pacific animals ranged
43°-56° (Kawamura and Satake, 1976, Table 3), and the South Pacific animal
seems to be angled more largely in the overall filter shape. In this connection, it isnoteworthy that there were two males whose relative spread of baleen row wasmore than a half of its across along the principal axis. No definite defferences were03000 0• NORTH PACIFIC

280

0

SOUTH PACIFIC

'i:
u~260

w

"'
00;;:! 240

••

__J

""~~ 220•..of':•• ea

00W-O"'200t,;

0z'.:! 180
130

•

f0

110~~_._......__._...._..._..__...._..__.___._.................._.__._......_.........
HO 180 200
220
240
260
280300320
340
LENGTH OF A ROW OF BALEEN PLATES ALONG GUM LINE (CM)

Fig. 2.

360

Two dimensions related to the shape of oral cavity in horizontal plane.

observed in this relationships between both sexes.
The filter area for the North Pacific animals develops proportionally with
their body length in the animals of larger than 11 m, while it was significantly small
in the younger animals (Kawamura and Satake, 1976, Fig. 9). Concerning this
discontinuous developmental :figures, Kawamura and Satake (1976) suggested apossible rapid development of :filtering apparatus around weaning period. On theother hand, the :filter area for the South Pacific animals showed fairely constantdevelopment (Fig. 4). It is, however, observed that the filter area in many South
Pacific animals was in the midst of both outside and inside filter area for the North
Sci. Rep. Whales Res. Inst.,
No. 30, 1978.

294

KAWAMURA

Pacific animals.
Comparing these figures, it was clearly noticed that the absolute values forthe filter area in the South Pacific animals were appreciably smaller, say, 0.20.3 m 2 , than that known in the North Pacific ones. To make smooth the variations possibly due to the different composition of body length between northernand southern populations, the filter area per unit of body length was calculated(Fig. 5 ). The values expressed by square meters of filter area per 1 m body length
again showed a clearly smaller relative filter area in the South Pacific animals, andthis trend may become more clearer especially in the animals larger than 12.5 m,i.e., the larger the animal, the smaller relative filter area per unit of body length.

<!le NORTH PACIFIC:;: 0.5o SOUTH ~AC!FICw

Cl-'~~-'~

0..

~

lL

6f,<JI

0:c

1-<!lz,,pw-'.._3~6'I"-'c(iiw
w

coOI;"'~"'z~ 0.4

~

p~

#

#
61

lL0·Clc(w0::0..
Vl::;:::::;:::.:::>~ 0.3""O~iU--~--L---'--'----'--'-__.___.___.__.
067891011 12
13BODY LENGTH (M)

1415

16

Fig. 3. Quotient between the spread of both baleen rows and the length of oralcavity. An oval shape of baleen rows in their horizontal arrangements is more
prominent in the South Pacific animal than that of the North Pacific, whichsuggests a possible larger trend in hunging angle of each baleen plate in the South
Pacific animal than the North Pacific.

The averaged relative filter area for both the North and South Pacific animals was0.145 and 0.136 (m 2 /m body length) respectively. Two instances of relative small
filter area (0.046 and 0.094 m 2 /m body length for Nos 79 and 80 in Appendix
Table 1) though not by far the extent found in the North Pacific animals, mayagain make us confirm a very rapid development of filtering apparatus aroundweaning period.
Sci. Rep. Whales Res. Inst.,
No. 30, 1978.

BALEEN FILTER AREA

295

Although the number of animals and/or materials examined to date is still
very few, it seems to be clear that the development of filter area in the South PacificBryde's whales may relatively be poorer by the magnitudes of 6.2-10.3% smaller
than the North Pacific animals in terms ofrelative filter area per unit of body length.
Comparing the total filter area for Bryde's whales with that of another baleen
whale species by interporating the data onto Fig. 8-6 by Kawamura (Kawamura,1974), it is observed that the Bryde's whales are intermediately characterized between sei and fin whales, and the figures for the former animals may correspond to2.8
2.6• NORTH PACIFIC

2.40

•

SOUTH PACIFIC

•

2.200

2.0

•
•

i 1.8
ui·::::>"
I-

1.60..
0..

1.4<!ll. 2et:
Cl<et:~••w_J•++•o ++1.000++~LL.

0

JI 0oo+o• +o+•Cl<I-0•ooOo

et:
z:0

•• 00LL.
00.8

et:
w
Cl<et:

0.6

++

0.4
00.2
078910111213 1415 16

BODY LENGTH (M)
Fig. 4. Total filter area for both the North Pacific and the South Pacific Bryde'swhales. An outer surface filter area for the North Pacific animal is shown bythe cross.

that of humpback and minke whales. The general food habits of baleen whales(e.g. Nemoto and Kawamura, 1977) may well describe the result due to thesecharacteristics in the structure of feeding apparatus.
So far as the result from 120 Bryde's whales in the South Pacific and the Coral
Sea, and 105 animals in the Indian Ocean are concerned, they fed solely upon
euphausiids, Euphausia diomedeae, E. recurva, and Thysanoessa gregaria (Kawamura,1977), while the 'offshore ' form Bryde's whales in the South African waters has
Sci. Rep. Whales Res. Inst.,

No. 30, 1978.

KAWAMURA

296
0.20

• NORTH PACIFIC•• ••0Io• o---.... --91tOo\----·---0 SOUTH PACIFIC

0.15oO-·-·-· -·-·--.0-·00 •00.100.050f oO• •000.01

78glon1213141516

BODY LENGTH (M)
Fig. 5. Filter area per unit of body length shows an appreciably more poorer
developments of filtering apparatus in the South Pacific Bryde's whales than in theNorth Pacific animals. Averages for both the North Pacific and the South Pacificanimals were 0.145(N=13, broken line) and 0.136 (N =20, chain line) respectively.
The unusual and relatively smaller figures for !two young animals (see Nos 79
and 80 animals in Appendix Table 1) were excluded in taking an average.

been reported to feed mainly upon Euphausia lucens, E. recurva, Nyctiphanes capensis,
Thysanoessa gregaria and several species of micronektonic fish (Best, 1977). To see
the dominancy of E. recurva in the stomach of fin, sei, humpback and pygmy blue
whales in addition to Bryde's whales at Durban (Bannister and Baker, 1967), E.
recurva may be considered to play an important role in the nutritional ecology ofbaleen whales widely over the warmer sea region. The coincidence with the food
habits in both above mentioned Bryde's whale populations may suggests that theanimals in the South Pacific are very similar to ' offshore ' form, and they must be
similar' form' to the animals occurring in the waters of Bonin Islands and southerncoastal regions. However, the former animals are possibly be separated morphologically from those occur in the pelagic North Pacific although Ohsumi (1977)
thinks the latter can also be reffered to the ' offshore ' form. On the other hand,
Nemoto and Kawamura (1977) gives a figure in the order of selection of foodby baleen whales as 88.9% of Bryde's whales fed upon euphausiids and the rest11.1 % was composed of fish diet. This may suggests the animal to be similar to'offshore' form. However, the food item of baleen whales itself is so variablewith the change of feeding ground under the multi-specific structure such as theNorth Pacific (see Kawamura, 1973; Nemoto and Kawamura, 1977), and hardly
be determined by the morphological character alone. The clear difference in thesize and shape of North Pacific pelagic form from those in the southern coastal
Sci. Rep. Whales Res. Inst.,
No. 30, 1978.

BALEEN FILTER AREA

297

waters of Japan indicates the former animals, if not entirely, could be separated
from the latter as well as the South Pacific Bryde's whales which also could be
separated from the northern population by their appreciably smaller filter area.
REFERENCESBANNISTER, J. L. and A. de C. BAKER, 1967. Observations on food and feeding of baleen whales at Durban.
Norsk Hvaifangst-Tid., No. 4 : 78-82.
BEsT, P. B., 1977. Two allopatric forms of Bryde's whale off South Africa. Rep. int. Whal. Commn, (Specialissue 1): 10-38.
KAWAMURA, A., 1973. Food and feeding ofsei whale caught in the waters south of 40°N in the North Pacific.
Sci. Rep. Whales Res. Inst., 25: 219-236.
KAWAMURA, A., 1974. Food and feeding ecology in the southern sei whale. Sci. Rep. Whales Res. Inst .. ,26: 25-143.
KAWAMURA, A., 1977. On the food ofByde's whales caught in the South Pacific and Indian Oceans. Sci.
Rep. Whales Res. Inst., 29: 49-58.
KAWAMURA, A. and Y. SATAKE, 1976. Preliminary report on the geographical distribution of the Bryde's
whale in the North Pacific with special reference to the structure of filtering apparatus. Sci. Rep. Whales
Res. Inst., 28: 1-35.
NEMOTO, T. and A. KAWAMURA, 1977. Characteristics of food habits and distribution of baleen whales withspecial reference to the abundance of North Pacific sei and Bryde's whales. Rep. int. Whal. Commn,(Special issue 1): 80-87.
0HSUMI, S., 1977. Bryde's whales in the pelagic whaling ground of the North Pacific. Rep. int. Whal.
Commn, (Special issue 1): 140-149.
OMURA, H., 1977. Review of the occurrence of Bryde's whale in the Northwest Pacific. Rep. int. Whal.
Commn, (Special issue 1): 88-91.
OMURA, H., S. NrsHIMOTO, and K. FUJINO, 1952. Sei whales (Balaenoptera borealis) in the adjacent waters ofJapan. Japan Whaling Assoc., 80 p.

Sci. Rep. Whales Res. Inst.,
No. 30, 1978.

KAWAMURA

298
APPENDIX TABLE I.
[.

815

Measurements on filtering apparatus for the South Pacific Bryde's whales caught
4559

60

62

68

71

72

7374

2.

30 x30X

31 x

1 XI

1 XI

2 XI

2 XI

2 XI2 XI

2 XI

2 XI

3.

25-06

23-32

24-49

24-32

25-00

24-42

24-38

24-49

24-45

24-49

24-48

177-34177-50177-48177-19177-40177-18177-27177-24177-25177-26177-18

4.

M

M

M

FM

FM

FFM

M

5.

13.4

13.2

13.6

15.5

13.0

13.0

12.1

13.5

14.9

13.1

12.5

6.

Nil

Nil

Nil

Eu+Eu-1\\1-Eu-\\t

Eu-\\tEu-\\tEu+tNil

Eu-\\t

None

None

7.

108 (M)

None

8.

4.0

3.5

4.0

5.0

4.5

4.0

3.5

4.0

5.0

3.5

4.5

9.

278

300

276

336273274

255

273

316

276

274

20.75

22.73

19.85

21.68

21.00

21.08

21.07

20.22

21.21

21.07

21.92

255

273

267

319

265

255

244

243

294

254

252

19.03

20.68

20.58

20.38

19.62

20.17

20.07

19.48

19.73

19.39

20.16

112

112

140

110

107

99

99

120

136

103

110

8.36

8.48

9.03

8.46

8.23

8.18

8.18

8.89

9.12

7.86

8.80

187

195

218

180

159

155

155

208

246

195

165
13.20

10.
11.
12.

13.96

14.77

14.06

13.85

12.23

12.81

12.81

15.41

16.51

14.89

13.

1.97

1.92

1.79

2.40

1.65

1.59

1.44

2.08

2.04

1.67

1.9914.

0.15

0.15

0.15

0.13

0.12

0.12

0.12

0.15

0.14

0.13

0.16

Key to the numbers,
to 14, in the appendix table[. Ser. No.
2. Date of catch (day/month)
3. Position of catch (south latitude and east longitude)
4. Sex
5. Body length of animal (m)6. Stomach contents
7. Body length of foetus (sex)
8. Thickness of blubber (cm)
9. Length, row of baleen plates along gum level (cm)
10. Length, row of baleen plates along palatal ridge (cm)11. Maximum spread of filtering apparatus across both baleen rows (cm)
12. Length, anterior end of baleen row to largest baleen plates (cm)
13. Total area of filtering apparatus (m 2 )*14. Total area of filtering apparatus/Body length (m 2/m body length)* Total inside surface filter area corresponds to 'Si' given in Kawamura and Satake (1976, Appendix IIand Fig. 8)

Sci. Rep. Whales Res. Inst.,
No. 30, 1978.

BALEEN FILTER AREA
by the Tonan Maru No. 2 fleet in 1976.
7576

77

79

299

Percentage proportions to the body length is given in bold faces.
808687889395104'2 XI

2 XI

3 XI

3 XI

3 XI

3 XI

3 XI

3 XI

3 XI

3 XI

4XI

24-30

24-47

24-50

24-45

24-49

25-02

25-08

25-08

24-52

24-37

25-35

177-39177-15177-22177-28177-26177-15177-11

177-11178-08178-04178-30

F

M

M

F

F

M

M

M

F

M

F

10.5

13.8

13.5

7.1

9.3

13.1

13.5

13.6

14.6

12.9

12.7

Eu+

Eu+t

Eu+

Eu+

Nil

Eu+t

Eu+

Eu+

None

Nil

Eu+

None

None

None

Eu+
None

4.0

4.5

3.5

3.5

3.0

4.0

4.5

4.5

5.5

4.5

3.5

220291273135

189

258

282

270

322

280

302

20.95

21.09

20.22

19.29

20.32

19.69

20.89

19.85

22.05

21.71

23.78

219

273

125

187

230

255

253

300

255

270

20.86

19.78

17.86

20.11

17.56

18.89

18.60

20.54

19.77

21.26

96

106

107

45

80

116

135

103

124

115

110

9.14

7.68

7.93

6.43

8.60

8.85

10.00

7.57

8.49

8.91

8.66

150

190

188

80

118

177

193

185

230

169

210

14.29

13.77

13.93

11.43

12.69

13.51

14.29

13.60

15.75

13.10

16.54

1.19

1.67

1.59

0.33

0.88

1.83

1.92

1.43

2.33

1.89

2.03

0.11

0.12

0.12

0.05

0.09

0.14

0.14

0.11

0.16

0.15

0.16

Sci. Rep. Whales Res. Inst.,
No. 30, 1978.

".""..;;.

~~~.~~.~~"~~~~

femalefemale1.19-2.40(1.95)
1.10-2.44(2.02)

0.113-0. 160(0.143)

1.43-1.99(1.75)
I.04-1.92(1.64)

0.105-0. 159(0.133)

12.23-16.54(14.97)
10.83-11.88(11.36)

0.103-0. 156(0.137)

12.81-14.89(13. 79)
9.91-12.96(11.22)

0. 102-0. 174(0. 154)

7 .57-10.00(8.40)
8.23-9.14(8. 79)

6.53-8.88(7.88)
8.02-8. 76(8.41)

c:;:<:!
19.48-21.26(20.30)

19.93-20.07 (20.00)

>

~>
~>
17 .56-20.38(19.50)

18.64-20.35(19.50):i\

19.69-22.73(20.91)
20.22-23.78(21.57)

19.20-22.14(20.65)
17.59-22.11 (20.96)

10.5-15.5(13.53)

96
10.8-14.2(12.93)

137

12.1-13.8(13.18)

30 X-4 XI 1976

24 VII-3 VIII 1976

10.1-12.7(11.87)

South Pacific**(Pelagic)

North Pacific*(Japan, coastal)* Based on data by Kawamura and Satake (1976)** Figures for those unusually smaller animals (Nos 79 and 80, see Appendix table 1) were excluded from the calculation on right column.

femaleTotal filter area/Body length, male

femaleTotal filter area, maleLength, anterior end of baleen row to largest baleen plates, male

femaleMaximum spread of filtering apparatus across both baleen rows, male

femaleLength, row of baleen plates along palatal ridge, male

femaleLength, row of baleen plates along gum level, male

femaleBody length, male

No. of animal examined, male

Period of catch

Locality

Averaged figure is given in parenthesis.

Comparison of proportions and filter area between the North Pacific andSouth Pacific Bryde's whales.

APPENDIX TABLE 2.

0""0