AN OBSERVATION OF EPIMELETIC BEHA VIOROF LAGENORHYNCUS OBLIQUIDENSTOSHIO KASUYA
Ocean Research Institute, University of Tokyo, TokyoANDNOBUYUKI MIYAZAKI
University of the Ryukyus, Naha, Okinawa

The records of the epimeletic behavior in various cetaceans are documented
in Caldwell and Caldwell (1966). On the Pacific whitesided dolphin Lagenorhynchiis obliquidens Gill 1865, he showed three cases where the behavior wasdirected to wounded or captured animals of the same species, and another casewhere it was directed to the dead carcass. The present observation adds anotherexample of the latter, and will show that the behavior is common in this species.
On board of the research vessel Tanseimaru, we had a cruise (KT75-7) for
the observation of marine mammals. The cruise started at Toyama (36°46'N,137°13'E) on 9 June 1975 and ended at Tokyo on 18 June. During the two
days' observation in the Sea of Japan, the surface water temperature wasbetween l 7°C and 21°C, and only two schools of L. obliquidens were observed
at 39°46'N, 139°33'E and at 41°15'N, 140°16'E. They were composed of about
30 and 10 animals respectively. In the Pacific area the species was concentrated
in the coastal waters between 38°N and 36°30'N. In the south and north of
this range, there, were observed tropical and boreal species respectively (Fig. 1).
Among many Phocoenoides observed, only one dalli-type was confirmed swimingwith 5 truei-type. The identified truei-type were 34 animals.
The sea was calm on 15 June, and at 1300 hr. a carcass of L. obliquidens
floating on the side by its own buoyancy was found. The position was 36°47'N
141°56'E. The surface water temperature at the spot was 17.9°C. When the ship
approached it to pick up, it was found that the carcass was moving rhythmically by a dorsal fin of the live animal of the same species. As the dorsal
fin of the latter was moving vigorously above and beneath the water, it wasconsidered that the animal was tossing the carcass. However, it is sure that thecarcass does not sink without this effort. When the ship came at the distanceof about 20 m, the dolphin which was larger than the carcass and probably .
an adult or subadult swam around beneath the carcass. It disappeared whenthe carcass was caught by a hook and pole. Though we found only one live
dolphin near the carcass, the captain Mr. K. Ueno who stayed at a higher placeobserved two L. obliquidens of the same size swam away from the carcass. At
this spot, there was observed no other dolphins in the sight.
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142

''''?

''L1) 1'338°N?/
41°N~21J//;tGr20

JY ~39°N

36°N

J.
/~/li/'"~25'v126',f~D2142°EFig. I. Distribution of marine mammals and surface water temperature (°C) observed
from 11 June to 17 June 1975. C: fur seal, D: delphinids unidentified, G: Globicephalasp., Gr: Grampus griseus, L: Lagenorhynchus obliquidens, P: Phocoenoides, Ps : Pseudorca crassidens, X: carcass of L. obliquidens. Numerals by the species indicate the number ofindividuals, and the dotted line course passed in the night.

The dead dolphin was a young male measuring 176 cm in body length.
On the decalcified and stained tooth slide, there were observed three postnatal
dentinal layers stainable by haematoxylin. The first stainable layer was thin,and the last was wide and situated on the pulp wall. If the layer is formed
annually and the stainable layer is accumulated in the season from autumn
to spring as in the case of S. attenuata (Kasuya 1976), the age of the deadanimal can be little more than two years. There was found no external orinternal injury on the carcass. The carcass was already cold and the skin andmuscle were very fresh, but the internal organ showed a very slight smell ofdecomposition. The stomach was empty. The several barnacles found at
the posterior edge of tail fluke were identified by Dr. T. Yamaguchi to be
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Xenobalanus globicipites Steenstrup 1851. Possibly the dolphin died of somenatural cause in the preceding day and had been floating since the death.
Though the succorant behavior may not be rare in this species (Caldwell andCaldwell 1966), it is not known in the present case if the live dolphins werecontinuously with the carcass after the death.
REFERENCESCALDWELL, M.C. and D.K. CALDWELL, 1966. Epimeletic (care-taking) behavior in cetacea.
In: Whales, Dolphins, and Porpoises (ed. K.S. Norris, Univ. of California press, 789 pp): 755789.
KASUY A, T., 1976. Reconsideration of life history parameters of the spotted and striped dolphinsbased on cementa! layers. Sci. Rep. Whales Res. Inst., 28: 73-106.

Sci. Rep. Whales Res, Inst.,
No. 28, 1976.