OBSERVATION OF TOOTH SCARS ON THE HEAD OF
MALE SPERM WHALE, AS AN INDICATION OF
INTRA-SEXUAL FIGHTINGSHIDEHIRO KATOWhales Research Institute, Tokyo

ABSTRACT

In order to examine the relation between intra-sexual fightings and sexual
maturity, observations of tooth scars on the head of sperm whales (Physetercatodon) were made collected in South Pacific Oceans during 10 to 18March 1979 on the Nisshin maru No. 3. Tooth scars on the head were observed on 48 males based on the following four relative stages; none, indistinct, distinct and heavy. Distinct tooth scars including "pallarel scar"
which suggest intra-sexual fightings occurred among whales over 43 ft, andscars of most heavey stage were observed among whales over 46 ft in bodylength. Whales having relatively heavier scars were taken in solitary or a pairin either high latitudes (>40°S) or northern parts of females's range. Although no whales was directly taken from mixed school, three solitary large
males taken around the mixed school had scars of most heavy stage. From theinformations of body length, school size and catch position, most of thesewhales having relatively heavy scars were classified to large bachelor, thesesuggest intra-sexual fightings took place among large bachelors.
The relation between tooth scar stage and testes weight were also examined. Mean weights of single testis (heavier) for males were 4.88 kg(combined both sides, 9.26kg) and 2.68kg (4.70kg) at scar stages of heavy
and distinct, respectively. Comparing testis weights among the whales ofsame body length, whales with heavier scar tend to have heavier testis.
In conclusion, it can be said that sexual maturity rate tend to increase
with increasing of body length and with development of scar stages. Thissuggests that tooth scars indicate one of the evidences of sexual maturity.
INTRODUCTION
Polygyny is the most characteristic behaviour among the social structure of sperm
whale, Phvseter catodon. Ohsumi (1971) estimated that a school master may serve
up to 14 mature females in a breeding season, and Best (1970) gave an estimation of
10-20 females.
Although there is sexual unbalance in the adult population of the sperm whale
due to the male's slower attainment of sexual maturity, it is only such a low magnitude as 2.6: 1 (Best, 1979). However, as suggested by Ohsumi (1966) and Best(1979) only 10-25% of mature males can become school master and join breeding
school in a year. There has to be expected large surplus males and serious intraSci. Rep. Whales Res. Inst ...
No. 35, 1984, 39-46

40K八TOsexua
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SPERM WHALE TOOTH SCARSTABLE I.

CRITERIA OF TOOTH SCAR ST AGES ON THE HEAD OF SPERM WHALES

Tooth scar stage

0IIIII

41

None
Indistinct
Distinct
HeavyCriterion
No tooth scar present on the head.
Small number of indistinct and sparse scars present.
Scars distinct, at least a pair of "parallel scars" present.
Tooth scars including "parallel scar" are more frequent thanprevious stages.

Ocean). The catches were 43 (all males) and 157 whales (70 males and 89 females), respectively.
I observed tooth scars on 48 males out of 70 males caught in the latter periods,
the approximate position of catch of those samples were on a line connecting twopoints; 41°S, 154°E and 26°S, 173°E. Tooth scars on the head region were observed on the flensing deck. Scars presumably caused by sucker and hooks on
cephalopod tentacles or by some other accidental scratchers were excluded. Thedensity of tooth scars was classified into following four relative categories; none
" 0 ", indistinct " I ", distinct " II " and heavy " III " (Fig. 1 and Table 1).
Both testes were weighed to nearest 50 g on the deck, school size and position
caught for each whale were taken from the operation report of respective catcherboats.
RESULTS AND DISCUSSION

Gaskin (1970) and Ohsumi (1971) recognized six types of school as the principallysocial units of sperm whale school; nursely school, harem school, juvenile school,
bachelor school, bulls school and lone bull. While Best ( 1979) proposed somewhat different interpretation of the social structure. He considered the mixedschool, which was composed of adult females, their calves and juveniles of both sex
as a basic social unit. This school changes into breeding school in breeding season.
Furthermore, he classified mature males into three developmental stages; smallbachelor (31-39 ft in body length), medium-sized bachelor (40-45 ft) and large bachelor(over 46ft). Best (1979) considered that, in a breeding season large bachelors will
join mixed school to serve as a school master only for short periods. For the convenience of the analyses, above three male body length criteria were adopted below
without further consideration. Furthermore, although the term of" social maturity " has recently been used for male's sexual maturity mainly by International
Whaling Commission (1979) due to unique social breeding behaviour of this species,
the term of" sexual maturity" was adopted in the present study.
Tooth scars were abundant on the side and front portions of the head, butsometimes few were seen even on the back of body. None of them were new.
This suggests that the intra-sexual fighting did not take place considerably before
the season of the present observation (March).

Body length
Table 2 shows relationship between body length and tooth scar stage in 48 male
Sci. Rep. Whales Res. Inst.,
No. 35, 1984

42KATOTABLE 2.

Length(ft)
3132
33
34
35
36
37
38
3940
41
42
43
44
45
46
47
48
4950Total
Mean length (ft)

LENGTH DISTRIBUTIONS OF OBSERVED WHALESBY EACH STAGE OF TOOTH SCAR
Stage of tooth scar
Total
0IIIII

222224496323863322222833.71

2836.72645.67647.83332148sperm whales. Mean body lengths for scar stages " 0 ", " I ", " II " and " III "were 33.71, 36.72, 45.67 and 47.83 ft, respectively. The difference between stagesof" I" and" II" was significant (t-test, 0.005<P<O.Ol). Itis clear that magnitude of scars on the head increase with increasing body length.
Best (1979) reported that the presence of" parallel scar" (Fig. I), which heconsidered as attributable to attack of another sperm whale, is one of the evidenceof intra-sexual fightings. This type of scars were peculiar to whales classified tothe scar density stages of " II " and " III " (Fig. I), and observed among whales
at 43 ft in body length or more (Table 2). This result coincides with the result
obtained off the west coast of South Africa (Best, 1979). The heaviest scars(" III ") were observed only whales over 46 ft in body length.

School size and position of catch
Best (1979) and Gaskin (1982) showed that males segregate latitudinally bygrowth stages (or by groups mentioned above) in Southern Hemisphere, the southern limits of migration for small and medium-sized bachelors are about 35 °S and 45 °S,
respectively, and large bachelors migrate to the Antarctic region.
The mean size of bachelor schools relates to the above mentioned growthstage, i.e. 15 whales, 4-6 whales and solitary (or sometimes a pair) for small, mediumsized and large bachelor, respectively (Best, 1979). Table 3 shows the relationshipSci. Rep. Whales Res. Inst.,
No. 35, 1984

SPERM WHALE TOOTH SCARSTABLE 3.

43

SCHOOL SIZES OF OBSERVED WHALES RECORED BY RESPECTIVE
CATCHER BOATS IN EACH TOOTH SCARS STAGES
Tooth scars stage

School size0
1.0
1.1-1.5
1.6-2.0
2.1-2.5
2.6-3.0
3.1-3.5
3.6-4.0;;::4.1
Unknown
Total

IIIIII

76514426633216828

between tooth scar stage of whales and school size of those whales. Mean schoolsizes decreased with increasing scar stage, 3.27 (stage "0 "), 2.58 ("I "), 1.30("II ") and 1.13 ("III "). However, since the school size tended to be recorded
after disruption of the original school by chasing, these school sizes might be underestimated, and the actual value of group size would be less important rather than
the trend. It is notable that whales having the relatively heavier scars ("II" and" III ") were mainly taken from solitary whales or those in a pair.
Fig. 2 shows the latitude of catch positions of present materials (males) together those of females which were not analysed in the present study. Whales
having relatively heavier scars (" II " and " III ") were mainly caught either inhigher latitudes ( >40°S) outside of females range or in northern parts of the range
20°S,,. ...

.'30°S''~'''•0~~ \'0'0'f'''.

''~'00,','Illffi

40°S

..

.. ..
.......

'•~@@@@50°8---------------

Fig. 2. Latitudinal catch positions of male sperm whales in each tooth scar stageand females (unobserved).
O: Stage 0
Stage I
Stage II(!): Stage III

e:Sci. Rep. Whales Res. Inst.,
No. 35, 1984

e:

44

KATO
TABLE 4. NUMBER OF MALES IN THE PRESENT MATERIALS CLASSIFIED BY TYPE
OF GROUP, SCARS STAGE AND KINDS OF SCHOOLS TAKEN FROMScars stage

Type of group0

Small bachelor{Small bachelor
Medium-size bachelor{Medium-size bachelor
Large bachelor
Large bachelor

IIIII

From bachelor school

From mixed schooln (%)

523356( o2.5)( 78.5)( 10. 7)
( 16. 7)
( 83.3)(100. 0)n (%)

3(37 .5)( 7. 2)( 3.6)(Fig. 3). Although three solitary males having scars of stage "III" were notcaught from the mixed school, they were found relatively near a mixed school(26°44'S, 165°04'E) from which five resting females and one pregnant female
were taken. Their positions were 27°2l'S, 163°57'E; 27°14'S, 164°27'E; 27°13'S,164°24'E. Distances from the mixed schools ranged from 44.7 to 70.5 nauticalmiles. There is no observation on the social relationship between these males andthe mixed school above.

Male group type
Table 4 was constructed using male growth stage criteria mentioned above (Best,1979) and information of schools recorded by the catcher boats. All the six whalesat scar stage " III " and five of six whales at scar stage " II " belonged to bodylength stage of large bachelor. Although the presence of " parallel scars " are notrecorded for all individuals, as mentioned previously, only stages of " II " and" III " had "parallel scars " which indicate possible intrasexual fighting (Best,1979), therefore, it can be said that most of intrasexual fightings take place between large bachelor whales.
Testes weight
Best (1969) reported that rapid increase of testes weight relative to body length
start at around 43-46 ft, which almost coincides with the length where 50% of individuals are sexual mature by his histological criteria. Furthermore, Gambell(1972) found on sperm whales off Durban that the increase in growth rate of testes
weight start at a body length of 45.4 ft or at a combined weight of both testes of
4.85 kg. They concluded that mean body length at sexual maturity is about 4545 ft, and Gambell (1972) suggested whales having combined weight of testes of
4.85 kg are sexual mature.
Fig. 3 shows the relation between weight of testis, body length and tooth scarstages. It is apparent that testis weight increases with increasing body length. And
if compared among the whales of same body length, the whales having heavier
testes tend to have heavier scars on the head. This trend is more evident among
the whales over 43 ft in body length. Mean weight of single testis (heavier in bothside) for males at scar stage" III" were 4.88 kg (range, 2.75-7.50 kg), which wasmuch larger than 2.68 kg (range, 1.45-3.80 kg) for males at the stage " II ". The
Sci. Rep. Whales Res. Inst.,
No. 35, 1984

SPERM WHALE TOOTH SCARS
8.015.0@o, Stage 0• , Stage I..,..., Stage I I@, Stage Ill

6.0

@

@

..."'..."'~2.0• •Q)

·:;

"'Q)

•• •• •• 0.t.

~.!:

0 1.0

...

0OlQ)

•...

_._

0@@...._......

Q)

.!:

@

@

~ 5.0.c,._

...

.!:
Ol::"O0 •Q)

cOl

Ci.::' 0.50

_J35(Log)

~

0u030

0

E0

Body40length45
in50

...

.•~

Q)

ii0••• •...

0::

@

Q)

0••

@

@, Stage III..."'..."'@+Q)•, Stage I+, Stage I I.::10.0

Ol-"' 4.0c@o, Stage 0Ol-"'@4500

1.030

feet

4035(Log I Body

length45in50

feet

Fig. 3. Relationship between body length (in logalithmic scale), tooth scar stage
and weight (in logalithmic scale) of heavier testis (left) or combined weight of bothtestes (right).

difference of above two weights was statistically significant (t-test, 0.01 <P<0.05).
The combined weights of testes for whales ranged 5.30-14.80 kg (x=9.26 kg) for
scar stage" III" and 2.85-6.60 kg (x=4.70 kg) for stage "II". The differenceof two mean values was also statistically significant (t-test, 0.01 <P<0.05).
Adopting the criterion of sexual maturity of the combined testes weight of 4.85
kg (Gambell, 1972), all males at stage "III", three of six males at stage "II" andone of27 males at stage" I" can be sexually mature (Table 5). On the other hand,comparing with body length criteria of male's group type and adopting the above
mentioned criterion of testes weight as sexual maturity, eight of 12 males in large
bachelor, two of four males in medium size bachelor can be sexually mature (Table 5 ).
TABLE 5.

RELATIONSHIP BETWEEN BODY LENGTH (FT), TOOTH SCAR STAGESAND SEXUAL STATUS OF SPERM WHALES
Tooth scar stage

Type of group(length)Sexual status

Small bachelor(31-39 ft)
Medium-size bachelor(40-45 ft)
Large bachelor(46 ft){Immature
MatureTotal{1mmature
MatureSci. Rep. Whales Res. Inst.,
No. 35, 1984

Total

08II

III

252{Immature
Mature{1mmatureMature

8027132336063302238381046KATO

Judging from testes weight, among the large bachelors all males having scars of stage
III are sexually mature, while three of five males of stage " II " are sexually immature (Table 5 ). Among four medium-size bachelors two sexually matured males
also exist; one from tooth scar stage "I" and the other from stage "II" (Table5). But it's doubtful whether males having scar of stage "I" actually contributeto reproduction of this species or not.
Summarizing the above, judging from testes weight of the present materials,
it can be said that sexual maturity rate tends to increase with increasing of bodylength and with development of scar stages. Moreover, even in males of the large
bachelors, although all males attained sexual maturity in the tooth scar stage" III",
both of sexually matured and immature males coexist in stage " II ". These suggest that magnitude of tooth scar closely relate to sexual maturity.
In conclusion, tooth scars on the head of sperm whales seem to increase
with growth and presumably indicate the experience of intra-sexual fighting. For
the further examination of this point, individual age information should be takenin account. It will be examined in future study.
ACKNOWLEDGMENTMy sincere thanks are due to Dr T. Kasuya, Far Seas Fisheries Research Laboratory, who kindly reviewed the draft manuscript and made valuable suggestions tothe present paper. I would also like to express my thanks to Dr S. Ohsumi, FarSeas Fisheries Research Laboratory, who gave valuable suggestions in earlier stageof the present work, and to Dr H. Omura, director of my institute who allowed
me to use the facilities during the course of the present work. Finally I was notable to carry out field observation without the co-operation of staffs and crew ofNisshin maru No. 3, especially Mr K. Yamaguchi (chief staff of £lensing and meatproduction), Nippon Kyodo Hogei Co. Ltd. Ms T. Shirai assisted in typing anddrawing of the manuscript.
REFERENCES
BEsT, P. B., 1969. The sperm whale (Physeter catodon) off the west coast of South Africa 3. Reproductionin the male. S. Afr. Div. Sea. Fish. Invest. Rep. 72: 1-20.
BEST, P. B., 1970. The sperm whale (Physeter catodon) off the west coast of South Africa 5. Age, growth andmortality. S. 4fr. Div. Sea. Fish. Invest. Rep. 79: 1-12.
BEST, P. B., 1979. Social organization in sperm whales, Physeter macrocephalus. pp. 227-89. In H. E.
Winn and B. L. Olla (eds.), Behavior of Marine Animals-current prespective in research. Vol. 3: Cetacean.,
Plenum Press, Newyork, 438 pp.
GAMBELL, R., 1972. Sperm whales off Durban. Discovery Rep., 35: 199-358.
GASKIN, D. E., 1970. Composition of schools of sperm whales Physeter catodon Linn, east of New Zealand,
N . ..(:'.].Mar. Freshwater Res. 4: 456-471.
GASKIN, D. E., 1982. The ecology qfwhales and dolphins. Heinemann, London, 459 pp.
0HSUMI, S., 1966. Sexual segregation of the sperm whales in the North Pacific. Sci. Rep. Whales Res. Inst.
20: 1-16.
0HsUMI, S., 1971. Some investigations on the school structure of sperm whale. Sci. Rep, Whales Res. Inst.
23: 1-25.

Sci. Rep. Whales Res. Inst.,
No. 35, 1984