Dall's porpoise (English spelling) Phocoenoides dalli; Dall's porpoise

Japanese: イシイルカ（英語表記）Phocoenoides dalli; Dall's porpoise

Dall's porpoise is a member of the genus Dall's porpoise and the suborder Odontoceti. Males are about 2.4m long, and females about 2.2m long. They can weigh up to 200kg. Their birth length is about 1m. They are divided into two types, Dall's porpoise and Ryke's porpoise, based on their body color. Both types have black body color and white spots on their sides, but the Ryke's porpoise type has larger spots than the Dall's porpoise type, which extend to the pectoral fin. Both types have a pale or white band on their dorsal fin, and the rear edge of the caudal fin is bordered with white. Rarely, they are found completely black. They have one blowhole located on the midline of the head. The head is small and becomes very thick from the tip of the snout to the dorsal fin. The dorsal fin is located forward of the center of the body, is wide, and is almost a right-angled triangle in shape, with a blunt tip and hangs backward. The pectoral fin is located relatively forward. The length of the rear edge of the caudal fin is less than one-third of the body length. The upper and lower keels (ridge-like protuberances) on the caudal peduncle are remarkably developed. There are 23 to 28 pairs of small spade-shaped teeth on the upper and lower jaws. The teeth are the smallest of all cetaceans, and barely protrude beyond the gums. They usually live in groups of 2 to 12 individuals, but occasionally form large groups of several thousand individuals. They give birth in spring and summer. They have a wide range of diet, preying on shoaling fish and squids that live in the surface to mid-depth layers, and are particularly fond of myctodonts and pacific squids. They are found in the North Pacific Ocean and its associated seas, from temperate to subarctic deep waters between 30° and 62° north latitude. They are the target of javelins and are caught as bycatch in gillnets.

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

クジラ目ハクジラ亜目ネズミイルカ科イシイルカ属。体長は雄約 2.4m，雌約 2.2mである。最大体重は約 200kg。出生体長は約 1mである。体色の違いに基づき，イシイルカ型とリクゼンイルカ型に分けられ別称される。いずれも体色は黒色で，体側に白斑を有するが，イシイルカ型よりもリクゼンイルカ型の方が斑が大きく，胸鰭 (むなびれ) 付近まで広がる。また両型とも背鰭は淡色あるいは白色の帯がみられ，尾鰭の後縁は白色で縁どられる。まれに全身黒色のものがみられる。噴気孔は1個で頭部正中線上にある。頭部は小さく，吻端から背鰭に向って非常に太くなる。背鰭は体の中央より前方に位置し，幅広であり，形状はほぼ直角三角形で，先端は鈍く，後方に垂れる。胸鰭は比較的前方に位置する。尾鰭後縁の長さは体長の3分の1未満である。尾柄部にある上下のキール (稜状の隆起) が著しく発達する。上下顎骨に小さいスペード型の歯が左右 23～28対並ぶ。歯はクジラ類中最も小さく，歯ぐきからほとんど突出しない。通常2～12頭程度の群れで行動するが，まれに数千頭の大群をなす。出産期は春と夏。食性範囲は広く，表層から中層に生息する群集性の魚類やイカ類を捕食し，特にハダカイワシ類やスルメイカ類を好む。分布は北太平洋およびその付属海で，北緯 30゜～62゜かけての温帯から亜北極域の深海域に生息する。突棒漁業の対象で，刺網により混獲される。

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