On the Sexual Maturity of the Sperm Whale(Physeter catodon) found in the North Pacific.
By
MASAHARU NISHIWAKIT AKASHI HIBIY A* and SEIJI KIMURAIntroduction

Since 1954, sperm whales have been caught by Japanese whaling
fleets in the northern parts of the North Pacific. The whaling groundis the waters of the coasts of Aleutian Islands: 175°E-164°W Longand 50°N-56°N Lat. as shown in fig. 1. Before these whalings operated, the data of the biological investigations of the sperm whales inthis area had not been got by us. It is interesting ecologically tostudy the sexual condition, for the school of whales in this area iscomposed of males alone, furthermore, the comparison of sexual maturity
between this school and that in the adjacent waters to Japan (Nishiwakiand Hibiya, 1951, 1952). So, we would like to report as the fourthreport on the sexual maturity of the sperm whales.
Our greatful thanks are due to the inspectors and biologist named
140E
Nr

60

I\\()

150E

16G£

Fig. 1.

\\ . l'ACW\C170E

180

170W

Location of Sampling area.

* The Laboratory of Fishery Zoology, Faculty of Agriculture, the University ofTokyo.

M. NISHIWAKI, T. HIBIYA and s. KIMURA

40

below for their immense cooperation in collecting the material and datafor this study.
Government Inspector: Mr. S. Nishimoto, Mr. T. Kawakami,
Mr. N. Ikeda, Mr. K. Iguchi.
Biologist:
Mr. K. Fujino.
We wish also to express our thanks to Miss K. Ogura who renderedmuch assistance in the preparation of histological preparats.
Material and Method

The material for this study are 1060 male sperm whales which werecaught and examined their testes in 1954 and 1955. And the histological examination was made on the 106 whales of them.
As the size limit of sperm whale is 38 feet by the case of factory
ship whaling, the investigation was made on the individuals 38-57 feetin body length. In them, the samples for histological examination werecollected more in small lengthed individuals than large ones (fig. 2),
and in the same length relatively light testes were collected many (fig.
6). Therefore the samples were not collected at random.

0 JOL41)

Fig. 2.

45

50
BODY LENGTH IN FEET55

The ratio of samples to total whales caught in each body length.

The period of the investigation and sampling was from the latterpart of May to the latter part of September.
As mentioned above, all the sperm whales caught in the area aremales, and we could not investigate the female whales.
The method for the present study is the same as was used in theprevious works (Nishiwaki and Hibiya, 1951, 1952).

41

On the Sexual Maturity of the Sperm Whale

Tests weight at spermatozoa formation

The lightest weight of testis measured was 0.7kg. and the heaviest
was 13.5 kg. And, the lightest weight of sampled testes was 0.8 kg.
and the heaviest was 8.7kg.
Based on the result of the microscopic examination, those testes mwhich spermatozoa were found are classified as mature and those inwhich no spermatozoa were found are classified as immature.
In all testes which were assumed to be mature judged by the condition of seminiferous tubules, spermatozoa were formed, excluded one
case of which weight of testis was 1.0kg. In other testis (1.4kg.)of this individual spermatozoa were clearly found. And there wereseveral testes which were mature in parts and were immature in otherparts. These testes were found in those of relatively light weighted
testes.

8.0

7.0

6.0

•

. ...

Sexual Mature
Sexual Immature (no spermatozoa found)

5.0

4.0

3.0

:
•xxee »<:•40

<...

.:.

•

. . . . . . . . . xx1r••• ~::• •leex~:::.
·1.0!"......x•• ......• •:-... ,.:••••• .,•,~

Xe

2.0

~­

·!: •4G50.

55

BODY LENGTH IN FEET

Fig. 3.

The weight of testes examined and the body length in the male sperm whales

As shown in fig. 3, the heaviest weight of immature testis was
3.3 kg. but most immature testes were under 2.3 kg. The mature testes
were found over 0.8 kg. There were 12 individuals of which one testis
was mature but the other one was immature. In one case of them

M. NISHIWAKI, T. HIBIYA and S. KIMURA

42

the weights of the right and left testis differed markedly: the twotestes weighed 3.8 kg. and 1.0 kg. But in most of them the two testes
weighed very close or slightly different.
Table 1. Number of mature and immature testis occurred for each 0. 5 kg.
testis-weight class
Number of testis
Weightexamined
PercentofI
Iof +Testis Total i +

10075

I

----

26 I
1.0
54
1.5
2.0 ! 43
21
2.5
10
3.0
5
3.5
4.0
104
4.5
5.0
1
5.5
1
6.0
13
6.5
85
7.0
4
7.5
8.0
1 !
8.5

7 i 19
47
740
319
2I 10
41
1041
I
113I 8
I 45

73.1
87.0
93.0
90.5
100.0
80.0
100.0
100.0
100.0
100.0
100.0
100.0
100.0
100.0

1

100.0i 206

20 I 186

:25

1.0

2.0

3.0

4.0

6.0

6.0

Weight of testis in Kg

Fig. 4.

The percentage of mature testes occurredfor each 0.5 kg. testis-weight class.

III
I

The result of histological determination of maturity was classified
by 0.5 kg. testis weight classes (table 1). In fig. 4 is shown the percentage that mature testes occurred for each testis-weight. The graphindicates that 75 % of the testes are mature at the weight of 1.1 kg.
Although it is not enough because we could not get the testes-weightclass under 1.0 kg., we regard this figure as the average testis weightof the male sperm whale in the Aleutian waters at the attainment ofsexual maturity.
Body length at sexual maturity

We determined those whose both testes were histologically immature
as sexually immature individual. The result of determination of maturityby the individuals sampled was classified by 1 foot body length classes.
(table 2). The percentage of mature individuals for each body lengthis shown in fig. 5. As the smallest percentage of maturity is 85 %(in 39 feet), we consider that almost individuals are sexually mature
over the 38 feet (limited size for whaling).
Therefore if 75 % mature body length is regarded as the bodylength at sexual maturity, that will be under 38 feet. As stated above,these material were not collected at random from each body lengthOn the Sexual Maturity of the Sperm Whale

43of captured whales, and their testes weight were lighter on the average than the total whales caught excluded 38 and 39 feet. Therefore
over 40 feet actually mature rate will be higher than the data.
Table 2. Number of mature and immature whales occurred for each bodylength class.
Number of whales
examined
Body
PercentLengthof +Total\ -JOO

75

'O 50
Aleutian Is.
Japan (Nishiwakiand Hibiya, 1951)
25

40
BODY LENGTH IN FEET

Fig. 5.

45

The percentage of mature whales occurredfor each body length class.

'38feetl
39
40
41
I
42
I
43
44
45
46
47
48
49
50
51
I
52
53
54
I55
!
56

II

I+

2
7
12
13
14
9
11
3
4
4
2
7
5
5
2
3
1
2

[ 106 I

1
1
1
1

I

2
6
11
12
14
9
10
3
4
4
2
7
5
52
3
1

100.0
85.7
91.7
92.3
100.0
100.0
90.9
100.0
100.0
100.0
100.0
100.0
100.0100.0
100.0
100.0
100.0

2100.04 [ 102Discussion

The body length of the male sperm whale at sexual maturity has
been calculated by some reporters (table 3).
Table 3.

The body length of the male sperm whale at sexual
maturity, calculated by some reporters.

Body Length atsexual maturity

Locality

37 19 11-41 10 11
41 1

Antarctic water

42 1

South-east coastof Kamchatka

under 381 (35 1-37 1)
361
35 1

"

Coast of Japan
Coast of British
Columbia
Coast of Kuril Is. andKamchatka

ReporterMatthews (1937)
Nishiwaki (1955)
Matsuura andMaeda (1942)
Nishiwaki andHibiya (1951, '52)
Pike (1954)
Sleptsov 1955)

In the value of the whale found in the North Pacific, the resultof Matsuura and Maeda (1942) is specially high, but that was based .on

M. NISHIWAKI, T. HIBIYA and s. KIMURA

44

observations with the naked eye; and the number of wnales observed,
was not so large, so that their conclusion can hardly be difinite. The
results of other reporters (Nishiwaki and Hibiya (1951, 1952), Pike (1954),Sleptsov (1955)) are almost the same.
However, they are not enough to determine the thorough bodylength at sexual maturity, because the limited size for whaling has
been established to be 35 feet in coastal whaling and to be 38 feet infactory ship whaling.

i.0

6.0

5.0~.s.~~ 4.0'<:~~ 3.0.,___.

Coa~tof Alenuan Is.
(1954, 55/*----K C;:,ast of Japan (19-!8. 49)

2.0

o-·-o T'1c Samp\e\;1.030

404il!jfl

BODY LENGTH JN FEET

Fig. 6.

Geometrical mean weight of heavier testis of the both testes and body lengthin sperm whales caught in adjacent water to Aleutian Islands and Japan.

Fig. 6 shows the relationship between body length of male sperm
whale and the geometrical mean weight of heavier testis of the bothtestes. And fig. 5 shows the relationship between the body length andthe sexual maturity by the histological examination of the testes. According to the two figures, we cannot find the difference between theschool found in the waters of Aleutian Island and that found in theadjacent waters to Japan. It is dangerous to estimate the identity ofthe two stocks, but the body length of the male sperm whales at sexualmaturity will be the same in various waters of the North Pacific.
Now, the school of the sperm whales in the adjacent waters toJapan is so-called "harem'', on the other hand the school ih the watersof Aleutian Island is composed of "lone bull". Judging from thesameness in the condition of testes of the two schools, the '' lone bull ''On the Sexual Maturity of the Sperrn Whale45

will be not sexually impotent and they are not always composed of oldwhales.
The body length of which testis is 1 kg. (75 % of sexual maturity)
is estimated to be 35 feet as shown in fig. 6. Therefore the bodylength at sexual maturity may be the same. However, for the sexual
maturity of the male sperm whales, microscopic observations are absolutely necessary. And in our examination the variation of immature
testes weight is considerably wide, so it is dangerous to separate matureand immature whales by means of only the weight of their testes.
The body length of the male sperm whale at sexual maturity foundin the Antarctic waters is over 38 feet (Matthews (1937), Nishiwaki(1955)). And the 75 % mature testis is 1.5 kg. in weight (Nishiwaki(1955)), these values differ from that of the North Pacific, but according
to our data in the curves of mean testes weight of north and south
hemispheres we cannot find the difference. On this subject we will
investigate further.
Mackintosh & Wheeler (1929) and Chittlebolough (1955) stated that
there was seasonal variation in testes of blue, fin and humpback whales.
Our investigation had been taken place during the month of May toSeptember. But we found individuals which have dense spermatozoa
in seminiferous tubules in their testes and there are some one which
has very dilute spermatozoa in seminiferous tubules. Furthermore wehavn not taken the samples of other seasons. So we cannot discuss
the seasonal variation of sexual activity in male sperm whales.
Conclusion

The school of sperm whales taken in the coast of Aleutian Islands
consist of lone bulls. And by the investigation of testes sampled fromthe school, it is estimated that the testis becomes mature at the average
weight of 1.1 kg., and almost individuals over 38 feet in body length
attain sexual maturity. It is not clear that from where the school
migrates, but when we compare the school with that found in thewaters to Japan, there is no difference in the two.
The above mentioned body length is smaller than the body length
at which the male sperm whales in the Antarctic waters attain sexual
maturity. On this subject, further studies will be necessary.

References
Chittleborough, R. C., 1955: Aspects of reproduction in the rnale humpback whale, Megaptera nodosa (Bonnaterre). Aust. J. Mar. Freshw. Res. 6 (1): 1-29.

46

M. NISHIWAKI, T. HIBIYA and s. KIMURA

Mackintosh, N. A. & Wheeler, J. F. G., 1929: Southern blue and fin whales. DiscoveryRep. 1: 257-540.
Matsuura, Y. & Maeda, K., 1942: Biological investigation on the whales found in the
Northern Pacific Ocean (in Japanese). Whaling Materials 9 (1). 59p.
Matthews, L. H., 1938: The sperm whale, Physeier catodon. Discovery Rep. 17: 93-168.
Nishiwaki, M. & Hibiya, T., 1951: On the sexual maturity of the sperm whale (Physetercatodon) found in the adjacent waters of Japan (I). Sci. Rep, Whales Ree. Inst.,
6: 153-166.
Nishiwaki, M. & Hibiya, T., 1952: On the sexual maturity of the sperm whale (Physetercatodon) found in the adjacent waters of Japan (II). Sci. Rep. Whales Ree. Inst.,
7: 121-124.
Nishiwaki, M., 1955: On the sexual maturity of the Antarctic male sperm whale (Physetercatodon). Sci. Rep. Whales Res. Inst., 10: 143-149.
Omura, H., 1950: Whales in the adjacent waters of Japan. Sci. Rep. Whales Res. Inst.,
4: 27-114.
Pike, G. C., 1954: Whaling on the coast British Columbia. The Norwegian WhalingGazette, 1954 (3): 117-127.
Sleptsov, M. M., 1955: The biology and industry of whales in the waters of the Far
East. (in Russian). Moscow. 63p.