THE GROWTH OF TWO SPECIES OF THE HARBOURSEAL IN THE ADJACENT WATERS OF HOKKAIDOYASUHIKO NAITO* AND MASAHARU NISHIWAKI*
ABSTRACT

We studied the growth of P. v. largha, pagophilic seal, and P. kurilensis,
pagophobic seal, in the southern Sea of Okhotsk and in the waters around
Hokkaido from 1968 to 1971.
P. v. largha: Adult type coat and white coat were observed in the fetus
stage. Parturition occurred from mid March and the end of March. Moultingof the white coat and weaning occurred 2-3 weeks after birth. The thicknessof blubber was 4.5-5.l cm in pups on the ice floe and decreased to 2.6 cm
after the ice melted. The fully grown body length was 170 and 161 cm inmales and females respectively.
P. kurilensis: Parturition occurred in the later half of May, and birthlength was 98.2 cm. Weaning occurred 4 weeks after birth. The thickness of
blubber was thinner than that of P. v. largha. The fully grown body length
was 186 and 169 cm in males and females respectively.
INTRODUCTION

It is today noted that there are 5 subspecies of the harbour seal (Phoca vitulina) in thenorthern hemisphere; P. v. vitulina in the eastern Atlantic, P. v. concolar in the western
Atlantic, P. v. mellonae in the Seal Lake, Canada, P. v. richardi in the eastern Pacific,
P. v. largha in the western North Pacific.
In the western North Pacific, more than 10 specific or subspecific names werereported for the harbour seal, but they were reduced to only one P. v. largha by
Scheffer (1958). However, recently by morphological and ecological studies, Belkin(1964) reported new species of Phoca named P. insularis, which is the same seal
reported previously as P. ochotensis kurilensis by Inukai (1942a). Concerning thespecific name of the new seal, McLaren (1966) used P. kurilensis instead of P. insularis,
recognizing the priority of the name kurilensis. Therefore, there exist two species of
Phoca, P. v. largha and P. kurilensis, in the western North Pacific.
In Hokkaido, it is noted that both of the above mentioned two species arecaught annually by commercial sealing or by fishing net (Naito, 1971). Biologicalstudies of these seals in the waters around Hokkaido and in the southern Sea of
Okhotsk were made fragmentarily by Inukai (1942 a, b), Wilke (1954), Nishiwaki
and Nagasaki (1960), Belkin (1964) and Belkin et al. (1969). Nevertheless, there arestill many general biological problems not yet solved.
It is noted that P. v. largha is a pagophilic seal and P. kurilensis is a pagophobic
seal (Belkin, 1964; Belkin et al., 1969). The present study was focussed to reveal* Ocean Research Institute, University of Tokyo, Tokyo.
Sci. Rep. Whales Res. Inst.,

No. 24, 1972, 127-144.

NAITO AND NISHIWAKI

128

unknown aspects of the growth of the seals, some of which may be related to such
ecological difference between two species.
In the present study, we follow McLaren (1966), and use the name P. kurilensis.
146°E

lllil.11---l-----l4
SoN

SEA OF OKHOTSK

46°N

PACIFIC OCEAN

Fig. 1. Sampling areas for P. v. largha and P. kurilensis in the southern Sea of Okhotsk
and the Pacific coast ofNemuro Peninsula.

MATERIALS AND METHODSIn the southern Sea of Okhotsk and the north east coast of Hokkaido, field surveys
were made between 1968 and 1971. In the present study, the area surveyed was
divided into the following 4 areas according to the sealing area (Fig. 1): I) the mouthofTerpeniya Bay of Sakhalin, II) the Kitami-Yamato bank, Lake Saroma, and Point
Notaro, III) the area between Shiretoko Peninsula and Nemuro Peninsula, IV) the
Pacific coast ofNemuro Peninsula. Studies of P. v. largha were made mainly in areas
I, II, III, and studies of P. kurilensis were made in area IV. In area I, studies were
performed on a sealing boat from the end of April to the beginning of May in 1971.
In area II, studies were made from December in 1968 to March in 1969 at Lake
Saroma and Point Notaro, and also made on a sealing boat in Kitami-Yamato bankfrom mid April to the beginning of May in 1969 and 1970. In area III, studies were
Sci. Rep. Whales Res. Inst.,
No. 24, 1972.

GROWTH OF THE HARBOUR SEALS IN HOKKAIDO

129

made from December in 1968 to March in 1969. In area IV, studies were made in
May and June in 1969, 1970 and 1971, and in October in 1969. In this area, fieldobservations of P. kurilensis were also made at Moyururi Island and other places in 1969
and 1971. P. kurilensis was chiefly caught in area IV in May and June. However,some of this species appeared in area III and were caught by fishing net occasionally(Salmon set net). P. v. largha seemed not to appear in area IV in May and June
except for pups or very young seals, but some appeared in area IV and were caught
by the fishing net in Autumn.
Through these studies, body length was measured from the tip of the snout tothe end of the tail in a straight line along the body axis in cm. Concerning the seals
collected on board, measurements were mostly made before rigor mortis occurred.
Some were measured in the condition of rigor mortis, and yet they were not so muchcurved that we could not measure in a straight line along the body axis. In small
embryos (under 100 mm) the length was measured along the curved body axis fromthe tip ofthesnouttotheendofthetailinmmbyusingtheuniversal projector, and thelength of middle sized embryos (100-400 mm) was measured by using the divider.
Large embryos (over 400 mm) were measured same as postnatal seals. Reproductive organs were preserved in 10 % formalin. In some cases, they were preserved in
10 % formalin after preservation in a freezer.
For age determination, canine teeth were taken from the skulls or lower jaws
after connective tissues rotted in the laboratory, and then they were cut longitudinallyby grinder and their surface was polished by wetstone. After they were glued to thetransparent plastic plate, the half of the remaining tooth was ground again to become
about 0.1 mm in thickness. The growth layers were observed by the binocular
microscope in reflected and transmitted light. In the present study, age determination was made following the method of McLaren (1958), Mansfield and Fisher (1960),
and Bigg (1969). In the seal under 7-8 years of age, both cementum and dentine
growth layers were examined, but only cementum growth layers were examined after
7-8 years of age. Ages were calculated from number of growth layers, assuming thatevery collected P. v. largha was born at the end of March and P. kurilensis was born in
mid May respectively.
PRENATAL GROWTH AND PURTURITION
The prenatal growth of P. v. largha and P. kurilensis is almost unknown. Tikhomirov (1971) reported the length of near-term fetuses of P. v. largha from the Bering
Sea. There are no record of fetus of P. kurilensis. However, Scheffer and Slipp(1944) and Bigg (1969) reported the prenatal growth of P. v. richardi from Washington
State and the southern Vancouver Island.
Concerning the parturition Tikhomirov (1971) in the Bering Sea, Wilke (1954)
in the southern Sea of Okhotsk, Belkin (1964) and Belkin et al. (1969) in the southern
Kurile Islands reported on P. v. largha, and Inukai (1942a), Belkin (1964) and Belkin
et al. (1969) stated on P. kurliensis from the southern Kurile Islands. In the present
study, mating season, growth of fetus in body length, parturition season and birth
Sci. Rep. Whales Res. Inst.,
No. 24, 1972.

NAITO AND NISHIWAKI

130

length were investigated.

Phoca vitulina largha
In area II from the 12th to the 16th of April in 1969, we collected 9 paired
females which were on ice floes with males and pups together. Couples of ovaries
were collected from 5 out of 9 paired females. The condition of these ovaries wascompared with that of single females which were alone on ice floes and were captured
from the 17th of April to the 2nd of May. As seen in Table 1, paired females were
TABLE 1.

CONDITION OF OVARIES IN THE SINGLE FEMALE AND
THE PAIRED FEMALE OF P. V. LARGHA.
SinglePeriod of catch
Number of specimens
Specimens with large follicles and no newly
formed corpus luteum in ovaries
Specimens with follicle changing to corpus
luteum in ovaries
Specimens with newly formed corpus
luteum in ovaries
Mean diameter of maximum-sized follicle(length+width/2; mm)

Pair

23

April 12th-l 7th
5

62

April l 7th-May 2nd

0

23

2

5.0

12.7

classified into three groups according to the condition of ovaries. 1) two paired
females had large follicles and no corpus luteum in their ovaries, which indicated that
fertilization had not occurred yet. 2) one paired female had the large follicle which
was partly changing to the tan-color corpus luteum, and partly contained theopaque gelatin like structure. This follicle indicated that the ovary was just after
the fertilization. 3) two paired females had the newly formed corpus luteum in theirovaries, and this indicated that fertilization had already occurred. The mean diameter of maximum sized follicles of 5 paired females was 12.5 mm. On the other
hand, in the single females only newly formed corpus luteum was found in the ovaries,
and this indicated that fertilization was over. The mean diameter of maximum
sized follicles was 5.0 mm and was less than half of that of paired females. Fromthese facts, it is indicated that the paired females were in the mating season, and in
the single females mating season was over. In the present study, it was difficult toknow exactly when the beginning of the mating season occurred, however, it may besupposed that mating occurred from early April to mid April.
Concerning the growth offetus, we examined 20 fetuses of P. v. largha collectedfrom survey area II and III. Figure 2 shows that body length offetuses increased inaccordance with time. In this study, the time of implantation is unclear, so thegestation period is also unclear. The fetuses collected in mid October, about 5
months before parturition season, were 175-268 mm in body length and the final
stage fetuses collected in later half of March, just before birth, was 780-925 mm.
The growth rate seemed to be same in both sexes.
Sci. Rep. Whales Res. Inst.,

No. 24, 1972.

GROWTH OF THE HARBOUR SEALS IN HOKKAIDO

131

Pups having an umbilical cord may indicate that they were born within thepast few days, and from such pups parturition season and birth length would be
estimated. In this study we could not collect pups with an umbilical cord, but 4
final stage fetuses were caught which were estimated that they would be born within a
few days. These fetuses appeared from the 16th to the 27th of March and did notappear after the 27th of March. Therefore, it seemed that parturition occurred fromthe mid to the end of March. According to other studies, Wilke (1954) reported
from the same area as our area II that parturition may occur in the early half of

~

.

./ .
•

R

/o o

800

/

E

~600>.r:.

~

-:(·

1000

/~

f-

/"
.

0.

_,~400>-

0/.0

200 -

.. A
I

5

l------i

1-----i
I

I

0

N

D

F

M

A

M

A

Month

Fig. 2. Prenatal growth of P. v. largha and P. kurilensis in standard length. e, 0,males and females of P. v. largha ; (!), new born pups with white coat ; .A, .6.,
males and females of P. kurilensis ; X, new born pups with umbilical cord ; - ,time of parturition of P. v. largha ; - - -, time of parturition of P. kurilensis.

March, the earliest record of parturition was in late January and the latest was on the
15th of April. Belkin (1964) suggested that pups were born on ice floes from the endof March to mid April in the southern Kurile Islands. However, Belkin et al. (1969)suggested that new born pups were observed from early March to the end of Marchin the same area.
In the present study, birth length was estimated from following considerations.
1) the largest fetus and the smallest new born pup may indicate the birth length. 2)
growth curve and parturition season also indicate the birth length. According to1), birth length was assumed to be 933 mm, since the largest fetus was 925 mm
and the smallest new born pup was 940 mm. According to 2), birth length wasestimated to be about 850 mm. Since the new born pup was not captured justafter birth, the result of the first was relatively large. Therefore, we employed thesecond result.
Sci. Rep. Whales Res. Inst.,

No. 24, 1972.

NAITO AND NISHIWAKI132

Phoca kurilensis
Concerning the mating season, 4 couples out of 67 population were observed tocopulate at hauling ground area of Moyururi Island from the 9th to 13th of June in1969. While copulations were rarely observed in 75 population from 22nd to 27th ofJune in 1971 at the same hauling ground area. From these data, it is concluded thatmating occurs in June, but is difficult to estimate the mating period exactly.
There was no report previously on the prenatal growth of this seal. In the present study, the length of 4 fetuses collected in October from Nemuro Peninsula was
95 mm in males, and 85, 84 and 39 mm in females (Fig. 2). In these fetuses nopigmentation was observed (Plate I).
To estimate the parturition season and the birth length, the appearance ofpups with umbilical cords was investigated. Figure 3 shows that parturition of thisseal may occur from the middle to the end of May in the Pacific coast of Nemuro
Peninsula and the mean body length at birth is 98.2 ± 3 .2 cm. The birth length of thisspecies is much larger than that of P. v. largha indicated in the present study and thatof P. v. richardi shown by Bigg (1969). Inukai (1942b) and Belkin (1964) and Belkin
et al. (1969) suggested that parturition of this seal occurs in mid May and copulation
occurs in July in the southern Kurile Islands.
~ 6

110

:::J

a.

~ 4

2

"'

.Q

E
~ 2

0

100 ~

:::J

'°

90 J

(20)

12

14

16

18

20

22

24

26

28

MAY

30

2

80

JUNE

Fig. 3. Frequency of new born pups with umbilical cord, at two days intervals,
and birth length(total 20 pups). Vertical line, range; box, standard error;
horizontal line in box, mean.

POSTNATAL GROWTH

I.

Moulting of white coat and weaning

It is generally believed that only P. v. largha of all 5 subspecies bears the creamy
white coat in its early pup stage for several weeks after birth, and also weaning seems
to occur subsequently with moulting of this coat. However, the moulting and weaning season are still unknown. As for P. v. largha, Wilke (1954) suggested the time ofmoulting in the southern Sea of Okhotsk, but the weaning seasons are not obvious.
Concerning weaning of P. kurilensis, Belkin (1964) and Bilkin et al. (1969) suggested
from his finding in the southern Sea of Okhotsk.
Sci. Rep. Whales Res. Inst.,
No. 24, 1972.

GROWTH OF THE HARBOUR SEALS IN HOKKAIDO

133

Phoca vitulina largha
In the fetuses collected in October, clear pigmentation was observed (Plate I).
Scheffer and Slipp (1944) traced three progressive changes in type of pelage in P. v.
richardi: 1) an early, sparse fetal coat, perhaps the forerunner of the third coat, 2) along, silky white lanugo coat, and 3) a short varigated coat. The first fetus on whichappeared fetus pelage according to Scheffer's 1), was caught in early November.
From early December, about 3.5 months before parturition season, the fetus began toshow the white lanugo coat, which corresponded with Scheffer's 2) change (Plate I).
There are no records of pups which have the fetus coat corresponding to Scheffer's 3)change. The near-term fetus of P. v. largha do not shed the white lanugo coat, but
continue to bear after birth. Stutz (1966) reported the changes oflanugo coat in thefetus of P. v. richardi. Firm and dirty white or pale yellowish-grey hair corresponding to Scheffer's 2) change, which resist tugging, appeared characteristic offetus at about half term. As the fetus neared parturition, this hair become looser
enough to be scraped from the skin, and almost near-term fetus lost their lanugo coat.
This near-term fetus seemed to exhibit the same pelage as Scheffer's I) change.
From the catch record of pups captured in area I from the 27th of April to the
4th of May in 1971, and in area II from the 13th of April to the 12th of May in 1969,
the time of moulting of the white coat and the time of weaning were considered(Table 2). In order to know the moulting season of the white coat, three pups stages
were considered from the condition of white coat: 1) stage of complete white coat, 2)stage of a partial white coat, 3) stage of moulting the white coat.
In area II, as shown in Table 2, pups were considered in the moulting season of
their white coat in mid April, and it seemed that the moulting season was over at theTABLE 2.

FREQUENCY OF PUPS OF P. V. LARGHA IN THE THREE MOULTING
STAGES. PARENTHESIS SHOWS PERCENTAGE.

Area II
1969 Apr. 12
Apr. 13
Apr. 14
Apr. 15
Apr. 16
Apr. 23
May 2
Area I
1971 Apr. 27
Apr. 28
Apr. 29
Apr. 30
May 1
May 2
May 3
May 4
Sci. Rep. Whales Res. Inst.,

No. 24, 1972.

Number of pups
in white-coat
stage

Number of pups
in second stageof moulting(45.4)(27.3)

Number of pups
in final stageof moultingl) l) Il

(27.3)~ } (0)~ }(20)~ }(80)

0
0
0
0
0
0
0
0

1
0
0
0
0
0
0
0

6
5
6
2
4
3
7

NAITO AND NISHIWAKI134

end of April. In area I, there were no catch records of pups bearing completely
white coat from the 27th of April to the 4th of May in 1971. Almost all pups captured in this area had shed their white coat. Therefore, we can suggest that themoulting season was already over at the end of April and the beginning of May inarea I in this year. According to Wilke (1954), pups of this subspecies landed byhunters at Abashiri in late April were in the moulting stage, and three stages classified
above have been reported. As it is possible to think that Wilke also treated thepups from the same area as area II, the time difference in the moulting season may berelated to the ice conditions in each year.
100 I - - - - - - ,areall-1969. 1970

50

>~

0

(1) (2) (3) (3) (7) (3) (0) (5) (2) (2) (O) (1)12
3
3 15 8072
30
3(0) (0)

0

0

:J

gwo

areall-1969. 1970~50(1) (2) (4) (3) (1) (0) (O) (0) (0) (0) (0) (0) (O) (O)01486200
00300

12

13

14

15

16

17

18 19 20 21

22

23 24

25

(0) (0) (0) (O) (0) (0)00003026

27 28 29 30

APRIL

1

2

3

4

MAY

Fig. 4. Frequency of appearance oflactating females (above) and pups cared by its
mother (below) in P. v. largha. Number in the parenthesis shows the number of
lactating females out of total number of sexual mature females, and the number ofpups cared by its mother out of total number of pups.

TABLE 3.

FREQUENCY OF PUPS OF P. v. largha WITH MOTHER IN RELATION
TO THREE MOULTING STAGES.

No. of pups with motherTotal No of pups
Percentage (%)

complete whitecoat stage

partly moulted
stage

completely
moulted stage

9
10
90

7
14.3

0
10
0

Since the parturition season in area II was considered from mid March to theend of March in 1969, it is considered that moulting of the white coat occurred
two or three weeks after birth in this year. This period from birth to moulting is thesame as that of King's suggestion (1964).
Time of weaning was estimated by the appearance of pups that were caught with
their mothers and the appearance of the lactating females in area II (Fig. 4). In
this study, a lactating female was determined when milk secretion was found in the
mammary glands. This figure shows that pups with their mothers appeared by mid
April, and may indicate that frequency of appearance of lactating females is decreasingfrom mid April to the end of April in 1969 and 1970. Therefore, it could be suggested
that weaning occurs in mid April in area II. We also studied weaning in relation
Sci. Rep. Whales Res. Inst.,
No. 24, 1972.

GROWTH OF THE HARBOUR SEALS IN HOKKAIDO

135

to moulting of the white coat. As shown in Table 3, weaning occurs simultaneouslywith moulting of the white coat. Since the parturition season in area II was considered to be from mid March to the end of March in 1969, as described above, it isconsidered that weaning occurred after two or three weeks from birth.

Phoca kurilensis
lnukai (1942b) reported that new born P. kurilensis in the southern Kurile Islands had the white coat, yet Belkin (1964) and Belkin et al. (1969) opposing lnukai,
said that pups of the same seal do not have the white coat. In this study, 20 pups
with umbilical cords were observed and the same result as Belkin was obtained.
In some cases, however, pups with lanugo coats were observed. One pup captured in the 20th of May 1969 had a grey long lanugo coat except for the head andflippers (Plate I), and also a pup captured the 25th of May in 1970 had such a coat alittle on its back. These facts may indicate that near-term fetuses have lanugo coats.
Although we have no record of a lanugo coat fetus, we obtained the informationfrom a fisherman that near-term fetuses which have such a coat were removed fromtheir mother seals caught in mid March by fishing net. This may suggest that pups
normally shed their coat in the uterus before birth. The same occurrance wasfound in P. v. richardi in the Alaska Peninsula by Stutz (1966) and Burns (1970).
The pups born in early parturition season in late May, retain all or most of theirlanugo coat for a short period after birth. Fisher (1952) has reported the yellowish
coat pup of P. v. richardi born in the peak of parturition on June 8, 1946 from the
Skeena River. In the present study, pups with lanugo coats were born not in early
but in mid parturition season.
The weaning season of this seal was estimated from the following three investigations: 1) existence of milk in the stomach of pup, 2) appearance of lactating
females, 3) appearance of pups together with their mothers in the hauling groundarea (Table 4 and 5). Table 4 seems to show that pups of which the stomachs had
contained some amount of milk, appeared in May and the beginning of June, anddisappeared at the end of June. Table 5 may show that lactating females appeared
TABLE 4.
Date
May 16
May20
May21
May22
May24
May31
Jun. 1
Jun. 2
Jun. 21Jun. 27
Jun. 28

Sci. Rep. Whales Res. Inst.,
No. 24, 1972.

FREQUENCY OF SUCKLING PUPS OF P. KURILENSIS.
Number of pupsof which stomach
contains milk

Number of pupsof which stomach
contains no milk

2

0
0
0
0
0
1
0
0

0
3
3
0
1
0

3

Total
8

0
1
9
3
4
1

136

NAITO AND NISHIWAKITABLE 5.
Date
May 13
May 16
May 18
May22
May25
May29
May30
Jun. 7
Jun. 16
Jun. 27FREQUENCY OF LACTATING FEMALES OF P. KURILENSIS.
Number oflactatingfemalesNumber ofnonlactating
females

1
2

0
0
0
0
0
0
0
0
0

I

2

1
0

Total
1
2

1
2

till mid of June.
The appearance of suckling pups in the hauling ground area was observed at
Moyururi Island. From the 9th to the 13th ofJune in 1969, all 4 pups were observedin suckling and being cared for by their mothers. From the 22nd to the 26th ofJune in 1971, 4 pups out of 7 rarely suckled, but they were observed to swim with
their mothers, and the other remaining three pups were observed in groups without
their mothers. From these three investigations, we conclude that weaning of thisseal begins to occur at the end of June. Belkin et al. (1969) suggested that the pups
caught at mid May and the Bth of August in 1963 had milk (100-450 g) in theirstomachs and their suckling continue till August, however, his result may be toolong compared with this result.

II.

Thickness of blubber in early stage of pups

Bigg (1969) and Tikhomirov (1971) suggested that the body weight of pups become
double their birth weight during the suckling period. This remarkable increase in
their body weight is mostly due to the increase in thickness of blubber. In this study,
comparison of the blubber thickness between ice breeding P. v. largha and land breeding P. kurilensis was made. The thickness of blubber was measured at the middle
point between the mammae and the umbilicus where the blubber seems to be thethickest.

Phoca vitulina largha
Measurement of blubber thickness was made on pups caught in area I, II and
III (Fig. 5). In area I, 21 pups were caught on ice floes from the 27th of April to the
2nd of May in 1971. Most pups captured here had already lost their white coats except one which still partly had its white coat, and it was estimated that weaning had
already occurred but not so long time before. Their mean blubber thickness was
5.1 cm, and seemed to be still in maximum condition. In area II, 9 pups werecaught on ice floes from the 12th of April to the 2nd of May in 1969. Seven of these9 pups were on the point of weaning and moulting the white coat, but 2 pups had
Sci. Rep. Whales Res. Inst.,
No. 24, 1972.

GROWTH OF THE HARBOUR SEALS IN HOKKAIDO

137

already shed their coats. The mean blubber thickness was 4.5 cm and estimated to
be in the thickest condition. Seven pups were caught in area III from the 22nd of
May to the 27th of June in 1970 and 1971. The mean blubber thickness was
2.6 cm. All pups were caught not on the ice floe, but in water by fishing net.
6

:8" 2
arerll"en:a - - - - - - J
1--------fa.rerm0.
' ·--'---c'=----'--.,.,,___.__,.,___.__,..,____,__..___._____,.,.,,.____._---1
(9)

;l]

30

~ 6
:c
..... 410 APRIL 2030

10 MAY20

30-+--i-Y-

_J_

1

(14)

(8)

(16)

0

15

MAY

!-------~

31

15
JUNE

30
JULY

15

30

Fig. 5. Change of blubber thickness in pups of P. v. largha (above) and P. kurilensis(below). Vertical line, range; box, standard error; horizontal line in box, meanand sampling period ; foot horizontal line, time of parturition ; foot brocken line,
time of weaning.

As seen in figure 5, pups on the ice floe (area I and II) had the pretty thicker
blubber than pups in swimming life stage (area III). However, it is not clear as towhat is reason why blubber thickness seen in pups of area III is much thinner than inpups of area I and II. The following reasons should be considered: Pups consume
their blubber by swimming in the cold water (-1 to 0°C) after weaning. Concerning
the difference of blubber thickness of pups found between area I and II, we could
not discuss for the sake of short data. Tikhomirov (1971) reported that the meanvalue of 8-12 day-old pups caught on the 15-20th of April was 26.3 kg and of 1.2-2
month-old pups caught at the end of May and June was 23.9 kg. In addition, therapid growth in body length during the first month from birth were reported (Tikhomirov, 1971). These facts suggest that decrease in weight is due to decrease inblubber thickness.

Phoca kurilensis
Sixty-five pups were caught on the Pacific coast ofNemuro Peninsula from the16th of May to the 6th of July in 1969, 1970 and 1971. Figure 5 shows the blubber thickness of 48 pups out of 65 pups that were measured. As shown in figure 5,
the mean blubber thickness of pups with umbilical cord caught in later half of
May was 2.1 cm, and it was increased rapidly until 3.4 cm in early half of June.
The maximum condition of the blubber thickness may occur in the end ofJune simultaneously with the beginning of weaning. The difference of maximum
Sci. Rep. Whales Res. Inst.,

No. 42, 1972.

138

NAITO AND NISHIWAKI

thickness of blubber between two species is related to the difference in breeding
environment. As described above, pups of P. kurilensis are born on narrow rocky
shores and they begin to swim with their mothers just after birth differing from pupsof P. v. largha which do not swim before weaning. Therefore, pups of P. kurilensis
may regularly consume their blubber by swimming, and therefore remarkable accumulation may not occur.

ill.

Growth of ovaries and testes

As the index of sexual maturity, weight of ovaries and testes, and existence of the
newly formed corpus luteum in ovaries and sperm in testes and epididymis were examined in relation to age. Data collected from area I, II, III during April andMay, were examined not in each but altogether. The testes were weighed together
with the epididymis. Concerning P. kurilensis, it was difficult to describe the sexual
maturity owing to scanty of data.
20

0

8

15

0

0

.,

0

~-o--o,---;;---0-00

00o /o 8

o

;o o

o

o

/;

~ii

o

B

10

15

20

25

30

Age (years)

Fig. 6.

Growth in the weight of the ovaries of P. v. largha.

Total number is 102.

In growth of weight of ovaries and testes, 102 specimens from females and 61
specimens from males were used in figure 6 and figure 7 respectively. As shown inthese figures, decrease in weight was observed in both ovaries and testes during thefirst year. Actually, however, these decreases of weight seemed to have occurred
within short period after birth. The same occurrence was reported by Tikhomirov(1971). After that, sharp increase in weight was shown in both ovaries and testes
from 1-2 years of age to 4-5 years of age. Then, weight of these organs increase
gradually until 10 years of age.
Existence of the newly formed corpus luteum was examined in 26 females out of
102 females described above. As seen in Table 6, females from 2-7 years of age
Sci. Rep. Whales Res. Inst.,
No. 24, 1972.

GROWTH OF THE HARBOUR SEALS IN HOKKAIDO

139

were used, and the corpus luteum was observed in 20% of females at 3 years of age.
All of 6 females at 4 years of age had the corpus luteum in their ovaries. Similary,
existence of sperm in testes and epididymises was examined in 15 males from 1-8
years of age. Table 6 shows that 20 % males of 3 years of age and 50 % males of 4
years of age were matured, and all of males matured from 5 years of age.

200

g

150

0

0

00

.r:.
01

"'

:;:: 100

0

50

0

0

Fig. 7.

1015
Age (years)

20

Growth in the weight of the testes of P. v. largha.

TABLE 6.

Total number is 61.

AGES AT SEXUAL MATURITY IN BOTH SEXES OF
P. V. LARGHA.
Females

Age
1
2
3
4
5
6
7
8

25

Number of
specimens
6
5
6
2
4
3

Males

Number of
mature females

Number of
specimens

0
6
2
4
3

5
4

Number of
mature males
00l2

From these data, it is difficult to estimate the age of sexual maturity in both
sexes exactly, but it is approximately considered that females and males of this species
reach sexual maturity from 3 years of age and mostly mature at 5-6 years of age.
Sci. Rep. Whales Res. Inst.,
No. 24, 1972.

140

NAITO AND NISHIWAKI

IV. Growth of body length
Postnatal growth was well shown by Tikhomirov (1971) in P. v. largha from the Bering
Sea and Bigg (1969) in P. v. richardi from the southern coast of Vancouver Island andAlaska. In addition, Belkin (1964) and Belkin et al. (1969) reported about P.
kurilensis, in the Kurile Islands.

Phoca vitulina largha
In this chapter, data collected from areas I, II, III were summed up to describe
the postnatal growth of body length. The number of specimens used here was 150
in males and 176 in females. The growth curves are shown in figure 8, which weredrown by eye, but as for the growth curve of females, the following growth formula
was approximately applied by using Walford's graphic methods:
0<t<2
It= 132(1-e-o.ss<t+o.so>),
lt=161(1-e- 0· 26 <t+ 4 .o>)(t ' ages·' 1t• length) •
t >=2
180

160

"E
-" 140
:5

"'

c

"'

...J

120

.--t
••o • -s .-=io ·~ •u• :e °·• • •o-o~

t .
0

:

0

0

0

~Ko~•"'
8

;'11
t'f'
•o •

0

(1)

8

0

0

0
0

•

·,

(2b

~

!h

:~~

180

160

(2) 140

0

0

{:8 ~
0

100

80

•:2'

""

·"
0

:

0

10

15

20

25

Age (years)

Fig. 8. Postnatal growth in body length of P. v. largha, males (1) and females (2).
Total number is 150 in males and 176 in females. Vertical line, range- box,
standard error ; horizontal line in box, mean.

Concerning the final growth length, mean body length was obtained from theseals over 15 years of age, since the formula did not fit accurately with plots fromabout 15 years of age. In this figure, the mean length at 0 years age was 97 cm inmales and 96 cm in females, which were calculated from the length of pups collected
about one month after birth during April and May. Since birth length was presumed to be about 85 cm in former chapter, it was assumed that pups grow more than
10 cm during the first month after birth. The mean length at 1 years of age was
119 cm in males and 117 cm in females, and pups grow 34 cm for males and about
32 cm for females during the first year. About 35 %of the body length growth during
the first year seemed to be attained in the first month after birth. The growth rate in
Sci. Rep. Whales Res. Inst.,
No. 24, 1972.

GROWTH OF THE HARBOUR SEALS IN HOKKAIDO

141

the first year observed in the present study is the same as Bigg (1969) showed in
P. v. richardi, but little lower than P. v. largha shown by Tikhomirov (1971).
From birth to 5 years of age, both sexes grow at about similar rate. The
growth continue until 14-15 years of age in males and 10-11 years of age in females.
Finally attained body length of the seals over 15 years of age was 169.9±4.0 cm formales and 159.0±3.1 cm for females, and the finally attained body length offemales
was 94.1 % of males.
According to Tikhomirov (1971 ), P. v. largha continues growing until 9 years ofage in males and 8 years of age in females, and physically matured body length was
168 cm in males and 162 cm in females. Sexual mature body length of females is
96.4% of males. Bigg (1969) suggested that P. v. richardi continued growing until
9-10 years of age in males and 5 years of age in females. He also reported that fullygrown body length was 161.1 cm and 147.7 cm in males and females respectively,
and sexual mature body length of females is 92.3 % of males.
Concerning the longevity, the oldest seal was 26 years of age in males and 32
years of age in females, and it seemed that females live longer than males. In another study, it was found 29 years of age and 35 years of age in male and female respectively for P. v. largha (Tikhomirov, 1971).
200

..

;{

180

'Eu

-

h

1·:
"/
0

140

Cl

c

"'

-' 120

100

80

..

.r-:

160

:

(1)
0

(2)

0

:

~·o

j
0
0

0

10

15

20

25

Age (years)

Fig. 9. Postnatal growth in body length of P. kurilensis, males (1) and females (2).
Total number is 49 in males and 57 in females.

Phoca kurilensis
Most of these data were collected from area IV, and a few from the southernpart of area III. The number of specimens used here was 49 males and 57 females,
which were collected from area IV. The extent of growth is shown in figure 9, which
was drawn by eye. In this figure, the mean length at 0 years of age was 109. 7 cm in
Sci. Rep. Whales Res. Inst.,

No. 24, 1972.

142

NAITO AND NISHIWAKI

males and 108. 7 cm in females, which was based on the pups collected about a monthafter birth during May and June. Since the birth length of this species was 98.2 cm
as shown former chapter, new born pups grow about 10-11 cm in length during
the first month. Concerning specimens over 2 years of age, we are short of data to
describe precisely the growth aspect, but we can discuss the general tendency. Males
and females grow at about the same rate until 5-6 years of age, and from this age
onward dimorphism in body length seems to become clear. By 9-10 years of age,males attain nearly the final growth length, and females attain such length by 7-8
years of age. The maximum body length observed was 191 cm in males and 175 cm
in females. Final growth length is assumed to be about 186 cm in males and 169 cm
in females, and the final growth length of females was 90.9 % of males. This ratio
was smaller than that of P. v. largha, and P. v. richardi according to calculation basedon Bigg (1969). Belkin et al (1969) suggested that the mean length of sexual mature
males was 174 cm and 160 cm in females, and the maximum was 181 cm and 180 cm
in males and females respectively. They (1969) also recognized the clear dimorphism
in body length in immature seals, describing the mean length of 3 males and 7 females
as 139.6 cm and 126.4 cm respectively.
Concerning longevity, it is difficult to discuss with these scanty data.
DISCUSSION
In the present study, we obtained some new facts on prenatal and postnatal growth in
P. v. largha and P. kurilensis.
It was appeared that mating season and parturition season of P. kurilensis
occurred 2 months later than that of P. v. largha, and the birth length of P. kurilensis
is larger than that of P. v. largha. After the parturition, pups of pagophilic P. v.
largha bears white coat for 2-3 weeks and live on ice floes without swimming. Weaning occurs simultaneously with moulting of white coat 2-3 weeks after birth. Concerning the weaning, it is exactly unknown whether weaning occurs suddenly or
gradually. If weaning occurred suddenly, pups would suddenly have the completely
independent life and would not have the swimming life with their mothers,
furthermore they would not learn the feeding from their mothers. Table 3 mayshow that departure from the mother occurs quickly as moulting begins to occur.
So that, pups may be left alone on ice floes and have the completely independent life.
It is also unknown whether pups have swimming life soon after weaning or some timeafter weaning. If they remained on ice floes, they would be carried by ice floes andtheir distribution would spread. On the other hand, pups of pagophobic P. kurilensis
do not have the white coat when they were born. They have the swimming life
with their mothers soon after birth, and their suckling is chiefly performed in thewater. Weaning occurs about 4 weeks after birth. This period is longer than thatof P. v. largha. It is also exactly unknown whether weaning occurs suddenly or
gradually. However, observation that pups were found with their mothers without
showing the suckling behavior may indicate that weaning occurs gradually in thisspecies, and pups may learn the feeding from their mothers.
Sci. Rep. Whales Res. Inst.,
No. 24, 1972.

GROWTH OF THE HARBOUR SEALS IN HOKKAIDO

143

Concerning the early stage oflife, we also studied the thickness of blubber. In
P. v. largha, pups on ice floes have the thicker blubber and pups in the water have thethinner blubber. This result seems to indicate that change in blubber thickness isdue to change in nutritional condition of pups during suckling and weaning period.
the other hand, pups of P. kurilensis had the thinner blubber as compared with
P. v. largha. The difference in blubber thickness between two species seems to berelated with the difference in nutritional condition of life in early stage describedabove.
Concerning the growth of body length, sexual dimorphism in body length wasobserved clearly in P. kurilensis as Belkin et al. (1969) reported.
ACKNOWLEDGEMENTGreatest thanks go to Drs. T. Kajihara, K. Numachi, and T. Kasuya for their valuable advice and discussions. In the field work, greatest thanks go to Mr. K. Shibuta
and Mr. Y. Suzuki, Engaru Fur. Co., who permitted us to be on board for collecting
specimens. Greatest thanks also go to Mr. N. Kanazawa, Kanazawa Fur Co., whohelped us in collecting specimens from a number of hunters. Special thanks go to
the Abashiri Light House Office and Nemuro Light House Office of Japanese Maritime Safety Agency for assistance in field observation. Special thanks also go to Mr.
I. Yoshida, Yoshida Fisheries Co. and Mr. T. Kasahara, Kasahara Fisheries Co.,
who permitted us to use some facilities.
REFERENCES
BELKIN, A. N., 1964. A new kind of seal from the Kurile Islands. Doklady Akad. Nauk SSSR., 158(2): 12171220.
BELKIN, A. N., G. M. KosYGIN, and K. I. PANIN., 1969. Marine mammals. Academy of Sciences of U.S.S.R.,
Ministry of Fisheries of U.S.S.R., Moscow., 157-175.
Bma, M.A., 1969. The harbour seal in British Columbia. Bull. Fish. Res. Bd. Canada, 172 : 1-33.
BuRNs,J.J., 1970. Remarks on the distribution and natural history ofpagophilic Pinnipeds in the Bering and
Chukchi Seas. J. Mamm. 51(3): 445-454.
FISHER, H. D., 1952. The status of the harbour seal in British Columbia, with particular reference to the
Skeena River. Bull. Fish. Res. Bd. Canada, 93: 1-58.
INUKAI, T., 1942a. Hair seals in our northern waters (I). Shokubutsu Dobutsu, 10(10): 927-932. (in Japanese).
INUKAI, T., 1942b. Hair seals in our northern waters (II). Shokubutsu Dobutsu, 10(11): 1025-1030. (inJapanese).
KING, J.E., 1964. Seals ef the world. British Museum, London, 154 pp.
MANSFIELD, A. W., and H. D. FISHER, 1960. Age determination in the harbour seal, Phoca vitulina. Nature,186: 192-193.
McLAREN, I. A., 1958. The biology of the ringed seal (Phoca hispida Schreber) in the eastern Canadian Arctic.
Bull. Fish. Res. Bd. Canada, 118: 1-97.
McLAREN, I. A., 1966. Taxonomy ofharbor seals of the western North Pacific and evolution of certain otherhair seals. J. Mamm., 47(3): 466-473.
NAITO, Y., 1971. A report on Japanese sealing. Geiken Tsushin, 238: 49-52. (in Japanese).
NISHIWAKI, M., and F. Nagasaki, 1960. Seals of the Japanese coastal waters. Extrait de Mammalia, (243):459-467.
Sci. Rep. Whales Res. Inst.,
No. 24, 1972.

144

NAITO AND NISHIWAKISCHEFFER, V. B., andJ. W. SLIPP, 1944. The harbor seal in Washington State. Am. Midland:Nat., 32(2):373-416.
SCHEFFER, V. B., 1958. Seal sea lions and walruses. Stanford University Press, Stanford, 179 pp.
STUTZ, S.S., 1966. Foetal and postpartum white coat pelage in Phoca vitulina. J. Fish. Res. Bd. Canada, 23(4):607-609.
TrKHOMIROV, E. A., 1971. Body growth and development of reproductive organs of the North Pacific Phocids.
Pinnipeds ef the North Pacific. (Israel program for scientific translations). Keter Press, Jerusalem, 213241.
WILKE, F., 1954. Seals of northern Hokkaido. J. Mamm., 35(2): 218-224.

EXPLANATION OF PLATE I
Fig. 1.
Fig. 2.
Fig. 3.
Fig. 4.

A female embryo of P. v. largha, 20 cm in length, about 5 months before birth (collected
on 14th of October).
A male embryo of P. kurilensis, 9.5 cm in length, about 7 months before birth (collected
on 14th of October).
A male white coat embryo of P. v. largha, 58.5 cm in length, about 2 months before
birth (collected on 19th of January).
A new born male pup of P. kurilensis with umbilical cord which beared grey lanugo
coat, 89 cm in length (collected on 20th of May).

Sci. Rep. Whales Res. Inst.,
No. 24, 1972.

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