日本海における曳縄実習 (天鷹丸242次航海) の報告

Report of Trolling Fishing Practice (T/V Tenyo-Maru's 242nd voyage) in Japan Sea

Creators Mohri Masahiko

Creators Tanoue Hideaki

Creators Okawa Takumi

Creators Hata Kazuhiro

Creators Okita Yukio

Creators Goto Hiroshi

Creators Kokatsu Masaki

Creators Sugawara Youhei

Creators Sakai Kenichi

Creators Wakabayashi Toshie

Creators Shimokawa Shinya

The trolling fishing operations were carried out off Yamaguchi Prefecture of Japan Sea using our training vessel Tenyo-Maru in September 11 to 14, 2016. The results were as follows: i) A total of 17 common dolphins, Coryphaena hippurus, were caught. Their total length ranged from 51cm to 95cm, and their weight, from 1.1kg to 4.5kg. Of the common dolphins caught, ten were females, six, males and one, of an unknown sex, which means that females had a largrer number and accounted for a little less than two-thirds. As for the content of the stomach, 12 individuals or a little larger than two-thirds had no content, and four took food. The content of the stomach included squid, Japanese anchovy, whitebait and some unknown small fish. ii) According to vertical sections of the water temperature and salinity obtained by our ocean observation with a CTD, the water temperature was ≧ 25℃ in the layers about 30m deep or less in all of the sea areas surveyed. The layers where the water temperature was ≧20℃ were distributed in the depth of about 30m or less in the north and became deeper in the coastal waters in the south, where the layers were equal to or more than about 50m in depth. Salinity was 32psu in all of the sea areas studied in the layers shallower than about 10m. The layers where the salt content was ≧33psu were deeper in the north and found in about 30m deep and grew shallower in the sea off the southern coasts, about a depth ≧10m. Common dolphins are distributed higher than about 25℃.

[ISSN]0370-9361