AGE DETERMINATION AND GROWTH OF THE SHORTFINNED PILOT WHALE OFF THE PACIFIC
COAST OF JAPANTOSHIO KASUYA *Ocean Research Institute, University of Tokyo, Minamidai, Nakano-ku Tokyo, 164 JapanAND

SUSUMU MATSUI
Taiji Whale Museum, Taiji, Higashimuro-gun, Wakayama-ken, 649-51 Japan

ABSTRACTThis study is based on data and specimens from 373 female and 170 male
Globicephala macrorhynchus collected off the Pacific coast of central Japan andcovering eight months of the year. The deposition rate of dentinal growthlayers was annual, the haematoxylin-stainable layer being formed from May
to October and the unstainable from December to February. The annual
deposition of cementa! layers continued after dentine deposition ceased, thus
enabling the age of old individuals to be determined.
The maximum age
attained by females was 62 years, that of males 45 years. Females almost
ceased growth at sexual maturity (nine years) and reached the asymptotic
length of 364.0 cm at age 22 years. Male growth was similar to that of females until age nine years, when the secondary male growth spurt started.
Males attained an asymptotic length of 473.5 cm at 27 years. Body length
could be converted into age with an accuracy of ±2 years, up to a bodylength of 280 cm (females; equivalent to age 5 years) or 320 cm (males; age
8 years). The relationship between body weight 0/V, kg) and body length(L, cm) of fetal and postnatal individuals of both sexes was described bylog W=2.8873 log L+log (2.377x 10-5).
INTRODUCTION

Sergeant (1959) examined the dentinal growth layers in the tooth of long-finned
pilot whale, Globicephala melaena (Traill, 1809), and suggested that these layers
might be used to estimate absolute age. He used this technique in his analysis of
the life history of G. melaena in Newfoundland waters (Sergeant, 1962). Sergeantalso observed cementa! growth layers in this species and suggested that they might
be used to age animals in which dentine deposition had ceased. However, he did
not use the technique, presumably because of technical difficulties.
Dentinal layer counts have subsequently been used in the study of the life

* Present address:

Far Seas Fisheries Research Laboratory, 5--7-1, Orido, Shimizushi, Shizuokaken, 424

Japan.

Sci. Rep. Whales Res. Inst.,
No. 35, 1984, 57-91

KASUYA AND MATSUI

58

history of several odontocetes as reviewed by Scheffer and Myrick (1980), despite
the limitations of the technique for determining the age of old individuals. In
recent years, however, the methods of preparing teeth for cementa! and dentinal
layer counts have been greatly improved (Perrin and Myrick, 1980).
The improved age determination techniques have been used to study the life
history of the short-finned pilot whale Globicephala macrorhvnchus Gray, 1846. We
report on age determination and growth in G. macrorhvnchus in this paper. Related
studies on the life history and reproduction of this species (Kasuya and Marsh, inpress) and on fundamental anatomy of the ovaries (Marsh and Kasuya, in press)
will be published elsewhere.
MATERIALS AND METHOD

Data source
Most of the data and specimen materials were collected between 1965 and 1980
inclusive from 24 schools of G. macrorhvnchus (Schools I through 24 in Table 1)caught on the Pacific coast of Japan by the driving fishery at Taiji (33°34'N,
135°54'E), Futo (34°54'N, 139°09'E), or Arari (34°49'N, 138°46'E), and from one
school stranded at Choshi (35°43'N, 140°52'E) in the Chiba prefecture. The
TABLE 1.
School
no.

2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24

MATERIALS USED IN THIS STUDY
Date ofNo. of individuals

Locality
Arari
Choshi
Arari
Taiji
Taiji
Taiji
Taiji
Taiji
Taiji
Taiji
Taiji
Taiji
Taiji
Fu to
Futo
Taiji
Fu to
Fu to
Taiji
Taiji
Taiji
Taiji
Taiji
Taiji

catch

data collection

drivenexamined

aged

lost

20 Oct. '65
13 Dec. '66- June '67
22 July '69
27 July '69
24 Feb. '71
17 Jan. '75
21 Jan. '75
24 June '75
22 July '75
13 Jan. '76
4 Feb. '76
7 Oct. '76
20 Dec. '77
24 Dec. '77
20 Feb. '78
4 Dec. '78
13 Dec. '78
6 Jan. '80
17 Jan. '80
2 Feb. '80
20 Feb. '80
21 Feb. '80
30 May '80

21 Cct. '65
15 Dec. '66
27, 28 June '67
July-Aug. '69
July-Aug. '69
24 Feb. '71
18, 19 Jan. '75
21, 22 Jan. '75
25 June-4 Jul.
22-24 July '75
13-17 Jan. '76
5, 6 Feb. '76
8, 9 Oct. '76
21 Dec. '77
25 Dec. '77
20, 21 Feb. '78
5 Dec. '78
13, 14 Dec. '78
6 Jan. '80
17, 18 Jan. '80
2 Feb. '80
23 Feb. '80
24 Feb. '80
31 May-3 June33
ea. 90
>30
31
46
24
28
52
ea. 230
33
28.
20
38
25
48
27
52
28
26
14
19
15
23
38

18
9
14
9
23
12
28
47
173
32
26
20
38
25
48
27
52
28
23
14
17
15
23
38

8
3
4
2
10
0
26
0
125
18
21
18
38
22
45
27
49
28
0
7
0
15
23
38

15
80
16
22
23
12
0
5
57
1
2
0
0
0
0
0
0
0
3
0
2
0
0
0

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

SHORT-FINNED PILOT WHALE

59

linear distance between the southernmost location, Taiji, and the northernmost,
Choshi is about 500 km.
The quality and quantity of data and samples varied between the schools.
In the early period of the study (Schools 1 to 6), effort was directed to the collection of materials for taxonomy, and the data obtained for the present analyses
were limited and biased to adult individuals. Information from four schools(schools 8, 19, 20 and 21) examined by volunteers was usually limited to sex andbody length. The 14 schools (Schools 7, 9 through 18, 22, 23 and 24) caught inthe seven years from 1975 to 1980 and examined by Kasuya constituted the major
source of data used for the study.
Field procedures
The information and samples listed below were collected by Kasuya, volunteers or
both, when the fishermen were flensing. At this stage each pilot whales was assigned a sample number which is a hyphonated combination of the school number
followed by the number of the animal within the school.
1. Sex
2. Bodv length Measured to the nearest 1 cm on a straight line parallel to thelong axis of the body from the anteriormost point to the bottom of the tail fluke
notch. Although the tip of the upper jaw is the anteriormost point of the bodyof juveniles, it lies posterior to the front end of the melon after the whale is about
240 cm long and becomes difficult to distinguish (Yonekura, Matsui, and Kasuya,1980). Thus the measurement of body length is not exactly comparable for adults
and calves less than one year old.
3. Teeth One to three contiguous teeth were collected from the center of thelower tooth row with a hammer and chisel and preserved in 10% buffered formalin.
The largest available teeth were selected.
4. Other specimens Mammary gland, testis, epididymises, ovaries, uteri andstomach contents were collected as detailed in Kasuya and Marsh (in press).
Laboratory procedures
1. Tooth preparation The age determination was done by Kasuya who counted
the annual growth layers in dentine or cementum. (One growth layer is equivalent to an annual Growth Layer Group of Perrin and Myrick (1980)). The bone
and connective tissue surrounding tooth selected were removed with a knife. The
tooth was then cut longitudinally with a low speed diamond saw. The cut surface was then polished with coarse (about 1,200 mesh) and fine (about 3,000 mesh)whetstones to expose the center of the tooth. The polished surface was dried andglued on a clear perspex plate (1 mm thick) with cyanoacrilate monomer. Afterthe glue had hardened, the other side of the tooth was similarly sawed off leaving
a 0.3 to 0.5 mm thick section on the perspex slide. This section was polished withthe whetstones to a thickness of 30 to 40 µm. The polished section was then decalcified in 5% formic acid for about 24 hours at room temperature, rinsed in running water for 5 to 12 hours, stained with Mayer's haematoxylin for 30 minutes,
Sci. Rep. Whales Res. Inst.,.No. 35, 1984

60

KASUYA AND MATSUI

rinsed in running water for several hours and mounted in Canadian balsam. (Acomplete removal of acid by long rinse or ammonia after staining prevent fading.)
2. Reading growth lavers The counting of annual growth layers was done undertransmitted light with a compound microscope (20 to IOOx) using the following
procedure. An ontogenetic series of 20 slides was initially prepared for each sex.
Factors taken into account in the selection of these slides included the quality of
preparation and the relative age suggested by the thickness of dentine and by thesize of the pulp cavity. The dentinal and cemental growth layers in the slide ofthese 40 teeth were counted. In most cases, there was reasonable coincidence between the number of growth layers in both tissues.
However, there were a few cases where the reading did not correspond. These
slides were re-examined for indication that dentine deposition had ceased. All
counts were then plotted against body length and sexual maturity for males andfemales separately. The pattern of increase suggested that the growth layer counts
were a reliable index of absolute age.
The age of the other whales were then determined based on the standard
established above but without reference to biological data. First the cementum
was read three or more times. The medium count was then taken as the true value.
Then the dentinal layers were counted three times without referring to the cementa! counts. The medium value was again used. If the deposition of dentine wasconsidered to have been continuing on at least part of the wall of the pulp cavity,
the dentinal count was used. In a few cases the range of dentinal and cemental
counts differed on a tooth with open pulp cavity. In these cases the growth layers
in both tissues were repeatedly checked until a good agreement was reached between the counts for both tissues. Kasuya used this method to train himself tobe able to make accurate cemental layer counts, enabling him to age whales withclosed pulp cavities, the age of these animals being determined from cemental layercount only.
The age of each individual was principally expressed as the number of growthlayer cycles, which was equivalent to years (see below). The age of individuals
below 10 years was roughly estimated to the nearest 1/4 year by considering the
thickness and nature of the first and last postnatal dentinal layers of incomplete
thickness. For whales over 10 years, the age was grouped into the nearest n+0.5
years (n=integer).
3. Other procedures The method used to determine the reproductive status ofeach whale are detailed in Kasuya and Marsh (in press) and Marsh and Kasuya(in press).
AGE DETERMINATION

Description of dentinal growth layers (Plates I to III)The prenatal dentine is capped by an enamel layer, which dissolves in the
decalcification reagent. In decalcified and haematoxylin stained sections, theprenatal dentine appears as either a moderately or strongly-stained layer in which
Sci. Rep. Whales Res. Inst.,
No. 35, 1984

SHORT-FINNED PILOT WHALE

61

10 to 20 indistinct short cycle layers can be detected with careful study. The
proximal border of the prenatal dentine is lined with a thin unstainable layer inmost postnatal animals. This is the neonatal line (Fig. 2 in Plate I). The thickness of the neonatal line ranges from 16 to 64 µm (X.=38 µm; n=25). The neonatal line could not be distinguished in four newborn individuals ranging from
136 to 142 cm in body length. Two of these whales (males 136 cm and 142 cmlong), had an erect dorsal fin, an indication that birth had occurred not less thanseveral hours before (Kasuya, Miyazaki and Dawbin, 1974). In contrast, theneonatal line was clearly seen in the teeth of five individuals from 154 to 190 cm
in body length and aged between 0.1 to 0.5 year (estimated from body length).
This indicates that the neonatal line in G. macrorhynchus is identifiable only after
the deposition of ordinary more stainable postnatal dentine.
4

7

2

3

4

5

6

7

8

Age in years
Fig. I. Thickness of postnatal dentine of G. macrorhynchus. The ranges, means andsample sizes are indicated. Open circles and dotted line represent females, closed
circles and solid line males.

In decalcified and stained sections, the growth layers in postnatal dentine areseen as layers of alternating stainability. The thickness of the annual growthlayers is about 0.5 to 0.6 mm in both the first and second complete layers (measured
at the level of the base of the prenatal dentine). This thickness decreases to about
0.1 mm at the 30th and subsequent layers (measured at the midlength of the pulp
cavity). No sexual dimorphism was observed in dentine thickness of young whales(Fig. 1). Within one annual growth layer, short cycle layers are usually detectable.
These tend to be conspicuous where the growth layers are wide, i.e. in the dentine
laid down near the tooth apex while the whale is young. Occasionally some ofthese short cycle layers are as prominent as ordinary annual growth layers.
The appearance of dentinal growth layers is variable within a tooth. The
layers deposited in the juvenile stage in the root of the tooth are composed of wide
stainable and narrow unstainable layers (Fig. 4 in Plate I). However if a stainable
layer is traced to the tip of the tooth its outer border gradually looses stainability,
Sci. Rep. Whales Res. Inst.,
N. 35, 1984

62

KASUYA AND MATSUI

while the stainability of its inner border increases. Furthermore, an accessory layer(Hohn, 1980) of strong stainability may appear in the unstainable layer near the tip.
Thus the pattern of stainability of these layers often appears to be reversed with aresultant apparent lag of about half a growth layer cycle between the cusp and theroot portions of the tooth. This feature is usually absent or negligible in subsequent layers. The annual growth layer deposited in the root of the tooth in adultwhales is usually composed of a narrow stainable layer and a wide unstainable
layer (Figs 2 and 3 in Plate II). Although accessory layers are still common mthese layers, they are less conspicuous than in the apex.
100

56

68

J

F

107

29

7

117

33

80

.....

c. 60
([/

u

....
([/

a.. 40
20
0

M

A

M

J

J

A

s

0

N

D

Month
Fig. 2. Seasonal change in the nature of the last incomplete deritinal layer of G.
macrorhynchus. Numerals at. the top indicate sample size. Thin horizontal lines:
wide unstainable layer. Stippling: thin unstainable layer. Black: wide stainable layer. Thick vertical lines: thin stainable layer.

Deposition rate of dentinal growth layers
Seasonality of stainability: Data were obtained from 270 females and 147 males inwhich the deposition of dentine was certainly continuing. The nature of the lastincomplete dentinal layer in the root of the tooth was classified as either a thin ora thick, stainable or unstinable layer. The thickness was judged by eye in comparison with the corresponding tissue in the previous cycle. Fig. 2 shows the seasonality of stainability of the last deposited dentine. In May/June most of the 29
individuals (86.2%) have started depositing stainable dentine. This continues inmost individuals until October. The number of individuals depositing an unstainable layer increases from 12.2% in December to 82.4% in February. Althoughdata are lacking from March to early May, we suspect that deposition of the unstainable layer peaks in February and March, and suggest that the alternations ofdentinal layers from unstainable to stainable and from stainable to unstainable may
occur in April to early May and in November, respectively. Thus each of the two
major components of a dentinal layer seems to represent approximately six months.
Sci. Rep. Whales Res. Inst.,
No. 35, 1984

SHORT-FINNED PILOT WHALE
FemaleMale

Female

63
Male

20
16

~ 12

m

::J
'U 8

>

4

'U

c

0

0 12
I...

8

OJ

..0

E 4
::J

z

0
/

4

0

DecemberJanuary

Fig. 3. Age and sex differences in the season when the stainable and unstainable
layers within a dentinal growth layer alternate in G. macrorhynchus. Thin horizontal lines: wide unstainable layer. Stippling: thin unstainable layer. Black: wide
stainable layer. Thick vertical lines: thin stainable layer.

Approximately 10 to 20% of our sample was not depositing dentine in accordance with this pattern. This may have been due to (1) exceptional individuals(2) errors in layer-identification due to the short cycle layers or (3) sex or age differences in dentine deposition. To test the last possibility the data for each month
were subdivided according to sex arid then into three age groups (1) below 15 years,(2) from 15 to 30 years and (3) over 30 years (Fig. 3). Age/sex differences in
the relative frequency of the four deposition stages was then statistically tested foreach month (Chi-square test). A statistically-significant difference (P<0.05) was
found only for samples obtained in December and January. The only combination where a significant difference was obtained between sexes was in intermediate age class (15-30 years) in January (P<0.01). Although this result indicates that males of intermediate age were more likely to deposit a stainable layer
than females, we consider this is probably an error caused by small sample size
because a similar trend was not observed in December (Fig. 3). A significant difference in the proportion of animals of the same sex laying down a stainble layer
was also found for the following age combinations in December:
Females young: intermediate, P<0.01intermediate: old, 0.02<P<0.05
old: young, P<0.001
Malesyoung: intermediate, P<0.01
Sci. Rep. Whales Res. Inst.,

No. 35, 1984

64

KASUYA AND MATSUI

Thus as the whales get older, proportionately fewer females tend to be accumulating a stainable layer in December. Although not always statistically-significant,the same trend is also observed in the male. The change in the deposition pattern from stainable to unstainable dentine seems to occur slightly later in younger
individuals possibly due to the larger relative width of the stainable dentine inyoung animals (see" Description of dentinal growth layers").

1.4
1.3

I
I
I

1.2

-

-1.1
N

t
I

:

l

I

'9"

:

I

I
I
I

1
I
I

:

:

I

I

1
\

~0.9

t
I
I
I

I
I
I
J

0.8

I

:

I
I

I

I
'

:

0.7
0.60

l!

I
I

:-A<---'"~----:0::"'.........]: .,.. ........ l------t::.?; 1.0
o.

a::

I
I

l'
·5

10

15

20

I
'

:

:

'

I

25

30

35

40

Age in years
Fig. 4. Rate of decrease in the width of dentinal growth layers indicated by the
thickness of the last complete layer (Y) and penultimate layer (Z) in G. macrorhynchus. The ranges and means for males (closed circles and solid line) and females (open circles and dotted line) are indicated.

Seasonal changes in dentine thickness: The thickness of dentinal growth layers wasmeasured with an ocular micrometer. The measurement was taken from thecenter of one stainable layer to the center of the next, except in the case of the lastincomplete set, the width of which was measured from the center of the last complete stainable layer to the predentine-dentine boundary near the edge of thepulp cavity (irrespective of nature of dentine being laid down). This latter measurement was often thicker than that of the penultimate measurement because
each stainable layer was defined only after the next unstainable layer had been
deposited. The uncorrected degree of deposition of the last growth layer (Rn)can be defined as;

Rn=~=where Xn is the thickness of the last (incomplete) growth layer of an n-year old
whale and Yn is the thickness of the (complete) penultimate growth layer of thesame individual. As the thickness of a dentinal growth layer varies with thewhales's age, Rn has to be corrected for this variation. The correction factor Cn
for an n-year old whale can be defined as;Sci. Rep. Whales Res. Inst.,
No. 35, 1984

SHORT-FINNED PILOT WHALE

Cn =

65

(f Zn+i,j
Yn+i,j) .__!__mi=lwhere m is the number of whales aged (n+ 1)-years and Z is the thickness of thelayer one cycle prior to r. Then the corrected deposition rate for the last incomplete layer of an n-years old individual can be defined as Rn/Cn. This method
is only applicable for whales older than two years.
2.0 ---------------------- ----- ------- -------------------- ----Ul
Ul

~

1.5

~

-~

....

..c

(])"

....c

~ 0.5
0

0

J

F

M

A

M

J

J

A

s

0

N

D

J

Month
Fig. 5. Seasonal change in the relative thickness of the last incomplete dentinal
layer in G. macrorhynchus. The dotted line joins the monthly means (open circles).
Black squares represent individuals depositing a stainable layer; white squares
those depositing an unstainable layer. The shaded areas indicate indiviuals thatare moved back (January) or forward (June/July-December) for one cycle inorder to correct for the individual variation in the seasonality of dentine deposition.

The relationship between age (n) and Yn/Zn is shown in Fig. 4. The meansof the five-year age classes increase until the whales are about 15-years old, andstays almost constant thereafter. The values for males are slightly higher than thecorresponding values for females indicating that the decline of growth layer thickness with age is slower in males. This may relate to the earlier cease of dentine
deposition in males mentioned below (see "Pulp cavity"). Because Yn/Zn showssuch large individual variation, it is not practical to calculate Cn for each age classand sex. Therefore, we have calculated Cn for both sexes and for four age classes
as follows;
2-5 yrs
Cn=0.8045-10 yrs
Cn=0.902
10-15 yrs
Cn=0.963;;::15 yrs
Cn=0.922
The resultant corrected values of the relative thickness of the dentinal layer
being deposited at the time of death in various months are shown in Fig. 5. In
January, about 40% of the individuals are still depositing stainable dentine while
Sci. Rep. Whales Res. Inst.,
No. 35, 1984

KASUYA AND MATSUI

66

Pulp cavity

80
60
40
~· 20
c 0

l!l!l closing, female•

closed , female[J closing, male

1111 closed , mcile

Cellular dentine

>o 80
cu 60

~ 40

O" 20

~

LL' 0
.Secondary
dentine

80
60
40
20
00

10

20

30

40

50

55 58 61

Age ·in years
Fig. 6. Growth of G. macrorhynchus teeth. Top: condition of pulp cavity. Middle: deposition of cellular dentine. The boxes represent four males whose pulp
wall was completely covered by cellular dentine. Bottom: deposition of secondary
dentine. The open circles and dotted line represent females, and closed circles
and solid line males.

the remainder have already started to deposit unstainable dentine. Therefore thevalues of the former individuals need to be moved backward for one cycle. In thesame way, the values for individuals depositing an unstainable layer after Julyneed to be moved forward one cycle. The mean monthly values of the corrected
thickness of the last dentinal layer thus calculated are shown by the open circles
in Fig. 5. The values increase from 0.3 in January to 1.3 in December. The increase is 1.0/year, and indicates that the deposition of the dentinal growth layers
is annual.
Growth of dentine
The postnatal growth of dentine is shown in Fig. 1. The thickness is measured
on the convex ramus of the tooth section from the proximal end of the prenatal
dentine to the pulp wall. Because the apex of the pulp cavity reaches the level ofthe base of the fetal dentine, this measurement is not possible on some males after
8.5 years of age or on some females after 6.5 years. The deposition of dentine is
rapid between 0.25 and 0.5 year of age. This period may correspond with thetime of tooth eruption and more indirectly with the start of taking solid food (seeKasuya and Marsh, in press). After 0.5 year of age the thickness increases at aslightly decreasing rate. The mean annual increment of the dentine in the juvenilestage is calculated from Fig. 1 as about 0.95 mm in the first year, 0.40 mm in thesecond year, 0.33 mm in the 3rd year, and 0.30 mm in the 4th year.
Sci. Rep. Whales Res. Inst.,
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SHORT-FINNED PILOT WHALE

67

The deposition of secondary dentine starts in some pilot whales of both sexes
at the age of seven years, and in most individuals by 16 years of age (Fig. 6). Although secondary dentine starts to form during the years when pilot whales mature
sexually, there is no correlation between the two phenomena in individual whales
and the age at which secondary dentine first forms varies between different teeth
in the same jaw (Table 3). Secondary dentine deposition starts at several points
on the pulp cavity wall as discussed by Sergeant (1962), and comprises increasingly
more of the tooth tissues as the whale ages. It appears translucent on thin undecalcified sections and is less stainable in the decalcified and stained sections(Plate II, Figs I, 2, 3, and 6). The annual growth layers in secondary dentine areless regular than in ordinary dentine and the contrast between stainable and unstainable layers is usually less pronounced (Plate II, Fig. 2). However, we consider that secondary dentine is not a real obstacle to age determination in G. macrorhynchus, because (I) even in old individuals some small areas of ordinary dentine
are usually evident along the wall of the pulp cavity and (2) reading the layers insecondary dentine is not very difficult in the decalcified and stained sections (Plate
II, Figs 2 and 3).
Another characteristic of the short-finned pilot whale tooth is the depositionof a tissue on the wall of the pulp cavity that we have tentatively called " cellulardentine " (Plate III, Figs 3 to 7). In decalcified and stained sections, this tissue
looks rather like cementum. Although the " cellular dentine " contains minute
growth layers, the spacings are irregular making counting almost impossible. The
deposition of "cellular dentine" starts at the base of the pulp cavity, but progresses further along the cavity in some individuals 10 years or more in age. The
boundary between the "cellular dentine" and cementum is less obvious than between this tissue and both other types of dentine.
While preparing teeth for age determination, it was noted that " cellulardentine " tended to be laid down by unusually fibrous pulp which adhered closely
to the wall of the pulp cavity. In few exceptional males, the entire wall of the(still open) pulp cavity was lined with " cellular dentine" making it impossible tocount the dentinal growth layers (Fig. 6).
Pulp cavity
We classified the condition of the pulp cavity as follows:
1. Open pulp cavity All dentinal growth layers continuous in a longitudinal tooth
section, dentine being deposited along the entire pulp cavity wall. Similar
numbers of dentinal and cemental growth layers.
2. Closing pulp cavity Some of the dentinal growth layers (at least the latest one)
discontinuous in a longitudinally sectioned tooth. Growth layers depositedalong a limited portion of the pulp cavity wall only, the remainder being
lined with a strongly-stainable thin layer of uniform structure, which does notcontain cells in it. The number of dentinal growth layers may coincide with
the number of cementa! layers within the range of reasonable error if the best
portion of the pulp wall is used for counting.
Sci. Rep. Whales Res. Inst.,
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68

KASUYA AND MATSUITABLE 2.

LIST OF WHALES WITH CLOSED PULP CAVITVAge (yrs)
ReproSampIe - - - - - - Gonad* ductive B.L.
dentine cement
status (cm)
no.
Male
9- 1
9-23
9-75
13-16
15- 8
Female
1-16
5-N3

7- 2
7- 4
9- 3
9-38
9-47
9-55
12- 4
12-11
12-18
13-10
15- 2
15- 4
15- 5
15-13
15-18

26.5+
30.5+
34.5+
28.5+
35.5+

30.5
42.5
41.5
34.5
39.5

33.5+
22.5+
22.5+
22.5+
34.5+
35.5+
29.5+
29.5+
33.5+
32.5+
22.5+
42.5+
38.5+
35.5+
40.5+
42.5+
22.5+

52.5
38.5
26.5
32.5
38.5
38.5
45.5
34.5
48.5
43.5
37.5
42.5
42.5
55.5
47.5
51.5
25.5

2235
1475
2150
2010
1570

l+
13
9

7
10
12
13
6
4+
10
8
10

Mat.
Mat.
Mat.
Mat.

510
478
491
479
438

Mat. 378
Preg. 340
Preg. 335
Preg. 354
Rest. 360
Rest. 364
Lact. 381
Rest. 368
Mat. 354
Lact. 376
Rest. 368
Lact. 381
Rest. 350
Rest. 382
Rest. 352
Rest. 355
Rest. 371

Sample
no.
Male
16- 5
18- 1
18- 3
18-49
Female
15-33
15-37
16- 8
16-19
17-20
17-41
20- 7
22- 2
22- 7

22- 9
23- 8
24-12
24-14
24-19
24-24
25- 3
25-30
26-12

Age (yrs)

Repro- B L
Gonad* ductive (;m·)
dentine cement
status

30.5+
31.5+
40.5+
40.5+

33.5
45.5
45.5
41.5

1850
1360
1750

46.5+
29.5+
47.5+
38.5+
33.5+
35.5+
25.5+
30.5+
34.5+
40.5+
32.5+
37 .5+
38.5+
41.5+
24.5+
37 .5+
38.5+
34.5+

57 .5
35.5
62.5
43.5
38.5
47 .5
36.5
55.5
43.5
44.5
47.5
45.5
50.5
46.5
35.5
39.5
45.5
48.5

12
8

Mat.
Mat.
Mat.
Mat.

473
431
463
444

16
5
7

Rest.
Lact.
Rest.
Lact.
Rest.
Lact.

13
14
9
14
8
13
6
15
17
12
12

358
339
363
353
368
353
375
381
382
380
363
365
382
377
372

Rest.
Rest.
Rest.
Rest.
Rest.
Lact.
Rest.
Lact.
Rest.
Rest. 352
Lact. 348

880

* Weight of one testis in gram or number of corpora in ovaries (Data from Kasuya and Marsh (inpress) and Marsh and Kasuya (in press)).
Abbreviations : B.L. : body length ; Mat. : mature ; Preg : pregnant; Rest. : resting; Lact. : lactating.

Closed pulp cavity Dentinal growth layers discontinuous in a longitudinallysectioned tooth. The wall of the pulp cavity entirely covered by a thin uniform layer of stainable dentine. The number of cemental layers equal to or
greater than the number of dentinal layers irrespective of where the dentinal
layers counted.
A closing pulp cavity may occur in males over 21.5-years old and in females over
24.5-years old, and the closed pulp cavity in males over 31.5-years old and in females over 24.5-years old (Table 2). At ages between 20 and 45 years, the proportion of closing or closed pulp cavities is higher in males than in females suggesting that dentine deposition tends to cease earlier in males. About 25 to 50%
of females over the age of 40 years still have an open pulp cavity (Fig. 6).
Figure 7 documents the changes in the (maximum) diameter of the pulp
cavity that occur with increasing age. The diameter of the pulp cavity tends to begreatest at the proximal end in animals less than a year old and in the middle
region in older whales. There is no sexual dimorphism in this character. The
diameter of the pulp cavity decreases from about 10 mm for whales less than two3.

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

69

SHORT-FINNED PILOT WHALE

12
8

E
E 4
c

-

0

~

Closing·

'

Cl>
Cl> 4

&

l

E

.!! 2
c

t\

/I\
I

l:

:

1

\

1

I

I

+.

1

I

I

I

I

I

I

I

l

I

"~·~<l'fy •, IJ...- .. •+- '9---4'' I '-i>--4-.-l-Y
\

\T

:

I

I

I

I

I

I

I

.....

I

I

0
Closed

.1
00

10

20

30

40

50

5558 61

Age in years
Fig. 7. The mean and range of the diameter of the pulp cavity in G. macrorhynchus.
Open circles and dotted line represent females, and closed circles and solid line
males.

1.5
6744413

E

0

2

E
1.0
c
Ill
Ill

Cb

c

13 0.5
:.c
I-

10

20

30

40

50

55 58 61

Age in years
Fig. 8. Thickness of cementum in G. macrorhynchus showing means, ranges, andsample sizes. Open circles and dotted line represent females and closed circles
and solid line males.

years old to about 3 mm in whales over 20-years old when the cavity starts to close.
" Closing" pulp cavities tend to have a relatively constant mean diameter of about
1 mm while the mean diameter of a "closed" pulp cavity ranges from 0.5 to
Sci. Rep. Whales Res. Inst.,
No. 35, 1984

KASUYA AND MATSUI

70

30

Pulp, closed

5'-o. •

'

--o.,

0
~
0

c

60

4

ffe.
I
'

Pulp, closing

'I
I
I

:a·
'

30

I

•

0

~

u

60

3

Pulp, open
>30 yrs

cCl> 30
::J

~ 6g

2

Pulp, openL.

15-30 yrs

LL 30
0

60

Pulp, open
<15 yrs

30
0

0

0.5

1.0

1.5

Ratio
Fig. 9. Ratio of the number of cementa! growth layers to the number of dentinal
growth layers in G. macrorhynchus. 95% confidence interval for the mean (box)and 2 X SD range (bar) are indicated on each side of the mean. Open circles anddotted line indicate females, and closed circles and solid line males. I : 68 males
and 61 females below 15 years of age. 2 : 53 males and 121 females between 15
and 30 years of age. 3: six males and 45 females over 30 years of age. 4: 22
males (20-40 years) and 46 females (25-52 years). 5: nine males (30-45 years)
and 32 females (25-63 years).

1.0 mm and shows no decline with age. These observations are consistent withdentine being deposited only along limited parts of the pulp cavity wall in the" closing" stage and deposition ceasing in the "closed" stage.
Cementa! growth layers
Figure 8 shows the maximum cementum thickness plotted against age. Cementum
is absent from the teeth of very young postnatal whales. The largest individual
without cementum was a male 154 cm long and aged about 1.5 months (age estimated from body length). The smallest individual with a cementa! layer was a
163 cm long female (estimated from its length to be two or three-months old).
Seven whales less than 200 cm long had tooth cementum. Therefore, we conclude that the deposition of cementa! layers starts in G. macrorhvnchus at a few
months of age. Cementa! growth is rapid between two and four years of age (Fig.
Sci. Rep. Whales Res. Inst.,
No. 35, 1984

SHORT-FINNED PILOT WHALE

718). After that the thickness increases at a lower rate, but continues throughout
life. After two years of age, males tend to have thicker cementum than females(Fig. 8).
Although the cemental growth layers are much narrower than the dentinal
growth layers, the accessory layers are less conspicuous and we consider that thereadability of both tissues is about the same (compare figures in Plates I, II, and
III). When reading the cemental growth layers it is important to remember that(1) the first or second layer is usually limited to the distal portion of a tooth and(2) in older whales the later layers are usually very thin or absent in the distal
part of the tooth. Therefore a whole set of cementa! growth layers of an old
individual cannot be seen in one cross section of the tooth. It is necessary to readthe layers from the inner distal layers to the outer proximal layers as in Berardius
bairdii (Kasuya, 1977).
Figure 9 shows the number of cemental growth layers expressed as a proportion of the number of dentinal layers. In young whales there is a tendency tounderestimate the number of cemental growth layers compared with the numberof dentinal growth layers.
For most whales with an open or closing pulp cavity, the counts of dentinal
and cemental growth layers were very close. The mean difference from parity of
the ratio of cementa! layer count: dentinal layer count was only 3.4%, even though
there were some exceptional individuals in which the ratio was as high as 1.8 (Fig.
9). We therefore conclude that the deposition of cementa! layers is also annual.
Even though we have not otherwise calibrated the cementa! layer deposition
rate, we consider that cementa! layers continue to be deposited after dentine deposition has ceased, for the following reasons. (1) The age at which dentine deposition ceases is very variable and the cessation occurs concomitant with redutionof pulp cavity after the transitional " closing" stage. Thus there is no evidence tosuspect that cessation is caused by a physiological change which would also affectcementum deposition. (2) The thickness of cementa! growth layers decreases constantly throughout life with no indications of an abrupt decline. (3) The technique of reading cementa! growth layers was repeatedly standardized by checking
young teeth.
Errors in age determination
Errors due to the position of the teeth used for age determination: Hui (1980) reported
that in Tursiops truncatus the deposition of dentinal growth layers ceases earlier inteeth near the anterior and posterior ends of the row than in the other teeth. Inorder to test whether this was also true in G. macrorhvnchus, we counted the growthlayers in a series of teeth from five jaws from three whales. Each of the growthlayer counts shown in Table 3 is the middle value of three repeat counts. Even
though the pulp cavities of all the teeth of the youngest whale (No. 17-7, estimatedage 19.5 years) were open, the dentinal growth layer counts of the teeth at the endsof the row were significantly less than those of the other teeth probably because theposterior teeth were smaller and tended to have irregular growth layers. In conSci. Rep. Whales Res. Inst.,
No. 35, 1984

72

KASUYA AND MATSUITABLE 3.

Sample no.
BL, SexCOMPARISON OF GROWTH LAYER COUNTS OF SEVERALTEETH FROM THE SAME WHALE

17-7
437 cm, male

c

D

23-5
366 cm, femalescUpper teeth (numbered from anterior to posterior)
20
13
11
1
2
20
20
11
3
20
18
13
4
17
19
13
5
17
17
9
19
6
19
11
7
19
16
11
Lower teeth (numbered from anterior to posterior)
1
21
17
11
29
2
20
20
9
30
19
20
29
3
14
20
20
13
29
4
5
21
20
13
28
20
20
11
6
30
20
12
7
19
30
19
17
12
25
8
9
19
17
14
20
10
15+

D

30
29
30
30
31
30
31
28+

18-3
463 cm, male

s

12
13
9
7
8
9
9
10+

c

D

s

44
47
44
44+
45+
45+
45+

20
32+
31
27+
28+
22+
19+

11
11

46
46
46
47
46
48
46
42

32+
34+
41
41
35
46
40+
22+

17
7+
12+
13+

12+
15+
13
15
14
13
13+
9+

Code: C: No. of cementa! layers; D: No. of dentinal layers; S : Age (no. of layers) when secondary
dentine first deposited ; + : Neonatal line or first cementa! layer lost by abrasion; BL: Body
length.

trast, similar differences were not observed in the 29.5-year old female (No. 23-5).
All the teeth of the oldest animal (No. 18-3, 45.5 years) had closed pulp cavities
with the exception of the 6th tooth of the lower jaw which had a " closing " pulp
cavity. Dentine probably ceased to be deposited in this animal when it had laid
down between 36 and 46 dentinal layers. However, only 20 dentinal layers werecounted in the anterior teeth.
In contrast, no significant differences were observed between the cementa!
growth layer counts of different teeth from the same whale except for the two
smallest teeth of No. 18-3 (Table 3).
These results suggest that errors in age determination due to tooth position
will not occur if the largest tooth near the center of the row is used.

Calibration errors: Errors can occur when the growth layer count is converted into
absolute age. The age of G. macrorhynchus older than 10 years was expressed as
the nearest n minus 0.5 years where n was the number of stainable layers counted(Any incomplete stainable layers in the first or last cycle were regarded as complete
and unstainable layers were ignored). As each complete stainable or unstainable
layer represents about six months, the true age of an individual with n stainable
layers is between n-1.5 and n+0.5 years i.e. a mximum error of± 1.0 year. For
Sci. Rep. Whales Res. Inst.,
No. 35, 1984

SHORT-FINNED PILOT WHALE

73

TABLE 4. INDEX OF ERROR IN AGE ESTIMATION (I, %) : DIFFERENCE BETWEEN
THE MIDDLE COUNT AND ITS CLOSEST COUNT IN THREE READINGS OF
THE SAME TOOTH EXPRESSED AS PERCENTAGE
OF THE MIDDLE COUNT
Age (yr) and Tissue usedll
Error (/)
0-15 (D)15-30 (D)>30 (D)>30 (C)

1.2
0.0
95.1
2.5
1.2
100.0
81
+0.07
1.22

4.5
7.6
87.9
0.0
0.0
100.0
66
-0.52
1.57

0.0
7 .1
85.8
0.0
7 .1
100.0
14
+0.27
1.93

0.0
0.0
55.6
44.4
0
100.0
9
-1.97
2.04

1.9
0.0
97.2
0.0
0.9
100.0
107
-0.10
1.38

3.1 2 l
6.2
80.6
7.0
3.1
100.0
129
+0.10
2.18

3.4
5.7
78.3
11.5
1.1
100.0
87
+0.02
2.24

0.0
6.5
80.6
9.7
3.2
100.0
31
+0.60
1.88

Males
<-5.0
-5.0--2.5-2.5-+2.5+2.5-+5.o;:::+5.oTotal, %No. of whales
Mean
SD
Females<-5.0-5.0--2.5-2.5-+2.5+2.5-+5.0;:::+5.oTotal, %No. of whales
MeanSD

Age based on counts of growth layers in dentine (D) (teeth with open or closing pulp cavities) or
cementum (C) (teeth with closed pulp cavities).
2l One reading of cementa! layer included.
ll

G. macrorhvnchus less than 10 years of age, the number of growth layers was counted
to the nearest 0.25 deposition cycle by estimating the thickness of the first and lastincomplete layers. The maximum error of this is 0.5 cycle (=year).
Counting errors: Since three repeat counts were done by the same reader for bothcementum and dentine with the middle value considered the best, the index oferror (/, %) is calculated by the following formula:where M indicates the middle reading and C the reading closest to the middle
reading. The result is shown in Table 4 arranged by sex, age, and tissue type.
The standard deviation of the index or error increases with the age of animals fromless than 1.4% to over 2.2%. The error expected for repeat counts done by thesame person has a standard deviation of about 2%, giving a 95% confidence rangeof about 2%X2=4% of the middle reading.
If the errors due to calibration and counting are added together, the 95%
Sci. Rep. Whales Res. Inst.,
No. 35, 1984

Fig. 10. Conversion of body length into age in G. macrorhynchus. Means and 95%
confidence intervals are indicated. Open circles represent females and closed
circles males.

confidence range for the age estimates at ages 10, 20, 40 and 60 years are estimatedto be ±0.9, ± 1.8, ±2.6, ±3.4 years respectively. The confidence range for the
youngest ages may be slightly narrower than indicated, because the value of I
tends to be overestimated in this instance.
Conversion of body length into age
The ages of juveniles from which teeth for age determination were not available
were estimated from their body lengths as follows. For whales in each 10 cm
size-class below 400 cm (males) and 320 cm (females), the mean and coefficient ofvariation of the ages were calculated. (For whales less than 230 cm long, data for
Sci. Rep. Whales Res. Inst.,
No. 35, 1984

SHORT-FINNED PILOT WHALE

75

both sexes were combined). As these mean ages fluctuated due to sampling error
they were smoothed by eye as in Fig. 10. For females, the coefficients of variation
were nearly constant and had a mean of 0.234. In the male, the coefficients ofvariation tended to decrease with increasing age (because males tend to be larger)
and had a mean of 0.182. The 95% confidence interval of the age corresponding
to each size class was calculated (assuming that age was normally distributed foreach size class and that the coefficient of variation was constant) as:(smoothed age)±(smoothed age)X (coefficient ofvariation)X2
The results are shown as squares in Fig. 10. In females and males less than
330 cm long, the confidence interval approximately coincides with the range of
observed values. In larger males the observed range tends to be smaller thanthe confidence interval, probably because the coefficient of variation was actually
decreasing not constant as assumed.
Using this technique it is possible to estimate age within two years for females
below 280 cm (mean converted age about 5 years) or for males below 320 cm(mean age about 8 years).
GROWTH CUR VE AND BODY WEIGHT
Body length frequencies
The body length frequencies in Fig. 11 are based on the data from 18 schools(Schools 7 through 24). The frequencies are biased, because the catch of a driving fishery may under-represent the juveniles in the population (see Kasuya andMarsh, in press) and because the whales below length 320 cm are missing fromone large school (School 9) (see Kasuya and Marsh, loc. cit.).
The largest of the 449 females was 405 cm long. The next longest females
were two animals of 400 cm. The adult female length frequency has a single mode
at about 360 cm (Fig. 11 ).
The maximum male body length measured in the present study was 580 cm(No. 9-171 ), which was followed by much smaller males of 525 and 520 cm. The
largest individual, which was measured by Ms C. Goebel, had testes weighing 1. 7
and 1.8 kg but no other biological data were collected. We consider that thisindividual was exceptional among the 201 males examined and may have belonged
to the larger of the two types of pilot whale recently recorded from Ayukawa*,
and that the maximum body size expected for males of the form usually taken off
central Japan will be 525 cm. The male length frequency is more diffuse than

* Since completing this study, Miyazaki and Kasuya (unpublished) have observed two types of pilot whales
off Ayukawa (38°20'N) on the Pacific coast of northern Japan in November. This is near the northernboundary of the range of G. macrorhynchus at this time of year. Both types have skull feature characteristicof G. macrorhynchus as described by Bree (1971). The smaller type is identical to those taken off central
Japan and studied in this paper. The other type is possibly a boreal form. It is from one to two meterslarger, and has more pronounced saddle mark. The forehead of the adult male is roundish rather thansquare as in the smaller type. The two forms are presumably geographical races corresponding to thosereported by Polisini (1980) from the eastern North Pacific.
Sci. Rep. Whales Res. Inst.,
No. 35, 1984

76

KASUYA AND MATSUI

80

Ill

[=::J IMMATURE
IIIIllIIlID EARLY-MATURING
fBilill LATE-MATURING
MATURE
Q ] UNKNOWN

60

Ill

::J
"O

:> 4o
:a
.£
0

449 females

20

z

0
10

200 males
200

300

400

500

Body length in cm
Fig. 11. Frequency histogram of body lengths and growth stages in G. macrorhynchus. All data from schools 7 to 24 are included. In school 9, individuals
below 320 cm are underrepresented. " Early-maturing " stage represent maleswith testes where more than 0 but less than 50% of tubules are mature, " latematuring" those males with testes where from 50% to 100% (exclusive) of tubules
are mature, and " mature " those males whose seminiferous tubules are all mature(equivalent to social maturity) (Kasuya and Marsh, in press). For further description of the stages of sexual maturity see Kasuya and Marsh (in press).

that of the female with a possible adult mode at about 4 70 cm body length. Boththe maximum and modal lengths of males are about 110 to 120 cm larger than thecorresponding figures for females.
Growth curve
In Fig. 12, the mean body length of each age group is plotted against the corresponding age for each sex. The mean growth curve between the mean birthlength of 139.5 cm (Kasuya and Marsh, in press) and asymptotic length has beendrawn by eye for each sex as an indication of the general growth trend. The
coefficients of variation of body length for each age group for each sex are shown at
the bottom. Age-length keys for the samples have been included as Appendices
1 and 2.
The mean growth curves are divided into the four phases; (1) a phase of rapid
neonatal growth, (2) a juvenile phase of less rapid but almost linear growth, (3)growth between puberty and mean asymptotic length, and (4) a phase of no increase in body length.
The first phase, in both sexes, is similar and seems to end at about 1.25 yearsof age. The mean growth in this period (mean length at 1.25 years (230 cm)mean length at birth (139.5 cm)=90.5 cm) represents a mean annual growth rateof 72.4 cm, slightly smaller than that in the first year after birth (225 cmSci. Rep. Whales Res. Inst.,
No. 35, 1984

77

SHORT-FINNED PILOT WHALE

5.0

..

4.5
MatureE
c: 4.0

Early- maturing

o 0

~

-

"'c:
C!>

-

o

00

0

--o-~<t-o--o- _2, 'ag_ -- - U SJ_o_o_ - .Q_o_ -0-0.. - - - - - - - - - - - - - - - - - - - - -2-

~;-o

o

o

o

o

o

Oo

oo

o

o_. ... o3.5• o ......o ...

Sex. maturity • o'.

---:----------

3.0

»
"'O
Sz.5

v

o

I

''
,'' ':'
''

:'
'''
''
''

'
''

2.0
1.5
0

10

30

40.

50

60

Age in years
Fig. 12. Mean growth curve of G. macrorhynchus. Open circles and dotted line represent females, and closed circles and solid line males. The mean ages and bodylengths at the onset of sexual maturity (females), of the "early-maturing" stage(male), and of the 'mature" stage (male) are indicated. Curves between birthand asymptotic length are fitted by eye. For description of the stages of sexual
maturity see Fig. 11.

139.5 cm=85.5 cm or 62.l % of the neonatal length). This phase may last slightly
longer in males because by the age of 2.5 years, males average 254 cm long, 6 cm
longer than females.
The second growth phase lasts, in females, until about the mean age of firstovulation (9.0 years, see Kasuya and Marsh, in press). During this phase the bodylengths of females tend to be several centimeters smaller than those of males ofsimilar age. The mean growth rate for females between 2.5 and 9 years is 11.4 cm
per year ((322-248) cm/6.5 years). In males, this second growth phase lasts
slightly longer until about 10 years of age but the mean growth rate is fairly similar,
about 12 cm per year ((344-254) cm/7.5 years).
The third growth phase ends, in females, at about 22 years when the growth
curve reaches the mean asymptotic length. The mean growth rate for females
during this phase is (364-322) cm/(22-9) years=3.2 cm per year. In males, thecorresponding growth phase begins at about 10 years of age with slightly accelerated prepubertal growth followed by a gradual decrease in the growth rate until
the growth curve reaches the asymptote at about 27 years. Under these circumSci. Rep. Whales Res. Inst.,

No. 35, 1984

78

KASUYA AND MATSUI

750
500
250

i

,,
I/
//

I/

'1

,,/1

100
75

'I

/1

I/
I

50

I

Ol 25

:::e.
c

-

10

..c.

Ol

•

5

(1)

~

>-

'U

0
CD

1
.75
.50
.25
.10
.05
10

15 20

30

50

70

100

150 200

300

500

Body length in cm
Fig. 13. Relationship between body length and body weight in G. macrorhynchus
plotted on a double logarithmic scale. Open circles indicate females, closed circles
males, and circle with bar individuals which died in an aquarium.

stances, calculation of a mean growth rate over this entire period is not meaningful.
The mean growth rate for males between ten years and fourteen years of age is(397-344) cm/4years=13.3 cm per year while that of males between 23 years and27 years of age is (473.5-461) cm/4 years=3.l cm/year.
The last phase starts at 22 years in females and at 27 years in males, when all
individuals stop growing. Presumably some individuals will cease growing at a
younger age and the proportion of individuals ceasing growth will increase withage until the ages mentioned above. The " mean asymptotic lengths " (in thesense usually accepted for cetaceans) for G. macrorhynchus are as follows :Sci. Rep. Whales Res. Inst.,
No. 35, 1984

SHORT-FINNED PILOT WHALE

Number ofsamples
181
35

Sex
FemaleMale

Mean asymptotic
length.
364.0 cm
473.5 cm

79

95% confidence
interval of mean
±1.9 cm±9.1 cm

These figures are close to the modal lengths in the body length frequencies.
TABLE 5. BODY WEIGHT OF G. MACRORHYNCHUS
No.
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29

30
31

Body length
(cm)
12.5
23.3
30.6
36.5
52.0
59.5
65.5
6ti.5
69.5
72.0
95.0
123
144
275
275
285
286
290
310
330
335
340
400
260
263
265
281
290
291
335
355

Body weight(kg)
0.03280.21120.500
0. 750
2.20
2.94
3.97
4.15
4.75
6.40
10.70
24.50
40.20
275
250
285
245
325
410
520
380
530
650
255
237 .19377 .90348
406
379.22484.60751.90

Sex

6
6
Q

6
Q
Q
Q

6
Q

6
Q
Q

6
Q
Q
Q
Q
Q
Q
Q
Q
Q
Q
Q
Q
Q

6
6
6
Q
Q

Remarks
Fetus

"
"
"
"
"
"
"
"
"
"
At capture
"
"
"
"
"
"
"
At death
after 547 days in captivity
"
"
"
"
"

270
225
311
362
192
11

228

"
"
"
"
"
"

Body weight
Table 5 shows the intact body weights of 13 fetuses and 18 postnatal individuals.
As shown in Fig. 13, whales weighed at death after being kept in the museum tend
to be heavier than those measured at capture. We considered this to be the resultof over-feeding and/or lack of exercise, and excluded those data from the following
analyses.
Figure 13 shows the relationship between body length (L, cm) and body
Sci. Rep. Whales Res. Inst.,
No. 35, 1984

80

KASUYA:AND MATSUITABLE 6. BODY WEIGHT OF G. MACRORHYNCHUS AT SEVERAL GROWTH STAGESCALCULATED FROM BODY LENGTH-BODY WEIGHT RELATIONSHIP
Growth stage and sex

Mean body length(cm)

Body weight
(kg)

Birth
( ~ d')
Sexual maturity(~)
Asymptotic length(~)
Early-maturing stage* (d')
Mature stage*(d')
Asymptotic length
( d')

139.5
315.6
364.7
401.1
422.1
473.5

37.0
391
593
781
904
1260

* For definitions see Fig. 11, and for detailed descriptions of these stages see Kasuya and Marsh (in press).

weight (W, kg) of specimens of G. macrorhynchus plotted on logarithmic scales. The
least squares regression of 10 postnatal females is,log W = 2.6642xlog L+log (8.403x I0- 5 )275:S:L:S:400
r = 0.93
The similar relationship of 13 fetuses of both sexes is,log W = 2.8772xlog L+log (2.432x 10-5 )
12.5:S:L:S: 144
r = 0.99
The gradients of these equations are not significantly different (T-test, P>0.3). Although a larger sample may provide evidence of significantly different
gradients for the fetal and postnatal stages, we consider that a single equation
fitted to fetal and postnatal individuals is more appropriate with the present sample size. This equation is,log W = 2.8873xlog L+log (2.377x 10-5 )
12.5:S:L:S:400
r = 0.85
This equation does not include postnatal males, which as adults develop a bulbous
melon larger than that of females (Yonekura, Matsui, and Kasuya, 1980). Yonekura et al (1980) described the changes in shape which occur in G. macrorhynchus
from a slender head with a pointed rostrum during early postnatal life to the moderately bulbous head of adult females or subadult males. This change does not
significantly affect the body length-body weight relationship mentioned above.
Therefore, we suspect that the above equation will approximately describe the bodylength-body weight relationship throughout life for both sexes and have accordingly used it in calculating the body weights shown in Table 6.

DISCUSSION

Our technique of determining the age of G. macrohynchus by counting dentinal and/or cemental growth layers in haematoxylin-stained longitudinal tooth sections proved
very satisfactory. We were able to age all 543 animals in our, sample using thisSci. Rep. Whales Res. Inst.,
No. 35, 1984

SHORT-FINNED PILOT WHALE

81

technique.
In contrast Perrin and Myrick (1980, p. 19) recommended that cemental
layers in G. macrorhynchus should be counted in transverse tooth sections. Even
though they appreciated that it was possible to lose the first cementa! layer using
this technique, Perrin and Myrick (1980) considered that transverse sections weresuperior to longitudinal sections because they were both easier to prepare and to
read.
However, our study indicates that, even when the position of the section was
carefully selected, more than one cemental layer (either the earliest or latest layers)
could be missed from the transverse section of a relatively old tooth (Plates I to
III). We consider that the cemental layers are easier to read in longitudinal sections. A wider range of tissue can be scanned in longitudinal sections thus enabling us to eliminate the accessory layers from the count. The variability of
repeated cementa! layer counts was similar to that of dentinal layers. The difficulty of preparation was minimal by using the method we have developed. In
addition, if transverse sections are used for counting dentinal layers, the count isoften difficult in older teeth in which secondary dentine is being deposited (Perrinand Myrick, 1980). However, using longitudinal sections enabled us to observe
whole pulp cavity and to choose the most readable portion of the tooth (Plates II
and III).
Our result indicated that the stainable growth layers in dentine was formedin spring to fall and unstainable dentine in winter to spring, although the time ofalternation of dentinal layers was not precisely defined. This seasonality of dentine
deposition in G. macrorhynchus coincides with that of Tursipos truncatus studied bySergeant (1959) and Pontopori blainvillei studied by Kasuya and Brownell (1979),
but differs from that of Stenella attenuata in the western North Pacific reported by
Kasuya (1976). The seasonality of deposition of haematoxylin stainable dentine
and/or correspondence of the stainability with optical density can be different between species.
Ogden, Lee and Conlogue (Ms.) listed body lengths of 46 male and I 08
female G. macrorhynchus stranded on the east coast of the North America. In males,
the highest body length frequencies were in the ranges 470 to 480 cm (three individuals) and 480 to 489 cm (three individuals). The largest male had a bodylength of 535 cm, while the next largest was 525 cm long. In females, the highest
body length frequency was in the 360 to 369 cm range (18 individuals). The
largest female was 397 cm long and the next largest 392 cm long. These figures
are identical to our results from central Japanese coastal waters. Alagarswami,
Bensam, Rajapandian and Fernando (1973) reported the body length frequencyof 77 whales in a mass stranding of 147 G. macrorhynchus in the Gulf of Manar on
the southeast coast of India. The identification of the species was based on theskull, teeth and flipper length. The body lengths ranged from 220 to 575 cm (sexwas not given). There were two modes in the length frequency, one at 375 to
425 cm, the other at 525 to 550 cm. We suspect that the smaller and larger modes
may correspond to the asymptotic lengths of females and males respectively. BeSci. Rep. Whales Res. Inst.,
No. 35, 1984

82

KASUYA AND MATSUI

cause these body lengths are larger than those of known G. macrorhynchus but almost
identical with those of G. melaena as reported by Sergeant (1962), we initially suspected that the method of measuring body length (not detailed in the report) differed from ours. However Alagarswami (pers. comm.) has since confirmed thatthe body lengths were measured on a straight line from the tip of upper jaw to thenotch of flukes. Thus there exists a possibility that the body length of G. macrorhynchus in the Indian Ocean may be intermediate between the two geographicalforms in the western North Pacific (see footnote on page 75 ).
Kasuya (1972, 1976) showed that the increase in body length in the first year
after birth is between 55 and 65% of neonatal length in several odontoceti i.e.,
Stenella coeruleoalba, 64%; S. attenuata, 60%; Tursiops truncatus, 55 % . Collet (1981)
obtained a corresponding value of 61.3% for Delphinus delphis. Thus the value weestimated for G. macrorhynchus, 61.2%, is in good agreement with the results forother species.
Perrin, Coe, and Zweifel (1976) found for several odontocetes the following
relationship between body length at birth (X, cm) and the difference between the
fetal growth rate during the linear phase and the average growth rate during an
initial postnatal period equal to the gestation period (Y, cm/month),log Y = -1.33+0.997 (log X)
Substituting the appropriate values for G. macrorhynchus (i.e., gestation time 452
days, neonatal length 139.5, and fetal growth rate in the linear phase 10.3 cm/
month (for values see Kasuya and Marsh, in press), the above equation predicts abody length of 197.4 cm, 452 days after birth. The corresponding figure, roughly
estimated from the growth curve (Fig. 12), is 228 cm.
Ralls, Brownell and Ballou (1980) concluded that males of polygynous
cetacean species will have larger body size and higher natural mortality rate compared with the females of the same species. The result of present study (males
growing 1.30 times larger than females and living 17 years shorter) and the polygynous social structure of the the species reported by Kasuya and Marsh (in press)
agree with their conclusion.
Sergeant (1962) obtained for G. melaena the following body length (L, cm)body weight (W, kg) relationship,
W=0.000025 L 2 •895
using fetuses and juveniles below 235 cm in body length. This relationship isalmost identical with the corresponding equation that we have obtained for G.
macrorhynchus.
ACKNOWLEDGEMENTS
We wish to extend our sincere thanks to all who helped in this study. The cooperation of the dolphin hunting teams at Taiji, Futo, Kawana and Arari made thework possible by allowing the senior author to examine whale carcasses, and to
Sci. Rep. Whales Res. Inst.,
No. 35, 1984

SHORT-FINNED PILOT WHALE

83

collect the necessary samples. The hunters also provided information on theschools which they had driven.
The Taiji Whale Museum provided laboratory facilities. Dr N. Miyazakicollected the body-length frequency data for one school. The field study was donewith the help of many biologists including Dr R. L. Brownell Jr., Dr S. Ohsumi,
Mr K. Kureha, Dr N. Miyazaki, Dr T. Otake, Ms E. Miyahara, Mr S. Shiraga,
Dr T. Kajihara, Dr K. Hirose and Dr S. Tanaka. Dr D. E. Sergeant kindly
cooperated in the cross-reading of several tooth slides of G. macrorhvnchus. We
thank Ms C. Goebel for her collaboration. This study was initially prepared for
the Report of the International Whaling Commission (special issue on cetacean
reproduction) as a part of a paper on the life history and reproduction of the species, but it had to be split by the financial difficulties. We wish to express ourthanks to the two anonymous referees and editor of the IWC volume for theirsuggestions and criticism. Dr H. Marsh critically read the manuscript and corrected the English. Their cooperation largely improved this paper.
The histology slides were prepared by Ms M. Oya. Ms T. Shirai, Ms M.
Nakagiri, Ms Y. Oka and Ms S. Wada assisted in data analyses, typing anddrawing.
REFERENCESALAGARSWAMI, K., P. BENSAM, M. E. RAJAPANDIAN and A. B. FERNANDO, 1973. Mass stranding of pilot
whales in the GulfofManar. Indian]. Fish. 20 (2): 269-279.
BREE, P.J.H. VAN, 1971. On Globicephala sieboldii Gray, 1846, and other species of pilot whale (notes on
Cetacea, Delphinoidea III). Beaufortia 19 (249): 79-87.
COLLET, A. S., 1981. Biology of the common dolphin Delphinus delphis L. in the NE Atlantic. Doctoral
thesis, Univ. Poitiers. 156 pp. (in French).
HoHN, A. A., 1980. Age determination and age related factors in the teeth of western North Atlantic bottlenose dolphins. Sci. Rep. Whales Res. Inst. 32: 39-66.
Hur, C. A., 1980. Variability of dentine deposits in Tursiops truncatus. Can J. Fish. Aquat. Sci. 37 (4): 712-

716.
KAsuvA, T., 1972. Growth and reproduction of Stenella caeruleoalba based on the age determination bymeans of dentinal growth layers. Sci. Rep. Whales Res. Inst. 24: 57-79.
KAsuvA, T., 1976. Reconsideration oflife history parameters of the spotted and striped dolphins based on
cementa! layers. Sci. Rep. Whales Res. Inst. (Tokyo) 28: 73-106.
KAsuvA, T., 1977. Age determination and growth of the Baird's beaked whale with a comment on the
feta! growth rate. Sci. Rep. Whales Res. Inst. 29: 1-20.
KAsuvA, T. and R. L. BROWNELL, jR., 1979. Age determination, reproduction, and growth of Franciscana
dolphin Pontoporia blainvillei. Sci. Rep. Whales Res. Inst. 31: 45-67.
KAsuvA, T. and H. MARSH (in press). Life history and reproductive biology of the short-finned pilot whale,
Globicephala macrorhynchus, off the Pacific coast of Japan. Rep. int. Whal. Commn. (Special Issue On Cetacean Reproduction)
KAsuvA, T., N. MIYAZAKI and W. F. DAWBIN, 1974. Growth and reproduction of Stenella attenuata in the
Pacific coast of Japan. Sci. Rep. Whales Res. Inst. 26: 157-226.
MARsH, H. and T. KAsuvA (in press). Changes in the ovaries of the short-finned pilot whale, Globicephalamacrorhynchus, with age and reproductive activity. Rep. int. Whal. Commn. (Special Issue On Cetacean
Reproduction).
OGDEN, J. A., K. E. LEE and G.J. CONLOGUE (Ms). Flipper development in Globicephala macrorhyncha I.
Sci. Rep. Whales Res. Inst.,

No. 35, 1984

84

KASUYA AND MATSUI

Growth of flippers. 22 pp.
PERRIN, W. F., CoE, J.M. and J. R. ZWEIFEL, 1976. Growth and reproduction of the spotted porpoise,
Stenella attenuata, in the offshore eastern tropical Pacific. Fish. Bull. 74 (2): 229-269.
PERRIN, W. F. and A. C. MYRICK, jR, (eds), 1980. Age determination of toothed whales and sirenians.
Rep. int. Whal. Commn. (special issue 3). 229 pp.
PousINI, J.M., 1980. A comparison of Globicephala macrorhyncha (Gray, 1946) with the pilot whale of theNorth Pacific Ocean: an analysis of the skull of the broad-rostrum pilot whales of the genus Globicephala.
Doctoral thesis Univ. Southern California. 299 pp'.
RALLS, K., R. L. BROWNELL jR andJ. BALLOU, 1980. Differential mortality by sex and age in mammals,with specific reference to the sperm whale. pp. 233-243. Jn: Sperm whales. Rep. int. Whal. Commn.
(special issue 2). 275 pp.
ScHEFFER V. B. and A. C. MYRICK,jR, 1980. A review of studies to 1970 of growth layers in the teeth ofmarine mammals. pp. 51--63. In: W. F. Perrin and A. C. Myrick (eds.) Age determination of
toothed whales and sirenians. Rep. int. Whal. Commn. (special issue 3). 229 pp.
SERGEANT, D. E., 1959. Age determination in odontocete whales from dentinal growth layers. Norsk
Hvaifangst-Tid. 48 (6): 273-288.
SERGEANT, D. E., 1962. The biology of the pilot or pothead whale, Globicephala melaena (Traill) in Newfoundland waters. Bull. Fish. Res. Bd Can. 132: 1--84.
YoNEKURA, M., S. MATSUI and T. KAsUYA, 1980. On the external characters of Globicephala macrorhynchus
off Taiji, Pacific coast of Japan. Sci. Rep. Whales Res. Inst. 32: 67-95.

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

APPENDIX TABLES""~>{:.. ~

~~

~~

"
~~

~

~

;,:,

~

19
20
21
22
23
24
25
26
27
28
29
30
31

18

12
13
14
15
16
17

11

n
0
1
2
3
4
5
6
7
8
9
10

Age

1

13 14 15 16 17 18 19 20 21l
l l l 4 2 l
1

l

3
2
1
l

2
3
2
1

1
1
2
1
l

1
1
3
l
l
1
l
1

1

1

1
l

1

1
1
1

l

1
1

2
4

l

22 23 24 25 26 27 28 29 30 31

Body length

1

1

1
1

3
1
1
1
2

1
2

1

2
1
2
3
1
1

3
3
3

2

3
1

2
1
1
2

1
2
4
1
1
1
4

2

1

1
3
1
4
3
1
7
5
2
3
1
3
2
1
1

3
1

4

1

4

1
4
4
2
2

2
2

1

1

1
3

1
2

3
4
1
1
4
4
2

1

2
1
2
1
3

4
5
5
4
1
1

6
4
15

11

11

1
1

1

1

2

1

1

1

9
4
5
12
5
9
8
13
10
6
10
9

11
11

3
8
7
9
5
3
2
8

11

32 33 34 35 36 37 38 39 40 No.

APPENDIX TABLE I. AGE-LENGTH KEY OF G. MACRORH'YNCHUS, FEMALE
Mean
185.45231.00245.50262.00264.00282.60294.33281.50317.50325.27332.81
343.33328.75340.22346.58350.00352.66345.00359.30354.10370.66355.60363.55369.00364.33363.00359.46363.81360.25367.20360.80366.50

S.D.

19.26
3.26
15.61
12.07
12.85
20.71
6.01
6.50
13.81
13.18
17.33
12.25
11.29
18.90
20.27
16.67
12.78
14.73
10.36
8.87
12.53
8.74
10.32
10.15
10.97
20.59
16.74
16.23
13.53
8.42
13.80
10.57

rJJ

rJJ

......

c:

~

tl

~

~

;;

c:

~
;i:..

en

00

N.

~~

<:)

;:;.

;;;-.

;->

"'
f;?

"""'1;;-

~""~
.....
~~

<.,,:::,,

Age: n:s;Age in years<n+ !. Body length: lOnsBody length in cmsl0n+9.
SD of this table=[I;(x-x)2/n]o.s

32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
1

1

1

1

1

1

1

1

3
2

1
1

3
2
1

1
2
2
1

1

1
1
1

1

4

1

1

1

1
1
4
3
2
3
3
1
1
1
1
2
3
2
2
2

1

1

1

1
1

1
1

1

1
1

2
2
1
3

2
1

2

1

1
1
1
1
1
2

1
1

1

1

1

8
3
8
8
7
6
8
2
4
4
5
7
5
5
4
6
2
1
3
1
3
0
0
4
0
1
0
0
0
0
2
369.00358.00373.25358.12373.66357 .12360.75365.00367.33367 .37348.50367.25369.75359.40363.85365.40371.40375.75356.83354.50373.00373.33355.00361.33

6.00

9.62

12.39

6.94

10.79
6.34
6.75
10. 75
10.92
11. 79
13.04
12.50
15.78
10.70
11. 72
11.30
9.62
8.21
13.32
6.84
0.50

::r:

~

-..J

trl

>
t""

~

>-l

0

"O
,.....
t""

t1

zz
l"'.I

>rj
,.....

~

0

rJl

88

KASUYA AND MATSUIAPPENDIX TABLE 2.

AGE-LENGTH

Age

Body

n

13 14 15 16 17 18 19 20 21

02

22 23 24 25 26 27 28 29 30 31 32 33 34

2
2

2

2

3

2

3

4
5
6
7
8
9
10
11

2

3
2

3
2
3

2
2

12
13
14
15
16
17
18
19
20
21
22

23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
Age: n:=:;;Age in years<n+ I.

Body length: lOn:=:;;Body length in cm:=:;; 10n+9.

SD of this table=[~ (x-Sci. Rep. Whales Res. Inst.,
No. 35, 1984

SHORT-FINNED PILOT WHALE

89

KEY OF G. MACRORHTNCHUS, MALE
length35 36 37 38 39 40 41

42 43 44 45 46 47 48 49 50 51

52

I
3
4
4

I
2
2

2

2
2
3

2

2

2
I

2
2

2
2
2
2
2

2

No.

Mean

S.D.

8
3
5
6
I
7
2
7
5
7
8
6
2
7
6
6
6
6
7

161.62229.00258.00265.50271. 00
296.00294.00314.28328.00337.42339.37366.50379.50393. 14406.50420.00417.16451. 33
430.00519.00455.80447.75452.75468.33456.20490.50474.50473.60522.50470.80463.50427.00488.50470.00489.00

26.31
8.52
12.29
8.51

5
8
4
3
5
2
2
5
2
5
4
2
2
4
0
I
0
I
2
2
0
0
2

x)z 1o.5.

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

20.06
13.00
14.52
8.85
10.67
15.91
I I. 91
1.50
15. 18
16.89
19.85
25.85
31 .95
25.16
37.64
25.66
28.64
10.20
12.79
0.50
15.50
19.94
2.50
8.54
41 .65
15.50
3.00
18.31

477.00509.00448.50448.00474.50478.00447.00

10.50
16.50

16.00

90

KASUYA AND MATSUIEXPLANATION OF PLATESPLATE IAll scale bars represent 0.1 mm.
FIG. I. Decalcified and haematoxylin-stained section from a newborn female G.
macrorhynchus (No. 17-46, 163 cm, 0.25-year old, tooth length 22 mm). N indicates the neonatal line in the dentine, and 2 and 3 the positions enlarged in Figs 2
and 3 (this plate) respectively.
Fig. 2. Higher magnification of position 2 in Fig. I (this plate). Arrow indicatesneonatal line in dentine, and E, cast of dissolved enamel.
Fig. 3. Higher magnification of the position 3 in Fig. I (this plate). Arrow andcircle indicate a stainable cementa! layer (annual layer).
Fig. 4. Decalcified and stained tooth section of an immature male G. macrorhynchus(No. 9-73, 326 cm, 5.25 years old with five annual stainable layers of full thickness and 6th (last) stainable layer of incomplete thickness (circles), tooth length
38.4 mm). N indicates the neonatal line, and 5 through 7 the positions enlarged
in Figs 5 through 7 of this plate.
Fig. 5. Higher magnification of position 5 in Fig. 4 (this plate), showing cementa!
growth layers near the neck of the tooth. Circles and arrow indicate lst to 4th
annual stainable layers.
Fig. 6. Cementa! layers at position 6 in Fig. 4 (this plate). The 2nd to 5th annual
stainable layers are indicated by circles.
Fig. 7. Cementa! layer at position 7 in Fig. 4 (this plate). Circles indicate the 3rd
to 6th annual stainable layers.
PLATE IIAll scale bars represent 0.1 mm.
Decalcified and haematoxylin-stained tooth section from a lactating female
G. macrorhynchus (No. 24-22, 366 cm, 27.5-years old, tooth length 42.8 mm). Dentine is still being deposited along the entire pulp cavity wall. C indicates cementum, E cast of dissolved enamel, N neonatal line in dentine, and the numerals the
positions enlarged in Figs 2 through 4 of this plate. The dots indicate the annual
stainable layers in dentine.
Fig. 2. Higher magnification of position 2 in Fig. I (this plate). Annual growthlayers are clearer in ordinary dentine (circles) than in secondary dentine. P indicates predentine.
Fig. 3. Higher magnification of position 3 in Fig. I of this plate. Anm1al growthlayers are clear in secondary dentine (circles). P indicates predentine.
Fig. 4. Cementa! layers at position 4 in Fig. I (this plate). Dots indicate lst to
28th annual cementa! layers.
Fig. 5. Cementa! layers at position 5 in Fig. 6. (this plate). Dots indicate 2nd to
36th annual cementa! layers.
Fig. 6. Decalcified and stained section of a tooth from a resting female G. macrorhynchus (No. 17-36, 35.5-years old, tooth length 39.5 mm). Deposition of dentine
is about to cease. C indicates cementum, E cast of decalcified enamel, N neonatalline, 5 the position shown in Fig. 5 of this plate.
Fig. I.

PLATE IIIAll scale bars represent 0.1 mm,
Fig. I. Higher magnification of pulp of the tooth in PLATE II Fig. 6. P indicates
predentine. Deposition of dentine is limited to this portion of the pulp wall.
Sci. Rep. Whales Res. Inst.,

No. 35, 1984

SHORT-FINNED PILOT WHALE
Fig. 2. Cementa! layers at position 2 in Fig. 7 (this plate). Dots indicate lst to
Sith annual growth layers.
Fig. 3. Top of the pulp cavity of tooth in Fig. 7 (this plate). A strongly-stainableuniform thin layer of dentine (S) indicates the cessation of dentine deposition
along most of the wall of the pulp cavity, but thin predentine (P) is still visible atthe top and an irregular thin unreadable layer of" cellular dentine" (C) is being
deposited. Formation of the cellular dentine has started secondarily on the pulp
wall.
Fig. 4. Middle portion of the pulp of tooth in Fig. 7 (this plate). The last two
dentinal layers merge in the pulp wall cavity which is covered by thin stronglystainable uniform dentine (S). Secondary deposition of" cellular dentine" (C)is also visible.
Fig. 5. Base of the pulp cavity of tooth in Fig. 7 (this plate). The last readable
dentinal growth layer was deposited as indicated by the arrow. " Cellular dentine " ( C) is still being deposited.
Fig. 6. Higher magnification of position 6 in Fig. 7 (this plate). Thick " cellulardentine " is being deposited.
Fig. 7. Decalcified and stained section of a tooth of a lactating female G. macrorhynchus (No. 24-14, 382 cm, 50.5-years old, tooth length 38.3 mm). There are 39
annual stainable layers in the dentine and 51 in the cementum. C indicates
cementum, E cast of dissolved enamel, N neonatal line in dentine, and 2 and 6 thepositions shown in Figs 2 and 6 of this plate respectively.

Sci. Rep. Whales Res. Inst.,

No. 35, 1984

91

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