GROWTH OF FIN WHALE IN THE NORTHERN PACIFIC
SEIJI (KIMURA) OHSUMI, MASAHARU NISHIWAKIAND TAKASHI HIBIYA*
On the growth of the fin whales (Balaenoptera physalus, Linn.), Mackintosh & Wheeler (1929) reported first in detail for the southern stock
At that time, however, available age characters were not yet known.
Therefore, chiefly on the age of the whale, their paper was incomplete.
They pointed out the possibility of the number of ovulations and ossification of vertebral column as age characters. Wheeler (1930) developed
this method and classified several groups by means of the number ofovulations. Peters (1939) calculated the number of ovulations in each
breeding season.
Ruud (1940, 1945) discovered the age determination for whales bymeans of baleen plates. And then Tomilin (1945), Nishiwaki (1950,
195la) and Utrecht (1956) advanced this method. Furthermore Nishiwaki(1951b) showed the colourlation of crystalline lens as an age character.
These age characters, however, are somewhat incomplete. In 1955,
Purves discovered lamination in the core of the ear plug. This is now
regarded as the best age character for baleen whales. Then, Laws &Purves (1956) and Nishiwaki (1957) studied the age of baleen whales
chiefly fin whales using the number of the laminations.
On investigations of life history for the southern fin whales, many
reports have been presented. On the other hand, the studies of growth
for the northern fin whale have been relatively scanty. The reason will bethat the whales caught in northern hemisphere have been relatively
rare and so we have not been blessed with chances of investigation ofwhales. On the growth of the fin whale in adjacent waters to Japan,
Tago (1922), Matsuura (1935), Omura (1950), Kasahara (1950), Mizue &Jimbo (1950), Sakiura, Nozawa & Ozaki (1953), Mizue (1956) and Mizue& Fujino (1957) reported. Pike (1953) reported on the fin whale fromthe coast of British Columbia. Papars of Matsuura & Maeda (1942),
Omura (1955) and Sleptsov (1955) were described on the fin whale in thenorthern part of the North Pacific. On the growth of the fin whale in
the North Atlantic, there are some papers by Ruud (1945), Jonsgard(1952) and Laws & Purves (1956). We shall discuss the above papers
in the following chapters.
Since 1952 Japanese whaling in the fleets have operated in northern partof the North Pacific. The area includes the Pacific northern 48°N and* Laboratory of Fisheries Zoology, Faculty of Agriculture, University of Tokyo.
97

98

S. (KIMURA) OHSUMI, M. NISHIWAKI AND T. HIBIYA

Bering Sea. Inspectors and biologists on board have been engaged in biological investigations on each whale pulled up on deck. The purpose of
the present paper is to describe the growth and age of the fin whalein the northern part of North Pacific. Although according to theinvestigation of blood groups by Fujino (1956), the northern fin whales
are distinguished into east and west populations, the result of the marking
investigation shows the intermixture between west and east groups in
the northern Pacific. Therefore, in the present paper we study thegrowth representing the total northern Pacific fin whale.
We don't think this paper shows the growth of the fin whale in total
North Pacific. In the North Pacific, several stocks of the fin whale will be
existed. For instance, Mizue & Fujino (1957) and Ichihara (1957) describethat the fin whale caught in the East China Sea should be regarded as a
independent stock because of a shape of baleen plates, body proportion,body length at sexual maturity and so on. Much less, we never think ourpaper will deduce the northern fin whale, for the fin whale in the North
Atlantic is thought as a different stock in the northern hemisphere.
We devide the process of growth into the following stages.
1. Fertilization
2. Birth
3. Weaning
4. Prepuberty
5. Sexual maturity
6. Physical maturity
In above stages, we have very little data on the weaning. So thisstage is substituted for the growth of calf.
We wish to express our thanks to inspectors and biologists and to
Kyokuyo Hogei Co., Taiyo Gyogyo Co. for the investigations and samplingof our material. We are indebted to Mr. Tadayoshi Ichihara of the Whales
Research Institute for his kind help to sampling and reading laminations in ear plug. We are also indebted to Mr. Takehiko Kawakami of
the Fisheries Agency for giving us the data of marking whales in thenorthern Pacific.
MATERIAL AND METHOD

The material for the present study is based on the data of the biologicalinvestigation of fin whales mainly caught in the northern part of theNorth Pacific for the six years from 1952 to 1957. The inspectors andthe biologists who pursued the investigation are as follows.
1952 Haruyuki Sakiura, Katunari Ozaki, and Kazuo Fujino.
1953 Yasutake Nozawa, Iwao Takayama, and Tahahisa Nemoto.

GROWTH OF FIN WHALE IN THE NORTHERN PACIFIC

99

1954 Setsuo Nishimoto, Tamenaga Nakazato, Takehiko Kawakami, Ikuyo Hasegawa,Kazuo Fujino, and Seiji Kimura.
1955 Yasutake Nozawa, Saburo Ikeda, Ken-ichi lguchi, and Kazuo Fujino.
1956 Heihachiro Kawamura, Sumio Matono, Sadao Ishii, and Seiji Kimura.
1957 Yasutake Nozawa, Takehiko Kawakami, Itaru Chihara, and Tadayoshi Ichihara.

The items of the investigation used in the present paper are datecaught, sex, body length, thickness and condition of mammary gland,
number of corpora lutea _and albicantia in ovaries, weight of testes andcollection of their samples, sex and body length of foetuses, conditionof ossiffication of vertebral column and the collection of ear plugs.
On the lactation it was judged whether white milk was secreted or not.
The thickness of the mammary gland was measured in the thickest portionof the gland, and then the maturity of the gland was judged by thecondition of the gland. The immature mammary gland was thin andwhite or pink in colour, but the mature gland was thick and brown.
TABLE 1. NUMBER OF FIN WHALES CAUGHT AND INVESTIGATEDBY JAPANESE EXPEDITIONS IN THE NORTHERN PACIFIC
Year
1952
1953
1954
1955
1956
1957
Total

Males
104
238
675
710
755
736
3218

Females
109
232
641
650
657
668
2957

The numbers of the corpora albicantia and lutea were counted withnaked eye by slicing the right and left ovaries. The right and left testes
were weighed in O.lkg unit with spring balances after cutting off theepididymis. Thereafter a small piece was cut off from each testis andwas directly fixed with the 10% formalin. The fixed samples were cut
into the sections 10 micron thick by the paraffin method, double-stainedwith haematoxylin-eosin, and subjected to the microscopic examination.
On the ossiffication of the vertebral column, it was cut along theaxis with a bone-saw and the presence of cartilaginous layer between
the epiphysis and the centrum was examined with naked eyes. Conditions
were classified as follows.
N: Not ankylosed. Thick cartilage.
n: Not ankylosed. Thin cartilage.
a: Ankylosed. Join visible.
A: Ankylosed. No sign of Join.

The samples of ear plugs were collected in 1956 and 1957, After
fixation with 10% formalin, the samples were grinded down to the levelof the longitudinal axis, and laminations in core were counted with nakedeyes or by means of a dissecting-microscope.

100

S. (KIMURA) OHSUMI, M. NISHIWAKI AND T. HIBIYA

THE BIRTHTHE GROWTH OF FOETUSESThe foetuses investigated in the northern Pacific from 1952 to 1956
consisted of 461 males, 461 females, 4 of indistinct sex because ofa small size, and 4 couples of twins. In the twins, three couples of
dizygotic (~Sf-, ~if-.~~) and one couple of monozygotic twins(~~) were
included. Frequency of the twins was 0.43 per cent in the total
foetuses. According to Kimura (1957), the frequency of multiplets insouthern fin whales was 0.872 per cent.

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May

June

July

Aug.

Sept.

Growth of fin whale foetuses from the northern part of the North Pacific.

Figure 1 shows the length and date (by the interval of ten days) of
killing of each foetus. The whaling season usually sets in the middleof May and closes by the end of September in the northern Pacific. It
is regrettable, therefore, that the growth of foetuses of the fin whales
cannot be investigated throughout the year.
It is obvious from this figure the length of foetuses disperse at any
time. This means that the pairing season is prolonged considerably,
and there is also an individual variation in the growth. According toKimura (1957), the difference of body length of two foetuses in a coupleof twins increases usually with the growth, and it will be about twofeet at birth.

GROWTH OF FIN WHALE IN THE NORTHERN PACIFIC

101

The average length of our material in each ten-day period shows infigures 2 and 3. The growth of foetuses shows nearly parabolic curve.
The growth equation in this stage is represented by the following
formula.
L=0.329M1 • 61
L : Body length in feet. M: Time in month.
12
10

~6
.3

i4
2

Feb.

Mor.

Apr.

Moy

June

July

Aug.

Sept.

Oct.

Fig. 2. Mean growth curve of fin whale foetuses from the northern Pacific,
adjacent waters to Japan and the North Atlantic. Dotted line: adjacent waterto Japan (Mizue, 1950). Solid line: northern Pacific. Cross: the North Atlantic.
TABLE 2. LENGTH OF FOETUSES IN THE MIDDLE OF EACH
MONTH AND THEIR CONCISE CALCULATION
Month
lst
2nd
3rd
4th
5th
6th
7th
8th
9th
lOth
llth
12th

Body length
in feet
0.1
0.6
1.5
2.4
3.5
4.8
6.3
8.2
10.4
13.4
16.7
20. 5

Concise calculation
lxlx0.1
2x3x0.1
3x5x0.1
4 x6x0.1
5x7x0.1
6x8x0.1
7x9x0.18x10x0.l
9x 12x0. l
10x13 x 0.1
11x15 xO.l
12 x 17 x 0 .1

Table 2 shows the body length of foetuses at the middle of eachmonth and the easy method of calculating it. In the growth curvesof both sexes we did not notice any variation. From figure 2 it is clear

102

S. (KIMURA) OHSUMI, M. NISHIWAKI AND T. HIBIYA

that the growth curve of the fin whale foetuses in the northern Pacificis almost similar to that in the coastal region of Japan and the North
Atlantic. Thus, it is supposed that the growth curves of the fin whale
foetuses are similar in all regions of the northern hemisphere. As shownin figure 3, if the growth curve of foetuses in the northern Pacific isremoved just six months, it coincides closely with the curve of thesouthern fin whale foetuses. This means that in gestation period thegrowth rate of fin foetuses is similar all over the world.
----------------------,..-length at birth------

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Fig. 3. Growth curve of the fin whale foetus from the northern Pacific and theAntarctic. Solid line: northern Pacific. Dotted line: Antarctic. Left solid line:
northern Pacific, slided down six months.

BODY LENGTH AT BIRTH

The largest foetus of our materials is 16 feet 4 inches (497 cm) long.
It was caught in the middle of September. But it is too short for a
foetus at full term. Tago (1922) reported a 22 shaku (one shaku ·.one foot)long calf which seemed to have been just born in the eastern sea of
Korea in winter. Matsuura (1935) estimated that the body length of
the fin whale at birth was about 6.0m (19 feet 8 inches). Kasahara(1950) estimated also that the fin whale was born at the length from18 to 21 shaku. According to Mackintosh & Wheeler (1929), the fin
whales were born at about 6.5m (21.3 feet) on the average. Table 3
shows the size of maximum foetuses, minimum calves and maximum
adult whales in the North Pacific in each year since 1910, and summarized
data from the Japanese Whaling Statistics from 1910 to 1945. The
maximum foetus is 20 feet and minimum calf is 20 feet in the table.
According to the International Whaling Statistics, the maximum foetus

GROWTH OF FIN WHALE IN THE NORTHERN PACIFIC

103

is 22 feet 10 inches long and there are two 20 feet foetuses of the fin
whales in the North Atlantic. We have suggested in above section thatthe mean growth curves of foetuses in various grounds of the world
are similar with each other. And discussing the previous papers andthe present data, we conelude that the body length at birth of the fin
whale in the northern Pacific is estimated to be from 20 to 22 feetlong and 21 feet long in an average.
TABLE 3. THE MAXIMUM AND MINIMUM BODY LENGTH OF THE
NORTH PACIFIC FIN WHALES IN EACH YEAR (1910-56)
Maximum length
Year

Minimum length

Maximum foetuses---~-~

Males
1936
72feet
1937
71
1938
66
1910-45*
75
1946
65
1947
66
1948
68
1949
70
1950
75
1951
73
1952
70
1953
69
1954
69
77
1955
1956
74
* Coast of Japan

Females
72f eet
68
69
76
70
72
69
69
70
73
71
72
73
74
74

Males
42feet46
50

Females
48feet48
50'--------,--------'

Sex and length Date
M.
F.

20
50
50
50
50
37
41
48
45
40
44
45

41
50
47
49
47
46
48
43
47
49
45

F.
F.
M.
M.
M.
M.
M.
F.
F.
F.
M.

10'-6 11
10-1
20
7-8
13-3
13-6
14-3
13-0
16-6
14-3
15-8
16-5
17-2
13-4

3/8
26/8
?/7
22/7
20/8
1/10
22/8
3/8
14/9
14/9
10/10
12/9
10/9
4/9

BREEDING SEASON

Owing to the limitation of whaling season (from May to September),
we do not know much about the breeding season of the northern fin whales.
Thus we must assume the breeding season by means of length of
foetuses in the whaling season.
In figure 1, each curve indicated the mean growth curve of foetuses
shifted to lateral intervals of one month so as to include all the points
plotted. If all foetuses grew at an equal speed, the foetuses measured
would be conceived within the term from September to July.
Figure 4 shows the pairing season which is obtained by counting thenumber of plotted points between two parallel curves in figure 1.
Majority of pairings take place between November and January, themaximum falling about in the middle of December. On the durationof pairing season, we found a very small foetuses 2.0cm long in the
beginning of September.
In figure 3, it is found that the growth is very similar to that of

104

S. (KIMURA) OHSUMI, M. NISHIWAKI AND T. HIBIYA

southern fin whales being just six months behind. According to Mackintosh & Wheeler (1929), May, June, July and August are the monthswhich the majority of pairing take place, the maximum falling at about
the end of June or beginning of July. Tago (1922) stated that pairing
season is not constant (he observed a copulation of fin whales in the
middle of March), but he assumed that pairing season of the fin whalesin the coast of Japan was the early spring. Kasahara (1950) assumed
that the season of pairing and parturition is winter.

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Oct.

Nov.

Dec

Jan.

i=eb.

Mar.

Apr.

May

June

July

,

Frequency curve of pairing for the fin whales from the northern part of theNorth Pacific.

We have no data on the gestation period and the season of parturition.
According to the Japanese whaling statistics a calf which is 20 feet longis caught in December in the coast of Japan. In the International
Whaling Statistics on the North Atlantic fin whales, a large foetus which
is longer than an 18 feet foetus occur mostly in October, November
and January. But a foetus of 22 feet 10 inches have been once caught inJune. Mackintosh & Wheeler estimated that the midseason of parturitionis the middle of June and the period of gestation is eleven months anda half.
Basing on the above result, we should expect that the season ofparturition of the fin whale in the northern Pacific will be winter, from
November to January, and gestation period will be almost one year.
THE GROWTH OF CALF

The period of nursing and the body length at weaning are very difficult
to determine owing to the size regulation upon the fin whale. We haveno data available on them. According to Mackintosh & Wheeler (1929),

GROWTH OF FIN WHALE IN THE NORTHERN PACIFIC

105

the nursing period is estimated to last about six months and the bodylength at weaning is assumed to be 12 meters (39 feet 5 inches). Considering the difference of the length at sexual maturity between southernand northern fin whales as we discuss in the following chapter, it isassumed that the length at weaning of the fin whale in northern fin
whale is about 37 feet.
The youngest fin whales of our materials employed have 5 laminationsin the ear plug. These are a male which is 56 feet and two females
which are 52 and 55 feet long. It has been suggested that two laminations are deposited every year (Purves, 1955 ; Laws & Purves, 1956).
If so, these whales are estimated to be two and a half years old. From
figures 18 and 19, the mean length at that time is about 51 feet inmale and 52 feet in female. In this stage fin whales are completly
immature.
Of the sexually immature whales, we defined the stage of prepuberty
as follows. The prepuberal female has ovaries of which ovarian follicles
grow approaching maturity. And in the testes of the adolescent maleas may be described in the following chapter, the majority of seminiferous
tubules are open while closed tubules are not uncommon.
The body length of prepuberal females are between 55 feet and 65 feetand the average is 58.8 feet, while immature whales are under 61 feet.
The former has from 8 to 12 laminations in the ear plugs and thelatter has under 8 laminations. Of the male prepubertal whale, thebody length is 57.7 feet in an average and the age corresponds withfrom 8 to 12 laminations. Estimating from above result it takes thefin whale about four years after its birth to attain its prepuberty.
SEXUAL MATURITY
DETERMINATION OF SEXUAL MATURITY IN FEMALE

The sexual maturity of female whales is determined easier than thatof male whales. That is to say, we can determine the sexual maturityof females by means of corpus luteum or corpus albicans in ovaries.
It is regarded that corpus albicans in ovaries remains recognizable
and countable throughout the life of the whales. And if corpora lutea
or albicantia are present in the ovary, the whale must, of course, bemature. Mackintosh & Wheeler (1929) stated that it might be argued
that a female need not be regarded as mature until it has actually
ovulated.
Concerning the sexual maturity of females, following characters areinvestigated.
Varginal band. We cannot determine sexual maturity by means ofS. (KIMURA) OHSUMI, M. NISHIWAKI AND T. HIBIY A

106

varginal band. Mackintosh & Wheeler (1929) reported that the bands
were present in 31 (21.4%) of the 145 immature females of the southern fin whales. As shown in table 4, of 34 whales which have neverbeen pregnant, 19 individuals (55.9%) have varginal bands, but 15
whales which have been pregnant have no bands.
Mammary gland. We can determine the maturity of mammary glands
by observing the colour of them, that is to say, the immature gland iswhitish pink while the mature gland is brown. This distinction is very
TABLE 4.

THE EXISTENCE OF VERGINAL BANDS
Exist

Sexually immature
Prepuberal
Sexually mature, butnever pregnant
Sexually mature

7
9

None
6
8

Total
13
17

53.8
52.9

3

1

4

75.0

15

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15

0.0

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Prepuberol

Mature,but neverpregnantFirst
pregnant

Pregenant

....
.
...
_
..............
............

LactatingResting

Fig. 5. Thickness of mammary gland in several sexual conditions for the female
fin whale from the northern part of the North Pacific. Closed circle: mature
type. Open circle: immature.

clear as stated by Mackintosh & Wheeler (1929) and in the macroscopic
structure, the former is fine but the latter is coarse. Nishiwaki & Oye(1951) classified the colour of mammary glands into 7 tones, but thoseare pretty difficult to distinguish one another. Figure 5 shows the
thickness and the maturity of mammary glands of the fin whales invarious sexual phases. In the immature stage, mammary gland is ofcourse immature type and the thickness does not exceed 3.0cm. (average thickness is 1.5cm). In prepuberty, the gland is almost similar with

GROWTH OF FIN WHALE IN THE NORTHERN PACIFIC

107

immature stage and average thickness is 1.8cm, but red gland of 4.0cm
thick appears.
After attainment of sexual maturity, there are some whales whose
mammary glands are still immature. These are supposed to be thewhales which have never serected milk. Mackintosh & Wheeler supposedthat it altered permanently after the first pregnancy. But we should
correctly change their word "the first pregnancy" into "the first lactation", because in early pregnant period, mammary gland does not alter
100

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Prepuberal Mature, Pregnant
but neverpregnant

LactatingResting

Width of uterus cornu in several sexual conditions for the fin
whale from the northern part of the North Pacific.

the condition as shown in figure 5. Then we can distinguish a mature
whale which has never been pregnant and the first pregnant whalefrom other sexually mature whales by investigating the mammary glandand the ovaries.
In sexually mature but mammary immature whales the thickness ofmammary gland is not different from that of sexually immature ones.
We have never found the whale whose mammary gland is mature but
is not sexually immature.

108

S. (KIMURA) OHSUMI, M. NISHIWAKI AND T. HIBIYA

Mature mammary gland usually exceeds 3.0m in thickness, and in asexually resting whale, mammary gland which is 8.0cm or more over inthickness are very rare. Average thickness is 4.5cm. The thicknessof the gland in pregnant whales of our material is not so different
from that of the resting stage and between 3.0cm and 7.5cm. The
gland during lactation varies between 8.5cm and 27.0cm.
As the conclusion of this section, in female whales we can easily
distinguish sexual maturity by investigating the mammary gland but
it is a rough method in sexually mature but never lactated whales, whose
gland still remain in immature stage.
Size of uterus. Size of uterus across the cornu was measured whenit lay in the collapsed condition.
Figure 6 shows the size of uterus in various sexual phases. In sexually
immature stage, the size is between 3.5cm and 8.5cm (average size is
5.lcm). In prepuberal whales, uteri grow a little and the sizes are
between 4.5cm and 10.5cm (average size is 3cm). We decided the sizeof uteri of sexually mature whales was over lOcm. This is a little
shorter than the result by Mackintosh & Wheeler.
In sexually mature but never pregnant whale, the range was fromlOcm to 16cm and the average was 12.3cm. In pregnancy the uterus grewto an enormous size. The smallest uterus of pregnant whale was 16cm
in size. This whale was pregnant with small foetus (lOcm). The largest
uterus of our materials was 95cm. After parturition, involution may
take place very rapidly. In lactating whales the largest size was 22cm
and smallest was 12cm. Resting whales had uterus of 13.5cm in averagesize. But the range was between 7.0cm and 20cm.
DETERMINATION OF SEXUAL MATURITY IN MALE

It is difficult to determine sexual maturity of male whale with naked eyes.
Mackintosh & Wheeler (1929) showed the maturity character of male asfollows.
1. Size of penis.
2. Size of testis.
3. Histology of testis.
As Mackintosh & Wheeler stated, the size of the penis can be used only
to distinguish definitely mature from definitely immature whales, although
it is the readiest method to distinguish mature from immature males.
Table 5 shows the length of the penis of ten males. A penis exceeding
1.3m usually indicate maturity for the fin whale in the northern Pacific.
Mackintosh & Wheeler used the size of the testis as a practical age
character. The size was calculated in a manner to multiply together
the length, breadth and depth in cm. And they said that if the size

GROWTH OF FIN WHALE IN THE NORTHERN PACIFIC

109

exceeded about 4 l the fin whale was generally mature. Although Mackintosh & Wheeler considered that the size of testis was more convenient
than the weight, recently many authors have employed the weight oftestes for judging the sexual maturity.
TABLE 5.

Body length(feet)
58
59
59
65
63
62
63
61
63
62

LENGTH OF PENIS OF FIN WHALES IN
THE NORTHERN PACIFIC
Length of penis
Length of circumference
Weight of testes(cm)
at root of penis (cm)(kg)
84
Immature
2.5
52
2.3
105
1.5
1.4
114
Mature
4.7
3.9
115
93
13.9 16.0
"
135
5.9
6.2
"
145
59
7.9
6.8
"
145
9.5
8.9
"
78
3.5
152
2.2
"
II
88
155
4.9
5.3
56
8.0
8.5
174

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60

65

Body length (Feet)

Fig. 7.

Relation between body length and weight of larger testis for thefin whales in the northern Pacific.

Figure 7 shows the relation between the body length and the weightof the larger testis in each specimen. In our material the heaviest
testis is 31.7kg, and the lightest is 0.3kg. Owing to size regulation,

110

S. (KIMURA) OHSUMI, M. NISHIWAKI AND T. HIBIYA

we have little data for the small whales under 54 feet.
From this figure it may be clear that the whale over 59 feet is sexuallymature and the testis over 4kg is mature. But we cannot determine
sexual maturity only by means of weight of testis. Therefore histologicalexamination of testis should be employed to determine the sexual maturityof male whale as stated by Mackintosh (1942).
We examined histologically on 118 individuals and 227 testes, andclassified as sexually immature, prepuberal and mature. The definitionis owed to Chittleborough (1955); that is to say, in the immature testes
all seminiferous tubules are closed, in the prepuberty testes the majority of tubules were open while closed tubules are not uncommon, and

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ox•
ox

0

°'m

o•
o••
00
xx
oo•
0000

~ss

56

57

00

OOO

0

0

..
6•

•
0

•••
•••
•x••
oo

o~•
ox
Ox

x

0
00
00
00

58

59

•
•
••
•

..• ..

60

61

•

•
•

•

X•
0

0

CJ;~

62~

Body Length (feet)Fig. 8. Body length and maturity of testis in the fin whales from thenorthern Pacific. Solid circle: mature. Cross: prepuberal. open circle:
immature.

in the mature testes all tubules are open. Confirming the exitense of
spermatozoa is not a suitable manner for determination of maturity,
because in the times but the breedings season spermatozoa are very
few in the tubules.
Figure 8 shows the weight of testis (the larger one of the two) and bodylength of males whose testes were examined histologically. We could findfrom this figure, sexual maturity is concerned not with body length butwith the weight of testis. So we should determine the sexual maturity byweighing testes which are examimed histologically simultaneously. Table
6 shows the weight frequency of immature, puberal and mature testes
examined histologically. The heaviest immature testis is 3.0kg and thelightest mature testis is 1.0kg. And from figure 9, the weight of the testis

111

GROWTH OF FIN WHALE IN THE NORTHERN PACIFIC

of 75% in maturity is estimated to 2.6kg. In conclusion, the whale
whose larger testis is 2.6kg or more over is regarded as sexually mature.
TABLE 6.

NUMBER OF IMMATURE, PRE PUBERAL AND MATURETESTIS EXAMINED HISTOLOGICALL Y

Weight of testis
in kg.
0.5-0.6
0.7-0.8
0.9-1.0
1.1-1.2
1.3-1.4
1.5-1.6
1.7-1.8
1.9-2.0
2.1-2.2
2.3-2.4
2.5-2.6
2-7-2.8
2.9-3.0
3.1-3.2
3.3-3.4
3.5-3.6
3.7-3.8
3.9-4.0
4.1Total

Immature

Prepuberal

11
13
20
24
13
3
13
9
2
2
1
3
1

4
3
5
2
4
2
1
1
1

23

115

Mature

Total

1
4
3
3
6
7
5
5
9
9
9
5
4
6
3
1
9
89

11
13
25
31
21
8
23
16
9
7
11
13
11
5
4
6
3
1
9
227

·-·-·-

JOO

75

25

05

LO

15

20

25

3.0

35

4.0

Weight of testis (kg)Fig. 9.

Mature curve of testis based on the histological examination.

Matsuura & Maeda (1942) indicated that in the male fin whale fromthe northern Pacific combined testes over 7.5kg in weight is al111013t

112

S. (KIMURA) OHSUMI, M. NISHIW AKI AND T. HIBIYA

mature. Omura (1950) states that in the case of whales in the adjacentseas of Japan, the borderline between immature and mature is probably 3lin volume and 2.5kg. in weight. According to Ruud (1945), combined
testes which are 6.7kg and less in weight are histologically immature
for the fin whale from the North Atlantic. Nishiwaki & Hayashi (1950)
states that if the combined weight of both testes is less than 5kg in
the Antarctic fin whales, they are considered immature.
TABLE 7.

Body
length (feet)

SIZE DISTRIBUTION OF SEXUALLY MATURE AND IMMATURE
FIN WHALES IN NORTHERN PACIFIC (1952-56)
Females

Males

Immature
50
1
51
52
2
53
3
54
5
55
71
56
75
57
89
58
54
59
48
60
22
61
10
62
10
63
1
64
65
66
67
68
69
70
71
72
73
74
Total
391
Average length 57 .13

MatureTotal
1

Immature

5
28
87
181
272
347
372
310
241
132
75
20
10
3

2
3
5
76
103
176
235
320
369
382
320
242
132
75
20
10
3

4
2
2
47
62
73
96
108
55
39
32
22
7
3
3
1
1

2,083
60.86

2,474
60.27

557
58.54

MatureTotal'

1
2
1
21
43
71
153
184
194
253
244
225
163
88
50
18
4
5
2
1
1,723
64.18

4
2
2
48
64
74
117
151
126
192
216
216
260
247
228
164
89
50
18
4
5
2
1
2,280
62.80

But above-mentioned results are not due to a histological examination
exceping that by Ruud (1945). However. Ruud's value (3.3 ig in one
testis) seems to be relatively heavier than our result.
BODY LENGTH AT SEXUAL MATURITY

By means of above method, we judged sexual maturity upon the fin
whales investigated. Table 7 shows size frequencies of sexually matureand immature whales. Total whales examined are 2474 males and 2280

GROWTH OF FIN WHALE IN THE NORTHERN PACIFIC

113

females. The largest sexually immature whales are 63 feet long in themales and 68 feet long in the females. The shortest sexually mature
whales are 55 feet in both sexes. Size regulation is in force on thefactory ship whaling in northern hemisphere and the size of limitation
is fixed as 55 feet. So we have scanty data on short whales under
54 feet. Therefore we wonder whether the shortest sexually mature
whales is under 54 feet long or not. According to Omura (1950) the
shortest sexually mature fin whales in Japanese coastal whaling (sizeregulation is 50 feet) are 56 feet in both sexes.

---~~---·---c----0,,,0,.,,.-

100

,,
o,,'

,,~

d'

80 -- - --------------- - -- - - - -- -- - • - - -- - --- -,":

,,

//I

*-; 60

I

·~

E

~ 40

I

i

/

~

I

/o

'I

o~/
,,,,

20
I

,/
0

50

/

l

52

54

56

.,..,,

'

:
I

58

60

62

64

66

68

70

Body Leogth (feet)Fig. 10. Sexual mature curve of the fin whale from the northern part of the North
Pacific. Solid circle and solid line: male. Open circle and broken line: female.

From our result it is known that the range of body length at sexual
maturity is very wide. The range is 9 feet in the male and 14 feetin the female.
Figure 10 illustrates the percentages of sexually mature males andfemales in body length. The curve in this figure indicates that the
body length in which the sexual maturity is 50 per cent is 57.1 feet in
the male and 59.8 feet in the female and the same in which thematurity is 75 per cent is 57.9 feet in the male and 60.8 feet in thefemale. Therefore the mean body length of fin whales at sexual maturity
in the northern Pacific will be 57 or 58 feet in the male and 60 or 61
feet in the female. And we conclude that the male attains sexual
maturity at 58 feet and female does at 61 feet. Body lengths at sexual
maturity of northern fin whales reported by previous authors are as
follows.

114

S. (KIMURA) OHSUMI, M. NISHIW AKI AND T. HIBIY A
AuthorBody length

Locality.-'-----..

male
femaleMatsuura (1935)
60'
64'
58'-59' 60'-61'
Omura (1950)
Kasahara (1950)
58'-59' 60'-61'
Sakiura & Others (1953)
58'-59'61'
Mizue & Fujino (1957)
59'
56'
Matsuura & Maeda (1942) 58 1-59'
61 1
Omura (1955)
58'
61'
Sleptsov (1955)
581 -62'
Pike (1953)
57'-59'60'
True (1904)
60'
Ruud (1945)
17. 5m(57'5") 18m(59'1")
Jonsgard (1952)
Laws & Purves (1956)

58'
58.5'

Coast of Japan
If
If

"

Eastern China Sea
Northern Pacific61'-62'

If
If

Coast of Canada
Newfoundland
North Atlantic
If
If

Excepting the fin whale from the Eastern China Sea, the body length
at sexual maturity of the northern fin whale is 57-59 feet in male and58-62 feet in female.
Figure 11 shows the size distribution of the northern Pacific fin whale.
Sexually mature whales distribute in nearly normal type. Average lengthof sexually mature whale is 60.86 feet in male and 64.18 feet in female.
These are about 3 feet longer than the length at sexual maturity.
AGE AT SEXUAL MATURITY

Now, the number of laminations in the ear plug is regarded as the best
age character of baleen whales. Since 1956 we have collected ear
plug of whales in the northern Pacific. And the results are shownin table 8. In males, the eldest of sexually immature whales had 12
laminations, and the youngest mature whale had 8 laminations. In
female, the eldest immature whale had also 12 laminations and youngest
mature whale had 9 laminations. Furthermore the figure of 12 laminations
and more is estimated as a mean age at sexual maturity. Purves (1955)
and Laws & Purves (1956) estimated that 2 laminations are formed
every year. If so, the fin whale in the northern Pacific will attainsexual maturity in early term of 7th year after birth. And the precocious
will be mature sexually by 5th year. By 8th year all the fin whales willattain sexual maturity.
On the southern fin whale, Mackintosh & Wheeler (1929) assumed
that the age at sexual maturity was three years old according to thesize distribution. Kasahara (1950) got the same result by the same
method about the fin whale in adjacent waters to Japan.
Mackintosh (1942) states, however, that it is not certain that thisestimation was correct, but the recovery of a mark showed that a fin

GROWTH OF FIN WHALE IN THE NORTHERN PACIFIC

115

whale did not take more than three years to grow from birth to sexual
maturity and could have down it into two years.
By means of baleen plates of the fin whale from the North Atlantic,
Ruud (1945) considered the age at sexual maturity as 3-4 years.
Nishiwaki (1952) stated that from the study of surface structure of

400
Males

300
.µ

200

..c

Ol
:J

'°

u

~J/00

'°3

..c
<-<0

©
_o

z§ 300

50

55

70

60

75

Females

200
100
50

55

60

65

70

75

Body length (Feet)
Fig. 11. Size distribution of sexually mature and immature fin whales from thenorthern Pacific (1952-56). Open circle and broken line: Immature, closed circle
and solid line: mature.

baleen plates, the females reach sexual maturity in the pairing season
following the fourth birthday and the males at the age of about three
years and a half in the case of the southern fin whales. In the modified
method of surveying baleen plates, Van Utrecht (1956) obtained a resultthat the age at which the female becomes sexually mature lies between
5 and 6 years.

S. (KIMURA) OHSUMI, M. NISHIWAKI AND T. HIBIYA

116

Since the discovery of laminations in ear plug, Laws & Purves (1956)
reported that sexual maturity was reaches at the age of from four to
six years in the male in the North Atlantic. Nishiwaki (1957) learnedin the same method the age of sexual maturity of the southern fin
whale was four or five years.
Referring to these results, the age determination based on the frequency of body length is incomplete owing to the bias of samples inthe selection of whales for profit by the whalers and the size regulation. The method with baleen plates is dangerous because of wearingof the tip of plate. Then laminations in ear plug will show the correct
periods. But now we have never confirmed the number of laminations
TABLE 8.
No. oflaminations
5
6
7
8
9
10
11
12
13
14
15
16
17

AGE OF SEXUAL MATURITY
Females

Males
Estimated age(Year)
II

} III
} IV
}v
} VI
} VII
} VIII----~----,

Immature
1
1
2
5
10
3
4
2

Mature

1
1
4
5
6
6
4
6
10

Immature
2
5
6
12
12
13
6
3

Mature

1
2
2
9
10
7
12
6
16

formed every year. And if 2 laminations do not be formed every year,
the age assumed by us should be corrected. Further studies on this point
are necessary.
PHYSICAL MATURITY
DETERMINATION OF PHYSICAL MATURITY

As an index of the physical maturity, the condition of cartilage layer
between the epiphyses and centrum of the vertebral column has been employed. On the southern fin whales Wheeler (1930) studied the process ofossification of the vertebrae and he stated that an ankylosis commenced
at both ends of the column and was completed among the anterior partof dorsal vertebrae. Of the northern Pacific fin whale there is no reporton the process of ossification of the vertebrae. Only Pike (1953) investigated the physical maturity but he did not discussed on it.
So we studied the process of ossification in 1954. First we counted the number of vertebrae for the 19 whales. Table 9 shows the

117

GROWTH OF FIN WHALE IN THE NORTHERN PACIFIC

vertebral formula. Then we selected 20 points as follows ; i.e., C2, C5,
Dl, D4, D7, DlO, D13, Ll, L4, L7, LlO, L13, Cal, Ca4, Ca7, CalO,
Ca13, Ca16, Ca20 and Ca24. Namely, the vertebrae was examined atintervals of three on each individual in the present study, while only
TABLE 9.

NUMBER OF VERTEBRAE OF THE NORTHERN PACIFIC FIN WHALES(EXAMINED 19 WHALES)
CaudalCervical
Total
LumbarThorathic
24-27
7
14-16
60-64
Range
14-15
25.3
7.0
62.0
Average
14.7
15.0

64

65
65
63
62
64

60

13.1
19.8

13.0
15.0
11.2
8.5
13.0

61
64

10.3

62
63
62
59
58
58
63
59
62
64
65

7.0
6.5 t

6. 1

i. i.

•••

9.4
7,4
7.0
7.8
12.2

66
63

9. l

7.0
6.8
11.0
7.0
6.2
6.8
3.7
3.1
10.4
1.1

2.8

2.0

••
••
••
•
x ;.
x x ;. •• •
••••
x • •
x
x x x ;,. •ex x ;. •0~ e .i. i. i.
7.7

6.2
7.2
12.2

••

i. i. i. • • •• • i. i. A i. e
• • i. x i. ;. • •e A ;,. x X ;. A e
X i.
.i.

14.5

64
61
64
62
62
65
58
56
61
56
60
60

•••
e e A

•

e

.i.

0
;,. i.
0
A i. X oi.XXXOx x;. ;. x

0
0
0
0

0 0 0

• ;,. x 0

x 0 0

••

0
0

x 0 0 0 0

.i.

0

x

0

0 0

i.

0
0

0

•x x

0
0
0
0

0 0
0 0 0
0
0

OOO
OOO

x

0 0

0 0
0 0

0 0

.•

x Ae
x A ;.
x ;,. •
x
A

0

0
0
0

0

0

•x ;. ••

00 X .i. ex x x x
xx

0
0

•

0
00

x •

0

x

OOO x •
0

0

;.

..

A A Ae0 X A A

oo

0000
0 0 0

0

Body Weight2 5
1 4 7 10 13 1
4 7 10 13 1 4 7 10 13 16 20 24'----v--' ~ ~ ~---~-----/
lengtbof
DorsalL"mbnr(feet)
testis Cervical
Caudal(kg)
Position o~ vertebral column

Fig. 12. Condition of cartilage layer between epiphyses and vertebral colurr.nin the ma'e fin whales from the northern P2cific. Open circle: not fused,
thick cartilage. Cross: not fused thin cartilage, Solid triangle: fused, butjoin visible. Solid circle: fused, no sign of join.

two or three vertebrae was examined in each individual by Wheeler(1930) and Laws & Purves (1957). Therefore the present method will
be better for investigating the process of ossification of vertebrae.
The results are shown in figures 12 and 13. We arranged the datain order from that of the physically youngest whales in these figures.

118

S. (KIMURA) OHSUMI, M. NISHIW AKI AND T. HIBIY A

And the data of body length, the weight of bigger testis and the numberof ovulations were shown on the left side of each figure. Total whales
examined were 34 males and 45 females .
66

22

72
70
65

17
11

67

18
15
12

66

11

65
68
66
68
65
65
66
65
69
67
65
69
64
64
65
67
63
63

12
12

66

10
11

7
9

5
8
8
9
4

6
6
5

6
5
6
6

66

6

63
65

3
3

61

1
3

67
64
66
67
66
66

6

66

4
4

63

3

61

2
0

55
67
62
66

X X X X A.

OOXXA..Aee.&X
XXXXee.A.AXXXXXX.Ae

•••
e

A .A

.....
x0
x0 0

63
58
66

0

Body
length(feet)

Total
ovula·
tions

1
)

o
o••
o o X X A. •0x j. •
x
..
0

0 0

0
0
0

xx

x0 0

2 5
~v--

Cerv;cal

1. 4

0

OOO 0
OOO 0

0
0
0

OOO
0 0

•••
••

0

x
xx
x
x x ••x x ••
x.
0

0000

0
0

x0

0 0 ... .
0 0 ...

0

0

00
00
x0 0 0

0 0 0

:X

00
0

0 0

0

00

••
• A •ex ... .
x x )< ... .
0
0 x 4 •ooee
00 x ••ooe
0x ... ...
0

0

00

x x

0

0

xx

xx•
0

0

)< 0

2
1
0

.A .A .A .A

)<

5

4
3

...

•••••
•
••
••••••...
••••• )( ...x .A...
••••• ... x x ... .
•
x
...
.
• •• • x x • •e ••••••x oooxe ••••

0
0
0
0
0
7

0

0

0
0

0

0
4 7

x•

••
xx

0
0 0

0 0

0

10 13 1

0 ...

10 13

1 4

x
x

oooox

0000
0000
0000

7 10 13 16 20 24--~--' ~~ ' - - - - . . . . , - - - - - - - <Dorso I

LumbarCaudalPosition o~ vertebral column

Fig. 13. Condition of cartilage layer between epiphyses and vertebral column
in the fennle fin weales from the northern Pacific. Mark is the same as infigure 12.

The points seen from figures 12 and 13 will be as follows. The
difference in the process of fusion of the vertebrae does not seen
between the male and the female. In sexually immature stage noossification of epiphyses occurs. The fusion of epiphyses begins fromboth ends of vertebral column, but the process of fusion from the

GROWTH OF FIN WHALE IN THE NORTHERN PACIFIC

119

anterior end progresses more slowly than that from the posterior end.
The fusion of cartilage layer at the anterior end appears in the stage
that fusion from posterior end attains at posterior parts of lumbar.
The end point of ossification throughout vertebral column is estimatedto be from the 3rd to 6th dorsal vertebrae. This agrees with the result
by Wheeler for southern fin whales.

20

tn

c

15

0

·.;::;
co

:;
~

'b JO

j
E
::::l

z

5

0
2 5 I 4 7 10 13 I 4 7 JO 13 1 4 7 JO 13 16 20 24
Cer. .,J.-_ Dorsal _,...I+- Lumbar -k-- Caudal
Position oF vertebral column

Fig. 14. Process of the fusion of the epiphyses cartilage layer for the female fin
whales from the northern Pacific. N: not fused, thick cartilage. n: not fused,thin cortilage. a: fused, but join visible. A: fused, no sign of join.

Therefore, for the purpose of investigation of physical maturity,
condition of epiphyses cartilage in 3rd to 6th dorsal vertebrae should
be examined. In figure 14 the process of fusion of the epiphyses cartilage
layer for female whales is shown based on the number of ovulations. When
we investigated the process of ossification of vertebrae, we did not sampled their ear plugs. So we use the number of ovulations as the age
character. It has been regarded as a good age character for whales.
Therefore this may show the periodical process of ossification of vertebrae.
Above-mentioned phenomena are clearly shown with this figure. And
the age at complete ankylosis, that is to say, physical maturity will be
14 to 16 ovulations. Laws & Purves (1956) gave similar figure for thefemale fin whale in the North Atlantic based on the number of laminations
in ear plug.

120

S. (KIMURA) OHSUMI, M. NISHIWAKI AND T. HIBIYA

Number of ovulation at physical maturity was calculated by Wheeler(1930), Peters (1939) and Nishiwaki & Oye (1948) for southern fin whale.
Their value are 14........15 ovulations. This accords with our result. But
Brinkmann (1948) calculated that it was 13. Furthermore, Pike (1953)
states that those whose number of ovulations is under 19 are physicallyimmature.
BODY LENGTH AT PHYSICAL MATURITY

Individual variation of body length becomes vast in progression of age.
Figure 15 shows the variation of body length on the condition of
ossification in verteblae. Although our data are scanty, the complete
ankylosis will bear little relation to length as stated Wheeler (1930).
0

0

70
0

00
0

0

0

,,.,..-, ,,.,...
,

o/
c{

..

o
0

eo
0

Oo

•

OCD

•

. .o

O

•

•

....

0

I

•

•

•

• •

0

+
?

0

_o;:::___o__ !)_ -o-- ..., __ - - - - -- - - -o-- -o----- -o---<J"-- o

oo

0

0

0

•
•

55
N 24 20 /6 13 JO 7

Caudal4

I13
10 7 4 1 '13- v
10- -7' F..___,,__.,

Lumbar

DorsalFig. 15. Variation of the body length on the condition of ossification in vertebrae.
Open circle and broken line: females. Closed circle and solid line: males.

Table 10 gives size distribution of sexually mature but physicallyimmature and physically mature female whales judging with the numberof ovulations. According to our result, those which are 15 ovulations andover are judged as physical mature.
From this table, the largest
physically immature whales is 74 feet long and the shortest physicallymature whale is 59 feet long. The largest physically mature whale is
72 feet. Mean length of physically mature whale is 65 feet 5 inches.
But by means of this table, the range of physically mature length cannot be given. Therefore, we used the number of laminations in ear plugas the standard to determine the physical maturity. According to figures
18 and 19, as we will mention latter, number of laminations at physicalmaturity are estimated to 40 to 45. So, we adopt 45 laminations and over

GROWTH OF FIN WHALE IN THE NORTHERN PACIFICTABLE 10. SIZE DISTRIBUTION OF PHYSICALLY MATURE AND IMMATURE
FEMALE FIN WHALES BASED ON NUMBER OF OVULATIONS
PhysicalBody length
Total(feet)
whalesMatureImmature*
55
1
1
56
2
2
57
1
1
58
21
21
59
42
1
43
60
69
2
71
148
61
5
153
62
179
5
184
63
186
8
194
64
241
12
253
65
226
18
244
66
203
22
225
146
67
17
163
68
81
7
88
42
69
8
50
16
70
2
18
4
71
4
4
1
5
72
2
2
73
1
1
74
1615
108
1723
Total
64.10
65.43
64.18
Average length* But Sexually mature.
TABLE 11. SIZE DISTRIBUTION OF PHYSICALLY MATURE AND
IMMATURE FIN WHALE (OVER 45 LAMINATIONS)
Males
Females
Body length(feet)
MatureImmature*
Immature*
Mature
1
55
2
5
56
1
9
57
4
22
1
58
1
4
23
5
59
1
3
9
29
60
1
3
23
16
61
3
5
38
20
62
2
14
20
63
2
3
7
29
64
5
4
6
31
65
4
1
29
8
66
2
20
67
2
1
14
3
68
9
3
69
3
4
70
1
1
71
182
29
208
Total
38
60.57
61.24
65.52.
64.44
Mean length* But sexually mature.
~--~

121

S. (KIMURA) OHSUMI, M. NISHIWAKI AND T. HIBIY A

122

as physical maturity. Table 11 shows that the size distribution of physically mature and immature but sexually mature whales based on the numberof laminations. The largest physically immature male is 68 feet andshortest physically mature male is 57 feet. For the female, the largest
physically immature whale is 71 feet and the shortest physically mature
whale is 58 feet. And mean length of physically mature whales is 61feet3
inches in the male and 65 feet 6 inches in the female from this table.

66
64

62
60
58
0

2

4

6

8

10

12

14

16

18-20

ZHO

31-

Number of ovulations
Fig. 16. Growth curve of the female fin whale from the northern part of theNorth Pacific, based on the total ovulation.

62

tss
c
_j

2
Fig. 17.

4

6

14
12
10
8
Weight of testis (k9\

16

18

20

Variation of the average size of fin whales in 1 kg groups of weightof testis.

Figure 16 shows mean length against number of ovulations. This
figure may show growth curve of the female fin whale. But the growthin sexually immature stage cannot be drawn in this figure.

123

GROWTH OF FIN WHALE IN THE NORTHERN PACIFIC

Now, from figure 16 it will be seen that maximum length is 66 feetlong and number of ovulations at maximum length is 14-15. The length
will be meant length of female fin whale at physical maturity. And the
mumber of ovulations at that point corresponds to the result in figure
14. After that time body length seems to shrink a little about one foot.

65
!•

..

: •••• :

_c

1J,

j
>

;g 55
5030

20

JO

40

50

60

70

80

90

100

Number of laminations

Growth curve of the northern male fin whales based on the numberof laminations in ear plug.

Fig. 18.

0

70

0

§
o

0
00

0

0

00

008
B 0800 o

0
0

0

ft

o 08 ooo o88 §00008 ,. ...0.....0000-8-00-.oo!i..B_o____ .. _o o08o§o"800 o 8 o o§
8 co .§'SSS Bo oo oo o

o

o

o oS

0

0

o""'-o----------o----------------8

oooBS,~§ o~o o oo o
08 1B8o 8S o 8

i 60
55

0

§80

o oooo9:>B~....~~~o'S o§ o 8~ o
-£
j "'

0

s

0

0~8ooo0o~~8 00
so!:~

01§:
o:

I
0

o ,oB

:

Nurnber of laminations

Fig. 19.

Growth curve of the northern female fin whales based on the numberof laminations in ear plug.

According to similar figure by Pike (1953) the body length at physicalmaturity is 68 feet.
Weight of testis is not a good age character as shown by Nishiwaki,
Ichihara & Ohsumi (1958). Although it is dangerous to use weight oftestis as an age character, we show the mean length against weight oftestis in figure 17. This does not show the growth curve of male124

S. (KIMURA) OHSUMI, M. NISHIWAKI AND T. HIBIYA

whale, but from this figure we can suggest the mean maximum lengthof male. It is 62 feet long.
Figures 18 and 19 shows relation between number of laminations andbody length of males and females respectively. With the discovery oflamination in ear plug by Purves (1955), we could obtain the best age
character for baleen whales. And then we can show the growth
curve of fin whale based on number of lamination. On the growth
curve we shall mention in the following chapter.
Even if vast individaul variation is seen, the mean maximum lengthis estimated to be 62 feet in males and 66 feet in females. Number oflaminations at maximum length is from 40 to 45.
Furthermore after attainment of maximum length the shrinkage isseen in both male and female like as figure 16. Average length ofshrinkage is seems to be about one foot. We have never known thepaper on the shrinkage of whales after physical maturity.
From these series of our results, although there is vastly individual
variation, the mean length at physical maturity is estimated to be 62
feet in male and 66 feet in female.
On the northern Pacific fin whale, the largest male is 68 feet long andthe largest female is 74 feet in our material. According to the International Whaling Statistics from 1936 to 1956, the largest male is 77 feetand the largest female is 74 feet for the fin whale in the North Pacific.
For the fin whale from the adjacent water to Ja pan, from 1910 to 1945
(during these periods Japan had not join the International Whaling Convention) these values are 75 shaku in male and 76 shaku (one shaku isalmost one foot) in female. Therefore the largest fin whale in the
North Pacific is 77 feet in male and 76 feet in female. But we wonder
male fin whales which are over 70 feet are exsist realy. They may be
mistaked the determination of the sex. Tago (1922) reported that thelargest fin whale in adjacent waters to Japan was 82 shaku. And
Cocks (1886) reported 24.6m (81 feet) long fin whale in the North Atlantic.
AGE AT PHYSICAL MATURITY

Nishiwaki, Ichihara & Ohsumi (1958) calculate number of ovulation in anyear by means of the figure between number of laminations and numberof ovulations. According to their study fin whale ovulates 0.8-0.9 times
an year. We estimate number of ovulation at physical maturity is 15,
and the age at sexual maturity is 5-6 years old. By means of these
data, the age at physical maturity is calculated. It is 22 to 25 years
old. Two laminations are estimated to deposit every year (Purves, 1955;
Laws & Purves, 1956). If so, 40-45 laminations which we estimate asphysical matulity are counted for 20-22! years of age.

GROWTH OF FIN WHALE IN THE NORTHERN PACIFIC

125

Table 12 shows estimated the age distribution of physically immatureand mature female whale based on number of ovulations. We consider
those who accumulate 15 and over corpora lutea or albicantia in theirovaries are physically mature. The elde3t physically immature female isestimated to 30 years old (60 laminations) and youngest physically mature
female is estimated 15 years old (30 laminations). And 25 years oldwhale (50 laminations) is recongnized to the age at physical maturity.
Age at physical maturity for male will be same as female, for figures
18 and 19 shows the almost simmilar growth curve in male and female.
As the conclusion, if the northern fin whales deposits 2 laminations in
ear plugs every year, they will attain at physical maturity by 22 to 25
years after birth.
TABLE 12.

AGE AT PHYSICAL MATURITY OF FEMALE FIN
WHELES IN THE NORTHERN PACIFIC
Physicary
Number of
Estimated age
laminations
Mature(Year)
Immature
26-29
XIII-XIV
24
30-33
XV-XVI
23
2
34-37
XVII-XVIII
1738,--412
XIX-XX
7
XXI-XXII
42-45
7
2
46-49
XXIU-XXIV
6
2
XXV-XXVI
350-53
8XXVII-XXVIII
1
54-57
4
XXIX-XXX
158-61
XXXI-II3
62-65

On the age at physical maturity, Wheeler (1930) states that the female
fin whale attains physical maturity at 6-8 years of age. He considers
that after attainment of sexual maturity at 2 years, of age 4 or 5 ovulations take place in every 2 years and it attains physical maturity after
14 or 15 ovulations. Nishiwaki (1952) states that southern fin whales
attain physical maturity at about 11 years after birth, for he supposed
female fin whale attains physical maturity at about 6 years after attainment of sexual maturity which is 5 years of age. According to thefigure in the paper by Laws & Purves (1956), they seem to suppose thatfemale fin whale attains physical maturity at 12-14 years of age.
Our result is significantly different from above papers. We consider
that it dues to the difference of number of ovulatfons in every breeding
season. The values of the authors are as follows.
Wheeler (1930)
Ruud (1940, '45)
Nishiwaki (1952)
Laws & Purves (1956)
Our result

4-5
6-7
2 in first year, 3.04 in succeeding period
2 .8
1.6-1.8

S. (KIMURA) OHSUMI, M. NISHIWAKI AND T. HIBIYA

126

Peters (1939) supports our result. He calculates 1.8 ovulations in every
breeding season. Chittleborough (1954) suggested that the rate ofnumber of ovulation in the humpback whale a little more than on per
breading season.
Ruud, Jonsgard & Ottestad (1950) suggested that in the blue whale
corpora albicantia accumulate at a rate of a little more than one a year.
GROWTH CURVE OF THE NORTHERN FIN WHALE
LONGEVITY

The oldest whale has 101 laminations in the ear plugs for male and 100
laminations in female. These whales are estimated to be 50-i years old
and 50 years old respectively. On the other hand, the number ofovulations which we had observed in the Northern Pacific is 49. If
0.8 or 0.9 corpora albicantia accumulate in one year (Nishiwaki, Ichihara& Ohsumi, 1958) and the age at sexual maturity is six years after
15

~

~

10

<Jl
<I)

Ci1
..c:

!;::

4-<

0

....

<I)

..0

6;:l

5

z

0
0

10

20

30

40

Number of ovulations

Fig. 20.

Frequency of total ovulations for the female fin whale from the northernpart of the North Pacific from 1952 to 1955.

birth, the whale is estimated to be from 60 to 67 years old. However,number of laminations of this whale was 100. So, this is estimatedto be 50 years old.
Figure 20 shows the frequency of number of ovulations for the fin
whale in the northern Pacific from 1952 to 1955. The number of female
whales which has more than 15 corpora lutea and albicantia in the

GROWTH OF FIN WHALE IN THE NORTHERN PACIFIC

127

ovaries are only 4.93 per cent of all sexually mature whales. Thus, thephysically mature female whales (more than 24 years old) are very rarein the northern Pacific.
Wheeler (1930) states that no signs of a climacteric have been observedin whales up to 20 years of age. Nishiwaki (1952) indicates that the
average life of fin whale would be 25 to 30 years under natural conditions. And according to Brown (1957), the oldest marked fin whale
had been recovered in the Antarctic is 22 years after marking. As
the first year when the marking for whales took place in the Antarctic
was 1934, we have not yet confirmed the whole life of the whales iswhether older or not.
GROWTH CURVE

From the above results concerning birth, sexual maturity and physicalmaturity, we drew the mean growth curve of fin whale in the northern

1 --------------------- ---- -------- - ~-_-,.;,;_-:.-:..---------~------------------

5~-;.,;-; ;-.- -;.;-;,; -. - - .-..---~-------

60 =:::~-~~~~~-=-~-:=~-~-~::;;;--;---:--:-:.;:-;,:.-;;;-----

,..
,,

I

I
I

,.'-

I

50

15

40

1

-~

I

Q)

ii

I z-.

~30

"'

:·~
'E
'
:g

c8

20 ----

10

E

-;;;
u

·~
-<=

Q.

' x

'Q)

5

,l/l
I

10

I

'I.:

I-£
CQ

I

I

0
Fig. 21.

v

x

xxv

Age (year)

Growth curve for the fin whale from th~ northern part of the North Pacific.
Solid line: male. Broken line: female.

Pacific as shown in figure 21. This is nearly sygmoidal curve. In thefirst 2 years after birth, fin whale grows very rapidly and it is notseen the difference of growth rate between male and female. But
after then it grows more slowly by degree and females exceeds males.
After attainment of physical maturity, the fin whale seems to shrink
a little. This figure is different from the previous growth curves drawn

128

S. (KIMURA) OHSUMI, M. NISHIWAKI AND T. HIBIYA

by Mackintosh & Wheeler (1929), Kasahara (1950), Laws & Purves(1956). The individual variation of the body length at birth has been
estimated to be two feet according to Kimura (1957). Furthermore asshown figures 18 and 19, it becomes very wide in adult whales. Therefore, we must perceive it on considering the growth curve of the whales.
DISCUSSION

We must discuss first in this chapter on the age of the fin whale. We used
the number of laminations in ear plug as the age character. Now, it
has been considered that two laminations deposit every year in thecore of ear plug. Purves (1955) assumes that each interlamellar space
TABLE 13.
Mark
number
4658
4543
3243
4267
3213
4552
6062
5995
6939
6923
4516
4451
4604
4641
7002
4461
6987
4558
5979

EstimatedSex
bodylengthFemale
61ft
ff
62
70
"
45
"
60
"ff
60
55
"
57
"
62
"
62
"
Male
65

"
"
"
"
"

"
"
"

55
63
60
57
50
65
60

THE GROWTH OF MARKED F:N WHALES
Actualbody
length
58ft
66
55
63
63
62
64
65
64
64
61
56
61
60
58
59
62
62
58

Lapse
of
time
0-11
0-11
3---0
2-0
3-2
1-10
1--8
1-11
1-11
2---0
0-10
0-11
0-11
1-1
0-10
1-11
1-10
2-10
2---0

No. oflutea

Foetus0-0, 0-0
0-5, 1-3
0-1, 0 0
1-0, 0-2
1-7, 0-8
0-1, 0-0
0-3, 0-6
0-13,0-2
1-5, 0-8
1-4, 0-3

None
F. 8-3None
F. 7-0F. 4-11
None
None
None
M. 11-6
M. 3-11Weight of Number ofTestis laminations
in ear plugin kg.

13

11

41
32
14.5, 15.0
1.0, 1.0
1.8, 2.0
11.0, 11.5
4.7,
7.2,
5.1, 5.0
5.8, 5.7
1.1, 1.0

21
9represents the period of migration north or south. Laws & Purves(1956), comparing with the estimated age from the baleen plates,
describes that if two laminations deposit in ear plug, these is fairagreement up to the fourth year after which the age as determined by
the ear plugs differs from that obtained from the baleen plates analyses.
According to Nishiwaki, Ichihara & Ohsumi (1958), the mean numberof ovulation in one year is calculated to be 0.8 or 0.9 if 2 laminations
deposit in one year. This result agrees with that by Peters (1939).
Mackintosh (1942) describes that the rate of accumulation of corpora
albicantia cannot have been much more than about one a year formarked fin whale caught in the waters off South Georgia.

GROWTH OF FIN WHALE IN THE NORTHERN PACIFIC

129

These results support our estimations, but for the certification of thetheory, further studies should be needed. Marking investigation willbe the most useful method for this purpose.
By the way, in the northern Pacific Japanese Government has continued
marking investigation since 1953. Table 13 indicates the marked fin
whales which recovered after the term of more than next whaling season
since marking. It is difficult to estimate the body length of swimming
whales. The estimated length of the whales which recovered within two
weeks after marking are 2 or 6 feet (average 4 feet) longer than theactual length. Considering this result, growth rate of fin whale will be
TABLE 14. BODY LENGTH OF FIN WHALES IN SEVERAL REGIONS AT BIRTH,WEANING, SEXUAL MATURITY, PHYSICAL MATURITY AND MAXIMUM
Northern Pacific Coast of Japan British Columhia North Atlantic~Male
At birth
Weaning
Sexualmaturity
Physicalmaturity
Largestlength21'~--~----,

Female Male Female Male
21'-23'a)

58'

61'

62'

66'

68'

74'

58'59 b)Remarks a) Mizue (1951)b) Omura (1950)c) Pike (1953)

60'61'b)

57'59'c)Female Male

60'c)

58'd)

68'c)
66'b)

72'b)

66h)

71h)

Antarctic~-··--~~

Female Male Female
21'3" e)39/4' 1e)61'62'd) 63'0"£) 65 '3"f)
70'd)

68'd)

69'g)

73'g)

{88'h)
73 'd) {82'h)
74'2"f) 80'5"f)d) Jonsg~rd (1952)g) Nishiwaki (1953)e) Mackintosh & Wheeler (1929) h) I.W.S.
f) Mackintosh (1942)

little. No. 3243 whale which was recovered in lapse of three years isaccumulated one corpus albicans in ovaries. Considering to existenceof verginal band and immaturity of mammary gland, this whale wasassumed to had attained just sexual maturity. This means that it needs
at least three years after birth to attainment of sexual maturity. This
whale has 13 laminations in the ear plug.
A male fin whale (No. 5979) is sexually immature after 2 years since
it was marked. As the estimated length is 60 feet, it might not be soshort at marking. Number of laminations of this whale is 9.
From the biological data of No. 3443, 4552 and 5979 whales, fin whaleis estimated to deposit at most 5 laminations in ear plug every year.
Laws (1956) reports on the growth and sexual maturity in aquatic
mammals. He describes that if we convert the length of the female
at puberty to a percentage of the size attained when growth ceases it
is seen to be remarkably constant, averaging in cetaceans 85.1 per cent(range 80.0-85.5). Now we obtained the result that body length atsexual and physical maturity for the female fin whale in the northern
PaCific are 61 feet and 66 feet respectively. Therefore, length at sexual

130

S. (KIMURA) OHSUMI, M. NISHIWAKI AND T. HIBIYA

maturity as percent of final length is 92.4. This differs from the valueby Laws.
Although Laws (1956) states in the same paper that male whale
attaines sexual maturity at a later age than the female, our result on
this subject differs from it. Both sexes of fin whale attain sexual
maturity at about six years of age. Furthermore, the age at physicalmaturity of male seems also to be the same as the female.
Table 14 shows the body length at several stage of growth in several
regions. Length at birth will be the same in all stocks of fin whales. However, after birth the stocks in the northern hemisphere will grow more
slowly than the other. The length at weaing has not been reported yet.
On the length at sexual maturity of northern fin whale all reporters obtain
almost at the mean length of 57-59 feet and female does at 59-62 feet.
These are about 5 feet shorter than the stocks of southern hemisphere.
The investigation of physical maturity for the stocks of northern fin
whales have been imcomplete. Comparing the size distribution of female
fin whale northern Pacific with British Columbia and the North Atlantic,
68 feet and 70 feet for the length of physical maturity seems too
longer than the theoretical value. The length of northern hemisphere
fin whale at physical maturity is considered about 7 feet shorter than
the southern stocks.

SUMMARY

The growth of the fin whale in the northern Pacific is studied by meansof some biological data investigated on board of factory ships from 1952
to 1957. The essential points are concluded as follows.
1. Although we have no data on the breeding in October to April, thepairing season is estimated to include almost all seasons. But majority
take place between November and January, the maximum falling at
the middle of December.
Growth rate of foetuses for the northern Pacific fin whale is closely
similar to that of other regions - coast of Japan, the North Pacificand the Antarctic.
Gestation period is estimated to continue till about 12 months. Thenthe body length at birth is supposed to be average 21 feet long in both
sexes growth curve of foetuses is parabolic and growth equation is
L=0.329M 1 •61 •2. The youngest fin whale caught in the northern Pacific is two anda half years old (5 laminations) and in this stage whales are completly
immature. After four years old fin whale approach to sexual maturity.

GROWTH OF FIN WHALE IN THE NORTHERN PACIFIC

131

3. By means of histological examinations male fin whale which has its
heavier testis of more than 2.6kg is regarded as sexually mature. The
largest sexually immature whale is 63 feet long in the male and 68 feetlong in the female. The shortest sexually mature whales is 55 feet inboth sexes. Furthermore the average lengths of sexual maturity is
estimated to be 58 feet in male and 61 feet in female.
Fin whale attains sexual maturity from four years of age till six
years of age. The average age at sexual maturity is eariler part ofsix years of age for both the male and female.
4. After attainment of sexual maturity, ossification of vertebral epiphises
begins from both ends of vertebral column and ends at 3rd to 6th
dorsal vertebrae.
5. Female attains physical maturity from 22 years of age till 25 yearsof age. The average age at physical maturity is estimated to be 24
years old. The largest physically immature whale is 68 feet in maleand 71 feet in female. On the other hand the shortest physicallymature whale is 57 feet in male and 58 feet in female. The average
length at physical maturity is 62 feet in male and 66 feet in female.
6. Shrinkage of body occurs after attainment of physical maturity.
Average length of shrinkage is about one foot.
7. The maximum life of fin whale is estimated to be 50 years old.
However, the physically mature fin whales (more than 24 years old) arevery rare in the northern Pacific.

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GROWTH OF FIN WHALE IN THE NORTHERN PACIFIC

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