A THIRTY FOUR YEARS OLD MALE KURIL SEALFROM SHIRETOKO PEN., HOKKAIDONORIYUKI OHTAISHI AND MASAAKI YONEDA
Faculty ef Dentistry, Hokkaido University, Sapporo
The Kuril seal (Phoca kurilensis INUKAI, 1942) is distributed from northern Kuril
Islands to the Pacific coast of eastern Hokkaido. The population in the Kuril Is.
is estimated at under 2,000-2,500 including those in the Shikotan and Habomai Is.
(Belkin, 1964). The Japanese population is limited to nine hauling grounds in theabove range, and the number is estimated at 200-250 individuals (Niizuma et al.,
1980; Fig. 1). The presence of the species along the Okhotsk coast of Hokkaido is
not confirmed at the present.
The present material was shot by Mr. H. Ohki, an expert seal hunter, in theSpring of 1980 on the coast of Kuzurehama at Shiretoko Pen. (Fig. 1). He identified the species by its black coat marked with white ring spots and its large bodysize. The sex was not recorded by him. The skull was brought to us for detailed
analysis, and registered as Protocol Number 1351 of Department of Anatomy,
Faculty of Dentistry, Hokkaido University.
The skull shows some of the features of P. kurilensis mentioned by Belkin et aL(1969); that is, as compared with harbour seal (P. vitulina larga), the posterior
margin of the zygomatic bone makes a corner, the inferior surface of the tympanica
is flat and the proboscis is massive (plate I). The skull measurements are as follows; condylobasal length 232 mm; zygomatic width 152 mm; mandibular length
161 mm. The condylobasal length of the present specimen is larger than the maximum •size (227 mm) of P. v. larga reported by Belkin et al. (1969), and come within
the range of male P kurilensis 226-248 mm. According to the data of Belkin (1964),
the range ofzygomatic width of the female P. kurilensis is 122.4-145 mm and that of
the male is 134.5-158.7, and the mandibular length of the female is 141.6-160.2
and the male is 149.2-174.8. All the above measurements on the present specimen
exceed the range of the female and come in the range of the male. This strongly
suggest the specimen may belong to a male rather than a female.
The preparation of tooth slides for age determination was done as follows.
At first step, several longitudinal sections of about 40 µ in thickness were takenfrom the root of a canine tooth using a fine saw with diamond wafering blades(Kosaka Laboratory Ltd, Cl-1). Then, they were decalcified with plank-Rychlo's
solution (Plank and Rycholol 1952) for 10-15 min. at room temperature, andstained with Delafield's haematoxylin for 1-30 min. Finally they were mountedwith Canadian balsam for permanent preparations.
There were observed 34 stainable layers in the cementum. And the age ofthe animal was considered to be 34 years old (Plate I). The age determination
by Naito and Nishiwaki (1972) on the un-decalcified thin sections of 49 males andSci. Rep. Whales Res. Inst.,

No. 33, 1981, 131-135.

OHTAISHI AND YONEDA

132l 43°E

145°E

144°E

SEA

OF

146°E

OKHOTSK

C. SHI RETOKO
Nenbutsuiwa Rk
Kuzureham KUNASHIRIASHIRETOKO
PEN.

44°N

44°N
SH!KOTANI.
SEA OF OKHOTSKNEMURO P.<tl

HOKKAIDOS!

.. HABOMAI IS.
f'Moyururi I. (h20)
Yururi I. (5<Vl6)
Futatsuiwa Rk (4<v27)
Gomeiwa Rk (6<v28)
Hokakeiwa Rk (9<v50)
Kembokki I. ( l <v 7)
Dai koku I. (30<V62)
C. Shiripa (2<Vl0)

Il l43°N

~I

43°N

L
PACIFIC

OCEAN
42°N

42°N
• C. ERIMO ( 50<v73)
143°E

144°E

145°E

146°E

Fig. 1. Geographical distribution of the nine hauling grounds ( •) of P. kurilensis
along the coast of eastern Hokkaido, Japan. Numbers show the result of censuses
taken by the Marine Mamm. Res. Group in the middle of June during the years
1974-1981 (From Niizuma et al., 1980 and unpublished data).
X indicates thelocation of present material.

57 females of the same species revealed that 98% of the males were under 10 years
and 95% of the females under 18 years, and that the maximum ages of the males
and females were 18 and 24 years respectively. According to Naito and Konno(1979), the maximum age of the P. v. larga obtained by the same method was 30years in males and 33 years in females, and the corresponding figures also obtainedby the same method (Y. Naito pers. comm.) of the ribbon seal (P.fasciata) was 26years and 21 years respectively. In the subgenus Pusa animals of over 40 years
have been found by the stained sections and the group is considered to be the mostSci. Rep. Whales Res. Inst.,
No. 33, 1981

KURIL SEAL FROM SHIRETOKO

133

longevous among the Pinnipedia (Helle, 1980). From the condition on the heavily
worn teeth of the present individual (Plate I), the age of 34 years is considered tobe close to the maximum age of the species in natural environment, as shown themaximum ecological longevity by Ohtaishi (1978) of this species.
It is thought that the present individual of P. kurilensis might be originatedfrom the southern Kuril Is. However, it is also possible to regard it as a survivorof a breeding colony previously existed on the Shiretoko Pen. According to Mr. I.
Nedefuji, an old seal hunter, P. kurilensis had bred untill about 1959 on the cliffy
coast between Kuzurehama and Nenbutsuiwa Rock on the east coast of the Shiretoko Pen. Since the male P. kurilensis tends to remain at its birth hauling groundalmost around the year (Marine Mammal Research Group, 1978), the latter consideration may be more plausible.
We wish to express our deepest appreciation to Mr. H. Ohki for providing uswith the materials, Mr. N. Hachiya of our laboratory, and the members of theSurvey Group of the Vertebrate Community, Shiretoko Peninsula and the Marine
Mammal Research Group for their help and kind advice.
REFERENCES
BELKIN, A. N., 1964. A new species of seal -Phoca insularis n. sp.-from the Kuril Islands. Dokl. Akad. Nauk.
SSSR, 158 (5): 1217-1220. (in Russian)
BELKIN, A. N., G. M. KosYGIN, and K. I. PANIN, 1969. New materials about the characteristics of theKuril seal. pp. 157-175. In: V. A. Arsenev, B. A. Zenkovich and K. K. Chapski (eds.) MarineMammals. Academy of Sciences of U.S.S.R., Ministry of Fisheries U.S.S.R., Moscow. (in Russian)
HELLE, E., 1980. Age structure and sex ratio of the ringed seal Phoca (Pusa) hispida Schreber population inthe Bothnian Bay, northern Baltic Sea.,.(:'. Siiugetierkunde, 45 (5): 310-317.
MARINE MAMMAL RESEARCH GROUP, 1978. A brief note 6th meeting Marine Mamm. Res. Group. Mammal.
sci., 36: 95-104. (in Japanese)
NAITO, Y., and M. NrnmwAKI, 1972. The growth of two species of the harbour seal in the adjacent watersof Hokkaido. Sci. Rep. Whales Res. Inst., 24: 127-144.
NAITO, Y., and S. KONNO, 1979. The post-breeding distributions of ice-breeding harbour seal (Phoca largha)
and ribbon seal (Phocafasciata) in the southern Sea of Okhotsk. Sci. Rep. Whales Res. Inst., 31: 105-119.
NnzuMA, A., Y. NAITO, T. !Too, K. WADA, H. ABE, N. 0HTAISHI, and M. NISHIWAKI, 1980. Number andpresent status of the Kuril seal, Phoca kurilensis INUKAI, 1942 along the Pacific coast of the eastern
Hokkaido. J. Mammal. Soc. Japan, 8 (2, 3): 97-104. (in Japanese with English summary)
0HTAISHI, N., 1978. Ecological and physiological longevity in mammals from the age structure of Japanesedeer. J. Mammal. Soc. Japan, 7 (3): 130-134.
PLANK,]. and RYCHOLO, A., 1952. Eine Schnellentkalkungsmethode. ,.(:'bl. Allg. Patho., Jena., 89: 252254.

Sci. Rep. Whales Res. Inst.,
No. 33, 1981

134

OHTAISHI AND YONEDAEXPLANATION OF PLATE
PLATE I
Fig. l. Cementum of the canine teeth. DC shows dentino-cemental junction; thenumbers show the age of each layer. Hematoxylin stain. X 22Fig. 2. Lateral view of skull. Posterior margin of zygomatic bone makes a corner,
the inferior surface of tympanica is flat and the proboscis is massive.
Fig. 3. Dorsal view of skull and mandible. The teeth are heavily worn.

Sci. Rep. Whales Res. Inst.,
No. 33, 1981

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