AGE CHARACTERISTICS OF EAR PLUGS OF WHALESMASAHARU NISHIWAKIINTRODUCTION

In the course of investigation of the sound conductivity in the Cetacea,
especially in the fin whale, P. E. Purves found the lamination of thewax plug fitted in the external auditory meatus. This fact was describedin the Discovery Reports Vol. XXVII published in March, 1955. To
Purves's study many respects are paid by this author, and he supported
that the lamination of the wax plug has periodicity very closely connected with age.
Purves further reported on the relation between age and body length
at the sexual maturity. But his explanation did not seem quite satisfactory. Afterward Purves with R. M. Laws stated about the ear plugof the North Atlantic fin whale and supplemented the forementioned
report. It is not very appropriated that the samples cited in their reports contain more males than females.
On board F/F "Tonan-maru" in the 1955/56 Antarctic whaling season,
the author collected several ear plugs from the fin whales mainly females.
The lamination of ear plug of these samples was compared with otherage-determination data in this report.
Greatful thanks are due to the Nippon-Suisan Co. for help in the collection of the materials on board of the F/F "Tonan-maru ". Acknowledgement is especially due to Mr. Koh taro Ono who assisted the author
in collecting ear plug, and it is also due to Mrs. Kazuko Morita who
prepared the materials for observation.
MATERIALS AND METHOD OF OBSERVATION

The data of the materials of this report are shown in Table 1. In thecollection of samples it so devised that samples as many as available becollected excepting unusual data. On the factory ship, however, every
possible care must be taken not to curtail the efficiency of flensing workof collection. To this end the materials were collected only by the author
himself and a specified person. This man had no experience of ear plugcollection and he carried out this collection as a side work. Next season
more samples should be collected to make the data available for age
determination of whales taken.
The materials were divided into halves; one part was dried in the air,and the other part was preserved in 10% formalin.
23

24

M. NISHIWAKITABLE 1. OBSERVATIONS ON WHALES CAUGHT IN THE
ANTERCTIC SEASON 1955/56
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AGE CHARACTERISTIC OF EAR PLUG OF WHALESTABLE 1.
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Ll:NSpecies: F=fin whale; B=blue whale: H=humpback whale.
F=female; M=male.
Sex:
Ossification: T=thoracic; L=lumbar; A=ankylosed, no sign of join;
a =ankslosed, but a sign of join visible; n=not ankylosed, thin cartilag;
N =not ankylosed, thick cartilage.

The lamination of ear plug was observed by two method. As the firststep the lamination was read by X-ray photographs. In this case thelamination of the dried materials could be observed clearly than theformalin preserved materials. In the young viz. thick lamination materials were read easily, but in the aged viz. very thin lamination mate-26

M. NISHIW AKI

rials were hard to read according to the two preservation methods. Theother method was to grind down the ear plug to the level of the longitudinal axis. The lamination was observed with a magnifying-glass ora dissecting-microscope. In this case the dried materials with thin lamination were defective, because they were broken into drops. The formalin preserved materials were suitable for grinding down, because
they had moderate stickness and hardness. But the young viz. soft
materials were not suitable for grinding down by the two methods. Itwas thought that they would be better to be observed by X-ray.

510152025303540

Number of lamination

Fig. 1. Growth curve of the core of the ear plug in several fin whales.

DISCUSSION

Purves illustrates the growth curve of the core of wax plug in respect
to a male specimen from the southern hemisphere with the same numberof laminations as Lillie's specimen. On the right side of his illustration,
he writes down the body length corresponding to the age shown by thenumber of laminations. In the impression from this figure is that thegrowth curve is very systematicaly and that the number of laminations
may be presumed from some length of core. And further more, it
seems that some rule may exist between the length of core and thebody length.

27

AGE CHARACTERISTIC OF EAR PLUG OF WHALESAs shown in Fig. 1, a sample (10T1613=No. 1613 whale of lOth
"Tonan-maru" expedition), which has almost the same growth curve
illustrated by Purves, was collected. Some samples (10T285, 10T1069)
in young stage viz. few number of laminations showed nearly the same
growth with Purves's curve. These samples were measured regarding
the thickness of each lamination according to the method of Purves.
On the other hand, it was quite different in the case of the length ofcore which is the sum of the thickness of each lamination. These data
are shown in Fig. 2. Each sign is plotted against the length of core100••EE•••·=•••
I<l>

0u 50...

•0•••

=C>

c<l>

-'........ Femeiie+Q)....... Lillie's specimen+·····"'mole515253545657585

Number of lamination

Fig. 2.

Variation of core length in different ear plug.

of ear plug in individual whales according to the number of laminations.
There are many variances in these plotted points, and big individual
variations are found in the increase of the thickness of lamination. Then,the example of the same number of laminations as in Lillie's specimen
shown by Purves seems to be an example of the least growth. This
fact is clarified in The Norwegian Whaling Gazette No. 1 of 1956 by
examples of H. W. Symons (Symons exampled only length of plug, except length of core or number of lamination).
The relation between the number of lamination and the number ofcorpora albicantia is shown in Fig. 3, The straight line in the figure
shows an average. The variances are relatively small and the relation

28

M. NISHtW AKIis settled well. Marks ( +) in the figure are the data from Laws andPurves. These data are limited and on young stages only, so they do
not seem to explain the aspect, but they are in the approval limit of
the average line. From Fig. 3 it is considered that 10 laminations areevenly matched to 1 corpus albicans. If the explanation of Purvesrefers to 10 laminations, that will take 4-5 years just to reach the sexual maturity. This age does not coincide with the principle of Mackintosh which was cited in the report of Purves, but coincides which theage of sexual maturity in the report of the author formerly published.
55•.!! 45'E0u:0035...0...0c. 25
0...
u0t.0

15........ individual data+E::>z+....., data from Laws & Purves

50•
51525354555

657585

Number of lamination

Fig. 3.

Relation between number of corpora albicantia and number oflamination in the ear plug.

If the two laminations grow up in a year, on the average line of thisfigure the ovulation is formed at the average rate of 2.4 per one breeding season. This fact almost coincides with the present :;;tudies in thisfield. Next regarding the body length according to the number of corpora
albicantia (in Fig. 4) and the number of laminations (in Fig. 5), it wasexpected that the co-ordinates of the number of corpora albicantia andthe number of laminations would be placed by the average rate in Fig. 3.
But they are not the same in these figures. Owing to the shortage ofdata, it might exaggerate the fact, but, the average line is much thesame in Figs. 4 and 5. In Fig. 4, nothing of corpora albicantia is minimum, so it is impossible to prepare the immature females. On theother hand, Fig. 5 shows that the immature females may be possible tobe classified according to the number of laminations (or in some agegroups). It is very useful that male's data can be compared in thefemale's figure with the same values. In the other study, it was observed

AGE CHARACTERISTIC OF EAR PLUG OF WHALES•75••••• ••70•29••••....Q)

....

Q)

.: 65..cCic~>.

"I+t(jJ0coIIIIII55•
II

010515202530403545El)

Number of corpora albicantiaFig. 4.

Increase of body length according to number of corpora albicantia.

•75·•QiQ)....

••+65+:Ea>c+ +~>.

••• •••••70.:• •._..... female(jJ"+·-····male

0co+55~~~-r-~~~--.--.-~.---r~.----.,.~.---,,--.-~,---,-~,----.,.~-r-~

5

15

25

35

45

55

65

75

85

Number of lamination

Fig. 5. Increase of body length according to number oflamination in the ear plug.

55

30M. NISHIW AKI

that the female fin whale of the southern hemisphere attained to thesexual maturity in 64 feet of body length and reached the physicalmaturity at 14-15 of corpora albicantia numbers. On the average line
30

••
•5~.!

2041,§]

t--i
u0c...010ll•<10051525354555

65

75

85

Number of lamination

Fig. 6.

Relation between light absorption of crystalline lens andnumber of lamination in the ear plug .

•Vlll

c

41
41c..c•VIE0..)::

IV·-• .. • • •••

55

65

•

0.
:::>

eCla.Cl

II

<0515

2535

45

75

85

Number of lamination

Fig. 7.

Relation between estimated age from baleen and number oflamination in the ear plug.

of body length in these figures, the body length at sexual maturity isjust the same as that study. It is considered that the number of lamination at the sexual maturity is 10, and that the age is 4-5 years.

31

AGE CHARACTERISTIC OF EAR PLUG OF WHALESThe points sidling along the average lines of these figures are considered
to show their attaining to the physical maturity, and they at 14-15 ofcorpora albicantia and 30-35 of laminations viz., 15-17 years. The data
shown by Laws and Purves are not quoted here because the growth rateof the fin whale body length is considered to have some differences between northern and southern hemisphere.
In the previous study of the author, he stated75
that the absorption of crystalline lens was also increased with age. Now the relation between thenumber of lamination and the absorption of crystal70
line lens is shown as a straight line as in Fig. 6.
But the variance is larger than the relation by Qi;
number of corpora albicantia. The author sug- ~ 65
•I+·=+/
gested in his previous reports that the absorption ..:::Ic,of crystalline lens would be possible to compare .!ci•/the data of males and females with same values. >- 00"'O• I
But now since the ear plug has proved to furnish Jl
I+
more accurate data. If these fact are correct, thei,'+
55
observation of the absorption of crystalline lens•.J.
would not be needed in future.
fThe data of the age group from baleen plates are
0 + II IV VI VIII
shown in Fig. 7 with the number of lamination.
Age-groupfrom baleen
The regular relation is expected make a rectilinealFig.
8.
Increaseof bodychange. But with advance in age from baleen thelength according to age
growth curve shows a sidling rightward curve. estimated from baleen.
This is by because the tip of baleen plate is chipped,and does not show the regular age. As stated in the previous report,
there are large individual variations in the age when the tip of baleen
begins to chip away. The growth curve of body length according
to age-group from baleen is shown in Fig. 8. But its accuracy is not
so high as others. The data of Laws and Purves as shown in dottedline do not coincide which may show the difference of the fin whale
body length between the northern and southern hemi-spheres. The
important characters of the age data from baleen plates are concernedwith the period where the plates does not chip away (under III or IV).
The data of this period and the number of laminations are considered
to constitute important subjects of future study.
I32

M. NISHIWAKICONCLUSION

This report is an introduction of the joint study on the ear plug observations which will begin in the near future.
1. The materials can be collected easily on a factory ship.
2. Keeping in 10% formalin solution is the best method for preservation of the ear plug.
3. It is easy to grind down the aged or hardened materials, but thebest observation method of the young or soft materials is to take X-ray
photograph.
4. The age characteristics of the ear plug are found clearily in thenumber of laminations, but there are considerable variations in the lengthof ear plug, the length of core and the weight of ear plug.
5. The female fin whales of the southern hemisphere reach theirsexual maturity in 4-5 years, then their ovulation is formed at theaverage rate of 2.4 per one breeding season.
6. They attain to their physical maturity in 15-17 years.
7. The absorption of crystalline lens is comparatively difficult to survey,
and does not offer the better data than the lamination of the ear plug.
8. It is considered necessary to make studies on the ear plug of thewhales whose baleen plate have not yet chipped away.
LITERATURE CITED}ONSGARD, A. (1952). On the growth of the fin whale (Baraenoptera physalus) in different waters. Norsk Hvalfangst-Tid., no. 2: 57-65.
LAWS, R. M.& PURVES, P. E. (1956). The ear plug of the mysticeti as an indication ofage with special reference to the North Atlantic fin whale. Norsk Hvalfangst-Tid.,
no. 8: 413-425.
MACKINTOSH, N. A. (1942). The southern stocks of whalebone whales. Discovery Rep.,
27: 197-300.
NISHIWAKI, M. (1952). Age-determination of Mystacoceti, chiefly blue and fin whales.
Sci. Pep. Whales Res. Inst., no. 7: 87-119.
PURVES, P. E. (1955). The wax plug in the external auditory meatus of the mysticeti.
Discovery Rep., 27: 293-302.
SYMONS, H. W. (1956). Some observations on the ear of blue and fin whales. Norsk
Hvalfanget·Tid., no. 1: 37-45.