STOCK OF THE ANTARCTIC MINKE WHALE
SEIJI OHSUMI*, YASUAKI MASAKI*
AND AKITO KAWAMURAINTRODUCTION
Although the minke whale belongs to genus Balaenoptera which is a main object ofmodern whaling, it has not been interested as an object for large-sized whaling
especially for the pelagic whaling, because it is the smallest species of the genus.
Minke whale has been caught as one of the objects of small-sized whaling in the
coast ofJapan, and in the coast of Norway many minke whales have been caught since1930's (Jonsgard, 1962). However, they had been seldom caught as a food of crew
during sperm whaling season in the pelagic whaling.
Now, the main object species of whaling have changed from larger species tosmaller ones in the history of whaling. For example, the sei whale (Balaenoptera
borealis) which had been seldom caught in the Antarctic whaling during 1950's has
become to the main object recently. So, it will be possible that the minke whale
becomes one of the objects of pelagic whaling in the Antarctic in future. Thereremain many technical and economical problems for the catch of minke whales bymeans of an expedition for large-sized whaling, but if they are solved, the minke
whales mu~t be noticed as the next whale stock, since other baleen whale stocks
have decreased. In actuality, Norway is planning to catch minke whales in the
Antarctic by means of a small factory catcher boat.
Not for the sake of repeating the same failure as the past whaling history, it isneed to prepare for the future operation studying proper policy for management ofstock of minke whale in the present time when a regular whaling does not start. On
this stand point, the present report aims to seize the initial condition of minke whale
stock in the Antarctic, and we will get several biological parameters for the assessment of the stock. Although our materials are not enough for this purpose, we will
be happy if they are used as a preliminary data for the future investigation of thisstock. At the same time, we examine on the identification of so-called minke whales
which distribute in the Antarctic, and try to unify some considerations on this problem.
There are not so many reports on the southern minke whales, and most of thesereports are on classification or morphology (Burmeister, 1867; Gray, 1874; Williamson, 1959, 1961; Utrecht and Spoel, 1962; Zemsky and Tormosov, 1964; Kasuya
and Ichihara, 1965 ), although there are few ecological reports (Taylor, 195 7; Arsenyev, 1960; Kasuya and lchihara, 1965; Gaskin, 1968). On the other hand, we
have more developed reports on the ecology of the northern minke whales (Matsuura, 1936; Jonsgard, 1951, 1962; Stephenson, 1951; Omura and Sakiura, 1956;
Tomilin, 1957; Sergeant, 1963). We will discuss on our results, comparing withthese reports.

* Far Seas Fisheries Research Laboratory, Fisheries Agency.
Sci. Rep. Whales Res. Inst.,
No. 22, 1970, 75--125.

76

OHSUMI, MASAKI AND KAWAMURA

MATERIALS AND METHODSJapanese whaling expeditions have been carried out whale sighting in the Antarctic
with scouting boats belonged to the expeditions. We estimated the distribution andabundance of minke whales using the sighting reports of whales during the seasons
from 1965/66 to 1968/69. As the sighting materials, navigation miles, noon positionand number of whales sighted per day for each scouting boats are used in the present
report.
A Japanese expedition caught many minke whales at the first time in 1963 /64
Antarctic season as shown in Table 10. Kasuya and Ichihara (1965) reported alreadyon these data, so we did not use them as our materials. In 1967/68 season, 597
minke whales were caught by Japanese expeditions. Before the season we planed toinvestigate this whale species. The items of investigation were; species, sex, bodylength (0.1 m unit), stomach contents, foetus, date, time, and position caught,
thickness of blubber (0.5 cm unit), weight of testis (0.1 kg unit), color on flipper andcollection of earplug, ovaries, food, external parasites and foetus for each whales£lensed. Body proportions were measured on 12 individuals, and body weights werealso measured on 6 whales. One of us (A. Kawamura) who was on board of a factory
ship made several detailed investigations and collections on 6 whales. Almost thesame investigations were made on 42 minke whales caught in 1968/69 season.
Collected ovaries were counted their number of corpora lutea and' albicantia.
Earplugs were prepared with the same method as other whale species, and read theirlaminations in the laboratory. Food and parasites were identified their species.
We used catch statistics from the International Whaling Statistics.
MORPHOLOGY

Body color
The general appearance of Antarctic minke whales shows much resemblancewith that of the northern minke whales, Balaenoptera acutorostrata Lacepede, as
having been described in previous reports (Jonsgard, 1951; Omura and Sakiura,
1956): the body is covered with dark grey or bluish dark grey which separates thecoloration of body into upper dark dorsal part and light ventral part along thedorso-lateral line. The dark grey on the dorsal surface expands widely to a wholebody covering the dorsal surface of head, flippers, dorsal fin and tail flukes. The
transitional line which lies between dark grey of black and white ventral side of the
body runs approximately along the dorso-lateral line from the tip of upper mandible
to the tip of tail flukes through just below the eyes and the base of flipper.
Both right and left margins of upper mandible are colored with dark grey inupper half, turning to white toward the lower margin. The coloration of lower
mandible follows almost the same way as that of upper mandible though white part
spreads out more widely so as to reach to the tip of upper or lower mandible.
There are distinct creamy white patch on the tip of right upper mandible being acSci. Rep. Whales Res. Inst.,
No. 22, 1970.

STOCK OF THE ANTARCTIC MINKE WHALE

77

companied by creamy white baleen plates as it is found in fin whales. The extent ofdark coloration on the upper surface of flippers varies with each individuals: someof them show a light slate grey as one may see in the Williamson's description(Williamson, 1959), and the others show a grey as dark as dorsal surface (Pl. I, Fig.I).
The dark grey on the back turns gradually to light silvery grey towards the ventral
side to form a broad transitional zone at the mid-dorso-lateral line. The
transitional zone runs from the angle of gape to the base of tail flukes with slightwaves along lateral side of the body as has been figured by Williamson (1959, 1961),
and Kasuya and Ichihara (1965 ), though the general appearance varies considerablywith each individuals. On the flippers and tail flukes as shown in Pl. I, Fig. 2,
the dark grey parts expand to the under surface to form a narrow dark emargination which grows thicker at the tips. The ventral side of the body including theventral grooves shows complete white such as fin whales, and dark grey patches
which are often seen in sei whales are not observed.
One of the distinct characters of Antarctic minke whales in comparison withnorthern species, B. acutorostrata, is the complete absence of white band on the uppersurface of flippers as having been pointed out by Williamson (1959) on the four specimens of" Balaena" expedition. Our observations on this matter agree well with theprevious records (Williamson, 1959, 1961 ; Utrecht and Spoel, 1962; Kasuya andlchihara, 1965); i.e., the surface of the flippers lacks white band, being coloredwith monotonous dark grey (Plate I, Fig. 1). It can be said in general that the
body color of Antarctic minke whales does not differ from those descriptions ofprevious workers, and some differences observed in the present study could beconsidered as individual variations.
The Japanese whalers catch sight of many minke whales every year while they
operate in the Antarctic. However, they report no evidence on the presence of minke
whales with white banded flippers. According to personal communication with
Williamson, Arsenyev (1960) convinces that no white band in the Antarctic minke
whales is considered as their own peculiar character. However, Taylor (1957) andKasuya and Ichihara (1965) suggested the presence of both kinds of individuals in thesouthern seas. As there are no clear evidences to discard " the presence of minke
whales with white banded flippers ", we cannot but recognize the presence of bothforms in the Antarctic at the present.
Baleen plates
The difference in the coloration of baleen plates comes next as a distinct character of Antarctic minke whales (Williamson, 1959), and we made observations on thenumber and the length of a row of baleen plates in the five individuals (Table 1).
The baleen plates gradually change to bristle-like hair near at the tip of snout to givesome confusions for counting the number of baleen plates. This makes to allow somedifferences in the results obtained by other workers. In practical measurement, we
took the length along the outer margin of gum as the length of a row of baleen plates.
The number of baleen plates was also counted along the same line as a way mentioned
above.
Sci. Rep. Whales Res. Inst.,
No. 22, 1970.

78

OHSUMI, MASAKI AND KAWAMURATABLE I.

This study

Measurements
Body length (m)Sex

Number ofbaleen plates 1>

R
{
L
Whi<•
D k
{ RL
ar
R
Total {
L
R
{L

Breadth (cm)Breadth of dark bandon plates
Breadth/Length2)
I)
2)
3)

8.5
M

!

Length (cm)BALEEN PLATES OF MINKE

{~
{~
{~

126( 56)
114
(121)
188
(177)
302 (167)
26.1
26.1
10.9
11.6
4.6
4.8
0.42
0.44

8.1
M

8.4
M

8.4
M

8.0
F

110( 61)107 ( 57)
59( 27)152
218(174)259
277 (201)
25.4
23.7
13.4
12.8
5.3
6.2
0.53
0.54

261 (182)
24.0
24.8
12.7
13.3
4.8
4.9
0.53
0.54

162(119)

(160)
25.3
24.l
10.8
10.6
3.9
5.0
0.53
0.44

(180)
359 (176)
22.3
22.0
13.7
14.1
3.9
4.1
0.61
0.64

Length of a row of baleen plates is given in parenthesis (cm).
Both right and left were averaged on 5 measurements of the plates.
Approximate value taken from the figure in the text.

The presence of small creamy white baleen plates as often being observed in fin
and sei whales is quite usual in Antarctic minke whales, though the latter carries
them on both right and left of upper jaw. However, the number of creamy whitebaleen plates varies with each individuals, and sometimes it was observed to lackthem completely (Williamson, 1959; Utrecht and Spoel, 1962). In our observations, two individuals carried more plenty cream white baleen plates on the rightthan the left as fin and sei whales (Pl. II, Fig. 2).
In the four individuals examined, a row of baleen plates on the left were consisted of 261-359 plates, and 299 plates spread out 177 cm long on an average. The
upper extreme in the number of baleen plates was 359 plates in 176 cm. long. So
each baleen plates grow thick keeping about 0.5 cm intervals while the others wereabout 0.6 cm intervals on an average. The number of baleen plates observed in ourobservations does not differ so much when compared with the result of 247 or 264
plates (Williamson, 1961) and 270 plates (Utrecht and Spoel, 1962), by allowing
some counting error by the observers. According to the monograph by Tomilin(1957), North Pacific minke whale carries 231-270 baleen plates while North
Atlantic's does 300-325 plates. It goes still more, 270-348 plates and 304 on anaverage in Norwegian minke whales Qonsgard, 1951), while it reduces down to266-295 plates, 275 on an average in the minke whales of Japanese waters (Omura
and Sakiura, 1961).
To figure out an external character of baleen plates the indices from thebreadth/length ratio on the largest baleen plates was calculated after the samemanner as described by Kasuya and Ichihara (1965, p. 40). The largest baleen
Sci. Rep. Whales Res. Inst.,
No. 22, 1970.

STOCK OF THE ANTARCTIC MINKE WHALE

79

WHALE CAUGHT IN THE ANTARCTIC
Williamson(1959),.----...
27.6 (ft)27 (ft)
M
F
70
30

110
75

(1961)

Utrecht & Spoel

Kasuya & Ichihara(1962)(1965)

~

8.4
M

F

8.4

75

134
103

(156)
28.0

264
247
29.0

8.41
M

270 (128)
270(128)
30.0

12.0
4.0
0.43

0.5

23.5
14.0

3.7

4.43)
0.6

plate was 26.1 cm long along the outer edge of the plate which was taken from
8.5 m male. As shown in Pl. III, Fig. 1, three types of baleen plates were noticed,
i.e., " sei whale type " with index number of 0.4, "fin whale type" with 0.6, and"intermediate type" with 0.5. The form of baleen plates described in previous
papers agrees well with our results within the range of individual variations (Table 1).
The breadth of the dark brownish band on the outer edge of baleen plates lies
3.9-6. 7 cm on the whole, and 4.5 cm on the right and 5.0 cm on the left on anaverage. However, as the breadth of the dark band varies even in the plates next
to each other within a few centimeters, this character is considered to be quite
variable in each individuals.

Ventral grooves
The number of ventral grooves at the line to discern both the right and left
anterior end of the flippers was counted on three individuals. The number ofventral grooves was 26 to 30 grooves with 28 as an average, though the number was
given as a half of actual numbers. This agrees well with the result of 30 grooves
counted by Williamson (1961). However, the number of ventral grooves varies
with each individuals and does also by the part of body where counting was madedue to obscure feature at the end of ventral grooves. Since Tomilin (1957) gives
50-70 grooves as a whole number of ventral grooves of minke whales, 56 grooves
for the Antarctic minke whales are considered as same as with those for northern
species.
Sci. Rep. Whales Res. Inst.,

No. 22, 1970.

80

OHSUMI, MASAKI AND KAWAMURA

Body proportions
One of the aims of our minke whale investigation was firstly to know the evidence which makes us assure some taxonomical criterions on several points which
Williamson (1959, 1961) and Utrecht and Spoel (1962) pointed out as a peculiar
charactor of Antarctic minke whales, and secondly, to figure out the details of
character being left unsolved by Kasuya and lchihara (1965). One of them wasa proportional relationship between the umbilicus and the posterior end of theventral grooves, and the other was the length of flipper. For this purpose we madea series of the measurement of body proportions on 10 males and 2 females after themanner of Discovery Investigation (Mackintosh and Wheeler, 1929) (see Table 2,
Appendix I).
Percentages

Me;is1Jrements

11

12

a

13

14

/;

I

b
Tip of snout
to blowhole

17

18

19

20

21

22

I

I

I

I

I

'

'

I

I

'

I

I

I

~-+-~

1------1------1
I

1---- - -- -\- --- --+I

Tip of snout toangle of gape

•

16

I

c

d

15

I

I

I

b

1--j--1cI- - - - - - I'--j- - - - - - - - -I
I

I

a

•'

'

'

I

b
Tip of snout tocenter of eyeI"'
f---1---+c'!--------~-------~
Id

I

1---------1----~

Percentages

37

38

39

40

41

42

43

44

45

46

I

I

I

I

I

'

I

I

'

'

a
Tip of snout to
tip of flipper

I

b
c

d

47

48

"'

1------l- -- ---+
Ir-------+- - ------;'!-----------------------~---------~

Fig. 1. Proportions related to head length on minke whales from the Antarctic, North Pacificand Atlantic Oceans.
- - - Males.
··· · · · · · · · ·· Females.
Antarctic
a: Williamson (1959) A, andUtrecht and Spoel (1962) /:::.,
b: Present study.
North Pacificc : Omuraand Sakiura (1956).
. North Atlantic
d: Jonsgard (1951)

In Table 2 it is noticed that the result agrees well on the whole within 1-2% of
Sci. Rep. Whales Res. Inst.,
No. 22, 1970.

81

STOCK OF THE ANTARCTIC MINKE WHALE

fluctuation notwithstanding the fact that measurements comprised from three different sources. This makes us acertain that the measurement error by each observers is negligible. The body length of the males was between 710 and 850 cm.
Judging from their body length, it is considered that they had almost attained at thephysical maturity. However, there were no individuals whose epiphysis of the fifth
dorsal vertebrae had fused completely.
Percentages

Measurements

23

24

25

'

'

'

b

Notch of flukes
to posteriorcemargination of
dorsal fin
d

27

28

I

I

29

30

31

32

33

34

'

'

I

'

I

I

~-+-;

1------- --- ---+-- ---1
1----- - - - --+---- -----+
I

I

a

I

I

I

I

I

'

....

A

'

I

I

I

49

50

51

52

'

b
Notch of flukescto anusd261---+---1

18.67

1---------+---------I'
I-----1

1--j\-- -- ---- --1---- -----

Percentages

41

42

43

44

46

47

48

'

A

'

Notch of flukes b
to umbilicus
c
d

45
I

a

I

'

1------1------1

1--- - - --- - - ---~- ---- ---1

37.33

I

1--s1- -- --- - - ---- -- ---!--- -- - -- --- - - - - - - --;Percentages

46'

aNotch of flukes b
to end ofventral grooves c

47

48

49

50

'

I

I

A

51

52

53

I

'

.

55

56

57

'

'

'

T

1------+------I'

60.5--+- -- -- --- ----IT--1I

1-- - - - - - - - - - - - - - - - - - - - - - -

d

54

43.5

58.7

K~--------------~--t----------------~T--1

Fig. 2. Abdominal proportions on minke whales from the Antarctic, North Pacific andAtlantic· Oceans. Legend as in Figure 1.
.

The proportions to the total body length in terms of the percentages on theanterior part of the body are shown in Fig. 1 with the results obtained previously.
It is clear in the figure that the result agrees well in general with those got by
Williamson (1954) and Utrecht and Spoel (1962). One of the distinct features ofAntarctic minke whales is more larger porportional length about 1.5-4.5 % at eachmeasurements than those of northern minke whales B. acutorostrata, though some of
Sci. Rep. Whales Res. Inst.,

No. 22, 1970.

82

OHSUMI, MASAKI AND KAWAMURA

them overlap each other. The great variation between the tip of snout to the tip offlipper must be the result due to the difference in resting position of the flipper when
they were measured. In addition to larger head in Antarctic minke whales, it isnoticed that the female shows much greater distances about 1.5-2.0 % than the
male. Although the results lack complete reliability due to the variation of age andsex, the difference between both sexes could be considered to be probable with confidence from the same evidence found in physically mature sei whales (Omura,1957) and also in those foetuses (Kawamura, 1969). The only curiosity is the resultof B. acutorostrata which shows the same or rather longer proportional length in the
male. One of the causative facts is that those variation might derived from thedifferent feeding habits in both northern (B. acutorostrata) and Antarctic forms, i.e., thenorthern forms chiefly feed on fishes (Omura and Sakiura, 1956; Jonsgard, 1951),
while the Antarctic minke whales chiefly feed on euphausiids and copepods.
In the Antarctic minke whales the distance from the notch of flukes to theposterior end of dorsal fin lies at middle of two measurements on B. acutorostrata.
However, the difference is included within 3 % on an average, and we have no otherevidence to separate those two types in this measurement. In the following distances
it is noticed that the individual variations are quite distinct between northernand Antarctic minke whales; the distances from anus, umbilicus and posterior endof ventral grooves to the notch of flukes, though the female of Antarctic forms always
keeps about 1 % larger distances than the male, while the male is similarly larger innorthern forms. However, it is difficult to get the conclusive evidence to separate
these two forms at the present state. We need still more data especially on females.
Williamson (1959) reported that there were about 30 cm distance between theposterior end of ventral grooves and umbilicus, and later he (Williamson, 1961)
denied his former description, i.e., the ventral grooves end just at the umbilicus.
Kasuya and Ichihara (1965) also followed the same description. In our observation,
however, the end of ventral grooves and the umbilicus was separated clearly (Plate I,
Fig. 1 and Plate II, Fig. 1) keeping the distance about 39.4 cm, 4-5 % (Table 2, Fig.
2). Utrecht and Spoel (1962) reports that this distance is 1 ft., and this agrees
with Williamson's former description. In northern minke whales, on the other
hand, the distance is slightly greater (5.4-7.6 %) than the Antarctic forms. Accordingly, we cannot but conclude that those are not fundamental difference in bothforms of minke whales.
The proportion of appendages are shown in Fig. 3. As we see in this figure, theflipper of Antarctic forms is longer with the range of 1.5-2.0 % than that of northern
forms. Judging from our result got by averaging the measurements of 12 specimens, the length (7 %) given by Utrecht and Spoel (1962) for Antarctic forms seems
to be a quite unusual case. Our result agrees well with those given by Williamson(1959). It is noticed on the whole in the figure that the flipper is longer in both
northern and Antarctic forms of the male than the female, and the female of Antarctic forms overcome the other among them. There are no differences in the breadthof flipper and the height of dorsal fin. Relatively small length at the base of dorsal finin the Antarctic minke whales suggests that they carry more slender shaped dorsal fin.
Sci. Rep. Whales Res. Inst.,
No. 22, 1970.

83

STOCK OF THE ANTARCTIC MINKE WHALE
Percentages

Measurements

9aFlipper, tip toanterior end oflower border

10

11

'

'

b

12

13

15

14

16

17

I

" .

18

19

20

I

I

I

8

9

10

A

f-------- ---l- - - - -- - ---fIc
I- - - - -- --l- - - - - - - - - --1
Percentages

1

2

4

3

Dorsal fin,vertical height

6

7

6.

"

1--j-----lb""'i--+-icIf----/---1dDorsal fin,length of base5Ia1---j---1bf--\--1Ic

I- - - - -{- - - --1
I

I

I

b
Flukes, width
at insertion

1--/--1i---+--tcId

1--t- ---1
II

1---j----1
Percentages

24aTail flukes,
tip to tip

b

c

25

26

27

29

28

30

31

32

33

34

35

6.

"

'

I

1---f---1
I

I- - - - - - - - --j- - - - -- - - --;Idf- --- -- - - - - - -/------- ---1

Fig. 3. Proportions of appendages on minke whales from the Antarctic, North Pacific andAtlantic Oceans. Legend as in Figure l.

On the total spread of tail flukes, Utrecht and Spoel (1962) pointed out that theAntarctic minke whales show wider spread than the northern forms. However, thespread in the present materials showed that there is considerable individual variation (Fig. 3). By taking the result by Williamson (1959) into consideration, it cannot
be concluded easily on this matter at the present state. The shape of the notch of
flukes showed quite usual one as we see in fin or sei whales (Pl. I, Fig. 2). According
to Williamson (1959, 1961), the tail flukes shows a triangular shape on the whole.
It is, however, indicated that the tail flukes vary with each individual, and some ofthem carry a round curve in the anterior margin to form a quite round tail flukes in
the whole shape (Pl. III, Fig. 2).
Sci. Rep. Whales Res. Inst.,
No. 22, 1970.

84

OHSUMI, MASAKI AND KAWAMURATABLE 2.

MEASUREMENTS OF BODY PROPORTIONS ON

Workers

Present authors

Sex

Males

Measurements

1. Total length
2. Tip of snout to blowhole
3. Tip of snout to angle of gape
4. Tip of snout to center of eye
5. Tip of snout to tip of flipper
6. Eye to ear (center)
7. Notch of flukes to posterior emarginationof dorsal fin
8. Flukes, width at insertion
9. Notch of flukes to anus
10. Notch of flukes to umbilicus
11. Notch of flukes to end of ventral grooves
12. Anus to reproductive aperture, center
13. Dorsal fin, vertical height
14. Dorsal fin, length of base
15. Flipper, tip to anterior end of lower border
16. Flipper, greatest width
17. Tail flukes, tip to tip

Range of proportions as
Meanpercentages
percentagesof totallengthRange oflength(cm)

Meanlength(cm)

710-850
104-120133-170
143-172315-400
39- 44

803.8
112.7
148.3
158.5
359.4
40.7

12.24-15.52
17.07-20.54
18.29-20.48
39.86-47.62
4.71- 5.70

100.00
14.07
18.45
19.73
44.73
5.07

190-254228.3

25.98-30.00

28.35

53- 80193-244330-410375-470
26- 7025- 3531- 60105-139
24- 32210-290

67.0
213.9
372.9
414.1
54.3
29.0
44.9
125.3
28.9
234.3

6.79- 9.41
23.5 7-31.28
41.88-49.52
45.18-55.95
3.33- 8.89
2.98- 4.23
3.69- 7.69
12.50-16.98
2.82- 3.98
25.06-35.80

8.31
26.65
46.54
51.58
6.78
3'62
5.63
15.61
3.61
29.16

TABLE 3. NUMBER OF VERTEBRAL COLUMN OF THE MINKE WHALE
FOETUSES FOUND IN THE ANTARCTIC IN 1967/68 SEASON
Sex

Body
length(cm)

Bodyweight(Kg)

Number of vertebral column
CervicalDorsalLumbarCaudalTotal

Female
Male
Male

48.6
46.5
50.5

2.35
1.80
2.29

7
7
7

11
12*
11

12
12
12

18
18
18

48
49
48

* Included one separated small lib.
Number ef vertebrae
To know the number of vertebrae of the Antarctic minke whale, three foetusescollected in the Antarctic during 1967 /68 season were dissected along their vertebral
column (Table 3), and the following vertebral formula was obtained: C7, DI 1-12,
L12, Ca 18=48-49. One of the foetuses which carried Dl2 proved to carry asmall free rib as the last one of a set. According to Tomilin's monograph on the 13
specimens of B. acutorostrata (Tomilin, 1957), 8 specimens among them had the vertebral formula; C7, Dll, Ll2, Ca 18=48, 3 specimens were 49 in all and 2 specimens
were 50. Later, he reported again on the number of vertebrae of the whales
examined that his specimen should be C7, DI 1, Ll2, Cal8=48. Omura (1957) gives
Sci. Rep. Whales Res. Inst.,
No. 22, 1970.

STOCK OF THE ANTARCTIC MINKE WHALE

85

MINKE WHALES CAUGHT IN THE ANTARCTIC OCEAN
Present authors

Utrecht & Spoel(1962)
Males

Williamson (1959)
Males

Females..-----.-.._

Range of proportions as
Meanpercentages
percentagesof totallengthRange oflength(cm)

Meanlength(cm)

800-930
128-140
162-180
176-190389-42040- 50

865.0
134.0
171.0
183.0
404.5
45.0

15.05-16.00
19.35-20.25
20.43-22.00
45.16-48.63
5.00- 5.38

100.00
15.52
19.80
21.23
46.89
5.19

236-265250.5

28.49-29.50

28.99

88.0
9.68-10.75
245.5
27.42-29.50
435.0
48.38-52.50
471.0
52.69-56.50
30.0
3.13- 3.76
33.5
3.76- 4.00
43.0
4.50- 5.38
(120>140.0) 10.75-17.50
34.0
3.70- 4.13
243.5
27.42-29.00

10.21
28.46
50.44
54.59
3.45
3.88
4.94
14.13
3.95
28.21

86- 90236-255
420-450452-49025- 3532- 3536- 50(100)-140
33- 35232-255

LengthPerLength
Length
PerPer(cm) centages (cm) centages (cm) centages

840

33

229

100.00

3.9

27.4

820
117

100.00
14.3

841
107

100.00
13.0

148

18.0

168
(400.5)
43

20.0
47.6
5.0

237

28.9

33

3.9

221
(388)
(421)
58
38
141.5

26.0
46.0
(50.1)
7.0
4.5
17.0

122

14.8

209

25.4

254

30.0

a following formula as a result obtained from 2 minke whales caught in Japanesewaters; C7, Dl 1, L12, Ca 17-18, Total 47-48. The number of vertebrae of Antarctic minke whales has been the last key point left behind to offer a decisive conclusionin the classification of both northern and Antarctic minke whales. The agreementin the number of vertebrae obtained in this study with those B. acutorostrata is considered to give somewhat conclusive evidence which supports the Antarctic minke
whales as only a subspecies of B. acutorostrata. However, it is still hoped to get andexamined on the skeletal specimens of physically mature individuals for a further
consideration on this matter.

Thickness of blubber
The thickness of blubber at the dorso-lateral line just below the dorsal fin wasmeasured with an accuracy of 0.5 cm. The mean thickness in December was shownin Fig. 4 by the sex and the body length. The blubber grows thicker as the bodylength increases. It is slightly thicker in the male than in the female within thesame class of body length. It is known that blubber of blue whale is variable inaccordance with their sexual conditions; pregnant female has the thickest blubber
and it was most slender in lactating female (Mackintosh and Wheeler, 1929). A
quite high percentages of pregnancy in the Antarctic minke whales supports the casementioned above by those evidence of other whales.
Sci. Rep. Whales Res. Inst.,
No. 22, 1970.

86

OHSUMI, MASAKI AND KAWAMURA

I',

I

\

I

4.5

I

'b

E

u

....
Q)

.D
.D
::l

:c

I

4.0

I

I

\

\

\

b---a.._

R

0

R

'-o-~

./

(/)
(/)
Q)

c
-"'
.~
..c
I-

3.5

3.0
6.0

7.0

8.0

9.0

Body length (m)Fig. 4.

Mean thickness of blubber at each body length in the Antarctic in December, 1967/68.
Open circle and broken line : females,
Closed circle and solid line : males.

Male

Deo. {
Female~---------+--------------!

Male

J'° {

t------t-------------J

Female

2.0

3.0

4.0

5.0

6.0

Thickness of blubber (cm)Fig. 5.

Range and mean of blubber thickness in minke whales in the Antarctic.

There were no enough data to show the seasonal variation in the thickness of
blubber of the minke whale except Omura's unpublished data (Omura, personalcommunication) which were obtained from the minke whale caught in Japanesewaters. As shown in Fig. 5, the mean thickness of blubber in December of 1967/68
season was 3.6 cm in the male and 3.8 cm in the female. In January of 1968/69
season they were 4.2 cm in the male and 4.4 cm in the female. Since the mean bodylength in both seasons can be assumed as the same, it is supposed that the blubber
grows thick during January-February as it is observed in the other baleen whales.
Sci. Rep. Whales Res. Inst.,

No. 22, 1970.

STOCK OF THE ANTARCTIC MINKE WHALE

87

This fact leads to the following consideration that the Antarctic during the australsummer is a main feeding ground for the Antarctic minke whales.
TABLE4.

BODY WEIGHTS OF MINKE WHALES IN THE ANTARCTIC

Items

Measurements (Kg)

Whale number
Body length (m)
Sex

22N l
8.0
Male

22N2
7.8
Male

22N3
7.l
Male

22N4
7.54
Male

22T2
8.2
Male

22T l
9.3
FemaleMeat
DorsalVentralVentral grooves
Munaita*
OthersBone
Skull
Mandibles
Ribs
Vertebrae
Flipper, Scapulae
OthersBlubber
Body
Head
Mandibles
Tail flukes
Others ("Aha ")Viscera
Heart
Lung
Liver
KidneyStomach and pancreas
Intestine
TongueOthersBaleen plates

3,216
1,409
756
320
280
451
837
234
84
82
348
74
15
776
604
89
34
49

2,564
1,104
581
257
165
457
629
168
52
66
274
60
9
(667)
437
67
33
48
82
284
22
26
50
17
25
75
8
61
25

3,285
1,476
646
327
311
525
924
285
82
98
362
85
12
(796)
564
91
39
39
63
343
23
44
54
17
28
73
104
37

4,310
1,844
874
472
453
667
796
248
85
75
305
82
1
922
732
97
26
54
12
494
30
40
76
20
31
81
16
200
36

5,078
2,007
960
525
567
1,019
941
262
115
104
435
100

397
17
39
49
16
28
63
39
146
29

2,970
1,358
696
292
298
326
734
207
62
74
299
82
10
1,725
462
66
52
43
102
550
20
44
65
16
21
142
89
153
34

Total

5,255

5,013

4,169

5,385

6,558

7,961

1,270
717
100
82
105
266
551
38
58
105
24
34
109
75
108
45

*BosomBody weight
The body weight was obtained from six carcasses caught in 1967/68 season byweighing each part of the body, separately (Table 4). The average body length andthe weight were 8.0 m and 5. 7 tons, respectively. To compare with the result
obtained from other balaenopterids, the percentage weights of several parts of the
body were given in Table 5. It is noticed from the table that the ratio of the meathas a tendency to increase against the size of species decrease, on the contrary,
Sci. Rep. Whales Res. Inst.,.No. 22, 1970.

88

OHSUMI, MASAKI AND KAWAMURA

whale oil materials (bones, blubber and internal organs) decrease, except the sei
whale. From the view point of relative weights of the whale parts, the Antarctic
minke whales should be utilized effectively as a resources for meat products rather
than those for the whale oil same as the sei whale.
TABLE 5.

Species

COMPARISON OF PARTIAL BODY WEIGHTS AMONG
SEVERAL SPECIES OF BALENOPTERA

Body length Bodyweight
(m)
(ton)

Blue whalea>
Fin whalea>
Sei whaleb>
Bryde's whale0 >Minke whaled>

24.3
21.1
15.2
13.1
8.0

87.29
51.67
18.15
14.00
5.72

Per cent of partial weight to total
Meat

Bones

39.4
45.5
59.2
46.1
62.4

17.7
16.9
11.1
15.4
14.2

Blubber Internal organs
27.1
23.9
17.1
22.1
15.0

11.6
10.4
10.4
10.6
7.6

a) Nishiwaki (1950), from the Antarctic; b) Omura (1950), from coast of Japan;(1955), from Bonin Islands; d) Present report from the Antarctic.

Others
4.2
3.3
2.2
5.8
0.8

c) Fujino

10 ~

6-

4Q)

tlO

ro
c
c

-8

>-

-0
0

co

Fig. 6.

2 ,_1-

Plot of body weight against body length
for minke whales.
Closed circle : Antarctic Open circle :a) Tomilin (1957),b) Zenkovich(1955),c) Scheffer and Slipp (1948),d) Fry (1935).

0.8 f-

oc)

0.6-

0.40

d)

4

6

8 10

Body length (m)The following formula as a length-weight relationship was obtained from thethe data shown in Fig. 6: that is,
w=0.0466L2.31
where, W: body weight (ton)
L: body length (m)Sci. Rep. Whales Res. Inst.,
No. 22, 1970.

STOCK OF THE ANTARCTIC MINKE WHALE

89

It is noticed in Fig. 6 that the length-weight relationship agrees well with thatobtained from northern minke whales within the body length of 6-9 m, and theformula would be needed some modifications for smaller individual less than 4.0 m
in body length. It is strongly hoped to be accumulated the data of body weight ofsmall individuals of the Antarctic minke whale.
GROWTHAge determination
Earplug is the most useful age character of the baleen whales (Ohsumi, 1967).
Ichihara (1959) and Sergeant (1968) described on the earplug of minke whale.
Ichihara (loc. cit.) notes that the glove-finger of the minke whale belongs to thesimilar type as that of sei and Bryde's whale (Balaenoptera edeni), of which glovefinger has no papilla. And he showed a photograph of a earplug which had 9laminae. Sergeant (loc. cit.) read lamination clearly on only one out of 11 minke
whales' earplugs which were collected in good condition.
The earplug of the Antarctic minke whale is small, and the shape is similar
to that of Bryde's whale. Its longitudinal section is not black as those of the blueand sei whales, and is not so difficult to be read as Sergeant described. But, earplugs of young individuals are so small and soft that it is very difficult to read them,and we think it is need to develop new technics for collection and preparation ofthem.
It has not been confirmed yet on the accumulation rate of lamination of earplug
for the minke whale, and Sergeant (1963) adopted the theory that two laminae
accumulated a year. However, it will be reasonable to adopt another theory that
one lamina accumulates per one year, as it is clearified for the fin whale (Ohsumi,
1964; Roe, 1967).
Jonsgard (1951), Stephenson (1951) and Omura and Sakiura (1956) tried to determine the age of minke whale by means of mode of size distribution, but this method
is not suitable for age determination of whales (Ohsumi, 1967). The age determinaion by means of baleen plate was tried by Stephenson ( 1951) for minke whale,
but the baleen plate can be used as an age character for only young stage, andJonsgard (1951) and Sergeant (1963) noted the ridge of baleen plate in the minke
whale was difficult to be read. Ovaries of minke whale are small, and so corpora
albicantia are small, but it is possible to count them by naked eyes. Although the
corpus albicans has some weak points as an age character, it is used for some problems on reproduction in the present report.
Growth curve
Figs. 7 a and b show the relation between age and body length on the individualsof which age was determined with earplug. Number of materials is not enoughfor drawing good growth curve. Stephenson (1951) drew growth curves in North
Atlantic minke whales, but they will be not true caused on wrong age determination.
Since we have no materials on the whales which are five years and younger,
Sci. Rep. Whales Res. Inst.,
No. 22, 1970.

90

OHSUMI, MASAKI AND KAWAMURA

9.0. ..:. .: ..: ........ . .. . . ...
.-.-- - - - - - - - .
. . ;_: ~: : ~ .. ·; .. :.
. . .. .
..

E

~·--.

~

:5
OD

8.0

/

c

~

>-

-0
0

7.0

.

CD

6.0

5

15

10

20

25

35

30

40

Age (years)
Fig. 7a.

Growth curve of the male minke whales in the Antarctic.

9.0E.....OD

0

.<::

c

8.0

0

00

0

_,

/

/
0

>-

CD

---------0-------0---0-------

/

~
-0
0

0

o o_,-;-o- -

oo

01

7.0

I

/

/

I

I

6.0
I

5

I

10

15

20

25

30

35

40

Age (years)
Fig. 7b.

Growth curve of the female minke whales in the Antarctic.

we can not know the growth of younger age. In addition, we have no knowledges
on the body length at the time of birth for the Antarctic minke whale. On thenorthern minke whales, Jonsgard (1951) and Stephenson (1951) estimated thatthe neonatal body length was 9 feet (270 cm), and Omura and Sakiura (1956) described it as 280 cm. Then, we may estimate the birth length of the Antarctic
minke whale will be 270-290 cm.
MATURITY

Weight of testis
Both right and left testes were weighed on the males which were caught in 1967 /68 and 1968/69 Antarctic seasons. Fig. 8 shows the relation between body length
and weight of larger side of testes for these whales. Although mature and immaSci. Rep. Whales Res. Inst.,

No. 22, 1970.

STOCK OF THE ANTARCTIC MINKE WHALE

91

ture testes as shown by Omura and Sakiura (1956), are not separated clearly in thisfigure the average testis weight increases suddenly at the body length of 7.1 m.
Frequency distribution of testis weight (larger testis for each individual) has
one valley at 0.3 kg, as shown in Fig. 9. The left mountain means immature
testis, and the right one will show the mature group. Separating these two mountains in the valley, the two mountains cross each other at 0.35 kg. Although it
will be need to examine testis tissues histologically, this 0.35 kg will be the mean
testis weight at maturity for the Antarctic minke whale.
3.0

2.5

Q()

..O<'.

2.0

(/)

...,,
(/)
Q)

. :.11; ~;;v::·:.
.. -~ :. :. . :....

+'

0 1.5
...,,
..c

• ••• •... - ..

Q)5:•• .t• .t.

................. '' .......

Q()

1.0

.. ..

.. .

:.
"'/'
• - ••• ·: ~},"-l\~.r-W- • :• ••o~~·"•le•••••\I". .:.:.::::~:'.~~::=:·:·=·.
.. . . .. .. .. ... .
::

0.5

·

.

.

.• ,. . :s. .

. /\ r---:1 ..

.. .. . .

7.0

7.5

d: y,. -:·· & a••.

-·-'N-":--•1-:i-..

6.0

6.5

8.0

8.5

9.0

Body length (m)Fig. 8.

Relation between body length and weight oflarger testis in the males.

Jonsgard (1951) determined the mature testes as 0.225 kg (both testes conbined) for the North Atlantic minke whale, and Omura and Sakiura (1956) reported
it was 200-300 gr (one side of testes) for the North Pacific minke whale. Our
result is larger than these two reports.

Body length at sexual maturity
Assuming that the male of which larger testis is 0.4 kg and over and the female
which has one or more corpus luteum or albicans are recognized as sexually mature,
we obtain size distributions of minke whales caught in 1967 /68 and 1968/69 seasonsby sexual maturity as shown in Table 12.
The maximum lengths of immature whales are 8.3 and 8.8 m for male andSci. Rep. Whales Res. Inst.,
No. 22, 1970.

92

OHSUMI, MASAKI AND KAWAMURA

50

40

(f)

~

co

-C

3:

0

30

ci

z

>c

u

20

"'
"'
~
::J

u

10

Weight of larger testis (kg)Fig. 9.

Frequency of weight oflarger testis in the southern minke whales and the estimationof testis weight at maturity. Broken curve: Immature, Solid curve: Mature100~·--·-·::~::-::®..=-==-@- -o- -o--o.
/~ .....

;O

/

f 80

I
I
/o

::J

-;;;

I

o I

E

I

0 60

I

------------ ---------------- -- - -- ---------- -- --[

+-'

c

I

I'
I :

~"' 40

ol
I

Q)

Q_

I

I

I

20

I
I
I

'

@.1--L®J.___J____J__l®.l.-l.@--l--L

6.0

6.5

/

.J.......J...o.L-J..oL..lo~'-'-L-..U.-'-..l.--'L-L.-'--'-'-'--'-'-'--'---'-'-'---'-~-'--'

7.0

7.5

8.0

8.5

9.0

9.5

Body length (m)Fig. 10.

Proportion of sexually mature minke whales at each length in the Antarctic Area IV.
Closed circle and solid curve : males,
Open circle and broken curve : female.

female, respectively, and the minimum lengths of mature males and females are
6.8 and 7.7 m, respectively. Change of sexual maturity rate by body length classis shown in Fig. 10, and the length at 50 % of maturity is 7.1 and 7.9 m for the
male and female, respectively. These values will be considered as the average
Sci. Rep. Whales Res. Inst.,
No. 22, 1970.

STOCK OF THE ANTARCTIC MINKE WHALE

93

lengths at sexual maturity for the Antarctic minke whale.
There are some reports on the sexual maturity length in the northern hemisphere minke whales (Jonsgard, 1951; Omura and Sakiura, 1956; Sergeant, 1963).
According to the report by Jonsgard, the body length at sexual maturity of theNorwegian minke whale is 24 feet (7.3 m) and 22 feet (6.7 m) for the female andmale, respectively. Omura and Sakiura estimates that it is 24 feet in the female
and 22-23 feet (6.7-7.9 m) in the males from the coast of Japan. The present
values are 0.1-0.4 m larger in the males and 0.6 m larger in the females than thoseof northern minke whales. According to Mackintosh (1965, Table 4), the southernstock is larger than northern stock in the body length at sexual maturity, andthe deviation of the lengths is the same for males as for the females in at least
Balaenoptera species. The average body length of mature Antarctic minke whales
are 8.12 and 8.88 m in the males and females, respectively, and the deviation
between both sexes is 0. 76 m. This value is almost the same as the deviation of
the average length of sexual maturity between both sexes (0.8 m) in the present
report. Therefore, our value of the length at sexual maturity will be true. Comparing the size distributions of North Pacific minke whales with those of Antarctic
minke whales, the deviation of modes is 2 feet (0.6 m) for both the males andfemales, equally. Then, it will be reasonable to consider that the average bodylength at sexual maturity in the males of the northern minke whales is 0.6 m smaller
than that of the Antarctic minke whales as same as in the females.
TABLE 6. AGE DISTRIBUTION OF SEXUALLY IMMATURE
AND MATURE MINKE WHALES IN THE ANTARICTIC
Females

Males
Age
Immature

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

I
2
2

2
3

MatureImmature

Mature

2
2
2
3
5
6
6
9
3
10
6
8
7

2
2
I
2

2

I
2

3

Age at sexual maturiry
We have not yet enough data to determine the age at sexual maturity of the
Antarctic minke whale. Table 6 shows the age distribution by sexual maturity,
based on the reading of earplug lamination. From this table, we estimate thatthe average age at sexual maturity is 7-8 years, and the female attains at sexual
Sci. Rep. Whales Res. Inst.,
No. 22, 1970.

94

OHSUMI, MASAKI AND KAWAMURA

maturity little later than the male. Estimating from the growth curves which
are shown in Fig. 10, the ages corresponded to the body lengths at sexual maturity(7.1 m in males and 7.9 m in the females) is considered to be 7-8 years. Furthermore, in the relation between age and number of ovulation in Fig. 11, the age at
one ovulation is about 8 years.
30

C1J

:;:;

25

c

C1J
0
.D
C1J

-0

0

20

c

C1J
C1J

....,
Q)

:::>

15
0

~

0

0

0
0..
~

0
0
4-

10

0
0

ci

z

0
0

0

0

5
00

0

0
0

/

0

00

5

<50000000

10

0

15

20

25

30

35

Age (year)
Fig. 11.

Relation between age and number of ovulations in the Antarctic minke whales.

Jonsgard (1951) and Omura and Sakiura (1956) determined age by means ofsize distribution, and they estimated that age at sexual maturity was two years forthe northern hemisphere minke whales. However, their result will not be correct,
for it is difficult to determine the age from size distribution in whales.

Physical maturity
Although the physical maturity should be determined with vertebral column
in the whales (Wheeler, 1930), we have only six materials. So, we estimated the
body lengths in which growth stoped from growth curves, adopting the methodby Ohsumi et al. (1958).
Estimating from Fig. 7, growth of females stops in 20-22 years, and the average
length after this age is 8.8 m. And the males stop their growth in 18-20 years
old, and the average length after then is 8.3 m. Fig. 12 also shows the average
body length in each number of ovulations. From this figure we estimate that theSci. Rep. Whales Res. Inst.,
No. 22, 1970.

STOCK OF THE ANTARCTIC MINKE WHALE

95

growth of females stop at 11 ovulations in average, and the average length after
then is 8.8 m. Then, we may conclude that the Antarctic minke whale attains
at physical maturity at about 20 years of age, and the average body length at physicalmaturity is 8.3 m in the males and 8.8 m in the females. The range of body lengthof the physically mature whales is estimated from growth curves to be 7.6-9.2 m
for the males and 7.8-8.8 m for the females, respectively.

30

25

~

20

0

:;::;

ro

:::i

>

.:=: 15
0
~

Q)

-0

E

-iE.

10

5

4.9 5.5

6.0

6.5

7.0

7.5

8.0

8.5

9.0

9.5

Body length (m)Fig. 12.

Relation between body length and number of ovulations in the females.
Solid line: Average number of ovulation,
Broken line: Average body length

Jonsgard (1951) estimated the body length at physical maturity on the minke
whale from the Norwegian waters as 27 feet (8.2 m) in the males and 29 feet (8.8 m)
in the females. However, these values will be too large, comparing with the deviations in the size distributions and age at sexual maturity between southern andnorthern hemisphere minke whales. Laws (1956) discusses on the relation between
body lengths at sexual maturity and those at physical maturity among marine
mammals, showing that the ratios of length at sexual maturity to that at physicalmaturity are almost constant, and 87-89 % for the case of female Balaenoptera
species excepting minke whale. The ratio in minke whales is calculated as 82. 7 %from the result by Jonsgard, and it is too smaller than above ratios. On the contrary, the present ratio of the Antarctic minke whale is 89.8 %, and it is near thevalues obtained for other Balaenoptera species. This discussion will confirm thatthe physically mature length shown by Jonsgard is higher than real one, and it
may be 27.3 feet for the female minke whales in the northern hemisphere.
Sci. Rep. Whales Res. Inst.,
No. 22, 1970.

96

OHSUMI, MASAKI AND KAWAMURAREPRODUCTION

Pregnancy rate
Out of 114 sexually mature females which were caught in 1967/68 season(mainly in December), pregnant whales were 90, and so pregnancy rate was 78.9 %.
There were additionally 12 individuals which had a corpus luteum in ovaries but
were not found foetus in uterus. Adding these individuals into the former whales,
89.5 % of mature females were estimated to be pregnant or ovulating. In 1968/69
season 5 whales (83 %) were pregnant in the sexually mature females.
According to Jonsgard (1951), 85 minke whales from Norwegian waters(95.5 %) were pregnant out of 89 mature females, and among these pregnant whales
13 were simultaniously lactating. Sergeant (1963) reported that in 14 sexuallymature females one was ovulating and others were all pregnant. Above results
indicate that the pregnancy rate of both the northern and southern minke whales
is nearly 90%, and as Jonsgard (1951) and Omura and Sakiura (1956) estimated,most minke whales give birth every year, and then the pregnancy rate in the minke
whale is the highest among Balaenoptera whales.
However, in general, the pregnancy rate of baleen whales in the feeding area
has a tendency to change seasonally, and that in earlier season is higher than thatin later season. Then, the obtained result does not always show the true pregnancy
rate. It is need to investigate pregnancy rate through the year for the sake ofsolution on this problem.
FoetusAll foetuses (102) were single, and multiplets were not yet found from theAntarctic minke whales. However, two individuals had two corpora lutea inovaries out of 107 whales which had corpora lutea in ovaries.
Concerning with the sex ratio of the foetus, we found that 43 were males,
51 were females and 8 were sex unknown. Although we have not enough materials,
it will be considered that sex ratio of the Antarctic minke whale is ({: ~= 1 : 1.
Fig. 13 shows size of foetuses by decades in the Antarctic minke whales. We
do not obtain the result to indicate that there are two breeding seasons in a year
as shown by Matsuura (1936) and Omura and Sakiura (1956) for the minke whales
from the Japanese coastal waters. Therefore, it will be estimated that the Antarctic
minke whale has one breeding season in a year as the same as the minke whales
from the North Atlantic (Jonsgard, 1951; Stephenson, 1951 ).
The size range of foetuses which were found in December is 1-73 cm, and theaverage length is 27.3 cm. This value is similar to that of the North Atlantic minke
whale in May (Jonsgard, 1951), and it also coincides to the value in June in thegrowth curve of foetus which were reported by Stephenson (1951). This will
estimate that there is half year's slip of breeding season between northern andsouthern minke whales as same as the fin whales (Ohsumi et al., 1958) and thesperm whales (Ohsumi, 1965).
Sci. Rep. Whales Res. Inst.,
No. 22, 1970.

STOCK OF THE ANTARCTIC MINKE WHALE

97

We do not obtain full foetal growth curve and gestation period for the Antarctic
minke whale, but they may be almost the same as those from the northern hemisphere.

Ovulation rate
Fig. 11 shows the relation between the age and number of corpora lutea andalbicatia in ovaries.

A corelation formula is calculated as follows:

Y=0.767 X-4.59
where,Y:
X:

Number of ovulations,
Age in years

It means that the average ovulation rate a year is 0.77. This value is higher
than that for the Antarctic fin whale (0.49: Ohsumi, 1964), and it is also relatedwith higher pregancy rate in this species than other Balaenoptera species. Omura
and Sakiura (1956) describes on the possibility that the pregnancy of minke whales
from coastal waters of Japan occures every one or one and half a year, and our resultmeans that the Antarctic minke whale ovulates once per 1.3 years in average.
FOOD

Species effood
In 1967/68 season 591 stomachs of minke whales were examined and 25 foodsamples were collected. In the following season (1968/69) 42 stomachs were again
examined. Japanese whaling expeditions which usually record the kind of stomach
Sci. Rep. Whales Res. Inst.,
No. 22, 1970.

OHSUMI, MASAKI AND KAWAMURA

98

contents by a rough classification such as euphausiids, amphipods, Calanus*,squid, fish, etc., and the euphausiids are recorded in three kinds by their bodysizes as follows: large (50 mm-), medium (40-50 mm), and small (-40 mm).
Although " empty ", the stomach with no food, was the most cases among theexamined whales, it is shown in Table 7 that the small sized Euphausia superba is achief diet of minke whales in terms of the feeding percentages, i.e., stomach withfood/stomach examined. There were several cases of mixed euphausian food withlarge-medium, large-small or medium-small, and the sizes given in Table 7 arerepresented by the quantitatively dominant forms among them.
TABLE 7. NUMBER OF MINKE WHALES BY THE KIND OF FOOD
ORGANISMS IN THE ANTARCTIC SEASONS 1967/68 AND 1968/69
Number of whales
Food
Euphausiids"Large""Medium""Small"Calanus tonsus
Empty
TABLE 8.
Species of food organisms

Euphausia superba
Euphausia spinifera
Calanus tonsus*>
*l

Male

Female

24
93
104
5
179

10
34
69
101

FOOD OF MINKE WHALES IN THE ANTARCTIC
Size

(:
s

Body length (mm)Condition of food

40<
20-40

SingleMixture of " Large "or" Small"
Mixture of " Large "SingleSingle10-20
16-21
2.8-3.5

Copepodite IV and V. Parathemisto gaudichaudii and furcillia larvae of euphausiids
were contaminated in the samples at times though they were very few in numbers.

The food organisms identified were: Euphausia superba, E. spinifera and Calanus
tonsus (Table 8). Although the kind of food species is relatively poor when it
is compared with that listed by Nemoto (1959, 1961) for the Antarctic baleen
whales, it is interesting that Calanus tonsus of adult female and copepodite V, and E.
spinifera were found firstly as a food of minke whales notwithstanding the fact thatthe most of minke whales as shown in Fig. 21 were sighted or hunted at relatively
higher latitudes, far south from the usual distributional area of C. tonsus (Vervoot,1957; Tanaka, 1960, 1964; Brodskii, 1964; Kawamura and Hoshiai, 1969). C.
tonsus had not yet been reported from the Antarctic waters as a food of baleen
whales but only records from South African waters off Cape Province as a diet ofsei whales (Best, 1967). Calanus tonsus of copepodite V and adult female having the
body length 2.8-3.5 mm were fed by 5 whales which were caught at 59°33'S;85°52'E and 61°27'S; 89°09'E. As the minke whales carry a considerably fine* " Calanus " means copepods
Sci. Rep. Whales Res. Inst.,
No. 22, 1970.

STOCK OF THE ANTARCTIC MINKE WHALE

99

and dense baleen fringes (Nemoto, 1959), it may be possible to feed on small sized
copepods. Since the diameter of baleen fringes of the Antarctic minke whales lies
between those of sei whales and Bryde's whales (0.2-0.3 mm) (Kasuya and Ichihara,1965), it is quite possible for Antarctic minke whales to feed on such a small sized
copepods as C. tonsus in the Antarctic, and their patchy distribution would make thewhales more easy to feed on them.
According to Vervoot (1957) and Tanaka (1960), C. tonsus is an important
epiplankton in the sub-antarctic region. They chiefly occur in 30-60°S which lies
between Antarctic Convergence and Subtropical Convergence (Brodskii, 1964).
The juveniles of copepodites IV and V are not only found in the sub-antarctic region
but also found off the south end of South Island of New Zealand during the
austral summer (Jillett, 1968). Occurring sometimes in great population densities(Jillett, 1968), they seem to keep an important position as a foregoing food staff
for the baleen whales which enter into the Antarctic region in the early summer.
As one of us (A. K.) described in the following report, a considerable numberof sei whales fed on C. tonsus in the Indian sector of the Antarctic Ocean, where
the latitudinal position of occurrence was found between 40° and 50°S. Therefore,
C. tonsus is considered to be one of the important food staff of baleen whales inrelatively lower latitudes of the Antarctic as well as those in South African waters(Best, 1967). From this fact the occurrence of C. tonsus at 59°33'S and 61°27'S
suggests quite unusual southward shift from their usual distribution area. As thesummer season proceeds, the copepodite V of C. tonsus gradually moves down to thedeeper water for wintering (Jillett, 1968), the whaling grounds formed by thiskind of food organisms would be limited within early summer, and not last for longthroughout the season.
As the size of E. spinifera is similar to that of young E. superba, they were notseparated as a different species in Table 8, since it was hardly possible to identify
them for the whalers. E. spinifera which was consisted of adult males and femaleswith body length 15.5-20.3 mm was fed by only one whale caught at 61°20'S;
101°08'E. It should be noted that E. spinifera did not occur as a mixture as observedin young E. superba.
No fishes were found as a food of the Antarctic minke whales while those
are the chief diet for the northern minke whales (Jonsgard, 1951; Omura andSakiura, 1956). Sometimes, however, a few small fishes were found among thebulk of E. superba though they might have been mixed and fed by a chance. Mostof those small sized fishes were Myctophid fishes about 10 cm in body length, andMyctophum subasperum was the most dominant species among them. As it is considered from Tables 7 and 8, the chief diet of minke whales in the Antarctic is considered as E. superba of I-year group with body length less than 40 mm. It is also
noticed that E. superba of " medium " and " small" never occurs in a pure population as a state of food but few cases.

Q;tantity offood and feeding habits
The quantity of food in the first stomach was recorded on each whales afterSci. Rep. Whales Res. Inst.,
No. 22, 1970.

OHSUMI, MASAKI AND KAWAMURA

100

the following five classes:r0
Empty Few
0-25

ClassesQuantity of foodApprox. per centRrr
Moderate

rrr
Rich

Full

25-50

50-75

75-100100,.--~-a-.,--~~--.-~~---.~~~-.--~~--.-~~-r~~~-.--~~-.-~.

I( 1 ind.),,...
........... __

_.,"

/

/

/

''

'

'

?

I
\

I
I

\

\

g;, 60

I

I

!l
c
Q)

~
Q)

0... 4020- - Female----Male

04

6

8

10

12

14

16

18

Hour
Fig. 14.

100

Feeding percentages of minke whales caught in the Antarctic (1967/68; 1968/69).
Open circle : female,
Closed circle : male.

r----r-----ir-----r----..,.----r----,----~----.-'X

I
I

I
I

0 (Empty)-x- r- c . - rr
-a--

80

Q)

bO

60

~

I

_.._

I
I

-

c

Q)

~
Q)

0...

40

Hour
Fig. 15.

Feeding percentages of minke whales caught in the Antarctic in terms of the degreeof repletion in the first stomach.
Sci. Rep. Whales Res. Inst.,.No. 22, 1970.

STOCK OF THE ANTARCTIC MINKE WHALE

101

In order to know the daily variations of feeding activity, the ratio of the numberof stomach with food repleted more than " r " against the total number of stomachs
examined was shown in Fig. 14. Fig. 14 shows that the most whales feed on actively
before dawn and the feeding activity is on decrease toward midday though it recovers
again gradually in the afternoon toward the evening. It is in the highest at justbefore and after sunrise; 04-06 hours. It is also suggested that the females feed on
more actively than the males. Mentioning on the daily variation of feeding activityof baleen whales, Nemoto (1957, 1959) convinced that the most causeful factors on
those variations lie chiefly on the vertical movement of food organisms rather thancontrol by the whale themselves. The minke whales in the Antarctic seem tofollow the similar way, because there are the fact that the feeding activity of sei
whales which feed on C. simillimus are considered to be completely controlled by
the diurnal movement of C. simillimus (Kawamura, 1970), though it varies alsowith another reasons such as the species of food, their developmental stages, andsometimes with the bottom topography of the sea (Nemoto, 1959). Fig. 15 showsthat the considerable number of whales (3-10 %) seem to feed still on food during
the daytime, since the whales with the first stomach repleted more than 50% areconsidered having been caught at least within several. hours after their feeding,judging from the freshness of their stomach contents. It leads to the considerationthat the bulk of food organisms still remain within the upper layer to make thewhales enable to feed on them, since there are the fact that relatively larger E. superba
are found in the surface throughout the daytime (Marr, 1956; Hardy and Gunther,
1935). Although most whales seem to feed early in the morning in the present
study, it is supposedly considered that the minke whales in the Antarctic feed onfood whenever the food organisms are available.
ECTOPARASITES

The general features of ectoparasites infected on the minke whales were poor bothin the number of individuals and species. The diatom films formed with Cocconeis
ceticola were found on six whales which were examined on F. S. Nisshin Maru.
The yellowish brown diatom films were usually found on the white skin of ventral
side especially around the anus and genital apertures. They formed not such apatchy colony as usually observed on the skin of fin whales but only homogeneousbrownish thin films.
The whale-lice, Cyamus balaenopterae were found in seven yvhales (Table 9). The
part of the body where they infected were only the ventral grooves. As Leung(1967) reported only C. balaenopterae being found on the Antanctic minke whales,
it seems that no other whale-lice occur in them. The whole individuals of C.
balaenopterae were collected from two whales. It is noticed that the number ofwhale-lice is quite few in minke whales. The juveniles of both sexes were judged
from their process on the base of gills and the developmental conditions of marsupium in females. The body length of juveniles which could not separate by
the sex by this way was less than 3.0 mm though the most of them were between
Sci. Rep. Whales Res. Inst.,
No. 22, 1970.

102

OHSUMI, MASAKI AND KAWAMURA

1.2-2.8 mm. The female overcame in the sex ratio though it was about 1: 1 byassuming the juveniles unidentified the sex were the male. The infection rate of
C. balaenopterae and other ectoparasites were too low to utilize them as an indicatorfor detecting the presence of any subpopulations as has been discussed on some possibilities in the south ern sei whales by thoracic cirripede, Xenobalanus s_,b. (Kawamura, 1969b).
TABLE 9.

WHALE-LICE, CYAMUS BALAENOPTERAE FOUND ON THE SKIN OF
MINKE WHALES IN THE ANTARCTIC SEASON 1967/68

Whale number

68

71

72

Part of body from which
specimens were collected

Ventralgrooves
I

Ventralgrooves
I

Ventralgrooves

7.3
18

6.2

Male

rtl·

Body length (mm)Juvenile
Body length (mm)

rdul•

l"

Body length (mm)4.9FemaleJuvenile
25
Body length (mm) 3.0-4.8
Juveniles of unknown sex
2
Body length (mm) 2.8-3.5
1)
2)
3)

Jll

6.9
20
2.8-3.5
12
2.2

97

192

183

430

2
5.7

3
4.2-5.75
4.6-5.39
4.3-5.42
4.3-4.4

2•>
5.0

2•>
4.4-4.952>
5.4

4
3.8-4.3
1
3.6
33)
4.6-5.4
19
2.8-4.3
4

5.4
3
1.2-2.07
2.2-4.8
32
1.9-2.6

Carrying eggs in marsupium.
Marsupium developped well but no eggs were observed.
Included one deformed individual whose gills were considerably stunted.

CATCH AND CATCH COMPOSITIONSCatchBased on the International ""Whaling Statistics, minke whales were caught
firstly by Soviet expedition in the Antarctic in 1951/52 season. Soviet expeditions
caught minke whales one handred and more every season during 1957 /58 to 1960/61,
but after then the catch has not increased so many by Soviet expeditions (Table 10).
Japanese expeditions caught 96 minke whales in the Antarctic in 1963/64 season(Kasuya and Ichihara, 1965 ), and then they caught 597 and 42 minke whales in
1967/68 and 1968/69 seasons respectively. Norwegian and U. K. expeditions havecaught 6 minke whales each, and a Netherlands expedition caught one in 1959/60
Antarctic season (Utrecht and Spoel, 1962).
Then, 1,827 minke whales were caught in the Antarctic during 1951/52 to1967 /68 seasons. Additionally, it is estimated that there are some unreported minke
whales which were caught as a food by some catcher boats in some sperm whaling
seasons. Nevertheless, the total minke whales caught in the Antarctic whaling
ground will be under 2,000 by 1968/69. Although minke whales have been increasing to be caught in Brazilian coast recently (488 whales in 1967, according to
the International Whaling Statistics), they have not been caught many in othercoastal whaling in the southern hemisphere. Therefore, it is considered that theSci. Rep. Whales Res. Inst.,
No. 22, 1970.

STOCK OF THE ANTARCTIC MINKE WHALE

103

catch has not so influenced to the stock of southern minke whale, and it remains
still in an initial stock level.
TABLE 10.

NUMBER OF MINKE WHALES CAUGHT IN THE ANTARCTIC(From International Whaling Statistics).Japan1945/46
1946/47
1947 /48
1948/49
1949/50
1950/51
1951/52
1952/53
1953/54
1954/55
1955/56
1956/57
1957/58
1958/59
1959/60
1960/61
1961/62
1962/63
1963/64
1964/65
1965/66
1966/67
1967/68
1968/69
Total

USSR

NorwayU.K.

Netherlands

Total

9

96
2
1
597
42
738

41
46
493
102
203
162
2
21
5
4
8
14
8
17
1,135

9
3

3

6

42
46
493
103
205
162
2
21
101
7
10
18
605
59
1,886

1*

1
2
3

6

* after Utrecht and Spoel (1962).
TABLE 11.

CATCH DATA ON THE MINKE WHALES SEPARATED FROM
MAIN GROUND AS SHOWN IN FIG. 16

Date Caught

Position caught

Sex

Body length (m)31/XII/64
1/ I/65
12/XIl/66
15/ 111/69

49°27'S, 25°05'W
50°12's, 46°22'W
40°37'S, 04°33'E
45°5l'S, 174°14'E

M
M
M
F

8.3
8.3
8.8
6.0

Testis (kg)1.8, 1.4

There is no record on catch areas of minke whales in the Antarctic in theInternational Whaling Statistics. Fig. 16 shows the catch positions of minke whales
which were caught by Japanese whaling expeditions in 1963/64, 1967/68 and 1968/69
seasons. Most whales were caught in Area IV (60°E-130°E), especially in thewaters along the Kerguelen-Gausberg Ridge. Other minke whales were caught byJapanese expeditions as shown in Table 11. Therefore, several biological results
which will be reported in the present paper are obtained from a stock in Area IV.
Concerning with catch days, Japanese expeditions caught minke whales during
Sci. Rep. Whales Res. Inst.,
No. 22, 1970.

OHSUMI, MASAKI AND KAWAMURA

104

January 6 to 8 in 1963/64 (Kasuya and Ichihara, 1965), and in 1967/68 season they
were mostly caught during December 11 to 21. They were also caught mainly
during January 18 to 25 in 1968/69. As minke whales are not a main object in
the Antarctic whaling, we have not yet obtained materiq,ls through all months. According to the International Whaling Statistics, the catch months of minke whales
by Soviet expeditions which caught many minke whales from 1955/56 to 1960/61
seasons were November, December and March, and the catch in January and February were relatively few.

so E
0

100°E

120°E

5o·s

•
60°s

60°E

140°E

ANTARCTICA

Fig. 16.

Positions of minke whales caught by Japanese expeditions.
Open circle: 1963/64, Closed circle: 1967/68, Circle and cross: 1968/69.

Because this whale has been caught concentrately in short days or seldomly
caught, it is difficult to get good values of catch per catcher day (CPUE) of thisspecies in the present stage. Nisshin-Mam No. 3 Expedition caught 579 minke whalesin the Antarctic concentrately with 9 catcher boats during 11 days from December
11 to 21in1967/68 season. From these data CPUE is calculated as 5.85. But it isdangerous to regard this value as the true CPUE of the minke whale stock in the
Antarctic in the initial population level.

Composition ef minke whales caught
The number of minke whales caught in 1967 /68 and 1968/69 seasons by J apanese expeditions is 597 (including one whale lost) and 42, respectively, and allwhales were caught in the waters southward the Antarctic Convergence in Area IV
excluding only one whale. We would like to obtain some biological parameters of
the Antarctic minke whale in the initial stock level by means of these catch data.
Sci. Rep. Whales Res. Inst.,

No. 22, 1970.

STOCK OF THE ANTARCTIC MINKE WHALE

105

As any catch regulational limits do not assign on catch of minke whales in the
Antarctic under the International Whaling Convention now, the present result will
be regarded to reflect well the stock which distributes in a part of the Antarctic.

Sex ratio
The sex ratios of males caught are 65.1 and 78.5 % in 1967 /68 and 1968/69
seasons, respectively. And according to Kasuya and Ichihara (1965), it was 82.3 %in 1963/64. In any seasons males are dominant in catch. This phenomenon meansthat there is a sexual segregation in this species, and males migrate dominantly inhigh latitudinal waters in the Antarctic, at least in Area IV.
Jonsgard (1951) found that female minke whales entered into Norwegian
fjords, males stayed in far seas, and females were dominant in the Arctic. And hedescribed that there is a tendency to separate into male and female groups, when
they migrate into the feeding areas. Omura and Sakiura (1956) and Matsuura(1936) also reported the similar phenomena on the minke whales in the waters
around Japan.
It may be considered that there is a sexual segregation in migration of minke
whale in the southern hemisphere, reviewing these report on the northern hemisphereminke whales. But it is still unknown where the females distribute dominantly insummer season, although we find that males are dominant in high latitudinal watersin Area IV. It is estimated that the female is dominant in high latitudinal waters in
the northern hemisphere, but this phenomenon is contrary to that in southern hemisphere. It will be hoped to investigate the minke whales in Ross Sea or Weddel
Sea in future, and it will be needed to investigate also them in the waters north of
the Antarctic Convergence in summer or in lower latitudinal waters in winter season
for solution of this problem.
Size distribution
Although whalers want to take larger individuals and it will be relatively
difficult to take a small minke whale, it may be regarded that the size distribution
represents the whale stock which distributes there.
Table 12 shows the size distribution of the Antarctic minke whales caught bysex. The smallest was 4.9 m (16 feet), and the largest one was 9.8 m (32 feet) in thefemales. The smallest was 5.5 m (18 feet), and the largest one was 9.8 m (32 feet)in the males. The maximum size will not exceed 10 m in both sexes.
The maximum body length of the minke whales in the northern hemisphere are
30 feet female and 28 feet male, according to J onsgard (1951 ), and they are 30 and 29
feet for the female and male, respectively, according to Omura and Sakiura (1956).
Beneden (1889) and Stephenson (1951) reported that the maximum length of theminke whales from European waters was 36 feet, but it is considered to be too high.
Size distribution of males is different from that of females, that is to say, there
are many large whales in the males, on the contrary, females have relatively manysmall whales. Modes of size distributions are 27 and 28 feet for males and females,
respectively. And the average body lengths are 7.92 and 8.13 m for males andSci. Rep. Whales Res. Inst.,
No. 22, 1970.

106

OHSUMI, MASAKI AND KAWAMURA

ft

I I

I ,\
I

I

20

\

I
I
I
I
I

Males

I

;
I
I
I

I
I

'I

I

;

I
I

1~

I

I

I
I

10

I
I

I
I

I

~

5

I

\

~

,...----.

I

>c

,

,/

(_)

\

I

\

.._
\
\

<I.)

:::J

15

rr
~

20

30

25

LL

f\

I

15

I
I

Females

~

I \
I

I
I
\

~

I

\
\

\

10

~

5

Body length (feet)Fig. 17.

Comparison of size distributions between the minke whales from the Antarctic and the coast ofJapan.
Open circle and solid line : from the coast of Japan,
Closed circle and broken line : from theAntarctic

STOCK OF THE ANTARCTIC MINKE WHALE

107

females, respectively.
According to Omura and Sakiura (1956), the modes of size distribution of theminke whales from the North Pacific are 25 feet and 26 feet for males and females,
respectively, and those from Scotland waters are almost the same as former ones
(Stephenson, 1951). Sliding them 2 feet, they fit with the size distributions of the
Antarctic minke whales. This shows that the Antarctic minke whales are 2 feetlarger than the northern hemisphere minke whales.
TABLE 12. SIZE DISTRIBUTIONS BY SEXUAL CONDITIONS OFMINKE WHALES IN THE ANTACTIC (1967/68 and 1968/69)
Body
length(m)
4.9-5.0
5.5-5.6
5.7-5.8
5.9-6.0
6.1-6.2
6.3-6.4
6.5-6.6
6.7-6.8
6.9-7.0
7.1-7.2
7.3-7.4
7.5-7.6
7.7-7.8
7.9-8.0
8.1-82.
8.3-8.4
8.5-8.6
8.7-8.8
8.9-9.0
9.1-9.2
9.3-9.4
9.5-9.6
9.7-9.8
Total
Mean body length
Sexual rate (%)

Males
Total

Immature

2
8

2
8

8
5
5
5
10
3
7
3

9
5
5
7

3
3
4
8
4
7
8
5
9
13
10
7
3
7
2
3

Immature

59
6.67
14.1

MatureFemalesUnknown

II

10
14
24
45
43
71
63
53
19
13
3

360
8.12
85.9

13
21
27
46
44
71
64
53
19
13
3

2
6.45

421
7.92

97
7.19
55.3

Mature

Total
3
3
4
8
4
7
8
5
9
13
10

4
5
16
13
27
21
14
13
4
2

II

8
23
15
30
22
14
13
4
2

I

I

120
8.88
44.7

217
8.13

Rate of sexual maturi~yRates of sexual maturity of minke whales caught are 85.9 and 55.3 %for males
and females, respectively, determining with reproductive organs, and that of males
is very high, notwithstanding there is no legal size limit on this species. This suggests that there is geographical segregation with not only sex but also with age in themales. Segregation with age is not so remarkable in females.
The average lengths of mature males and females are 8.12 and 8.88 m, respectively, and those of immature males and females are 6.67 and 7.19 m, respectively.
Sci. Rep. Whales Res. Inst.,

No. 22, 1970.

OHSUMI, MASAKI AND KAWAMURA

108

Age composition and mortality rate
The age composition of minke whales caught in 1967 /68 Antarctic season isshown in Fig. 19. 'Ve have not enough materials for drawing age composition by
sexes. The youngest whale which were able to be determined its age with earplug
lamination is 5 years old, and the oldest one is 40 years old. Mode of distribution isfound at 15 years.

70
60
50

..... 40
bO

~

..c

:J

co
0

(/)
Q)

co

..c

:;::

0
ci

z

30
20
10

>.

5.0

0

c

10.0

Q)

:J

O'
Q)

30

......
LL.

20
10
5.0
Body length (m)Fig. 18.

Size distributions of minke whales caught in the Antarctic in 1967/68 and 1968/69 seasons.
Open circle and broken line: Immature,
Closed circle and solid line : I\1ature.

Calculating a total mortality coefficient from the frequencies of 15 years andover, it is 0.102. In the present stage when the catch has not begun in large scale,this value will mean the natural mortality coefficient.
The most number of ovulations is 31, and if this whale has an average age atsexual maturity and an average rate of ovulations, its age is estimated to be 4 7-48
years. Therefore, the longest life span of the minke whale will be under 50 years,
and it is the youngest among Balaenoptera species.
Frequency distribution of ovulations is shown in Fig. 20. A total mortality
coefficient calculated from this distribution and the average number of annual ovulaSci. Rep. Whales Res. Inst.,
No. 22, 1970.

STOCK OF THE ANTARCTIC MINKE WHALE

tions is 0.104.
tion.

109

It is the almost the same value as that obtained from age distribu-

ff. 4

.

'
10

5

15

20

40

Age (years)
Fig. 19.

~

(/)

~
CU

..c

:;::

Age distribution of male and female minke whales caught in the Antarctic in 1967/68 season.

1086......
0

ci

4

z

>,

u
c

Q)

::J
O"

2

0

~
Ll...

1

5

10

15

20

25

J

0

30

No. of ovulations
Fig. 20.

Frequency distribution of number of ovulations in the Antarctic minke whales.

Natural mortality coefficient of the Antarctic minke whales is higher than thoseof the Antarctic fin whale (0.042: Doi et al., 1969) or of the Antarctic sei whale(0.06-0.08: Doi et al., 1967). As it is considered that the natural mortality coefficient has a tendency to decrease with the decrease of population size, we mustpursue the change of natural mortality on this species after the begining of ordinal
whaling.
There is a mode in ovulation distribution at 4 ovulations. This may be
estimated that there is segregation by age in females as well as in males.
Sci. Rep. Whales Res. Inst.,
No. 22, 1970.

110

OHSUMI, MASAKI AND KAWAMURA

DISTRIBUTION AND ABUNDANCE

Distribution
Whale sighting has been continued with scouting boats belonged to Japanesewhaling expeditions in the Antarctic. Fig. 21 shows number of minke whales
sighted per day in each 2° squares during the seasons from 1965/66 to 1968/69.
Although we have few data in Area I and higher latitudinal waters in Areas II and
III, it is estimated that the minke whales distribute in all waters in the Antarctic insummer and the distribution density is generally low in north of the Antarctic Convergence, on the contrary, it is high in south of the Convergence. Especially, minke
whales distribute in high density in the waters from eastern margin of Area III to
Area V.

Fig. 21.

Distribution of minke whales sighted by Japanese scouting boats in the Antarctic seasons 1965/661968/69.

Table 13 shows the density distributions of baleen whales in each Sectors during
Sci. Rep. Whales Res. Inst.,
No. 22, 1970.

STOCK OF THE ANTARCTIC MINKE WHALE

111

the seasons 1966/67-1968/69. Density is represented as the numberofwhales sighted
per 100 miles navigations. The density of minke whales is the highest in Area IV,
and the higher the Sector is in each Areas, the higher the density becomes. Among
all Sectors Sector IVB is the highest density for the minke whales.
TABLE 13. WHALE SIGHTING WITH SCOUTING BOATS BELONGED WHALING
EXPEDITIONS IN THE ANTARCTIC SEASONS 1966/67-1968/69
SectorNavigation(miles)

ID
IA
II E
IID
III E
III D
III A
IVE
IVD
IVA
IVB
VE
VD
VA
VB
VID
VIA
VIB
Total

208
209
1,075
2,929
11,922
143,446
5,222
18,74590,484
76,637
4,139
3,704
71,92018,051
4,191
24,29830,704
7,722
515,606

Blue

Remarks:

Number of whales sighted
per I 00 miles navigation

Number of whales sighted
Fin Hump.

3
4
11
565 1,611
4
34
9
75
502
28 3,864
4
2
4
2
7
162
4
538
6
6
78
5
45
705 6,866

6
2
16
20

5
2
I
2
2
6
66

Sei

18
54
9
750
6,279
26
603
2,251
1,789
6
145
3,343
336
19
730
1,448
113
17,919Right Minke Blue

I
2
10
15
287
74
32
20
183
2 2,695
291
2
5

45
189
133
3
8
67
29
63 4,041
82

Fin Hump. Sei Right Minke

0.00 0.00
0.00 0.00
0.00 0.00
0.00 0.00
0.03 0.09
0.39 1.12
0.08 0.65
0.00 0.05
0.08 0.56
0.04 5.04
0.05 0.10
0.11 0.05
0.01 0.03
0.02 2.98
0.14 0.00
0.00 0.03
0.00 0.25
O.Q7 0.58
0.14 1.33

0.00
0.00
0.00
0.10
0.00
0.00
0.00
0.01
0.02
0.03
0.02
0.00
0.01
0.01
0.02
0.01
0.01
0.08
0.01

0.00
0.09
5.02
0.31
6.29
4.38
0.50
3.22
2.49
2.33
0.15
3.92
4.65
1.86
0.45
3.00
4.72
1.46
3.48

0.00
0.00
0.19
0.17
0.00
0.01
0.00
0.00
0.02
0.00
0.00
0.00
0.01
0.01
0.00
0.00
0.03
0.00
0.01

0.00
0.00
0.09
O.Q7

0.08
0.20
1.42
0.17
0.20
3.52
7.03
0.00
0.06
1.05
3.17
0.01
0.22
0.38
0.78

E: 30°S-40°S, D: 40°S-50°S, A: 50°S-60°S, B: 60°S-70°S, I: 60°W-120°W,
II: 60°W-0°, III: 0°-70°E, IV: 70°E-130°E, V: 130°E-170°W, VI: 170°W120°w.

Arsenyev (1960) showed a longitudinal distribution of the minke whales sighted
by USSR expeditions in the Antarctic whaling grounds between 60°W and 170°W
eastward. According to his paper, minke whales do not distribute equally in the
Antarctic, and there are three peaks of distribution in l0°-20°W, 60°-70°E and160°-l 70°E. He also estimated that the stock in the Indian Ocean had larger
populations than that in the Atlantic. There is no record of the latitudinal distribution in his report, and we did not investigate in higher latitudinal waters in Area II.
So, it is difficult to compare the present result with the record by Arsenyev, but it will
be certain that relatively many minke whales distribute in the Indian Ocean watersof the Antarctic in summer. And the catches of minke whales by Japanese expeditions concentrate mainly in this area.
It is difficult to separate stock units only by means of distribution in the present
report as Arsenyev also described. Stock identification will be need to be donewith other methods in future.
According to Taylor (1957), many minke whales swim in opening ice waters in
Sci. Rep. Whales Res. Inst.,

No. 22, 1970.

112

OHSUMI, MASAKI AND KAWAMURA

distal ice of the Antarctica (63°S, 57°W), and they can live in cold water temperature.
We have no data on the distribution of the minke whales in the waters southward
70°S in the present paper.
Minke whales have been caught in the waters near Spitsbergen, and they
distribute in Davis Straight (Jonsgard, 1951). According to Sleptzov (1955), they
are also found in north of the Bering Strait. Then, minke whales distribute in thehighest latitude in both hemisphere among Balaenoptera species.
The distribution of southern minke whales in lower latitude is not so certain,
but the catch in Resife of Brazil (8°S) have increased recently. Whaling season inthis waters is during June to November, and the optimum season is October (International Whaling Statistics, No. 61). According to an information by a whaler
who opearated in these waters and a sample of baleen plates, the minke whales in
Brazilian waters have the same morphological characters as so called " Balaenoptera
bonaerensis ". Clarke (1962) reported that some minke whales were found in theposition of33°S, 73°W, but they were not found during a cruise of3°S-l 0N, 8l 0W940W. Minke whales were sighted off the west coast of Australia (Chittleborrough,1953), and a new born calf or near term foetus of the minke whale was stranded on
the coast of New Zealand (Gaskin, 1968).
TABLE 14.

SCHOOL COMPOSITION OF MINKE WHALES SIGHTED
IN THE ANTARCTIC
Average number of whales in a school

Latitude40°S-50°S
50°S-60°S

106
106

2

3

4

5

6

31
144

15

3
52

2

2
2

88

9

We have no knowledge on migration of the minke whale in the southern hemisphere. However, as Lillie (1915) noted that minke whales were common in the
Antarctic inJanuary-Feburary, it is clear that they distribute concentratley in highlatitudal waters of the Antarctic in summer season, and some of them stay in thesewaters in winter season (Taylor, 1967). Some minke whales of the northern hemisphere are considered to stay in higher latitude in winter season, for they strand
through all months on the coast of North Scotland (Stephenson, 1951 ). There aresome records on the stranding of minke whales in New Zealand in February, May,
June, September and October. Whaling season in Brazil is during winter to spring.
It has been clearly shown that the northern minke whales migrate seasonally(Matsuura, 1936; Jonsgard, 1951; Stephenson, 1951; Omura and Sakiura, 1956;
Sergeant, 1962). And it has been also known that migration season and area aredifferent with sex, age and sexual condition for the northern minke whales.

School composition
Table 14 shows frequency distributions of average number of whales composed aschool, using records of number of total minke whales and total schools. In thewaters north of 50°S lone whales are dominant, on the other hand, number of whales
Sci. Rep. Whales Res. Inst.,

No. 22, 1970.

STOCK OF THE ANTARCTIC MINKE WHALE

113

in a school increases in south of 50°S. There is a tendency that school composition is
many in the day when many minke whales were sighted. These phenomena will
mean that minke whales gather each other in high latitudinal waters of the feeding
ground. We have no data on the maximum number in a school.
Arsenyev (1960) describes that school composition is 10, 20, 50 and more than
50 in the Indian areas of the Antarctic. Jonsgard (1951) reported that lone minke
whales were many in the western coast of Norway, but school composition became
large in the Arctic waters, and he estimated that this was a result that lone whalegathers each other in the end of migration in summer. Nemoto (1964) says thatfin whale changes school composition in feeding ground, and there is no consort
relationship. We consider that minke whales has almost the same tendency.

Comparison ef distribution density with other whale species
As shown in Table 13, the density distribution of minke whales is the third of
the whale species sighted (sei whale is the first, and fin whale the second). Considering that the minke whales are economically valueless, observers will pay little
attention to find them, and they are more difficult to be find, because they are thesmaller species, the real density will be higher than the values obtained in Table 13.
Density distribution of the sei whales is high in lower latitude (D-sector ), andthat of the fin whales is the highest in A-sector, on the other hand, that of the minke
whales is the highest in B-sector, and it becomes lower in lower latitude. Then, thistendency seen in minke whales is almost the same as that in the ordinal blue whales(Balaenoptera musculus).
TABLE 15.

ESTIMATED STOCK SIZE OF THE MINKE WHALES BY MEANS
WHALE SIGHTING IN THE ANTARCTIC
Area

Sector

II

III

IV

v

VI

I

D
A
B

270

930
5,370

810
11,41010,940

220
3,400
6,610

40
590
750

?

c
Estimation ef population size
Mackintosh and Brown (1956) tried in the first time to estimate population sizeof whales by means of whale sighting, and N asu and Shimadzu (in press) developed theformer method. In the present paper, we used as the materials the Sector size (A),navigation miles (L) and number of whales sighted (n), and adopted needful coefficients as visible width= 11. l miles, rate of sighting=0.344 at finding efficiency=O. 7
from Nasu and Shimadzu, the population size will be calculated as the following
formula:A·n
N = 0.344x 11.1 L

Result of calculation of the population size in areas south of 40°S is shown in
Sci. Rep. Whales Res. Inst.,

No. 22, 1970.

114

OHSUMI, MASAKI AND KAWAMURA

Table 15. Excepting Area IV other Areas are not got total population sizes covering
all sectors. Therefore, we have not got the total population size in the whole
Antarctic. The population size in Area IV is calculated to be 23,200, and the total
sizes in the waters investigated are also calculated as about 41,000. Perhaps 70,000
minke whales and over will distribute in the Antarctic in summer. Considering thatdensity distribution of the minke whales is high in the high latitude, there are wide
areas where are not investigated and the finding and records are possiblly more
scarce than other larger whale species, the real population size will be remarkably
larger than the figure estimated. Furthermore, whale sighting is only one of themethods to assess a population size, and some assessment of population will be introduced after the beginning of regular whaling on this species.
PRODUCTION

Amount of production
Nisshin-Mam No. 3 Expedition caught only minke whales exclusively in the
Antarctic during 11 days from December 11 to 22 in 1967. The amount of production from these minke whales is shown in Table 16. The average body length of thewhales disposed is 7.9 m, and the biomass is calculated from a formula of body lengthbody weight relationship.
TABLE 16. PRODUCTION FROM MINKE WHALES WHICH WERECAUGHT BY NISSHINMARU NO. 3 IN 1967/68 ANTARCTIC SEASON
Items

Production(ton)

Production
per whale (ton)

578
3,190
933
332
90
63
13
1,432

1.61
0.57
0.16
0.11
0.02
2.48

Number of whales carried
Calculated biomass
Frozen meat
Whale oil
Meal
Bone meal
Extract
Total

Oil production per a whale was 0.57 tons. According to Tomilin (1957),
usually one ton of whale oil is produced from a large and fatty minke whale. However
the present figure is smaller than this value. Whalers produced 1.61 tons of meat pera minke whale, and the total production from a minke whale are 2.48 tons in average.

Discussions on the Blue Whale Unit of the minke whale
There is no catch limit on the minke whale in the Antarctic under the present
International Whaling Convention, and therefore, a value of Blue Whale Unit
(BWU) has not put on this whale species. Of course, as population management
should be set up for each whale species and each stock units, it is not reasonable tocalculate the value ofBWU on the minke whale for a purpose of population manageSci. Rep. Whales Res. Inst.,.No. 22, 1970.

STOCK OF THE ANTARCTIC MINKE WJALE

1.15

ment. However, we think it will be useful to calculate it as a standard for examination of production of this species.
Calculation ef Blue Whale Unit from whale oil: BWU system began to be used for anagr~ement of production regulation among whalers since 1932, and it was determined based on oil production of each whale species.
Determining the oil production per one blue whale as 110 barrels, exchange
rate of each species were calculated using oil production per each one whale. Oil
production per one BWU in 1966/67 Antarctic season calculated by Omura (1969)
is 109.5 barrels. This figure is almost the same as the original.
Average oil production per one Antarctic minke whale was 0.57 tons (3.42barrels) from Table 16. Then, regarding oil production as the standard of BWU,
32 minke whales are considered to be regarded as one BWU. Average total production per one BWU (catch of sei whales were 96 % of total catch) by Japanese
expeditions in 1966/67 Antarctic season was 85.40 tons. One BWU is 34.4 minke
whales, if total production is regarded as a standard. This value is almost the sameas that formaly obtained from oil production.
In the present time there is no legal size limit on the Antarctic minke whale,and so small individuals were also caught. If legal size would be set up at larger
length than actually caught, number of minke whales per one BWU will become
smaller than those obtained in the present report.
Calculation ef Blue Whale Unit from biomass: Crisp (1962) examined BWU in view ofbiomass. According to his paper, the average body weight of the blue whale as thestandard of calculation of exchange rate was 83.9 tons. As the average body lengthof the minke whales caught by Japanese expeditions in 1967/68 was 7.90 m, theaverage body weight was calculated to be 5.52 tons. from the formula of length-weight
relationship. Then, based on biomass, 15.2 minke whales will be regarded as one
BWU.
BWU exchange rate obtained from oil production is about twice of that frombiomass. Table 5 shows comparison of proportional weights of meat, blubber andbones among several Balaenoptera species. Above phenomenon is caused from thatthe minke whale has small proportion of oil materials, and has large proportion ofmeat materials.
DISCUSSION

Problem on classification ef the Antarctic minke whale
A minke whale with no white band on flippers which was found by Williamson(1959, 1961) in the Antarctic has been regarded as different species or different subspecies from so called minke whale, Balaenoptera acutorostrata. He also reported
that the former whale was the same as B. bonaerensis from Argentina which hadreported by Burmeister in 1867, and B. huttoni was also a synonym of this species.
Utrecht and Spoel (1962) and Kasuya and Ichihara (1965) reported the same
type of species as that by Williamson from the Antarctic. Gaskin (1968) also describesthat the minke whales which had stranded on the coast of New Zealand were mostly
Sci. Rep. Whales Res. Inst.,
No. 22, 1970.

116

OHSUMI, MASAKI AND KAWAMURA

same type. Nishiwaki (1965) adopted the Williamson's report, and he proposed toname "Kurominku kuzira" in Japanese and "New Zealand piked whale" inEnglish as a common name for this species.
All individuals which were dealed in the present report have the same morphological characters as so called New Zealand piked whale, having no white bandon flipper, large baleen with wide black band on the outer margin. There are somedifferences in measurements of body proportions, and the Antarctic minke whale isabout two feet larger than the northern hemisphere one. However, we could not
find any qualitative differences between them, that is to say, both the Antarctic
minke whale and northern hemisphere minke whale (Balaenoptera acutorostrata) havethe same number of baleen plates, same rate of breadth to length of baleen plate,same number of ventral grooves, same position relation between umbilicus and endof ventral grooves and same number of vertebrae. We think the minke whales
which was observed by Williamson (1961) and of which both positions of end ofventral grooves and of umbilicus coincided each other was an exceptional. Kasuya
and Ichihara (1965) estimated similar whales only with photograph. We can find aminke whale of which umbilicus and end of ventral grooves coincide from the coastal
waters of Japan in a report by Omura and Sakiura (1956, Appendix-Table, No. 21
Specimen, p. 33). We heard that whalers sometimes found minke whales with nowhite band on flippers from the Okhotsk Sea. On the other hand, it is noted that
there are some minke whales with white band on flippers in the Antarctic (Taylor,
1962; Kasuya and Ichihara, 1965 ). Individual variations of body colour are verylarge in the humpback whale (Megaptera novaeangliae). Although the Antarctic
minke whale is about two feet larger than the northern hemisphere minke whale,in other Balaenoptera species southern hemisphere stocks are clearly larger than thenorthern stocks, but they are classified into the same species. Black band in outermargin of baleen plates is found in some northern hemisphere minke whales. We
must notice that there is individual variation in qualitative characters.
As a conclution of above discussion, we support a report by Utercht and Spoel(1962) that Balaenoptera bonaerensis is a synonym of B. acutorostrata from the northernhemisphere, and it will be regarded as a variation or subspecies of the latter. Therefore, we used the name of minke whale for the whales which were treated in thepresent paper.
For the purpose of further study on the problems of classification of this stock,
we should examine osteologically by a collection of skeletons of the Antarctic minke
whale. It will be also need to study on the minke whales with white band on
flipper in the Antarctic and to compare with the Antarctic minke whales with nowhite band.

Stock management ef the minke whales in the Antarctic
It will be desirable that any animal stocks should not be left to chance tobe utilized, but should be utilized under the carefull management so as not to letthem decrease under the stock level which give the maximum sustainable yield.
In this meaning, we hope to exploit the minke whales more in the Antarctic in
Sci. Rep. Whales Res. Inst.,
No. 22, 1970.

STOCK OF THE ANTARCTIC MINKE WHALE

117

future. However, we think we should prepare some plans for the stock management firmly for maintenance of optimum stock level in future minke whaling. For,
past history of whaling teaches us that it is very difficult to recover a stock which
had been decreased under the level of maximum sustainable yield.

0.30

;

0.20

> 0.10

L--..-M-~,-,-

50

Fig. 22.

Estimation of sustainable yield curve for the Antarctic minke whale.

Some characteristics of the Antarctic minke whale among the biological parameters concerned with population assessment are estimated that the sexual maturity
attains at younger age, rate of reproduction is higher and natural mortality rate ishigher than other species of genus Balaenoptera. As a mortality coefficient at initialstock level was calculated to be 0.102-0.104, it will be 0.10. Natural mortality
rate will decrease as population decreases. The smallest mortality coefficient at
the lowest population level is unknown, but we set it as 0.06. Recruitment rate(r) must be the same value as mortality coefficent at the initial population level(0.10). The recruitment rate at the lowest stock level is calculated from the following equation:

Where, p is a pregnancy rate, and it is assumed to be 0.85 at the lowest stock level,
for the present pregnancy rate is 0. 75 and it will increase as population decreases.
Notation of T is age at recruitment, and it is also assumed as 5 years at the lowest
stock level. Then, r-value is calculated to be 0.315. This value is considered as
the upper limit at the lowest stock level, so we estimate it is 0.30 at that level.
If rand Mare assumed to change straightly with stock level, r-M changes as
Sci. Rep. Whales Res. Inst.,

No. 22, 1970.

118

OHSUMI, MASAKI AND KAWAMURA

shown in Fig. 22. And then, sustainable yield curve is obtained which is also
shown in the same figure. The stock level which gives maximum sustainable
yield will be half of the initial stock level, and the maximum sustainable yield willbe 0.13 times of the half of the initial stock size.
Although we have not yet obtained satisfactorily the whole population sizeof the minke whales in the Antarctic, it will be estimated to be about 70,000 bymeans of whale sighting. If it is true, the population size at maximum sustainable
yield level will be about 35,000 and maximum sustainable yield will be about 4,200.
That is to say, if 4,200 minke whales are caught in the Antarctic every year, we
can continue a minke whaling safely for ever. Above result is only one of trial
calculations, for there are too many assumptions in this calculation. But it will
be need to antisipate catch size before a regular whaling start and to endeaver tomaintain a population at proper level, correcting continuously by the investigationin every year.
According to the above calculation, annual catch amount of the minke whales
is only about 130 BWU based on oil yield, and it is about 280 BWU based on
biomass. So, it will be dangerous to continue large amount of catch of minke
whales in the Antarctic, using such a large scaled expeditions which operate atpresent.
It is needless to set up size limit, if a quater is set up for the regulation of whaling, but if not, size limit is practical as one of the methods of regulation. In thethird meeting of the International Whaling Commission, a proposal that size limitof minke whale should be 25 feet was offered as one of the agenda, but it waswithdrawed at that time. Then, there have been no size limit on this whale species.
It will be worth to consider how many length it will be, if size limit will be set up.
Present legal size limit for the baleen whales are all set up under the body length
at sexual maturity. Legal sizes for the Antarctic blue, fin and sei whales are about
90 % of the length at sexual maturity. If a legal size of the minke whale is set up
in the same ratio, it will be 6.8 m, or 23 feet, based on the average body length atsexual maturity of both the males and females. Even in the present situation
catch of males under 7 m is very scarce in the high latitude of the Antarctic. Therefore, size limit is needless on the males. Catch of 83 % of females is over 6.8 m inthe present situation, and so catch of the females is also not influenced by settingof legal size limit for minke whaling in the Antarctic. However, there is a possibility to increase small individuals on the minke whales which distribute in lower
latitude.
SUMMARY

Following results were obtained studying for the purpose of estimating some biological parameters in the initial stock level of the minke whale in the Antarctic, bymeans of materials which were got with Japanese expeditions.
1. Minke whales caught in 1967/68 and 1968/69 Antarctic seasons had all no whiteband on the flipper.
Sci. Rep. Whales Res. Inst.,
No. 22, 1970.

STOCK OF THE ANTARCTIC MINKE WHALE

119

2. Number of baleen plates on the left side was 261-359, and 299 on an average.
Although there is individual variation, the black band in the outer margin of baleen
plates was wide, and the ratio of the breadth to length of the longest plate was 0.40.6.
3. Number of ventral grooves was 52-60 between both flippers, and the posterior
end of the ventral grooves was in front of umbilicus, and clearly separate each other.
4. There were some difference in the external proportions between the Antarctic
and the northern hemisphere minke whales, and between both sexes.
5. Vertebrae formula was C7, Dll-12, Ll2, Ca18, Total 48-49.
6. From above morphological characters, so called New Zealand piked whale(Balaenoptera bonaerensis) should be a synonym of the minke whale (B. acutorostrata) in
the northern hemisphere.
7. Ages were determined with earplug. Although materials were not so enough,growth curves were drawn after the age determination.
8. Testis weight at maturity was estimated to be 0.35 kg for each sides.
9. Average body length at sexual maturity was 7.1 m and 7.9 m for males andfemales, respectively. And the average age at sexual maturity will be 7-8 years.
10. Average length at physical maturity is 8.3 m for the males and 8.8 m for thefemales, respectively. Age at physical maturity was estimated as 18-22 years.
11. Pregnancy rate of mature females was considered to be 80-90 %, and annual
ovulation rate was also estimated to be 0. 767. Therefore, reproduction rate of thiswhale is considered to be higher than other species of genus Balaenoptera.
12. Sex ratio of the foetuses is 1 : 1, and the seasons of fertilization and parturition
slip about half a year between the Antarctic and northern hemisphere minke whales
each other. Breeding season will be once a year.
13. As the stomach contents, one year group of Euphausia superba were mostfrequently found. E. spinifera and Calanus tonsus were also identified from stomach
contents. Daily fluctuation was observed in the feeding activity.
14. Cocconeis ceticola and Cyamus balaenopterae were found as ectoparasites.
15. Catch of minke whales in the Antarctic has not been many still, so that population is considered to maintain the initial level.
16. Most catch of minke whales with Japanese expeditions were from the waters
southward the Antarctic Convergence of Area IV.
17. Sex ratio of whales caught was 70-80 % of males at least in the high latitudinalwaters of Area IV.
18. Maximum body lengths were 9.2 m for males and 9.8 m for the females, respectively, and so the Antarctic minke whale is considered to do not exceed over 10 m.
Average body length of whales caught were 7.92 m and 8.13 m for males and females, respectively.
19. There is a tendency of ageal segregation for the males which distribute inhigher latitude of the Antarctic, and sexually mature males were 86 % of total males
caught. On the contrary, females distribute fewer than the males in that waters,
and ageal segregation was not so remarkable in the females.
20. Natural mortality coefficient was estimated to be 0.10, which is higher thanSci. Rep. Whales Res. Inst.,
No. 22, 1970.

120

OHSUMI, MASAKI AND KAWAMURA

other species of genus Balaenoptera. The longest life span is considered not to exceed
50 years.
21. Based on whale sighting, minke whales distribute widely in the Antarctic insummer, but density distribution was higher southwards of the Antarctic Convergence, and it was considered to be the highest in Area IV.
22. Lone whales were many in lower latitude, and the number of whales in a school
had a tendency to increase in higher latitude.
23. By means of whale sighting population size in Area IV was estimated to beabout 23,000. It is still difficult to estimate the whole population size of the minke
whales in the whole Antarctic, but it may perhaps exceed 70,000.
24. If the initial population size is 70,000, maximum sustainable yield is calculated
to be 4,200, and catch of 4,200 minke whales will be permitted safely every season.
25. Thickness of blubber is more in the females than the males, and they were 27 cm at the position of side under the dorsal fin. Thickness of blubber had a tendency to increase from December to January.
26. Body length/body weight relationship was shown in the following formula:
W=0.466 L2· 31

27. Production per whale was 0.57 ton. of whale oil, 1.61 ton. of whale meat and2.48 ton. of total production.
28. Number of minke whales per one Blue Whale Unit was calculated as 32 basedon whale oil production, and 15 based on biomass.
ACKNOWLEDGEMENTS
Materials used in the present report were obtained from the investigations and collections by Japanese expeditions operated in the Antarctic. We wish to acknowledge
with many thanks for many staff of the Expeditions of Taiyo Gyogyo Co., Nippon
Suisan Co. and Kyokuyo Hogei Co. Without the leading and activity by inspectors
on board of the expeditions, these materials were not obtained. We wish to express
ou.I sincere thanks for them.
Professor M. Nishiwaki of the University of Tokyo kindly gave us pertinent
criticism on our preliminary report, and Dr. H. Omura, Director of the Whales Research Institute, also kindly read our draft and gave many suggestions. Our sincere
thanks are also due to them.
REFERENCES
ARSENYEV, R. K., 1960. Distribution of Balaenoptera acutorostrata Lacep. in the Antarctic. Norsk HvaifangstTid., 49(8) : 380-2.
BENEDEN, P.J. VAN, 1889. Histoire naturelle des Ctftaces des Mers d'Europe. Brussels. pp. vii+664 (cited by
Stephenson, 1951).
BEST, P. B., 1967. Distribution and feeding habits of baleen whales off the Cape Province. Div. Sea Fish.
Invest. Rep., 57: 1-44.
BRODSKII, K. A., 1964. Distribution and morphological features of the antarctic species of Calanus (CopeSci. Rep. Whales Res. Inst.,
No. 22, 1970.

STOCK OF THE ANTARCTIC MINKE WHALE

121poda). In: A. P. Andriyashev and P. V. Ushakov (Ed) ; Biological reports of the Soviet Antarctic
Expedition (1955-1958). !PST Vol. 2, 194-256. Jerusalem, (1966).
BURMEISTER, H., 1867. Preliminary descriptions of a new species of finner whale (Balaenoptera bonaerensis).
Proc. ,(,ool. Soc. (London) Pt. II: 707-13.
CHITTELEBORROUGH, R. G., 1953. Areal observations on the humpback whales, with notes on other species.
Aust. J. Mar. Freshw. Res., 4: 219-26.
CLARKE, R., 1962. Whale observation and whale marking off the coast of Chile in 1958 and from Ecuador
towards and beyond the Galapagos Islands in 1959. Norsk Hvalfangst-Tid., 51 (7): 265-87.
CRISP, D. T., 1962. The tonnages of whales taken by Antarctic pelagic operations during twenty seasons andan examinations of the Blue Whale Unit. Norsk Hvalfangst-Tid., 51(10): 389-93.
Dor, T., S. 0HSUMI, and T. NEMOTO, 1967. Population assessment of sei whales in the Antarctic. Norsk
Hvalfangst-Tid., 56(2): 25-41.
Dor, T., S. 0HsuMI, K. NAsu, and Y. SmMADzu, 1969. Advanced stock assessment of fin whales in the Antarctic. IWC Rep. No. 20 (in press)
FARRAN, G. P., 1929. Copepoda. British Antarctic ("Terra Nova") Expedition, 1910. Nat. Hist. Report, ,(,ool.,
8(3) : 203-306.
FRY, D. H., 1935. Sharp-headed finner whale taken at Los Angeles Harbor. J. Mamm. 16(3): 205-7.
FUJINO, K., 1955. On the body weight of the sei whales located in the adjacent waters of Japan. Sci. Rep.
Whales Res. Inst., No. 10: 133-141.
GASKIN, D. E., 1968. The New Zealand cetacea. Fish. Res. Bull. (New ,(,ealand), No. 1, 92 p.
GRAY,]. E., 1874., On the skeleton of the New Zealand piked whale, Balaenoptera Huttoni (Physalus antarcticus, Hutton). Ann. Mag. Nat. Hist., 13(4): 448-52.
HARDY, A. C. and E. R. GUNTHER, 1935. The plankton of the South Georgia whaling grounds and adjacentwater, 1926-1927. Discovery Rep., 11 : 1-456.
laHIHARA, T., 1959. Formation mechanism of ear plug in baleen whales in relation to glove-finger. Sci.
Rep. Whales Res. Inst., 14: 107-35.
laHIHARA, T., 1966. Criterion for determining age of fin whale with reference to ear plug and baleen plate.
Sci. Rep. Whales Res. Inst., 20: 17-82.
International Whaling Statistics., (1930-1969) Vols. 1-62, Oslo.
JrLLETT,J. B., 1968. Calanus tonsus (Copepoda, Calanoida) in southern New Zealand waters with notes on
the male. Aust. J. Mar. Freshw. Res., Vol. 19: 19-30.
]ONSGARD, A., 1951.
Studies on the little piked whale or minke whale (Balaenoptera acuterostrata Lacepede).
Norsk Hvalfangst-Tid., 40(5): 209-32.
]ONSGARD, A., 1962. Population studies on the minke whale Balaenoptera acutorostrata Lacepede. In: Le Cren,
E. D. and Holdgate, M. Vv. The exploitation of natural animal populations. Oxford, 159-67.
KASUYA, T. and T. lcmHARA, 1965. Some informations on minke whales from tbe Antarctic. Sci. Rep.
Whales Res. Inst., 19: 37-43.
KAWAMURA, A., 1969a. Siamese twins in sei whale (Balaenoptera borealis Lesson). Nature, 221: 490-1.
KAWAMURA, A., 1969b. [Some consideration on the stock unit of sei whales by the aspect of ectoparasitic
organisms on the body.] Bull. Jap. Soc. Fish. Oceanogr., 14: 38-43. (in Japanese).
KAWAMURA, A., 1969c. [Food of sei whales in the Antarctic (1) Calanus tonsus GIESBRECHT.] Geiken
Tsushin, 213: 8-11 (in Japanese).
KAWAMURA, A. and T., HosHIAI, 1969. Data on copepods collected in the 7thJapanese Antarctic Research
Expedition, 1965-66, Antarctic Ree., 36: 73.
KAWAMURA, A., 1970. Food of sei whale taken by Japanese whaling expeditions in the Antarctic season
1967/68. Sci. Rep. Whales Res. Inst., 22: (in press).
LAws, R. M., 1956. Growth and sexual maturity in aquatic mammals. Nature, 178(4526): 193-4.
LAws, R. M., 1959. The foetal growth rates of whales with special reference to the fin whale, Balaenoptera
physalus Linn. Discovery Rep., 29: 281-308.
LEUNG, Y.-M., 1967. An illustrated key to the species of whale-lice (Amphipoda, Cyamidae), ectoparasitesof cetacea, with guide to the literature. Crustaceana, Vol. 12, Pt. 3: 379-91.
LILLIE, D. G., 1915. Cetacea. Brit. Ant. (" Terra Nova") Exp. 1910. ,(,ool. 1(3): 85-124.
Sci. Rep. Whales Res. Inst.,
No. 22, 1970.

122

OHSUMI, MASAKI AND KAWAMURA

MACKINTOCH, N. A., 1965. The stocks of whales. Fishing News Ltd., London. 232 p.
MACKINTOSH, N. A. andJ. F. G. WHEELER, 1929. Southern blue and fin whales. Discovery. Rep., 1: 257540.
MACKINTOSH, N. A. and S. G. BROWN, 1956. Preliminary estimates of the southern populations of larger
baleen whales. Norsk Hvaifangst-Tid., 45(9): 257-540.
MARR, J. W. S., 1956. Euphausia superba and the Antarctic surface currents (an advance note on the distribution of the whale food). Norsk Hvaifangst-Tid., 45(3): 127-34.
MATSUURA, Y., 1936. On the lesser rorqual found in the adjacent waters of Japan. Bull. Japanese Soc. Sci.
Fish., 4(5) : 325-30.
NASu, K. and Y. SmMADZU, 1969. A method of estimating whale population by whale sighting. 20thRep.
IWC (in press).
NEMOTo, T., 1957. Food of baleen whales in the northern North Pacific. Sci. Rep. Whales Res. Inst., 12:33-89.
NEMOTO, T., 1959. Food of baleen whales with reference to whale movement. Sci. Rep. Whales Res. Inst.,
14: 149-290.
NEMOTO, T., 1962a. Food of baleen whales collected in recent Japanese Antarctic whaling expeditions. Sci
Rep. Whales Res. Inst., 16: 89-103.
NEMOTO, T., 1962b. Higekuzira no Jiryo (Food of baleen whales). Geiken Sosho No. 4, Whales Res. Inst.,
Tokyo, 136 p. (in Japanese).
NEMOTO, T., 1964. School of baleen whales in the feeding areas. Sci. Rep. Whales Res. Inst., 18: 89-110.
N1smwAKI, M., 1950. On the body weight of whales. Sci. Rep. Whales Res. Inst., 4: 184-209.
N1smwAKI, M., 1965. Geirui Kikyakurui (Cetacea and Pinnipedia.) Univ. Tokyo Press. 439 p. (in Japanese).
0HSUMI, S., 1964. Examination on age determination of the fin whales. Sci. Rep. Whales Res. Inst., 18 : 4988.
0HSUMI, S., 1965. Reproduction of the sperm whale in the North-West Pacific. Sci. Rep. Whales Res. Inst.,
19: 1-35.
0HSUMI, S., 1967. Age determination of cetacea. Bull. Jap. Soc. Sci. Fish., 33(8): 788-98.
0HSUMI, S., M. N1smwAK1, and T HrnIYA, 1958. Growth of fin whales in the Northern Pacific. Sci Rep.
Whales Res. Inst., 13: 97-133.
OMURA, H., 1950. On the body weight of sperm and sei whales located in the adjacent water of Japan.
Sci. Rep. Whales Res. Inst., 4: 1-13.
OMURA, H., 1957. Osteological study of the little piked whale from cost ofJapan. Sci. Rep. Whales Res. Inst.,
12: 1-21.
OMURA, H., 1969. On the BWU system. Geiken Tsushin, No. 211: 4-8 (inJapanese).
OMURA, H. and H. SAKrnRA, 1956. Studies on the little piked whale from the coast ofJapan. Sci. Rep. Whales
Res. Inst., 11 : 1-39.
SCHEFFER, V. B. and J. VI/. SLIPP., 1949. The whales and dolphins of Washington State with a key to thecetaceans of the west coast of North America. Ameri. Midland Nat. 39(2): 257-337.
SERGEANT, D. E., 1963. Minke whales, Balaenoptera acutorostrata Lacepede, of the western North Atlantic.
]. Fish. Res. Bd. Can. 20: 1489-1504.
SLEPTSOV, M. M., 1955. The biology and industory of whales in the waters of Far East. (in Russian) 63 p.
STEPHENSON, W., 1951. The lesser rorqual in British waters. Dov. Marine Lab. Rep., 3(12): 7-48.
TANAKA, 0., 1960. Pelagic copepoda. Biological results of the Japanese Antarctic. Reserch Expedition.
Special Pub. Seto Mar. Biol. Lab., No. 10: 1-176.
TAYLOR, R.H. F., 1957. An unusual record of three species of whale being restricted to pools in Antarctic
sea-ice. Proc. :(ool. Sci. London 129: 325-31.
ToMILIN, A. G., 1957. Cetacea. Translated by 0. Ronen into English. (1967) 717 p.
VAN UTRECHT, W. L. and S. VAN DER SoPEL, 1962. Observations on a minke whale (Mammalia, Cetacea)
from the Antarctic. :(eit. Siiugetier 27(4): 217-21.
VERVOOT, W., 1957. Copepods from Antarctic and sub-antarctic plankton samples. B.A.N.Z. Antarctic
Research Expedition 1929-1931. Rep. Ser. B (:(oolog)' and Botany), Adelaide 160 p.
WHEELER, J. F. G., 1930. The age of fin whales at physical maturity. Discovery Rep., 2 : 403-34.
Sci. &p. Whales Res. Inst.,
No. 22, 1970.

STOCK OF THE ANTARCTIC MINKE WHALE

123

WILLIAMSON, G. R., 1959. Three unusual rorqual whales from the Antarctic. Proc. ,Zoo!. Soc. (London) 133:
135-44.
WILLIAMSON, G. R., 1961. Two kinds of minke whale in the Antarctic. Norsk Hvalfangst-Tid., 50(4): 13341.
ZEMSKY, V. A. and D. D. ToRMOSON, 1964. Small rorqual (Balaenoptera acutorostrata) from the Antarctic.
Norsk Hvalfangst-Tid., 53(11): 302-5.
ZENKOVICH, B. A., 1955. On the lesser rorqual fishery. Rybnoe Khozyaistvo, No. 7 (cited from Tomilin 1957).

Sci. Rep. Whales Res. Inst.,
No. 22, 1970.

~ _;-

~~

--~ ~

~~
"'
l'-0 ~~~~~

Tip of snout to angle of gape

Tip of snout to center of eye

Tip of snout to tip of flipper

Eye to ear (center)

Notch of flukes to posterior
emargination of dorsal fin
Flukes, width at insertion

Notch of flukes to anus

Notch of flukes to umbilicus

3.

4.

5.

6.

7.

8.

9.

10.

* Unreliable.

Flukes, tip to tip

17.

16.

Flipper, tip to anterior endof lower border
Flipper, greatest width

Dorsal fin, length of base

15.

14.

11.

Notch of flukes to end ofventral grooves
12. Anus to reproductive aperture(center)
13. Dorsal fin, vertical height

Total length
Tip of snout to blowhole

!.
2.

Sex

Whale number
M
840
113
(13.52)
162(19.29)172(20.48)374(44.52)40(4.76)
252(30.00)79(9.40)
198(23.57)368(43.81)389(46.31)46(5.48)
25(2.98)
37(4.40)
105(12.50)27(3.21)
248(29.52)

M

840
112(13.33)160(19.05)170(20.24)400(47.62)44(5.24)
250(29. 76)78(9.29)
220(26.19)400(47.62)470(55.95)50(5.95)
35(4.17)
31(3.69)
139(16.55)31(3.69)
280(33.33)M
828
116(14.01)170(20.53)160(19.32)330(39.86)39(4.71)
239(28.86)59(7.13)
225(27.17)410(49.52)445(53.74)70(8.45)
35(4.23)
52(6.28)
131(15.82)32(3.86)
228(27.54)M

810
108(13.33)153(18.89)162(20.00)366(45.19)40(4.94)
232(2.8.64)76(9.38)
220(27.16)396(48.89)431(53.21)61(7.53)
25(3.09)
40(4.94)
120(14.81)29(3.58)
290(35.80)

22 N4

22 N3

22 N2

22 NI

850
104
(12.24)147(17.29)163(19.18)374(44.00)40(4.71)
254(29.88)80(9.41)
217(25.53)356(41.88)384(45.18)56(6.59)
32(3.76)
48(5.65)
130(15.29)24(2.82)
213(25.06)

M

22 N5

800
128
(16.00)162(20.25)176(22.00)389(48.63)40(5.00)
236(29.50)86(10.75)236(29.50)420(52.50)452(56.50)25(3.13)
32(4.00)
36(4.50)
140(17.50)33(4.13)
232(29.00)

F

22 N6

710
105
(14.79)133(18. 73)143(20.14)315(44.37)40(5.63)
190(26.76)60(8.45)
193(27.18)330(46.48)375(52.82)55(7.95)
29(4.08)
53(7.46)
110(15.49)28(3.94)
218(30. 70)

22 III
N425
M
754
117
(15.52)136(18.04)147(19.50)350(46.42)43(5. 70)202(26. 79)55(7.29)
200(26.53)350(46.42)403(53.45)67(8.89)
27(3.58)
46(6.10)
128(16.98)30(3.98)
210(27.85)

22 III
N511
M
780
120
(15.38)144(18.46)158(20.26)350(44.87)39(5.00)
211(27.05)53(6.79)
244(31.28)365(46.79)400(51.28)26*(3.33)
29(3.72)
60(7.69)
128(16.41)29(3. 72)210(26.92)22 III
N221
M
806
112
(13.90)138(17.12)160(19.85)365(45.29)40(4.96)
240(29. 78)65(8.06)
222(27.54)384(47.64)423(52.48)46(5.71)
28(3.47)
40(4.96)
130(16.13)31(3.85)
216(26.80)22 III
N171
M
820
120
(14.63)140(17.07)150(18.29)370(45.12)42(5.12)
213(25.98)65(7.93)
200(24.39)380(46.34)421(51.34)66(8.05)
25(3.05)
42(5.12)
132(16.10)28(3.48)
230(28.05)M

22 T2

APPENDIX I. BODY PROPORTIONS OF THE MINKE WHALES CAUGHT IN THE ANTARCTIC OCEAN DURING
1967/68 SEASON. THE PERCENTAGES TO TOTAL BODY LENGTH (CM) ARE GIVEN IN PARENTHESIS

930
140(15.05)180(19.35)190(20.43)420(45.16)50(5.38)
265(28.49)90(9.68)
255(27.42)350(37.63)490*(52.69)35(3.76)
35(3. 76)50(5.38)
100*(10.75)35(3. 76)255(27.42)

F

22 TI

::r:

>

~
~
c~

>

:;:::

tJ

z>

......

>
rJl
>
:;:::

~

~

~
......

c

rJl

0

,j>.

Nl

STOCK OF THE ANTARCTIC MINKE WHALE

EXPLANATION OF PLATESPLATE I
Fig. 1. Dorsal side of right flipper, the posterior margin of ventral grooves andumbilicus. Arrow shows umbilicus.
Fig. 2. Ventral side of tail flukes.

PLATE II
Fig. I.
Fig. 2.

Post-ventral view. Arrow shows umbilicus.
Right side of rostrum showing the color of baleen plates.

Fig. I.
Fig. 2.

Baleen plates
Ventral view of tail portion.

PLATE IIISci. Rep. Whales Res. Inst.,
No. 22, 1970.

125

I'
.
I
ムV寸d

0ど6!'
u・めV
・
1w
1・
r
a
ur
a
1
m
1
M ψl
l・
n
s

6

v<In ：：~v 九\V)I a~v I ~I VSVJ!ll '
I
F
叩f
1
S
HO

I
PLATE I

"D KAWAMURA¥i,MASAKI A
OHSUMIt・3sns.I.WhalesRe
.Rψ
i
c
S
.
0
7
9
,1
2
.2
o
N

I
J
I3
.
ムV1d

.L6f・
u・
ON
・
＜
／3
/
j

し1
S
l
l
f"
S
3/
j日 ／V
l
f
M

...，妥

V~ 日開 VN1V)lα NV I
予I
VSVW I
列 QSHO