On the Sexual Maturity of the Antarctic Male
Sperm Whale ( Physeter catodon L.)
By
M. N ISHIW AKI(Read at the meeting of the Japanese society of scientific fisheries on Nov. 4, 1953)

Introduction

Since all the sperm whales that have every been caught in theAntarctic whaling ground were males, and many of them were largesized, it has been generally believed that the sperm whales found inthese waters are old lone bulls which were driven away from their
harem. As shown in Figure 1, the modal length of the male spermwhales caught in these waters is 50 ft., and is much longer than that- ---Total Antarctic---Summary Afric •i_ -Total Adjacent JapanI i ·-Japanese AntarcticI l l
1100050150-{\80040120-\/•I \" ,· .

I \v
I \J"' \II~6003090 ,J ;I~/'oI tl
IJ
Ia
4002060

J-~ 2001030

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I

1~:'S'1,\"''~Iji\\, "/•-.: ,ti,1 .· \\:!

'\\,/.·---'J/"'•./f'1 1'\!

" : ..,~•\\\'-Bady length in feet""\',I~"/I\frg:\(',g~~i\'455055

Fig. 1 The Size Distribution of the Male Sperm Whaleof the catch in the adjacent waters of Japan, 36 ft.
In comparison, two modes are recogenized, at 36 and 45 ft., in thelength frequency curve for the male sperm whales caught in theAfrican waters (Fig. 1). Probably, these two modes represent respectively
the sexually immature and the sexually mature group within the single

144

M. NISHIWAKI

population of male sperm whales, from which the catch was drawn.
Since these two modes coincide considerably with the aforementioned
modes for the male sperm whale catches in the Antarctic and theJapanese waters, one may be inclined to postulate that male sperm
whales in the latter two regions belong to a single population, theAntarctic catch representing the sexually mature group and the Japanesecatch, the immature group.
Recent studies, however, have revealed that sexually mature malesperm whales are found in the adjacent waters of Japan, as well as
sexually immature males. In addition, preliminary investigation indicated that some of the male sperm whales caught in the Antarctic
whaling ground gave relatively small testis weight, and were probably
sexually immature. For the purpose of ascertaining this point, thepresent study was undertaken, in which were studied 961 sperm
whales-all were males-caught by the Tonan Maru Fleet of the Nippon
Suisan Co., Ltd., the Nisshin Maru Fleet of the Taiyo Fishing Co., Ltd.
and the Baikal Maru Fleet of the Kyokuyo Whaling Co., Ltd. in the
Antarctic season 1951-52.
I would like to express my sincere thanks to the above mentioned
three whaling companies and to the government inspectors andbiologists named below, for their immense cooperation in collecting thematerial and data for this study.
Government Instructor: Mr. H. Sakiura, Mr. Y. Teraoka,
Mr. Y. Nozawa, Mr. R. Ohyama and Mr. H. Kawamura.
Government Biologist: Mr. Z. Kakuwa, Mr. T. Kawakami andMr. K. Iguchi.
My thanks are also due to Mrs. S. Nogami who rendered muchassistance in the preparation of histological preparats.
Material and Method

The material for this study are the aforementioned 961 malesperm whales caught during the Antarctic season 1951-52. Histologicalexamination was made on pairs of testes of those 164 males whosebody lengths were under 40 ft. or whose smaller testis weighed lessthan 4.0 kg. From the depth of about 1 cm. of the middle part of suchtestes, a small sample piece (about 1 cm. cube) was cut out after thetestes were weighed on board. These pieces were immediately fixedin the alcohol-formalin mixture (9 parts of 60% alcohol and 1 part of
10% formalin).
Fixed sample pieces were transported to the laboratory, where
they were cut into sections in the paraffin method, double-stained withOn the Sexual Maturity of the Antarctic Male Sperm Whale

145

10.0

not examined histologically• th '! mature testis (Spermatozoa present)
1

O the im.mature testis (Spermatozoa absent)
9.0.

s.o

7 .0

G.0

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55

Rody length in feetFig. 2 The Weight of Examined Testes against the Body Length of Whales.

146

M. NISHIWAKI

haematoxylin and eosin, and subjected to microscopic examination.
Careful observation was made to determine whether spermatozoa
were present or not.
Table I.

Number of the whales caught and those whose testes
were examined histologically, by fleets.

~~------Fleet---iI~1Whalescaught(Number)

I,-Whales whose testes were examined

II(Number)

362

37

Nisshin-maru

377

73

Baikal-maru

222

54

Total

961

164

Tonan-maru

I(Percentage)

17.1%

Testis Weight at Spermatozoa Formation

Based on the result of the microscopic examination, those testes
in which spermatozoa were found are classified as mature and those inwhich no spermatozoa were detected are classified as immature,irrespective of the presence of well developed spermatocytes.
In Figure 2 is plotted the weight of histologically examined testes
against the length ofJOO
whales, and discrimination is made between
mature and immature
75testes.
In Figure 3 is shown
the percentage that mature testes occurred for50
each 0.1 kg. testis-weightclass. The graph indicatesthat 75% of the testes ~were mature at the ~" 25
weight of 1.5kg. I regard ....E0
this figure as the average
testis weight of the malesperm whale of the Ant2.5
1.5
2.0
1.0
arctic waters at theWeight of the testis in kg.
attainment ofsexual Fig. 3 The Percentage of Mature Testes occurredfor each 0.1 kg. Testis-weight Class.
maturity.

147

On the Sexual Maturity of the Antarctic Male Sperm Whale

Comparison of the Weights of the Rightand the Left Testis

In the whalebone whale species, such tendency is not known thatthe testis on a definite side of the body is heavier than that on the otherside ; in other words, the right testis is heavier in as many individuals
as the left testis. Accordingly, the testes weight-right and left
testis combined at the attainment of sexual maturity is reasonably
estimated in these whales as twice of the testis weight at spermatozoa
formation, which is determined by the method indicated in Figure 3.
From the testes weight at sexual maturity thus estimated and thelength-testes weight relationship, the length at sexual maturity canbe determined.
In the sperm whale, however, the left testis is heavier than theright one in the majority of the cases, as indicated in Table 2. This
Table 2. Number of the male sperm whale caught in the Antarctic season
1951-52 as classified according to the relative weight of the right and left testis.

----·-----------

Both testes I R"1 ht t t" i Uuknownequal in '~.es is ' because
weighteaviersingle lost

Name offleet

Left testis
heavier-~~~~~-r

212

27

122

1362

220

55

100

2377

110

2164

27222

Nissin-maru
Baikal-maru\Total-------------------------

tendency, probably related with the bilateral asymmetry which is seenin the blow hole and other organs of this species, preclude us fromaccepting twice of the testis weight at spermatozoa formation (1.5 kg.)
as the testes weight at sexual maturity.
Body Length at Sexual Maturity

For the reason mentioned in the preceding section, the length of
the sperm whale at sexual maturity was estimated in the followingway.
Based on the abovementioned result, testes weighing 1.5 kg. ormore are considered as mature, and the percentage of the testes
weighing 1.5 kg. or more is calculated for each length class of thewhale. The result is represented by the broken curve in Figure 4.

148

M. NISHIWAKIAs another approach, the percentage of the testes containing
spermatozoa is calculated similarly, and the result is shown in Figure 4
as the solid curve.
100In either curve ofFigure 4, the body length
at which 75% of thetestes are ma tu re is 4175 -- -- ----•Jo:/:42 ft.

/. :

1:50

Conclusion

II
I

From the foregoingevidences and discussions,% of the testes
I •,'' it is estimated that, inE
containing
spermatozoa
I.....0- % of the testes
25
the male sperm whale ofweighing 1.5 kg. or more'"
the Antarctic waters, thetestis matures, (i. e. spermatozoa are formed) at
0-t------,.~-r'~-r----..---r~-.--~..----.~--.-~
theaverage weight of414549Body length in feet
1.5 kg., and the bodyFig. 4 The Body Length of the Antarctic Malelength at sexual maturity
Sperm Whale at Sexual Maturity.
is 41 ft.
The abovementioned body length is greater than the body length
at which the male sperm whale of the adjacent waters of Japan attainsexual maturity, which is certainly below 38 ft. and probably between
35 and 37 ft. It may be then that the body length of the male sperm
whale at sexual maturity differs in the northern and the southernhemishpere, as is the case in whalebone whales.
Calculation based on the foregoing results indicates that 0.5% ofthe male sperm whales caught in the Antarctic waters in the 1951-52
season were sexually immature.

"'...
...."

0'References
Y. Matsuura: On the Sperm Whale found in the Adjacent Waters of Japan (in Japanesewith English Summary): Bulletin of the Japanese Society of Scientific Fisheries,
Vol. 4, No. 2. (1935).
L.H. Mattews: The Sperm Whale, Physeter catodon: Discovery Reports, Vol. XVII.
(1938).
Y. Matuura & K. Maeda: Biological Investigation on the Whales found in the Northern
Pacific Ocean. (in Japanese); Hogei Shiryo (Whaling Materials), Vol. 9, No. 1.
Nihon Hogeigyo Suisan Kumiai (Japan Whale Fisheries Association), Tokyo,Japan. (1942).
H, Omura: Whales in the Adjacent Waters of Japan: The Scientific Reports of theWhales Research Institute, No. 4, (1950).

On the Sexual Maturity of the Antarctic Male Sperm Whale

149

M. Nishiwaki & T. Hibiya: On the Sexual Maturity of the Sperm Whale (Physeter catodon) found in the Adjacent Waters of Japan (I): The Scientific Reports of theWhales Research Institute, No. 6. (1951)
M. Nishiwaki & T. Hibiya: On the Sexual Maturity of the Sperm Whale (Physeter catodon) found in the Adjacent Waters of Japan (II): The Scientific Reports of theWhales Research Institute, No. 7. (1952)
G.C. Pike: Whaling on the Coast British Columbia: The Norwegian Whaling Gazette,
No. 3, 1954. (1954)