日本産イルカの研究(IV) : イシイルカPhocaenoides dalli (TRUE) の〓游及び胎仔に就て

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概要

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• Two allied species of Phocaenoides are found in the Japan waters. Phocaenoides truei (called “Rikuzeniruka” in Japan) is distributed in the northern region of the pacific coast of Japan and migrate twice in a year. Its spring migration begins in February from south to north, from off Choshi, China prefecture to Kurile Islands. The autumn migration begins in September, from Kurile Island southward to off Fukushima prefectue, or off Choshi, Chiba prefefecture. The otherspecies, Phocaenoides dalli (called “Kitairuka” or “Ishiiruka” in Japanese) is found mostly in the Japan Sea. They are observed off Tajima, Hyogo Prefecture from the end of February to the middle of May and in the middle of June off Akita Prefecture and from the end of June to the beginning of July along the Hokkaido coast. They have occurred in Ohkotsk Sea in Jul and August and disappeared at the beginning of September. They may probably go down to south of the Japan Sea in the autumn. Both species have definite breeding season as other mammals. In phocaenoides dalli, this season is suspected during the end of June and the beginning of July, abo ?? t one month duration. The reason is that almost specimens of the presnt species, provided with sm ?? ll embryos of 5.5mm in body length, were collected in August in Okhotsk Sea. The copulation therefore must have occured before this season. The delivary period may cotinued about seven to nine months, as for the reason of following facts. The adult with emdryo of 5mm body length was caught commonly in the Okhotsk Sea during the summer from June to August, while the adults collected off Tajima, Japan Sea, during March and April are mostly finished the confinement or with large foetus of 1 meter body length. The detailed descriptions of the embryos will be made in the Miscellaneous Report of the Faculty of Fisheries, the prefectural University of Mie in near future.

• 公益社団法人 日本水産学会の論文

著者

• 岡田 彌一郎

  三重県立大・水産

• 林 良二

  富山大学理学部

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