A SECONDARY SEXUAL CHARACTER OF FIN WHALESTAKAHISA NEMOTO
Up to these days, the body length of baleen whales is considered as
only a secondary sexual external character of baleen whales. Usually
female baleen whales are larger than male whales in each species
especially after they attained their sexual puberty and maturity, andother external body characters and proportions do not display the sexual
dimorphism (Mackintosh & Wheeler, 1929; Ohsumi, 1960). The length
between the anus and the genital is the clear distinction of the sex ofwhales, however, this is already clear in the youngest fin whale, evenin the foetal stage in mothers' body.
In the whaling expedition in the North Pacific in 1960 when I wasaboard, the protuberance in the tip of the snout of upper jaws of male
fin whales was noticed as the secondary sexual character and this characterhas been examined in the North Pacific expeditions in 1960 (Kataoka 1960)
and 1961, by staffs of the Whales Research Institute and inspectors.
The protuberance in the tip of the snout is easily found by observers
from the side or infront of the head part of the body of fin whales on
the deck of factory ships. The tip of the snout of a full grown male
fin whale becomes thicker and swells like the goose neck along thesurface streching about 50 cm long and wide from the very pointed endof the snout as illustrated in Fig. 1. This protuberance varies considerably according to the stage of the sexual maturity of fin whales, andimmature males lack the protuberance. Although full grown female fin
whales have thicker tips than immature whales, they completely lack
this protuberance in the tip of the snout. As younger male fin whales
also lack the protuberance, full grown male fin whales are easily distinguished from female and immature fin whales in this point at a glance.
The relation between testicle weight and the presence of the protuberance in the tip of the snout is illustrated in Fig. 3. According toFig. 3, those fin whales which have testicles heavier than 5.0 kg
demonstrate typical protuberance in the tip except two whales. Usually
fin whales are considered to attain to their sexual maturity at each testicle
weight 1 to 3 kg. And all testicles over 3 kg weight have the sexual
mature character when they are examined histrogically (Ohsumi, Nishiwaki & Hibiya, 1958). As illustrated in Fig. 3, the younger males lacking
the protuberance are sometimes have a mature testicle when it is examined histrogically, but the weight is far lighter. From the above29

T. NEMOTO

30

A

BFig. 1. Top protuberance in the tip of the snout of a sexually mature male :finwhale. A-From the side; B-From the front.

-·-----'----------

ABFig. 2. Tip of the snout of a sexually mature female fin whale.
side; B-From the front.

•20.0• • • ••I•••••a••••••• ••••••••
•

15.0

(J)
(J"'~·10.0•

00:cO>
(J)

~

••

O>
-'>L.

A-From the•

05.0

oo
2.Skg
----0-------- -----0---- -u------- -----------0--------------

§o o
17.0

08~

013.0

Body length

19.0

( m)

Fig. 3. Testicle weight in :fin whales with or without the protuberance in the tipof the snout. Black symbols-The protuberance present; White symbols-Theprotuberance absent.

31

SECONDARY SEXUAL CHARACTER OF FIN WHALES

fact, it is considered the young fin whales which begin to form spermatozoa in their testicles will not bear the protuberadce at the same time,
and the protuberance is gradually formed with the increasing of weightof testicles and the developing of sexual ability after the beginning ofspermatozoa formation. If laminations of ear plugs show the age ofwhales as they have been considered (Purves, 1955, etc.), among the finwhales possessing the protuberance in their tip of snouts, the youngest
male fin whale has the ear plug of 10 laminations, but the heavier
testicle weight of which is 5.5 kg. This value is far higher for usual
fin whales having 10 laminations in their ear plugs. Other whales withthe protuberance have ear plugs of 18 laminations or more, and theoldest whale has 82 laminations in its ear plug.
There are three exceptional fin whales without the protuberance shownin Fig. 4, which are considered to be rather older whales as they haveQl]1:;:

0:;;

ABS~NT..a sEz40

50607082Number of l(lminot;onsFig. 4. Number of fin whale in each ear plug lamination.
ance present; Oblique-The protuberance absent.

Black-The protuber-many laminated ear plugs. But they have comparatively light testicles
respectively. One of these whales has 19 laminations in the ear plug,
but the heavier testicles is only 3.6 kg in weight. The heavier testicles
of other two fin whales are 5.5 and 8.6 kg respectively. These twovalues are also not so high among the whales possessing the protuberance although they are mature in the histrogical examination of theirtesticles.
From observations on the Balaenoptera whales up to now, only fullgrown male fin whales possess this distinct secondary sexual character.
Full grown male Bryde's whales also have the slight protuberance inthe tip of the snout as illustrated in Fig. 5, but this observations are

32

T. NEMOTO

only based on several specimens caught in the adjacent waters to Japan.
So, further investigation will prcve the convincible result as to thepresence of the tip protuberance in Bryde's whales.
Other two baleen whales, blue and sei
whales have not been observed to show
this sexual dimorphism, and I have noinformation on humpback and little-piked
whales.
In some other aquatic animals, thisFig. 5. Top protuberance in the tip type of the secondary sexual characterof the snout of a sexually mature in head parts is often observed. Fullmale Bryde's whale.
grown male elephant seals in southernand northern hemisphere have the tremendous sexual character-proboscis,
which gradually develops after their sexual maturity (Matthews, 1929).
Laws (1960) describes that male elephant seals in southern hemisphereattain to their sexual maturity at an average age of four years by theexamination of the testis, but bulls of this stage do not usually play
an active part in the social organization of the breeding rookeries until
they become six years old. According to Matthews (1929), these younger
sexually grown bulls of three or four years old have no typical developed
proboscis (Matthews, 1929, pl. 23, Fig. 2). On the other hand, every
harem bull has excesively developed proboscis, and it is always inflated
when they fight against or frighten other males and human intruders.
Of course fin whals do not form the harem like elephant seals when
they are breeding in the warmer waters. But if the protuberance inthe tip of the snout of males means the greater activity in sexual
behavior than the younger male whales without the protuberance, fin
whales play the active part in the breeding after they have heavier
testicles more than 5 kg in weight with having the developed protuberance. And the laminations of ear plugs are more than 20 in general. It
seems reasonable to consider the younger whales without the protuberance do not take a part in sexual movements. Because usually about thehalf of mature females are pregnant or lactating in winter, and thenumber of free adult fem ales is far smaller in number than males if
all the sexually mature males are capable of perfect copulating directly
after their sperm formation.
Another example of the secondary sexual character of this type isfound in fish. In some salmonoid fish, the second sexual character inupper jaw is also very distinct. Male Oncorhynchus salmons, Dogsalman 0. keta, pink salmon 0. gorbusha and Silver salmon 0. kisutch
have strong curved nostrils (Becarts) when they are breeding in theSECONDARY SEXUAL CHARACTER OF FIN WHALES

33

river (Hikita, 1956). The slight curve is sometimes observed in thesexual mature salmons in the sea, when they are feeding and migrating.
The curve becomes the strong second sexual character with going up
rivers for breeding. This example also means that there is a delay
between the sexual maturity and the completion of a secondary sexualcharacter in the upper jaw.
There is a question still remained, if this secondary sexual character
lasts for the life or vanishes with the passing of seasons. The data infigures have been collected in the late of July and August in Bering
Sea, when fin whales have swarmed to feed on fish, Alaska pollack(Theragra chalcogramma). As fin whales usually come to this northern
feeding area from the beginning of summer, May and June, those fin
whales have already taken their foods considerably in the sea. Thismay help the appearance of this sexual character growing for thenext breeding season in coming winter.
This secondary sexual character has not been examined about theAntarctic fin whales yet, although some unpublished data have beencollected. Not a few examples prove the same tendency observed in
fin whales in the North Pacific. And it is said the protuberance in thetip is also a clear mark for the weight of testicles of male fin whalesin the Antarctic at a glance, as observations on the size of penis may
be useful as a means of deciding whether a fin whale is sexually matureor not (Mackintosh & Wheeler, 1929).
Finally I thank Mr. Seiji Ohsumi of the Whales Research Institute,and Mr. Shokiti Kataoka of the Shimonoseki College of Fisheries, forvaluable discussions and collections of materials.

REFERENCESHIKITA, H. (1956). [Pacific salmonoids caught in the adjacent waters to, and in the riverin Hokkaido.] Sci. Rep. Hokkaido Fish. Hatchery, 11: 25-44.
KATAOKA, S. (1960). [Tip protuberance in upper jaws of fin whales] Geiken Tsushin no.
109: 22-24.
LAWS, R. M. (1960). The southern elephant seal at South Georgia. Norsk Hvalfangst-Tid.,49 (10): 466-76, 49 (11): 520-42.
MACKINTOSH, N. A. & J. F. G. WHEELER (1929). Southern blue and fin whales. Discovery
Rep., 1: 257-540.
MATTHEWS, L. H. (1929). The natural history of the elephant seal with notes on otherseals found at South Georgia. Discovery Rep., 1: 233-56.
OHSUMI, S. (1960). Relative growth of the fin whale, Balaenoptera physalus (Linn.). Sci.
Rep. Whales Res. Inst., no. 15: 17-84.
OHSUMI, S., M. NISHIWAKI & T. HIBIYA (1958). Growth of fin whales in the northern
Pacific. Sci. Rep. Whales Res. Inst., no. 13: 97-133.
PURVES, P. E. (1955). The wax plug in the external auditory meatus of the Mysticeti.
Discovery Rep., 27: 293-302.

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T. NEMOTO

EXPLANATION OF PLATESPLATE I
Fig. 1. Top protuberance in the tip of a sexually mature male fin whale.
Fig. 2. Tip of the snout of a sexually mature female fin whale.
Fig. 3. Slight protuberance in the tip of the snout of a sexually mature male Bryde'swhale.
Fig. 4. Tip of the snout of a sexually mature sei whale.
PLATE II
Fig. 1. Top protuberance of the sexually mature fin whale from the front.
Fig. 2. Tip of the snout of the sexually mature female fin whale.
Fig. 3. Tip of the snout of the sexually mature sei whale.

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