AGE DETERMINATION AND GROWTH OF THE BAIRD'S
BEAKED WHALE WITH A COMMENT ON
THE FETAL GROWTH RATETOSHIO KASUYA
Ocean Research Institute, University of Tok_vo, Tokyo

ABSTRACTTwo kinds of cycles exist in the alternation of the stainability of dentine
and cementum of the species. The longer is of annual, and the stainable layer
is deposited from August to January and the unstainable in the rest of theyear. The shorter cycle ranges from 27 to 31 days with possible individual
variations. The deposition of dentine ceases within several years after birth,and the short cycle is distinguishable in the first few annual layers. In cementum, on the other hand, the annual layer is possibly formed for all thelife time, and the short cycle on the anterior tooth until 40 to 60 years of age.
The length oflife time is 70 years. The gestation will last for about 17 months,
one of the longest among the cetaceans ..
INTRODUCTION

The morphology and life history of the Baird's beaked whale, Berardius bairdii Stejneger, 1883 in the western North Pacific and adjacent seas were studied by Omura
et al. (1955) based on the catch statistics of the Japanese commercial whaling in the
period from 1~48 to 1952 and on many specimens investigated by them. Later
Nishimura (1970) discussed the distribution of the species in the Sea of Japan basedon several stranded animals. Nishiwaki and Oguro (1971) analysed the statistics
of Japanese catch of the species in the years from 1965 to 1969. In recent years,
the catch of B. bairdii is mostly restricted, by the economical factors, to the coastal
waters of the Boso Penninsula on the Pacific coast of central Japan, and the annual
catch seems to be less than 30 whales (Dr. Y. Naito, person. comm.).
In spite of the effort of these authers, very little is known about the life historyof the species. The main obstacle in the study exist in the difficulty in obtaining theadequate number of samples and in the absence of the age determination technique.
Though, Omura et al. (1955 ), studying the anatomy of the tooth of B. bairdii, indicatedthe presence of the annual layers in cementum and suggested the possibility of theage determination, they did not show the reason for the conclusion nor try to estimate the age of the whales. The present study was made in order to reconsider
their study and provide some clue of the age determination of the species.

Sci. Rep. Whales Res. Inst.,

No. 29, 1977, 1-20.

2

KASUYA

MATERIALS AND METHOD

Nineteen samples, in the twenty used in this study, were collected from the catch ofcoastal whaling off the Boso Penninsula (35°N, 140°E), of which 18 animals by
Omura in 1957 through the cooperation of the Takai Gyogyo Co., Ltd, and anothersample WD-9 by Dr. Y. Naito. Whale no. 20 was collected at an whaling station
at Ayukawa (38° 20'N, 141° 30'E) on the Pacific coast of Japan through the field
investigation of the Whales Research Institute.

TABLE l.

Tooth

Whale
no.

Date of catch

4-, - ''57
13, Oct., '59
5, Aug., '57

9.8m
10.8m

6.4 , 5.8
0.44 , 1.55

6, Aug., '57

10.6m

4.10 , 4.10

8, Aug., '57
15, Aug., '57

11. l m10.6m

5.20 ' 5.30
4.80 , 4.90

16, Aug., '57

10.9m

4.70, 5.80

18, Aug., '57
27, Aug., '57

ll.4m
10.7m

0.205, 0.245
4.10, 3.90

28, Aug., '57

10.7 m8.20 ' 8.20

30, Aug., '57
30, Aug., '57

10.7m
10.8m

5.60 , 5.80
7.00, 6.90

1, Sept., '57

7.8m

0.40 , 0.36

1, Sept., '57
15, Sept., '57
14, Oct., '57

10.4m
6.4m
10.1 m0.320, 0.275
0.062, 0.060
5.50 , 5.50

15, Oct., '57

10.8m

7.00, 9.80

6, Nov., '57

11.0m

0.235, 0.245

14, Nov., '57

l0.7m

1.20, 1.15

4, Aug., '76

10.5 m

20
365>
36
377>
37
38
40
40
41
41

44
49
49
50
50
51
52
52
53
53
54
55
57
57
58
58
60
60
61
61
WD-9

LIST OF MATERIALS

Body length

Sex

if

Gonad 10> (kg)3.62 , 4.94

position1>

thicknessheight

Post.
Ant.
Ant.
Post.
Ant.
Post.
Post.
Ant.
Post.
Ant.
Post.
Ant.
Ant.
Post.
Ant.
Post.
Ant.
Ant.
Post.
Ant.
Post.
Post.
Ant.
Ant.
Post.
Ant.
Post.
Ant.
Post.
Ant.
Post.
Ant.

16mm
26mm
35mm
15mm

48mm
73mm
81 mm
49mm
76mm

13mm
21 mm
28mm
16mm
34mm
18mm
32mm
34mm
14mm
34mm
15mm
43mm
36mm
18mm
33mm
16mm
18mm
32mm
35mm
20mm
4lmm
18mm
35mm
18mm
39mm
18 mm
32 mm

52mm
73mm
48mm
89mm
90mm
84mm
80mm
51 mm
56mm
47mm
68mm
79mm
64mm
86mm
5lmm
62mm
66mm
74mm
50mm
84mm
57mm
85mm
59mm
90mm
60 mm
67 mm

2> - : Not erupted, + : Erupted and osteodentine
covered, •> In parentheses: Pulp cavity filled with osteodentine, Italics: No. of annual layers (long78> 30 shortPregnant with 12 mm fetus (Omura, 1958), physically mature.
> Physically immature.
All the testes, except for the whale no. 20, were weighed by the Tokai Gyogyo Co., Ltd., and the ovaries
1> Ant. : Anterior tooth, Post. : Posterior tooth.

Sci. Rep. Whales Res. Inst.,

No. 29, 1977.

3

AGE DETERMINATION OF BERARD/US

The body length recorded by foot (0.305 m) or shyaku (0.303 m) was converted into metric system. The records of sex and weight of gonad were obtained
directly by the biologist or by the whaling company as in the case of the body length.
Teeth of 19 whales, other than that of WD-9, were preserved in dry condition
after cleaning by boiling. Each tooth was cut on a lingua-buccal medial plane,
and one 2 to 3 mm section was taken with a saw. Then, usually, either lingua or
buccal half of the section was polished with whet stones and glued on a clear plastic plate. The other side was polished with the same way to a thickness between

USED IN THIS STUDY
No. of long cycles 4l
attrition2l

+
-tt

+
+
-tt
-tt

+
+
+
+
+
-tt

+
-tt

+
+
+
-tt

+
-tt

+
-tt

+
+
+
-tt

root8lin dentine

in cementum

closedclosedclosedclosedclosedclosedclosedclosedclosedclosedclosedclosedclosedclosedclosedclosedclosedclosedclosedopen
openclosedopen
closedclosedclosedclosedclosedclosedclosedclosedclosed[5][7]

38, 44, 46
40, 41, 42
35, 36, 38
30, 33, 35
16, 17, 17
17, 17, 17
25, 26, 27
56, 57, 61
56, 58, 63
40, 47, 51"
37, 40, 40
22, 25, 29
20, 21, 22
23, 23, 24
66, 67, 71
54, 67, 68
68, 71, 72
29, 30, 31
30, 30, 32
3, 3ai, 3
3, 3, 335, 36, 37
2, 2oi, 2
51, 58, 59
49, 51, 56
50, 50, 52
46, 47, 48
37, 39, 40
44, 46, 51
40, 40, 41
37, 39, 41
64, 65, 66

[4]
[5]
[6]

[4]
[7]
[5]
[5]
[4]
[5]
[5]
[5]
[6]
3
3
[7]
2
[6]
[6]
[5]
[5]
[6]

Age with
completeshort cycle

Last Jong
cementa! cycle6J

~41
~36

Unstainable (wide, -)Stainable(thin, 2)
Unstainable (wide, 7)~17Unstainable (wide, 7)~57

Unstainable (wide, -)Stainable(thin, 2)~47

Stainable(thin, I)~25~21

Stainable
Stainable(wide, 3)(thin, 2);;;;52

Unstainable (wide, - );;;;42~30

Unstainable (wide, -)Stainable(thin, I)~

Stainable(wide, 3)~

Stainable
Stainable(thin, -)(thin, 2)~50

Stainable(wide, 3)~39

Stainable(wide, 3)~40

Stainable(wide, 4);;;;56

Stainable(thin, -)3

2;;;;57

not exposed, -t+ : Osteodentine exposed, si Closed: Root covered with cementum, Open: Root notcycle) used in other part of this study. 5l In parentheses number of short cycles if observable. 6)
10)cycles in cementum and 31 in postnatal dentine. 9J 22 short cycles in dentine and cementum.
by Dr. H. Omura after the fixation in 10% formalin.

Sci. Rep. Whales Res. Inst.,
No. 29, 1977.

4

KASUYA

40 µm to 70 µm. The thin ground section was decalcified in 5% formic acid forseveral hours, stained with Mayer's haematoxylin solution for 30 minutes and mounted with permanent mounting medium. In case of the tooth of WD-9, which was
fixed in 10% formalin, the section was at first step embedded in polyester resin,
and then processed with the same method to a thinner decalcified and stained preparation. Its thickness was about 25 µm. This method did not give different
result except for the technical convenience to produce thinner section. Manyother ancillary thin preparations (10 to 15 µm) were made from small pieces of
cementum, and used for limited observations.
The observation of the growth layers was made with a microscope ( X 40 and
X 100) under transmitted light, and counting was always made on the stainable
layers.
Though, the same process was made, if available, on both anterior larger toothand posterior smaller tooth, the latter was used for restricted purpose. If it is not
specified, in the latter part of this study, the analysis are for anterior tooth.
RESULT

Grozvth of the tooth
About 80% of individuals of B. bairdii have two pairs of mandibular tooth,and the rest of animals more (Kirino 1956). The tooth is shaped of a bilaterallycompressed cone, and the fundamental structure is same for both the anterior andposterior tooth (Pl. I). In case of the unerupted tooth, the cusp is covered withthin enamel layer, as already indicated by Omura et al. (1955) on a fetal tooth. The
enamel layer of the postnatal individuals is often covered with cementum (Fig.

1).
Beneath the enamel layer there are dentinal layers and large pulp cavity. Thispulp cavity is later filled with osteodentine arid only narrow root canal, which isconnected to the outside of the tooth through the thick cemental layer, is often left

Fig. I. Schematic figure of the lingua-buccal section of the tooth of B. bairdii.
1 : Enamel. 2 : Cementum, only three layers are indicated. 3 : Feta! dentine.
4 : Postnatal dentine. 5 : Osteodentine. Alphabets indicate the positions forcounting the layers used in Figs. 2 and 3.

Sci. Rep. Whales Res. Inst.,
No. 29, 1977.

AGE DETERMINATION OF BERARD/US

5

in case of the older animals.
The cementum covers almost the entire length of the lateral surface of the toothof postnatal animals. In young individuals such as nos. 53 and 55, of whichages are estimated in the later part of this study to be about 30 months, and 21 months
respectively, the osteodentine is exposed on the base of the tooth, however, in theolder animals, the root is covered with cemental layers. This stage is classified
into the" closed" state in Table 1. This definition is different from that of Omura
et al. (1955 ), where the root was considered to be closed if the osteodentine fills thepulp cavity. The closure of the root seems to occur at the age between 3 and 17
years.
The eruption of tooth was recorded at the whaling station and it was confirmedin the laboratory using, if necessary, a microscope. The eruption is considered tooccur in relation to the attainment of sexual maturity (Omura et al. 1955). The
present scanty materials suggest that the eruption of anterior tooth occurs at anage between 3 and 17 years, and the posterior smaller tooth between 21 and 30.
The sexual difference of the eruption was not detected in this study. Matsuura(1942) considered that the posterior tooth of the female does not erupt, however,the present data, whale nos. 36 and 60, indicate that the posterior tooth of female
also erupt at some age as already indicated by Kirino (1956).
Dentinal growth layers

As shown in Fig. 1 and Plate I, the outermost layer of the dentine is the fetal
layer. This is the largest in the thickness, and the length of the contour is longest
next to the first postnatal dentinal layer. There are observed obscured layered
structures in the fetal dentine both in the thin ground section and in decalcified
and stained section. Though most of the layers in the prenatal dentine are obscure, several contiguous layers are clear in most of the individuals (Pl. II). These
clear layers are formed at the various stage of the deposition of the prenatal dentine, and the number of the clear layers is usually from 3 to 7 with 2 exceptional
cases of 0 and 12 layers (13 individuals examined). The condition is same in theanterior and posterior tooth of the same individual. The total number of the layers in the prenatal dentine has a mode at 14 layers (Table 2).
The postnatal dentine is separated from the fetal dentine by a thin clear
unstainable layer, and distinguished from the latter by the good stainability andclearer fine layers in it. Though the postnatal dentinal layers are irregular and
TABLE 2.

FREQUENCY DISTRIBUTION OF FINE LAYERSIN PRENATAL DENTINE
Frequency

No. of layers
anterior tooth

posterior tooth

12
13

14
15

Sci. Rep. Whales Res. Inst.,
No. 29, 1977.

1
3

3
2

6

KASUYAthe counting is difficult, there are observed two kinds of accumulation cycles. The
one is of long interval, which possibly corresponds to the annual growth layers ofthe dolphins and sperm whales studied by Ohsumi et al. (1963) and Kasuya (1976).
These layers decrease in length and thickness in accordance with the progress ofdeposition, and the last layer is observed only near the apex of the pulp cavity. The
number of these long cycle layers is between 4 and 7 layers on either anterior orposterior tooth where the pulp cavity is completely filled with osteodentine, clearly
showing the end of the deposition at those ages (Table I).
In the postnatal dentine, there are observed many alternation of stainability possibly reflecting the physiological changes of the shorter cycle. These layers
are most conspicuous in the dentine deposited in the younger stages, and are almost
indistinguishable in the 5th to 7th layers oflong cycle described above. It is notable that in the anterior tooth of the whale no. 53 there are observed 31 small layers
in the 3 long cycle layers, and 22 small layers in the 2 long cycle layers of the anterior tooth of whale no. 55 (Pl. II).

Cementa! growth layers
There are observed two kinds of cycles in the alternation of the stainabilityof cementa! groundsubstance, as in the case of dentinal layers. The one is oflonger
interval and the other the shorter. In other words, the stainable and unstainable
layers of the long cycle are, usually, composed of several short cycles, and the cyclicchange of the stainbility of these short cycle layers constitutes the long cycle (Pls.
II and III). The cementocytes are diffusedly distributed at all the part of thecementum, and there is detected no relationship between its arrangement and thestainability of the cementa! groundsubstance.
As the deposition of the cementum is restricted, after the eruption, to the proximal part of the tooth, the count of the cementa} layers must be made for the correct age determination on the area connecting the lateral margin of the fetal den-

~

50

"jr

II

,.!?

' '
I I

0

~

>-

40

fA\.. ,,

u

c 30

,.,.

l!J

:;,

CJ"
l!J

... 20u..
/10,,/+,,''
,

'

+'

/'~
, I

\',

\~

.I

I

''

"i-

,.+

0-----0-.----0

0

80

90

/

100

110

'

120

Deviation in °lo
Fig. 2. The variation of the counts oflong cycle cemental layers. Closed circle andsolid line indicate the anterior tooth, open circle and dotted line the posterior
tooth, and cross mark and chain the ratio of the number of layers in posterior
tooth to that in anterior tooth of the same animal.

Sci. Rep. Whales Res. Inst.,
No. 29, 1977.

AGE DETERMINATION OF BERARDIUS

7

tine and the external margin where the layer of cementoblasts is present. In thepresent study, the cementoblasts were still observable on the section prepared fromthe tooth preserved for many years in dry condition.
The number of the long cycle cemental layers shown in Table 1 was counted
on the area corresponding to" C" in Fig. 1, where the cementa! deposition is most
rapid and the two kinds of cycles are most clearly recorded. Usually three counts
were made independently and a value at their middle was taken as the numberof the cycles. The fluctuation of other two counts expressed by the percentage ofthe central value are shown in Fig. 2. It is usually within the range of 15% ineither case of anterior or posterior tooth. The diversity between the anterior andposterior teeth of a same whale was expressed by the ratio of the two central values.
Most of the difference is also found within the range of 15%. However, as thereading of the layers in the posterior tooth is difficult, its data is used only when theanterior tooth is not available.

99
Whale no. 37--<>--

B

Whale no. 52

95
90

fC J>B
A

,IJ
0

~

I
I
I

~

80

,,,_ ---0'~~..o- - -o- - -o""'

<Ii

>

~

5 60

I

f'

I

'3

I
I

§ 40

/

.t:J

P'

u

I
I

I

20

I

I

I

10
5

I

A'0

c

B

11

2

3 4

5

6

7

8

9 10 11 12 13 14 15

No. of short cycles
Fig. 3. Probability plot of the frequency distribution of the number of short cycles
in a long cycle cementa! layer. Alphabets indicate the position shown in Fig. I.

The short cycle alternation of the stainability of cementum of the anterior
tooth is analysed below. Fig. 3 shows the probability plot of the frequency of thenumber of fine layers in one long cemental cycle. If the number of the fine layers isnormally distributed, the cumulative frequencies plotted in this way lie on a straightline. It seems that the points corresponding to 10 or more short cycles come on astraight line and considered to be normally distributed. However, the frequencyof the long cycle layers which contain 9 or less fine layers is not normally distributed
Sci. Rep. Whales Res. Inst.,
No. 29, 1977.

8

KASUYAand the abundance of such long cycle layers decreases from the distal portion to thebase of the tooth. This may suggest the next two possibilities, one is that the shortcycle is not fully recorded nor distinguished on the distal part of the tooth where
the deposition of the cementum becomes slower at earlier age, the second is thatthe distinction of long and short cycles is not correctly done at the distal part of the
tooth.
Fig. 4 will solve the above question. In this figure, the numbers of short cycles in one long cycle are arranged in the order of their deposition. As the first and

14

12

~ 10

u>-

u

6 8

.c
Ill

0
d

z

I
I
I

c

B'I
I

6

I

I

4I

6

I

I
I
I

4

""-<i

\

'~
\,

2

30

20

JO

0

No. of long cycle

105Frequency

Fig. 4. Age and locality difference of the number of short cycles in a long cycle
cementa! layer, whale no. 52. Alphabets indicate the position shown in Fig. I.

Whale no.
Sex
No. long cycles present
No. long cycles checked
No. short cycles
9
10
11
12
13
14
15
16
17
mean
Mean days in a short cycle 2>
1>

Mean of the 13 mean values.

TABLE 3.

FREQUENCY DISTRIBUTION OF NUMBER OF

55

53

~

6

6

6

6

~

1.8

2.4
2

17
16

21
19

30
30

37
16

3
9
8
9

3
4
7

37

4
3
4
4

12.0
30.4
2> 365

12.0
30.4

12.7
28.8

49

8
5
2
2

13.0
28.2

52

60

2

12.7
28. 7

12.6
28.9

days are assumed for long cycle.
Sci. Rep. Whales Res. Inst.,
No. 29, 1977.

AGE DETERMINATION OF BERARDIUS

9the last layers are incomplete, they are not adequate for the present discussion. The
disagreement of one layer between the number of long cycles distinguished at distal
area (B) and proximal area (C) is within the reasonable range of the error. Then
Fig. 4 indicates that in the proximal portion of the tooth, about 10 to 14 short cycles are distinguished in every long cycle cemental layers, and that the same numberof cycles are present in the distal portion only up to the age of 22 long cemental
cycles. After this age the number of short cycles observed in the distal portion
rapidly decreases. This was confirmed by the direct tracing of some long cycle
layers, in which higher number of short cycles are observed in the proximal portion
but only lower number in the distal portion. The thinner section, about 20 µm, ofthe latter part could not increase the number of observable short cycles. Accordingly, it will be safe to conclude that, after a certain age, the deposition of cementum
becomes slower at the distal area of the tooth and the alternation of the stainabilityof short cycle is not fully recorded. This change will progress towards the proximal
portion in accordance with the progress of the eruption of tooth. This is supported
also by the fact that the number of long cycle layers where the complete number ofshort cycles are clearly recorded is very few on the posterior tooth. As the cementa!
layers are thin on the posterior tooth, the growth must be slower than the anterior
tooth.
In order to estimate the relative length of the accumulation cycles of long andshort cycle layers, the number of short cycles was counted on several contiguous
long cycle layers at the selected position of 13 anterior teeth. As shown in Table
3, the fluctuation of the number of short cycles in one long cycle layer is wide. Thisis partially because the alternation of the stainability of long cycle is gradual andthe distinction of each long cycle layer is not very definite. Accordingly, if one
long cycle layer contains a relatively small number of short cycles the next long
cycle layer often gives the higher count, and the reliability of the mean value inTable 3 might be higher than that expected from the fluctuation. The range of
SHORT CYCLES IN A LONG CEMENTAL CYCLE OF B. BAIRD!!

20

41

58

40

57

50

51

J

J

J

J

J

J

J

41
7

47
7

50
21

57

58
13

67
15

71

2
3
4

12.7
28.7

12.0
30.4

Sci. Rep. Whales Res. Inst.,
No. 29, 1977.

11

4
3
4
6
4

5
3
2

3
3
5
2

4
7
3

12. l
30. l

11.9
30.6

12.5
29.3

12. l
30.2

11

2
4
4

13.4
27.3

Total

169

100%

8
28
47
43
31
6

4.7
16.6
27.8
25.4
18. 7
3.5
0.0
0.6
12.41>
29.4 1>

12. l
30.1

KASUYA

10

the mean values is between 11.9 and 13.4 short cycles per one long cycle, and there
is detected a significant difference of the mean values between some of the individuals as indicated in Fig. 5 and dealt with in the next section. The mean for the
13 whales is 12.4 short cycles per a long cemental cycle.
The number of short cycles constituting one stainable layer of long cycle wascounted in 15 anterior teeth with from 5 to 10 long cycle layers each, and shown in
Fig. 6. The mean counts per long cycle layer of each individual lie between 5.0
and 6.9 cycles, and the mean number of the short cycles calculated for all of the 86
data is 5.86 cycles. This result indicates that the stainable and unstainable layerof the long cycle represent approximately the same length of time, but only if eachlayer of short cycle represents equal time periods.
The age when the deposition of full number of short cycle layers (~ 10 layers)ceases in the cementum of anterior teeth is estimated from the direct observation of=--_ -

3

"'"'

Gl

r~1

r~1

~*1
N

I

<'> <D

r~~o

H.
29

"'"'
I

I

-

"'"'

~l

28
30
Length of short cycle (days)
Fig. 5. Individual variation of the mean length of short cementa! cycles. Numerals in the squares indicate the whale number, and the line the combination
where the difference is statistically significant (p<0.05 ).

40
~

t

30

>-

u

c 20

~

g...

u..

10

.·.·.·.·......-:·-:-:·:·:·:·:·:-:-:·:·:::::::::::::::::::::::.·:..:

57..

0'----'-~~'---~-"":..:.:.::..:.:.::.:i.:.::uJ..-1:.LJ..1_~-L--l

3

4

6

8

Number of short cycles
Fig. 6. Variation of the number of short cycles in a long cycle stainable layer inthe cementum. Solid line and closed circle indicate the frequency, and dotted
area the distribution of the mean values of each animal. Mean and the rangeof 2 standard errors are indicated at the top.
Sci. Rep. Whales Res. Inst.,

No. 29, 1977.

AGE DETERMINATION OF BERARDIUS

11

the teeth (Table 1). The youngest age when the short cycle layers deposition ceases
is 39 long cycle layers, and the cumulative frequency of such animals increases withthe age. The oldest animal found to be still forming the full number of the shortcycle cemental layers is 57 long cycle layers and the cumulative frequency increases
in the younger age. The two cumulative frequencies become equal at the age of
49.5 long cycle layers, which is the mean age at the cessation of the deposition ofcomplete number of short cycle cemental layers.

Seasonal alternation of the layers
The condition of the last cemental layer, concerning the long cycle, was analysed in relation to the date of the catch. As shown in Tables 1 and 4, there areobserved two kinds of layer states at equal abundance in August. One is in theprocess of forming the unstainable layer on the outer margin and the other stainable layer. The thickness of the former layer is large and the number of short cycles
in it is 7 cycles in 2 countable cases. Whereas the thickness of the latter layer isthin and the number of short cycles in it is only 1 to 3 cycles in August. All the
TABLE 4.

Stainable

Unstainable
wide

Month
Aug.
Sep.
Oct.
Nov.
1>

SEASONAL CHANGE OF THE CONDITION
OF THE LAST CEMENTAL LAYER1>
Total
thin

5

wide

5
2

11

3
2
2

l

2
concerning the long cycle

13

12.4

11

i

9

i 7
VJ

0

5.9

d

z

/

5

/

3

D

F

M

A

M

A

Month

Fig. 7. Seasonal variation of the number of short cycles in the last incomplete long
cycle cemental layer. Closed circle and solid line indicate the stainable long cycle
layer, and open circle and dotted line the unstainable. Mean number of shortcycles in one long cycle and that in one long cycle stainable layer are indicated.
For further explanations see text.

Sci. Rep. Whales Res. Inst.,
No. 29, 1977.

12

KASUYA

seven whales killed after August were depositing the staniable layer of long cycle,
and the thickness seems to increase with the progress of the season. It is safely
concluded, from these informations, that the alternation of the layer from the unstainable to the stainable, occurrs, in the average, in August.
As the present sample is restricted to 4 months, it is impossible to detect theseason when the deposition of the stainable layer of the long cycle ceases and thatof unstainable layer starts. However, the analysis of the seasonal increment of theshort cycle layer gives a suggestion for it. In Fig. 7, the number of short cycle layers
in the last incomplete long cycle layer is plotted against the date of death. The
two whales, nos. 36 and 37, which were accumulating the unstainable long cycle
layer in August, are extended forward by 12 months and the number of short cycles in the preceding stainable long cycle layer was added. Then the linear regression was calculated by the least squares for the 8 whales, excluding the 5 whales
killed in August, that had recently started the deposition of the stainable layer.
The inclusion of these whales will cause a bias toward the higher number of shortcycles, because half of the whales are still accumulating the unstainable long cycle
layer in August. The regression is shown by
y = 0.03184x+0.58
where x indicates the days from the first of August and y the number of short cycles
accumulated since the start of the last stainable long cycle layer. It is, in a strict
sense, incorrect to project the two whales for 12 months, because the accumulation
rate of the long cycle is not proved to be 12 months. However the annual accumulation of the long cycle is considered to be correct based on the following reasons.
1. The gradient of the regression fits to the data of September and November,and other gradients assumed for the cycles shorter than one year do not.
2. If the length of the cycle longer than 1 year is assumed, there must be observed more varieties in the condition of cemental layers being accumulatedin August and September.
Above regression indicates the accumulation of one short cycle in 31.4 days, and12.4 short cycles, the mean number in one long cycle, in 389 days. This is sufficiently within the range of error for the conclusion of the annual formation of thelong cycle cemental layers. The alternation from the stainable long cycle layer tothe unstainable seems to occur in January. In other words, the long cycle stainable
layer is formed in the season when the length of the daytime decreases, and the unstainable in the opposite season. This seasonal alternation is similar to that of the
spotted dolphin studied by Kasuya (1976) except for the slightly earlier change in
B. bairdii.
When the annual cycle is assumed for the long cemental cycle, the mean lengthsof short cemental cycle of 13 whales come in the range of 27.3 to 30.6 days (Table
2). As shown in Fig. 5, the difference of the mean length of the cycle is significant
between some animals (p<0.05), and there are expected the presence of 4 modes
at 27, 28, 29, and 30 or 31 days. However it will be safe to retain the definite conSci. Rep. Whales Res. Inst.,

No. 29, 1977.

AGE DETERMINATION OF BERARD/US

13

clusion on this problem until the study is made on more animals, because the individual variation in the readability of the short cycle layer may influence the result.
In the natural environment, such a cycles which may cause the 29 or 30 days
cycle of the cemental deposition seems to be the lunar cycle. For the check of thisproblem, the comparison between the state of the outermost cementum and thelunar cycle of the day of catch was made on selected 13 animals using the thinly prepared section (10 to 15 µm). However it gave a negative result. The stainable
or unstainable layer of short cycle is considered to be formed at any period of a lunar
cycle. Though more study is needed on this problem, it is probable that the shortcycle is not a direct reflection of the environmental change, but a cycle hereditarily
decided individual specific cycle just as the menstrual cycle of some of the female
primates. This hypothesis can support the presence of the individual variation in
the length of short cycle.
DISCUSSION AND CONCLUSION
In the present study no tooth offetus or of newborn calf was studied. This obstructed
the conclusion on the start of the deposition of cementum and on the relative rateof the formation oflayers in dentine and cementum. However, Omura et al. (1955)
studied the anatomy of the tooth of9 feet, 2.7 m, fetus which had no cemental layer
on it. The observation on the cementum of postnatal individuals showed that there
is no clear layer such as neonatal line observed in dentine, and that the numbers ofshort and long cycles in cementum and postnatal dentine are almost same in theanterior tooth of young whales, nos. 53 and 55. In case of the dolphins, Stenella
attenuata and S. coeruleoalba, the cementum is lacking on the tooth of fetal or newborn
animals on which no postnatal dentine is deposited (Kasuya 1976, Kasuya unpublished), and it was considered that the cementum is laid down soon after the birth(Kasuya 1976). Accordingly I conclude that the deposition of cemental layer
will start in B. bairdii soon after the birth as in the case of other odontoceti, and thatthe accumulation cycle of dentinal layers is fundamentally the same as that of cementa! layers except for the earlier cessation of the accumulation in the former
tissue. In order to estimate the age of the young animals of the species, it will be
accurate to count both the long cycle layers (annual) and the short cycle layers(about 29.4 days) in dentine and cementum. However it is practical, in case ofanimals older than 3 years of age, to count the annual cemental layers. The ageof the oldest animal thus estimated is 71 years, and seems to be reasonable compared with the same figure of the female sperm whale 64 years (Ohsumi et al. 1963).
The present study suggests that the short cycle layering in the postnatal dentine
and cementum is probably caused by a genetic physiological cycle of about 29.4
days in the average. However, the effect of the lunar cycle is still left to be studied.
The long cycle layer is formed by the enhancement of some of the short cycle layers,which seems to be caused by the annual cycle of the physiological condition possibly relating to some environmental changes. As the cause of the formation of thelayers in the prenatal dentine, both the genetic physiological cycle (29.4 days in theSci. Rep. Whales Res. Inst.,
No. 29, 1977.

14

KASUYAaverage) of the fetus and of the mother can be expected. If the both factors work at
the same intensity and the length of the cycle of the mother and of the fetus is equal,
all the prenatal dentinal layers can be obscure by the complete masking of the opposite phases or can be clear by the complete or partial overlapping of the same phase.
However, if the lengths of the cycle is not equal, the complete coincidence occurs
once in the 27 to 31 cycles and the nearby several layers will be seen clear. Amongthe present materials, the prenatal dentinal layers of the whale no. 4 are almost
completely obscure, in the whale no. 40 so many as 12 layers are clear, and other11 individuals had 3 to 7 clear layers in the prenatal dentine. These facts can be
explained by the above hypothesis, if the length of the gestation of the species isabout 17 months as suspected from the fetal growth rate in later part of this section.
However, it is also possible to explain the presence of the clear and obscure layers in
the prenatal dentine solely by the strong effect of the mothers physiological changesof the short and long cycles, because the layers in the prenatal dentine formed in
the season when the unstainable long cycle layer is deposited in the mother can be
faint. Though the conclusion on the above problem must be left for the future
study and the counting is not fully reliable at present, it will be possible to expectthat the length of the cycle of the prenatal dentinal layering is nearly same with thatof the short cycle layers in the postnatal dentine and cementum.
Omura et al. (1955) estimated the body length of the species at birth 15 feet (4.6m) and the mean body length at the attainment of sexual maturity between 32 and 33
feet (7.8 and 10.1 m) for males and between 33 and 34 feet (10.1 and 10.4 m) for
females. The length at the attainment of physical maturity was not estimated bythem. However, there are, in the odontoceti, usually observed the coincidence ofthe body length and one of the modal length-if there are multiple modes that of thelargest body length (for the bottlenose whale see Christensen 1973 and 1975, for the
sperm whales see Clarke 1956 and Gambell 1972, and for the sppotted and striped
dolphins see Kasuya 1972 and 1976 and Kasuya et al. 1974), and this is expectedalso for B. bairdii. The length frequencies of B. bairdii shown in Fig. 3 of Omura
et al. (1955) indicates the mean length of the females at the attainment of physicalmaturity about 36 feet (11.0 m), and that of the males 35 feet (10.7 m). These
values fit well to the age-length data in Fig. 8, and physical maturity of the species
seems to be attained at an age over 20 years.
The growth curves in Fig. 8 are the von Bertalanffy growth equations calculated from the length at birth 4.6 m, asymptotic length 11.0 m (females) and 10. 7 m(males), and 7.1 m the mean length of the two juvenile whales nos. 53 and 55 at
the mean age of 2.1 years. The equations are shown by the following formulae
male: y = 10.7 (1-e-0.5620-o.2s11x)
female: y = 11.0 (l-e-0,5416-o.2sssx)
where y indicates the body length in m, and x the age in years. There is, at present,
no reason to believe that the mean growth of B. bairdii can be exactly expressed by
the von Bertallanffy equation and most of the known examples are opposite cases
Sci. Rep. Whales Res. Inst.,

No. 29, 1977.

AGE DETERMINATION OF BERARDIUS

150f<?m<lle
Male

11
PMO

PI

0

10

E 9
.£
..c

&

~ 8
>-

'O
0

IXl

7

6

5

0

10

20

30

40

50

60

70

Age in years
Fig. 8. Relationship between body length and the age of B. bairdii. Closed circle
indicates male, open circle female, PM a physically mature female, and PI physically immature male. The ranges of the mean body length at the attainment ofsexual maturity are cited from Omura et al. (1955). For the growth curves see text.

as seen in both sexes of the sperm whale (Nishiwaki et al. 1958), of the bottlenose
whale (Christensen 1973), of the pilot whale (Sergeant 1962), of the white whale(Sergeant 1973), and of the striped and spotted dolphins (Kasuya 1976). One ofthe peculiar features of the growth curves of these species is the presence of a long
prepubertal period when the growth is rather linear. Accordingly, if the above
three points are given correctly, the von Bertalanffy growth equation gives slightly
higher body length at pubertal stage. However, B. bairdii does not seem to have apost-pubertal growth spurt of the male often observed in polygynous marine mammals (Bryden 1972) because the asymptotic length of the male is smaller than thatof the female and possible difference of social behavior is expected (Omura et al.
1955 ). Accordingly it is considered, at the present status of knowledge on thisspecies, that the above growth equation will roughly indicate the mean growth of
the species. These growth curves and the mean body length at sexual maturity
presented by Omura et al. (1955) suggest that the species attains the sexual maturity
at about 8 to 10 years of age (Fig. 8), which is close to that of the female bottlenose
whale (Christensen 1973).
Omura et al. (1955) estimated 10 months for the length of gestation of B. bairdii
based on the seasonal change of the fetal length. However, if the accumulation
cycle of 29.4 days is assumed for the fine layers in the prenatal dentine as in the caseof short cycles in postnatal dentine and cementum, the fetal period of the species
Sci. Rep., Whales Res. Inst.,
No. 29, 1977.

16

KASUYAafter the start of deposition offetal dentine is 29.4xl4=412 days or 13.5 months.
Laws (1959) indicated that the fetal growth of odontoceti in body length isexpressed by a earlier curvilinear growth and later linear growth, and that the period from the start of gestation to the x-intercept of the extended growth curve of thelatter, to, varies between 7 % and 15 % of the total longth of gestation (tg) in accordance with the length of tg. There are indicated large between species variation of
the length of gestation and the fetal growth rate at the period of the linear growth(Laws 1959, Frazer and Huggett 1973), and there is observed a general tendency
that the odontoceti species with large neonatal length has longer gestation period
and faster fetal growth rate. In Fig. 9 the daily increment of the body length at

E

u

.~

.i

.5

•

>.

5

·a

0

100

200
N~natal

300

400

500

length in cm

Fig. 9. Relationship between the neonatal length and the feta! growth rate inodontoceti. 1 : Phocoena phocoena, Laws 1959. 2: Tursiops truncatus, Tabolga andEss:ipian 1957. 3: Stenella attenuata, Kasuya et al. 1974. 4: S. coeruleoalba, Kasuya et al. 1974. 5: Delphinapterus leucas, Hudson Bay, Sergeant 1973. 6: D. leucas,
Kara and Barents Sea, Sergeant 1973. 7: Globicephala melaena, Sergeant 1962.
8: Physeter catodon, Ohsumi 1965. Arrow: neonatal length of B. bairdii, Omura
et al. 1955. For further explanations see text.

the linear stage of the fetal growth is plotted against the mean length at birth citedfrom various authors. For Tursiops truncatus the neonatal length 90 cm and gestation length 12 months are cited from Tavolga and Essapian (1957), and to wasestimated as 0.135 X (gestation time)= 49 days. This indicates the daily increment90/(365-49)=0.285 cm/day. There is observed a linear relationship between
the two parameters of the delphinoidea as shown below (thin solid line in Fig. 9).
Sci. Rep. Whales Res. Inst.,
No. 29, 1977.

AGE DETERMINATION OF BERARD/US

17

y = 0.001462x+0.1622
Where y indicates the daily increment in body length (cm) and x the mean neonatal
length (cm). A set of parameters for the sperm whale seems to be slightly above
the regression. If all the 8 data are dealt together, the least square regression isexpressed by the following equation (thick solid line in Fig. 9).
y = 0.001802x+0.1234
Though the former may fit better for smaller odontoceti, the latter seems to be suitable for the relationship in the general odontoceti. Using the latter equation, thelength of the linear growth period, tg- t 0 , is expressed as follows, when x indicatesthe mean neonatal length in cm.
tg-to = x / co.001802x+o.1234)
As the neonatal length of B. bairdii is 15 feet or 458 cm (Omura et al. 1955), (tg-to)
and the growth rate of the period for the species is estimated from the above equations to be 483 days and 0.949 cm/day respectively. Accordingly, the days fromthe start of gestation to the x-intercept of the linear growth curve, t 0 , is (0.07 X 483)
/ 0.93=36 days, and the total gestation time is 36+483=519 days or 17.0 months
for B. bairdii.
The approximate age of the fetus of B. bairdii at the start of the deposition of
the first dentinal layer is 519-412= 107 days of gestation. The body length at thetime is (483-412)X0.949=67 cm. In case of Globicephala macrorhynchus, the fetal
dentine starts to be laid down at about 40 cm in body length (Kasuya unpublished),
the above figure is reasonable and the correctness of the estimation of the gestation length of B. bairdii is suggested. This fetal growth curve and the fetal length
frequency reported by Omura et al. (1955) and Omura (1958) indicate that themating peak of this species exists in October and November and the birth occurs
from November to July with a peak in March and April. This feature is the reverse of that of the northern sperm whale (Ohsumi 1965).
The above equation indicates that the (tg-to) of odontoceti has an asymptote
of 1 / 0.001802=555 days or 18.2 months. For the total asymptotic gestation time,
t 0 or about 1 month shall be added to this value. Then it is considered that thegestation period of any recent odontoceti will not exceed 19 months, and that the
fetal growth of the sperm whale or of the Baird's beaked whale is one of the most
specialized. This specialization seems to have started from the fetal growth patternof the small delphinids, which are less migratory staying usually in one water massand have the mating and parturition in a same season in connection with the gestation of about one year, and attained the modification to have the mating and parturition in the opposite season of a year. This may have a relationship with theattainment of the augmentation of the body and that of the m:igration habit oflonger
distance, both of which are observed in the sperm whale and the Baird's beaked
whale.
Sci. Rep. Whales Res. Inst.,
No. 29, 1977.

18

KASUYAACKNOWLEDGMENTS

The greatest thanks are due to Dr. H. Omura, director of the Whales ResearchInstitute, and Dr. Y. Naito of the Tokyo University of Fisheries for providing thetooth samples for the present study. The Tokai Gyogyo Co., Ltd. is also acknowledged for the cooperation in collecting the data and samples. Sincere thanks are
due to Mr. A. C. Myrick of the University of California, who critically read themanuscript and gave invaluable suggestions. The influence of lunar cycle ron thedeposition of the tooth layers of odontoceti was first suggested by him in the discussion with Kasuya, and this suggestion was very helpful in analysing the growthlayers of the present species.
REFERENCES
BRYDEN, M. M., 1972. Growth and development of marine mammals. in: Functional anatomy of marine mammals (ed. R.J. Harrison), 1: 1-79. Academic Press, London and New York.
CHRISTENSEN, I., 1973. Age determination, age distribution and growth of bottlenose whales, Hyperoodon
ampullatus (Forster), in the Labrador Sea. Norwegian J. ,Z,ool., 21 (4): 331-340.
CHRISTENSEN, I., 1975. Preliminary report on the Norwegian fishery for small wha!Ps: expansion of Norwegian whaling to Arctic Northwest Atlantic waters, and Norwegian investigations of the biology ofsmall whales., J. Fish. Res. Bd. Canada, 32 (7) : 1083-1094.
CLARKE, R., 1956. Sperm whales of the Azores. Discovery Rep., 28: 237-298.
FRAZER, J.F.D. and A. ST G. HUGGETT, 1973. Specific foetal growth rates of cetaceans. J. ,Z,ool., Land.,

169: 111-126.
GAMBELL, R., 1972. Sperm whales off Durban. Discovery Rep., 35: 199-358.
KASUYA, T., 1972. Growth and reproduction of Stene/la coeruleoalba based on the age determination bymeans of dentinal growth layers. Sci. Rep. Whales Res. Inst., 24: 57-79.
KASUYA, T., 1976. Reconsideration of life history parameters of the spotted and striped dolphins basedon cemental layers. Sci. Rep. Whales Res. Inst., 28: 73-106.
KAsUYA, T., N. MIYAZAKI, and W. H. DAWBIN, 1974. Growth and reproduction of Stenella attenuata in the
Pacific coast of Japan. Sci. Rep. Whales Res. Inst., 26: 157-226.
KIRINO, T., 1956. On the number of tooth and its variability in Berardius bairdi, a genus of the beacked
whale. Okojimas Folia Anat. Jap. (Tokyo), 28: 429-434.
LAws, R. M., 1959. The foetal growth rate of whales with special reference to the fin whales, Balaenoptera physalus Linn. Discovery Rep., 29: 281-308.
MATSUURA, Y., 1942. On the northern porpoise whale, Berardius bairdi Stejneger, in the adjacent watersof" Bosyu ". Dobutsugaku ,Z,assi, 54 (12): 466-473. (In Japanese with English summary).
NISHIMURA, S., 1970. Recent record of baird's beaked whale in the Japan Sea. Puhl. Seto Mar. Biol. Lab.,18 (1): 61-68.
NISHIWAKI, M., T. HrnIYA, and S. 0HSUMI (KIMURA), 1958. Age study of sperm whale based on reading of
tooth laminations. Sci. Rep. Whales Res. Inst., 13: 135-153.
NrsmWAKI, M. and N. 0GURO, 1971. Barid's beaked whales caught on the coast of Japan in recent 10
years. Sci. Rep. Whales Res. Inst., 23: 111-122.
0HSUMI, S., 1965. Reproduction of the sperm whale in the northwest Pacific. Sci. Rep. Whales Res. Inst.,

19: 1-35.
OHSuMI, S., T. KASUYA and M. NrSHIWAKI, 1963. The accumulation rate of dentinal growth layers in the
maxillary tooth of the sperm whale. Sci. Rep. Whales Res. Inst., 17 : 15-35.
0MuRA, H., K. FUJINO, and S. KIMURA, 1955. Beaked whale Berardius bairdi of Japan, with notes on ,Z,iphiuscavirostris. Sci. Rep. Whales Res. Inst., 10: 89-132.
Sci. Rep. Whales Res. Inst.,
No. 29, 1977.

AGE DETERMINATION OF BERARD/US

19

1958. Note on embryo of Baird's beaked whale. Sci. Rep. Whales Res. Inst., 13: 213-214.
SERGEANT, D. E., 1962. The biology of the pilot or pothead whale Globicephala melaena (Traill) in Newfoundland waters. Bull. Fish. Res. Bd. Canada, 132 : 1-84.
SERGEANT, D. E., 1973. Biology of white whale (Delphinapterus leucas) in western Hudson Bay. J. Fish.
Res. Bd. Canada, 30: 1065-1090.
TABOLGA, M. C. and F. S. EssAPIAN, 1957. The behavior of the bottlenosed dolphin (Tursiops truncatus):
mating, pregnancy, parturition, and mother-infant behavior. Z,oologica, 42 (1): 11-31.
OMURA, H.,

Sci. Rep. Whales Res. Inst.,

No. 29, 1977.

20

KASUYA

EXPLANATION OF PLATESPLATE I
Lingua-buccal medial ground sections of the teeth of B. bairdii. Photographed undertransmitted light and the contrast is reversed. The outermost structure is the artefact of the resin, actual size. 1 : Feta! dentine, 2 : Postnatal dentine, 3 : Osteodentine, 4 : Cementum, 5 : Resin.
Fig. I. Anterior tooth of the whale no. 55, 6.4 m, female, about 1.8 years old.
Fig. 2. Anterior tooth of the whale no. 53, 7.8 m, male about 2.4 years old.
Fig. 3. Anterior tooth of the whale no. 41, 10.9 m, male, 47 years old.
Fig. 4. Posterior tooth of the whale no. 53. For the explanations see Fig. 2.
PLATE II
Decalcified and stained sections of the teeth of B. bairdii. Scale indicates 0.1 mm.
Fig. I. I : Cementum, 2 : Feta! dentine, 3 : Postnatal dentine. Bar indicates thelong cycle stainable layer, and circle the short cycle stainable layer. Anterior
tooth of the whale no. 55, 1.8 years old.
Fig. 2. Cementum of the same tooth. Circle indicates the short cycle stainable
layer.
Fig. 3. Feta! dentine of the anterior tooth of the whale no. 53. Circle indicates
short cycle stainable layer.
Fig. 4. Cementa! layers of the whale no. 37, anterior tooth. Pulp side at the top.
For the marks see Fig. I.
Fig. 5. Cementa! layers of the whale no. 51, anterior tooth. Pulp side at the top.
For the marks see Fig. I.
PLATE III
Decalcified and stained section of the anterior tooth of B. bairdii, whale no. 49. Scaleindicates 0.1 mm.
Fig. I. Lower magnification, pulp side at the bottom, dentine is lost. Closed
circle indicates the stainable layer of the long cycle.
Fig. 2. Higher magnification of the upper left part of Fig. I.

Sci. Rep. Whales Res. Int.,
No. 29, 1977.

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