On the Sexuai Maturity of the Sperm Whaie(Physeter catodon) found in the Adjacent
Waters of Japan (II)BY
MASAHARU NISHIWAKI and TAKASHI HIBIYA(Received Dec, 5, 1951)

Material and Method

The material which serves as the basis for this study covers all
the sperm whales caught by the Baikal Maru fleet of the Kyokuyo
Whaling Co., Ltd. in the waters east of the Bonin Is., 25°19'N-26°50'N
and 142°17'E-145°10'E (Fig. 1), during the period March 17-June 10,1951. They consist of fifty five males of the body lengths between 38
and 53 Eng. ft. and one female of 38 Eng. ft. long.
13SE

140°

145°

15d'E

39-.---~---n---r-----t-------;'390.. Ayukowo"- Ohshimo

BONIN IS

2i.Kl-------l------l----~---'-f2iN
13SE

140°

145°

Fig. 1. Location of sampling area.

t50°E

i22

M. N1smwAKi and T. IlrnIYA

The method for the present study is the same as was used in theprevious work (Nishiwaki & Hibiya: 1951).
We express our hearty thanks to the Kyokuyo Whaling Co., Ltd.
for their immense cooperation in collecting the material and data forthis study. We are grateful also to Messrs. Setsuo Mishimoto andTakehiko Kawakami, government inspectors of the Fisheries Agency,
Ministery of Agriculture and Forestry, who directed the collection of
the material on board. Our thanks are also due to Miss Hisako Jimbo
who rendered much assistance in preparing the preparats for the histological study.
Result and Discussion

The result of the histological examination is presented in Fig. 2,
where the right and the left testis of each whale are counted individuallyand those testes from which no spermatozoa were detected are classified
into the "minus" or immature group irrespective of the feature ofdevelopment of the testis tissue, as was done in the previous study.
o10

Sexually mature
Sexually immature(no spermatozoa found)

..• .

•. .•

e.•
..
..•a ..
00

•
••

c:n

~

c:

...

5

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.
:...
•.
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.

Ill:;::
Ill....
....0(I)-. •0•. i::.Q)
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::II

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:0

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000
40

4550

Body length in feetFig. 2.

Weight of testis and body length in the sperm whale caught
in Bonin area, March-June 1951.

55

Sexual Maturity 0£ the Sperm Whale123

As is clear from Fig. 2, spermatozoa were found in all the examined testes except three, which respectively belonged to the malesof 41, 44 and 49 Eng. ft. These males, however, were undoubtedly
sexually mature, for spermatozoa were certainly found in their othertestes.
In two of these males the weights of the right and the left testis
differed markedly: the two testes weighed 0.6 and 2.7 kg. in the maleof 41 Eng. ft. and 2.8 and 5.6 kg. in the one 44 Eng. ft. long. As it
is usually the case that the weights of the two testes of a whale arevery close, though they are not always exactly equal, it may be said
that in these two males one of their testes represented unusually poorer
development than the other. And it was in these smaller or poorly· developed testes that the spermatozoa were not found. In the thirdmale, of the length 49 Eng. ft., weights of the two testes were very
close, measuring 2.3 and 2.5 kg. Though the detection of spermatozoa,
which was made with the sample piece of the size of 1 cc., gave anegative result for one of the testes of this male, its two testes werehardly distinguishable from each other in point of the feature of thespermatids.
It seems that the foregoing evidences collectively lead to a conclusion that the male sperm whales in the adjacent waters of Japan
reach sexual maturity at body lengths less than 38 Eng. ft., confirming
the theory proposed in the previous study (Op. cit.).
In the course of the histological examination of testis samples, wecame to notice that in the present study more spermatozoa could befound with less efforts than in the previous study. Such difference inthe case with which spermatozoa are detected may closely be related
to a periodicity in the activity of testis. This problem will be discussed
when data covering different seasons and whaling grounds become
available.
The only female sperm whale caught during the expedition withwhich this study is concerned measured 38 Eng. ft. in length. Her
twelve corpora lutea, five to the right and seven to the left, were allold: as a matter of course, she was not pregnant.
Bibliography
Matsuura, Y.: On the Sperm Whale Found in the Adjacent Waters of Japan. (InJapanese with English summary) Bull. Jap. Sec, Sci. Fish., Vol. 4. No. 2 (1935).
Matsuura, T. and Maeda, K.: Biological Investigation on the Whales Found in the
Northern Pacific Ocean, (In Japanese) Hogei Shiryo (Whaling Materials), Vol.

M. NISHIWAKI and T. HIBIYA
9. No. 1. Nihon Hogeigyo Suisan Kumiai (Japan Whaling Fishery Association),
Tokyo, Japan (1924).
Matthews, L. H.: The Sperm Whale, Physeter catodon. Disc. Rep., Vol. 17 (1938).
Ni~hiwaki, M. and Hibiya, T.: On the Sexual Maturity of the Sperm Whale (Physetercatodon) found in the Adjacent Waters of Japan (I). Sci. Rep. Whales Res.
Inst. No. 6 (1951).
(The Whales Research Institute and the Laboratory of Fishery
Zoology, Faculty of Agriculture, Tokyo University)