東北海區に於ける流網による漁獲サンマの組成(豫報 I)

概要

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3084 individuals of drift-net skipper were collected from 7 fishing grounds from September 24th, 1934 to January 12th, 1935. Of all of them, the body length and weight were measured and the age was determined by counting the winter rings on scales, and the sex and maturity were determined on 2170 individuals of them. We know that: (1) The drift-net skipper was composed of the III and IV age groups. The IV age fish amounted to 49-66% in the water off Iwate and Ibaragi Prefs. from Sept. 24th to Nov. 11th, and to 8-25% off Tiba and Mie Prefs. from Nov. 20th to Jan. 12th. (2) The sex composition was nearly constant (1:1). The spawning fish amounted to 1% in the water off north-east of Iwate in Sept. to 18-35% off Iwate and Ibaragi from Oct. 13th to Nov. 11th, and diminished to 6% off Tiba Pref. on Nov. 20-24th due to immigration of the III age immature fish, but it was increased thereafter to 98% in the water off Mie Pref. in Jan. (3) The spawning mark was observed in the most of rings from IV age fish. This fact shows that the most of IV age fish performed the first spawning in the last season. (4) The body length of III age fish was ranging from 21.3cm to 27.8cm and that of IV age fish from 26.1cm to 31.8cm.