PERIN ATAL GROWTH OF DELPHINOIDS:INFORMATION FROM AQUARIUM REARED
BOTTLENOSE DOLPHINS AND FINLESS PORPOISESTOSHIO KASUYA*, TERVO TOBAYAMA**,
TAKESHI SAIGA*** AND TERVO KATAOKA****
ABSTRACTThe early postnatal growth ofbottlenose dolphins and finless porpoises
was studied using 97 body length records of 61 individuals born inaquariums. The growth rates observed were similar to those estimatedindependently for wild dolphins assuming that dentinal growth layers aredeposited annually. The perinatal growth parameters thus estimated werealso close to those predicted using published interspecific relationships.
These results suggest that (1) the dentinal growth layers are depositedannually in these species and (2) the interspecific relationships of theparameters can be used to examine the correctness of growth layerinterpretation.

INTRODUCTION

Although some studies use daily or monthly growth layers in tooth (Kasuya,
1977; Myrick, 1980; Myrick, Shallenberger, Kang and Mackay, 1984), mostodontocete age determination studies are based on annual growth layers in
dentine or cementum (Perrin and Myrick, 1980). This approach limits theprecision of individual age estimates, and makes it difficult to study the rapid
perinatal growth of dolphins, an important component of their reproductive
biology.
Some authors attempted to overcome this problem by defining theinterspecific relationship between the growth parameters of better known
species. Scott ( 1949) and Ohsumi ( 1966) tried to estimate neonatal body lengthfrom the size of adult whales. Perrin, Holts and Miller ( 1977) and Kasuya( 1977) defined relationships between neonatal length and gestation time or
between neonatal length and fetal growth rate. Perrin, Coe and Zweifel (1976)
tried to estimate the early postnatal growth rate of dolphins using gestation* Far Seas Fisheries Research Laboratory, 5-7-1 Orido, Shimizu-ski, Shizuoka-ken, 424 Japan** Kamogawa Sea World, 1464-18 Higashi-machi, Kamogawa-shi, Chiba-ken, 296 Japan.
*** Taiji Whale Museum, Taiji, Higashimuro-gun, Wakayama-ken, 649-51 Japan.
**** Toba Aquarium, 3-3-6 Toba, Toba-shi, Mie-ken, 517 Japan.
Sci. Rep. Whales Res. Inst.,
No. 37, 1986, 85-97

86

KASUYA, TOBAYAMA, SAIGA AND KATAOKA

time and neonatal length. Kasuya (1972), Collet (1981) and Kasuya and Matsui( 1984) deduced that delphinoid calves grow about 60 % of the neonatal bodylength in the first year after birth. However, some of these studies were notfree from the age determination problem mentioned above, because growthlayer readings were used in the analyses as well as data from known age
individuals.
There is still also considerable disagreement concerning the interpretationof growth layers of some toothed whales (Perrin and Myrick, 1980; Jones,
Kasuya, Gosho and Miyazaki, 1985). This problem will be solved throughexamination of growth layers of known age individuals or by comparing
growth layer deposition in aquarium-reared individuals and wild individuals
assuming that growth does not differ significantly between these two groups
at least for the age classes being compared.
In this study, we use data from the bottlenose dolphin, Tursiops truncatus(Montagu, 1821), and the finless porpoise, Neophocaena phocaenoides (G. Cuvier,1829), to compare the early postnatal growth of aquarium-reared individuals
with that of wild individuals estimated from dentinal growth layer counts
assuming an annual deposition rate. We then evaluated published interspecificrelationships between the growth parameters as a means of calibrating growth.
layer readings.
MATERIALS AND METHODS

Body length data of known age individuals were available for 55 bottlenose
dolphins and 6 finless porpoises born in aquariums (Tables 1 to 3). Althoughmost body lengths were measured at death, live measurements were obtained
from three bottlenose dolphins and two finless porpoises over period of up to
4.7 years. We did not distinguish between deaths due to accident and disease,assuming that the effect of disease might be smaller on body length than on
body weight. Parents of these aquarium-reared bottlenose dolphins wereobtained from the catch of the drive fishery off the Pacific coast of Japan, andthose of the finless porpoise from the intended or incidental take in the Ise Bay
or in the Inland Sea (Kasuya, Tobayama and Matsui, 1984). No teeth fromthe individuals born in aquariums were examined.
Body length frequencies of bottlenose dolphins taken off the Pacific coastof Japan (the same stock as the parents of the aquarium-reared materials)
were also available, as well as body lengths and dentinal growth layer counts
from bottlenose dolphins from the Iki Island area, which is located in the
Tsushima Pass connecting the Sea of Japan and the East China Sea. Although
there is no basis for our assumption that these two samples belong to thesame population, no significant differences of the body length frequencies, orin the body length at sexual maturity were detected i.e. 50 % of the females
off the Pacific coast of Ja pan were sexually mature at a body length of between
265 and 275 cm (presumably close to the former figure, Fig. 1), while theSci. Rep. Whales Res. Inst.,

No. 37, 1986

87

EARLY GROWTH OF DELPHINOIDSTABLE 1. POSTNATAL GROWTH OF MALE TURSIOPS TRUNCATUS
Sample
No.
I
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24

Days
after
birth
0
0
0
0
0
0
0
0
3
4
9
11
21
63
147
154
189
212
1164
297
654
782
1418
242*
299*
362*
422*
472*
513*
569*
595*
620*
813*
859*
953*
959*
1219*
1619*
1655*

Birth

Data

yr mo dayyr mo day'73. 2. 6'76. 6.16'76. 7.30'77. 8.12'84. 6.10'78. 6.14'81. 7.25'77. 7. 5'81. 7.14'84. 6. 3'75. 7.19'80. 7. 4'82. 9.26'78.10.17'75. 7.15'77. 6.22'73. 2. 6.
'76. 6.16'76. 7.30'77. 8.12'84. 6.10'78. 6.14'81. 7.25'77. 7. 5'81. 7.17'84. 6. 7'75. 7.28'80. 7.15'82.10.17'78.12.19'75.12. 9'77.11.24'76. 8.17'79. 2.22'77. 3.17'82. 5. l'78. 7. 2'80. 7.16*: measured while alive.

Sci. Rep. Whales Res. Inst.,
No. 37, 1986

'77. 8.17'76. 9. 9'81. 7. 6'77. 5. 9'77. 7. 5'77. 9. 6'78.11. 5'77.12.25'78. 2. 4'78. 4. I'78. 4.27'78. 5.22'78.12. I'79. 1.16'79. 4.20'79. 4.26'80. 1.11'81. 2.14'81. 3.22

Body
length(cm)

Bodyweight
(kg)

140.0
126.0
126.0
132.0
116.0
125.0
122.0
134.0
133.0
132.0
139.0
127.0
136.0
149.0
181.0
165.0
183.0
197.5
254.0
197.0
246.0
221.0
263.0
188.0
208.0
220.0
224.0
223.0
228.0
230.0
230.0
234.0
245.0

29.0

244.0
250.0
248.0
265.0

30.0
23.0

47.0
77.0

126.0
136.0
161.0
156.0

156.0
178.0
191.0
190.0
190.0
197.0
224.0

Remarks
Taiji, StillbirthTaiji, StillbirthTaiji, StillbirthTaiji, Stillbirth
Chita, Unknown sex
Mito, Unknown sex
Taiji
Misaki
Taiji
Taiji
Taiji, Unknown sex
Taiji
Taiji
Kamogawa
Taiji
Taiji
Honda (1979)
Awashima
Enoshima
Honda ( 1979)
ShimodaHonda (1979)
Taiji
Kamogawa

88

KASUYA, TOBAYAMA, SAIGA AND KATAOKATABLE 2. POSTNATAL GROWTH OF FEMALE TURSJOPS TRUNCATUS

Sample
No.
l

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

Days
after
birth
0
0
0
0

9
10
32
35
37
118
194
201
247
262
275
370
398
410
578
627
808
1,032
1,151
1,345
1,466
1,729
1,742
354*
404*
467*
510*
567*
724*
835*
944*
955*
986*
1,081 *
1,157*
1,182*

Birth

Data

yrmo dayyr moday'72. 6.19.
'72. 7. 2.
'77. 7.20.
'77. 6. I.
'79. 8. 2.
'81. 7.28.
'79. 8.30.
'76. 6.21.
'76. 6.29.
'71.10.30.
'71. 6.16.
'76. I. 4.

'72. 6.19.
'72. 7. 2.
'72. 7.20.
'77. 6. I.
'79. 8. 3.
'81. 7.29.
'79. 9. 8.
'76. 7. I.
'76. 7.31.
'71.12. 4.
'71. 7.23.
'76. 5. I.

'79. 7.26.

'80. 2.13.

'80. 9.17.
'74.11. I.

'81. 6.19.
'75.11. 6.

'77. 5.20.
'82. 8.13.
'75. 7.18.
'78. 7. 6.
'81. 7. 5.

'79. 2. 6.
'84.10.29.
'78. 5.15.
'82. 3.20.
'85. 3.10.

'79. 7.28.

'79. 7.17.
'80. 9. 4.
'80.11. 6.
'80.12.19.
'81. 2.14.
'81. 7.21.
'81.11. 9.
'82. 2.26.
'82. 3. 9.
'82. 4. 9.
'82. 7.13.
'82. 9.27.
'82.10.22.

Body
length(cm)

Bodyweight
(kg)

120.0
140.0
128.0
115.0
118.7
121.0
132.0
130.0
144.0
139.0
145.0
165.6
179.5
194.0
193.0
193.0
200.0
226.0
204.0
200.0
235.0
200.0
252.0
238.0
258.0
262.0
279.0
265.0
259.0
200.0
202.0
228.0
218.0
218.0
228.0
233.0
238.0
239.0
240.0
238.0
239.0
238.5

19.0
30.0

25.0
30.0
35.2
44.0
68.2

185.0

200.0

Remarks
Taiji, StillbirthTaiji, StillbirthTaiji, Stillbirth
Misaki
ShimodaShimodaAwashima
Taiji
Taiji
Taiji
Taiji
ShimodaHonda (1979)
Taiji
Honda (1979)
Honda (1979)
Awashima
Awashima
Honda (1979)
Honda (1979)
Honda (1979)
ShimodaTaiji
Awashima
Shimoda
Taiji
Honda ( 1979)
Honda ( 1979)
Honda ( 1979)
Kamogawa

150.0
160.0
150.0
155.0
140.0
130.0
130.0
(Continued)
Sci. Rep. Whales Res. Inst.,
No. 37, 1986

89

EARLY GROWTH OF DELPHINOIDSTABLE 2. (Continued)
31

635*
833*
865*
1,026*
1,231*
1,237*
1,257*
1,332*
1,357*
1,569*'79. 6.28.

'81. 3.24.
'81.10. 8.
'SI.II. 9.
'82. 4.19.
'82.11. IO.
'82.11.16.
'82.12. 6.
'83. 2.19.
'83. 3.16.
'83.11. 6.

236.0
253.0
261.0
271.0
260.0
264.0
265.0

Kamogawa
170.0
180.0
210.0
230.0
225.0
215.0
225.0
220.0
245.0

*· measured while alive.
TABLE 3. POSTNATAL GROWTH OF NEOPHOCAENA PHOCAENOIDES
Sample
No.

Days
after
birth

Birth

Data

yr mo day

I
2
3
4
5
6

O*
4
17
28
1,719**
864**'84.4.16'77.5. 9.
'76.4.17.
'81.4.21.
'79.5. I.
'82.4.20.

*: stillbirth,yr mo dayBody
length(cm)

Bodyweight(kg)'84.4.16.
'77.5.13.
'76.5. 3.
'81.5.19.
'84.1.14.
'84.8.31.

77.5
79.0
81.5
83.0
159.5
153.5

6.6
7.4
7.2

39.5

Remarks
Yashima, Male
Toba,
Male
Toba,
FemaleMiyajima, Female
Male
Toba,
Toba,
Male

**: measured while alive.

corresponding figure for the Iki Island sample was 267 cm (Kasuya, 1985).
Body lengths and estimated ages of finless porpoises from the Inland Sea
were also used.
The ages of these individuals were estimated from dentinal growth layercounts in decalcified and haematoxylin-stained sections as outlined in Kasuya
and Matsui (1984). Growth layer readings were done without biological data.
BOTTLENOSE DOLPHIN

Gestation time and neonatal length
Body lengths of neonatal bottlenose dolphins (measured within 11 daysof birth) ranged from 116 to 140 cm. No differences were detected between
the length of stillborn dolphins, those that died within two days and those thatdied on the third to eleventh days. No differences in neonatal body length was
detected between the sexes in the present small sample. Combining the data.
from these 20 neonates, an average of 128 cm was estimated as the mean
neonatal length for this species off the Pacific coast of Japan (Table 4).
Scott (1949) found for both mysticeti and odontoceti the following linear
relationship between the maximum body length of adult (among both sexes,
Sci. Rep. Whales Res. Inst.,
No. 37, 1986

90

KASUYA, TOBAYAMA, SAIGA AND KATAOKA

20

Males

10
I/)

11:1

:J

"O

0

>
"O

.£
0

ci

30

20

z

10

150

200

250

300

Body length in cm
Fig. 1. Body length frequencies of the catch of bottlenose dolphins in the drive
fishery off the Pacific coast of Japan (173 males and 165 females sampled from 8
schools driven during 1973 to 1983, represented by the histogram). The parents of
the aquarium-reared individuals in the present study were taken by the same fishery.
This body length frequency is similar to that of 190 males and 255 females sampledfrom 6 drivings in the period from 1979 to 1980 in the Iki Island area (indicatedby numerals at the top). In the female samples from the Pacific, dotted areas
represents sexually immature individuals and shaded areas mature individuals(male maturity was not determined).

X in cm) and the neonatal body length (Y in cm):
Y = 0.2441X + 44.3
Equation 1
Of 165 female and 173 male bottlenose dolphins taken off the Pacific coastof Japan and measured by Kasuya, the largest individual was a male of 328 cm
and the next largest 325 cm. The former figure and the above equationsuggest a neonatal length of 124.4 cm, which is only 3 % smaller than the
figure estimated from the neonates in our sample.
Using data from Physeter, Berardius, Delphinapterus, Phocoena and several
species of Delphinidae, Ohsumi ( 1966) suggested the following relationshipbetween mean neonatal body length (Y in m) and mean body length offemales at the attainment of sexual maturity (X in m):
Y = 0.532X0 ·916
Equation 2
The Iki Island sample suggests 2.67 m as the body length at which 50 % offemales are sexually mature. Using this figure and Equation 2, the mean
neonatal length of bottlenose dolphins is estimated as 1.31m(~asuya,1985).
This is 2 % larger than the estimate obtained above.
The good agreement between observed and predicted neonatal body
Sci. Rep. Whales Res. Inst.,

No. 37, 1986

91

EARLY GROWTH OF DELPHINOIDSTABLE 4. ESTIMATION OF NEONATAL BODY LENGTH OF TURSIOPS TRUNCATUS (cm)Length of
postnatal life

Male

FemaleMean

Stillbirth

126.0
126.0
132.0
140.0

120.0
128.0
140.0

130.3

After 0 to 2 days

116.0*
122.0
125.0**
134.0

115.0
118.7
121.0

121.7

After 3 to 11 days

127.0
132.0
133.0
139.0

130.0
132.0

132.2

Mean

129.3

125.6

127.8

*: living on 204th day after birth,**: Jiving on 2364th day after birth.

lengths is probably, in part, due to the fact that Equations 1 and 2 were basedon sample sets that include Tursiops.
Substituting a neonatal length 128 cm (as estimated above) in the equationof Perrin et al. ( 1977) which describes the relationship between gestation time
(Y months) and neonatal length (X cm) for five stocks of Delphinidae:
logY = 0.4586 logX + 0.1659
Equation 3
gives a predicted gestation time of 13.6 months, slightly longer than one year
(Odell, 1975) estimated for the Atlantic bottlenose dolphin which has a neonatal
length about 10 cm smaller than Japanese coastal population (Nakajima,
Takahashi, Ogura and Sawaura, 1963; Hohn, 1980). However, there is no
reason at present to conclude that the gestation time of the Japanese population
is longer than that of the Atlantic, because above Equation 3 describes theinterspecific relationship between these parameter in several delphinoid
species rather than the relationship among several populations of a single
species.
Kasuya ( 1977) suggested the following relationship between neonatal
length (X in cm) and the daily fetal growth rate for the linear part of the fetal
growth phase (Y cm/day) for several species of Delphinidae, Phocoena andDelphinapterus:
Y = 0.001462 X + 0.1622
Equation 4This equation and the neonatal length 128 cm calculated from neonates givea fetal growth rate as 0.3493 cm/day or 10.63 cm/month for T. truncatus.
Sci. Rep. Whales Res. Inst.,
No. 37, 1986

",:
I'
'

92

KASUYA, TOBAYAMA, SAIGA AND KATAOKA
270
2.0

250
19

230
23

210

u

24

150

rt!

rtl

c

130

1.0 ~

c
.s:. 110

OI

c

c

0

270

Cl>

Cl>

>-

"O
0

cc

g'

~

170

E

.c

1.5

190

2.0 .:::

Females

250

rtl

230

...

210

.c

Cl>

OI

190

1.5

10

Cl>

25

170

c

>-

"O

0
Ill

150
130

1.0

110
0

300

600

900

1200

500

Age in days
Fig. 2. Bottlenose dolphin body lengths plotted on age. Each independent closed
circle represents one aquarium-reared individuals; those connected by solid lines
represent repeated measurements of one individual. The diamonds and verticallines represent the mean body lengths ± 2SD plotted against ages estimated fromdentinal growth layer counts (wild individuals taken off Iki Island, for their bodylength composition see Fig. 1). The numerals indicate the number of individuals
whose ages have been estimated. Ages between n and n + I years were expressed as
n+0.5 years (n being integer). The thin solid lines represent extraporation of thelinear part of the feta! growth curve through the mean neonatal length (128 cm).
Left scale indicates body length in cm and the right scale body length relative tomean neonatal length.

Early postnatal growth
Individual body lengths of aquarium reared individuals and the mean
body length of the species from Iki Island area are plotted against age in Fig. 2.
The agreement between the two data sets is good, suggesting that (I) thegrowth in a given range is similar between wild and aquarium-reared
individuals and (2) deposition of dentinal growth layers is annual as shown for
the Atlantic stock of the species using aquarium reared specimen (Sergeant,Caldwell and Caldwell, 1973).
Sci. Rep. Whales Res. Inst.,
No. 37, 1986

EARLY GROWTH OF DELPHINOIDS93

The rate ,~increase in neonatal body length decreased with increasing
age, and except for some individuals less than 40 days old, the data for mostneonates came below the line of the mean fetal growth curve extended
through the mean neonatal length. Furthermore, the size of individuals older
than 200 days significantly diverged from the line (Fig. 2). These data suggestthat the growth rate of postnatal individuals never exceeds that of a fetus
during the linear part of its growth.
The mean body length of the present sample of aquarium-reared calvesat one year of age falls within the range of 200-220 cm or 1.56-1. 72 times
the mean neonatal length (Fig. 2). This is in good agreement with the rangeof 1.55-1.64 times found for five species of Delphinidae (discussed by Kasuya
and Matsui, 1984). Perrin et al. ( 1976) deduced, using data of Physeter, Phocoena,
Delphinapterus, Globicephala and Stenella, the following relationship between
mean fetal growth rate (X in cm/month), mean postnatal growth rate during
the period equivalent to the length of gestation (Yin cm/month) and neonatal
length (Z in cm):log(X-Y) = -1.33 + 0.997 logZ
Equation 5
Using this equation, a mean fetal growth rate of X = 128/12 or 128/13.6 anda mean neonatal length (Z = 128), suggests a mean body length of 184.6 cm
at age 12 months or 192.0 cm at 13.6 months. These predic~ed values areabout 10 % smaller than the observed figure and come below the range ofindividual variation (Fig. 2).
Sexual maturity
A male that lived for 1,655 days (4.5 years) in captivity had left and righttestis weighing 15.0 and 14.0 g, respectively. It showed no behavioral signs ofpuberty, and was considered as sexually immature based on the similarity of
its testis weight to those of the immature Atlantic bottlenose dolphin (Harrison,
Brownell and Boice, 1972).
The oldest female in the present material lived for 1,182 days (3.2 years)
and attained a body length of 238.5 cm, smaller than the smallest sexuallymature wild individuals (Fig. 1). There were no corpora in the ovaries. In the
Iki Island area, the youngest mature and oldest immature females appeared
at ages of 3.5 and 8.5 growth layer cycles (years), respectively (60 individuals
in the age range). This material suggested that 50 % of the females were
sexually mature at an age of 7 years (Kasuya, unpublished).
FINLESS PORPOISE

Gestation time and neonatal length
Kasuya and Kureha (1979) listed 14Japanese records of neonates of thisspecies with body length ranging from 68.8 to 97 .6 cm (x = 78.6 cm). Theirages at death were usually unknown. The lengths of four known age neonates
Sci. Rep. Whales Res. Inst.,
No. 37, 1986

94

KASUYA, TOBAYAMA, SAIGA AND KATAOKA

I

150

c

-

....

Ol

c:
Cl.I

-....

I

130

LI

4

"'

4

"'

I

£.

O'I

.c.

I
I
I
I
I

E
u

2.0

•

IO

1.5

IO

c:

0

Cl.I

~

c:
.c.
.....

>-

c:

c

110

Ol

'tJ
0

m

Cl.I

90

:;...

1.0

"O

0

Ill

70
300

600

900

1100

1800

Age in days
Fig. 3. Body lengths of known-age individual finless porpoises plotted against age(closed circles) and body length of fishery-caught individuals plotted against ages
estimated from dentinal growth layer counts (triangles). The ages of the latter were
estimated to nearest 1/4 year for animals 1 year or younger and to the nearest
n+0.5 years for individuals between n and n+ 1 years (n being integer, n ~ 1). The
thin solid line indicates the linear part of the feta! growth curve extraporated
through the mean neonatal length (80 cm). Left scale indicates body length in cm
and right scale body length relative to mean neonatal length.

(some of which were listed in Kasuya and Kureha (1979)) are now available.
They range between 77.5 and 83.0 cm (died within 28 days) (x = 80.0 cm)(Table 3 and Fig. 3).
Although this sample size is small, the largest individuals available to us
were 187 cm (out of seven adult or subadult males) and 164 cm (out of sevenadult females). The neonatal body lengths predicted using Equation 1 andeither of the above adult sizes, 89.9 or 84.3 cm, seem to be overestimates. Thisequation may not give reliable prediction for small species such as the finless
porpoise. There are no data on the mean body lengths of finless porpoise at
the attainment of sexual maturity to use in Equation 2. Therefore we decided
to use the mean of the four neonates of known age (80.0 cm) as the mean
neonatal length of the finless porpoise in Japanese coastal waters.
The Equation 3 and the above neonatal length suggest a gestation timeof 10.9 months. Assuming an error of ±5 cm in this neonatal length estimate,
the resultant range in the gestation period is 10.6 to 11.2 months. The error
in our estimate of neonatal length has only a negligible effect on the gestation
period of small delphinoids calculated using Equation 3.
Using Equation 4, the growth rate at the linear part of fetal growth was
Sci. R~p. Whales Res. Inst.,
No. 37, 1986

EARLY GROWTH OF DELPHINOIDS

95

estimated using a neonatal length of 80 cm as 0.279 cm/day or 8.49 cm/month.
Early postnatal growth
In Fig. 3 the body lengths of both known age aquarium-reared and wild
finless porpoise (which ages have been estimated from dentinal layer count)are plotted against age. All the values for wild individuals fall between thoseof aquarium-reared individuals suggesting that the dentinal growth layers aredeposited annually. All the values are far below the extended fetal growth
curve suggesting that the decline in the neonatal growth rate after birth isfaster in this smaller species than in the bottlenose dolphin.
Assuming that growth layers are deposited annually the mean bodylength at one year of age is estimated between 120 and 130 cm or 1.50-1.63
times the neonatal length (Fig. 3). This fits the general rule deduced by Kasuya
and Matsui (1984) for delphinoids. The mean neonatal length, 80 cm, andEquation 5 suggest a body length at an age equivalent to the gestation period(about 11 months) as 116. l cm with a range of 113-126 cm due to theuncertainty about the neonatal length estimate. Although the agreement ispossibly better in this smaller finless porpoise than in the bottlenose dolphin,the calculated figure is still smaller than the corresponding figure directly
estimated from age determined from dentinal growth layer counts (Fig. 3).
Sexual maturity
Of two individuals still living in the Toba Aquarium, a male whichmeasured 153.5 cm at 2.4 years of age (No. 6 in Table 3) shows no behavioral
sign of sexual maturity. Another 4.7-years-old 159.5 cm long male (No. 5)
often indulged in sexual play with his mother (but not with other adult females
in the tank). His penis was erect but no intromission was confirmed. We regard
the maturity of this male as questionable.
Among the six males over 140 cm caught in the wild, four had sperm intheir epididymides (body lengths 144, 148, 157 and 187 cm), but two (bodylength 155 and 165 cm) had no sperm (Kasuya, unpublished). Of nine females
taken in the wild, eight individuals measuring between 141 and 164 cm inbody length were sexually mature. One immature female was 118 cm long.
These are not inconsistent with our observations of aquarium specimens.
DISCUSSION

Our analyses show that the bottlenose dolphin and possibly the finless porpoise
have annual cycles of dentine deposition usable for age determination. The
growth of the aquarium-reared individuals was, a~ least in their early postnatal
stage, similar to that of the naturally grown individuals. This allows a detailed
analysis of early postnatal growth which was not possible based on age
determination using annual growth layer counts from wild individuals.
This study showed that the early post natal growth of bottlenose dolphinsSci. Rep. Whales Res. Inst.,
No. 37, 1986

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KASUYA, TOBAYAMA, SAIGA AND KATAOKA

and finless porpoises follows the established pattern for Delphinoidea andindeed for Odontocetes in general. Some unknown growth parameters ofthese species can be predicted with various degrees of precision using published.
equations describing the interspecific relationship of these parameters. The
use of these equations enhance our ability to interpret dentinal growth layers
deposited in the early postnatal stage. Such layers are often difficult to interpretcorrectly without data from known age individuals.
The recommended procedure is firstly to examine if the age determination
technique for the species being examined suggests an average increase of 55
to 70 % of the neonatal length in the first year after birth. If the neonatal
length is not available, it can be estimated from the adult size, preferablyusing the mean body length of females at the attainment of sexual maturity.
The technique of age determination should be questioned if the resultant
estimate of postnatal growth exceeds the growth rate of the fetus during thelinear part of the fetal growth stage as estimated using Equations 4 and 5.
ACKNOWLEDGEMENTS

We wish to express our sincere thanks to the following aquariums for providing
records of dolphins born in captivity: Awashima Aquarium, Chita Beachland,
Mito Sea Paradise, Misaki Sea Aquarium, Miyajima Aquarium, Shimada Sea
Aquarium and Yashima Aquarium. Dr H. Marsh of James Cook University
kindly repeated checking the draft and corrected English. Dr S. Ohsumi of
the Far Seas Fisheries Research Laboratory critically read the manuscript. Mrs
K. Yano, S. Toba and Y. Yamamoto helped with data analysis, typing anddrawings.
REFERENCES
COLLET, A.S., 1981. Biology of the common dolphin Delphinus delphis L. in the NE Atlantic. Doctoral thesis,
Univ. Poitiers, 156pp. (in French).
HARRISON, R.J., R.L. BROWNELLJR, and R.C. BOICE, 1972. Reproduction and gonadal appearances in someodontocetes. pp.361-429. In: R.J. Harrison (ed.) Functional anatomy of marine mammals vol. 1.
Academic Press, London and New York. 45lpp.
HOHN, 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.
HONDA, M., 1979. Breeding the bottle-nosed dolphin, Tursiops truncatus, at Enoshima Aquarium Marineland.
]. Jap. Assoc. Zool. Gardens and Aquariums, 21 (1): 4-9. (in Japanese).
JoNES, L., T. KASUYA, M. GosHo, and N. MIYAZAKI, 1985. Variability by readers and method of preparation
in Dall's porpoise age determination. INPFC Document No. 2878. 19p.
KASUYA, T., 1972. Growth and reproduction of Stenella caeruleoalba based on age determination by meansof dentinal growth layers. Sci. Rep. Whales Res. Inst., 24: 57-79.
KASUYA, 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.
KASUYA, T., 1985. Fishery-dolphin conflict in the Iki Island area of Japan. pp.253-272. In: R.J. H. Beverton(ed.) Marine mammals and fisheries. Academic Press, London and New York. 354pp.

Sci. Rep. Whales Res. Inst.,
No. 37, 1986

EARLY GROWTH OF DELPHINOIDS

97

KASUYA, T. and K. KUREHA, 1979. The population offinless porpoise in the Inland Sea of Japan. Sci. Rep.
Whales Res. Inst., 31: 1-44.
KASUYA, T. and S. MATSUI, 1984. Age determination and growth of the short-finned pilot whale off the
Pacific coast of Japan. Sci. Rep. Whales Res. Inst., 35: 57-91.
KASUYA, T., T. TOBAYAMA, and S. MATSUI, 1984. Review of livecapture of small cetaceans in Japan. Rep. int.
Whal. Commn, 34: 597-602.
MYRICK JR, A. C., 1980. Examination of layered tissue of odontocetes for age determination using polarized
light microscopy. Rep. int. Whal. Commn (special issue 3): 105-112.
MYRICK JR, A.C., E. w. SHALLENBERGER, I. KANG and D.B. MACKAY, 1984. Calibration of dentinal growthlayers in seven captive Hawaiian spinner dolphins, Stenella longirostris, based on tetracycline labelling.
Fish. Bull., 82 (1): 207-225.
NAKAJIMA, M., K. TAKAHASHI, M. OGURA and H. SAWAURA, 1963. On the growth of infants of the small size
toothed whales.]. Soc. Zoo!. Gardens and Aquariums, 5 (1): 16-22. (in Japanese).
ODELL, D. K., 1975. Status and aspects of the life history of the bottlenose dolphin, Tursiops truncatus, inFlorida.]. Fish. Res. Bd Can., 32 (7): 1055-1058.
0HSUMI, S., 1966. Allomorphosis between body length at sexual maturity and body length at birth in the
cetacea.]. Mamm. Soc. jap., 3 (1): 3-7.
PERRIN, W.F.,J.M. COE andJ.R. ZWEIFEL, 1976. Growth and reproduction of the spotted porpoise, Stenella
attenuata, in the offshme eastern tropical Pacific. Fish. Bull., 74 (2): 229-269.
PERRIN, W. F., D. B. HoLTs and R. B. MILLER, 1977. Growth and reproduction of the eastern spinner dolphin,a geographical form of Stenella longirostris in the eastern tropical Pacific. Fish. Bull., 75 (4): 725-750.
PERRIN, W.F. and A.C. MYRICKJR(eds), 1980. Age determination of toothed whales and sirenians. Rep. int.
Whal. Commn (special issue 3), 229pp.
SCOTT, E.0.G., 1949. Neonatal length as a linear function of adult length. Pap. and Proc. Roy. Soc. Tasmania,
1948: 75-93.
SERGEANT, D. E., D. K. CALDWELL and M. C. CALDWELL, 1973. Age, growth, and maturity of bottlenose
dolphin (Tursiops truncatus) from northeast Florida.]. Fish. Res. Bd Can., 30 (7): 1009-1011.

Sci. Rep. Whales Res. Inst.,
No. 37, 1986