北洋産DALL'S porpoiseの生態について

• Main Authors: 水江 一弘, 吉田 主基, 竹村 暘
• Format: Report
• Language: Japanese
• Published: 長崎大学水産学部 1966
• Subjects: Bering Sea; Cornu; Pacific
• Online Access: http://hdl.handle.net/10069/31459; https://nagasaki-u.repo.nii.ac.jp/?action=repository_uri&item_id=8671; https://nagasaki-u.repo.nii.ac.jp/?action=repository_action_common_download&item_id=8671&item_no=1&attribute_id=18&file_no=1

As a result of our investigation on the stomach contents of 148 animals and the gonad of 103 animals from among many DALL'S porpoises which had been caught by the Japanese salmon fishing gill nets in the Bering Sea and the North Pacific Ocean in 1964 and 1965, the following characteristics have been ascertained. The sampling period in each year lasted for three months from the latter part of May to the first part of August. 1) The stomach contents of infant porpoises were their mother's milk in all cases; no other food was found; and there was no empty stomach. 2) In this sea area, small marine animals (squid, fish and shrimp) for the food of porpoises were very abundant in this season, but generally the quantity of their stomach contents was not so large. 3) No significant difference was recognized in quantity and kind of stomach contents between male and female, but there was a distinct difference between pregnant and nonpregnant animals. The contents were less in quantity and more polyphagous in the former than in the latter. 4) Squid were very abundant in this sea area in this season, and porpoises ate mostly these squid. Sometimes fish and shrimps were found among the stomach contents but these were very small in quantity in camparison with squid. 5) There was only one sample of red salmon in the investigated stomachs, but it is most likely porpoises do not eat adult salmons as their food. It is not clear whether or not small size salmons in this sea area are caught by porpoises. It is subject to future investigations. 6) As a result of the investigation in 1965, it was clarified that the period of parturition for the porpoises in this sea area is between the latter part of July and the first part of August. 7) It is presumed that the body length of a baby porpoise at the time of parturition is about 100cm. 8) It is believed that the pregnant period of porpoises is less than a year. Fetuses were found in the left uterine cornu in all cases. 9) A sexually mature male is 185cm in body length or more, and ...