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母船式鮪漁業の漁況に関する研究―9 : 南太平洋におけるマグロ類の体長組成について(1960年5月~8月)


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Title: 母船式鮪漁業の漁況に関する研究―9 : 南太平洋におけるマグロ類の体長組成について(1960年5月~8月)
Other Titles: Studies on the Fluctuation in Catch of the Tuna-fishing Fleet―IX The Body-length Compositions of Tunas in the South Pacific Ocean during four months from May to August 1960
Authors: 古賀, 重行
Authors (alternative): Koga, Sigeyuki
Issue Date: 31-Aug-1961
Publisher: 長崎大学水産学部
Citation: 長崎大学水産学部研究報告, v.11, pp.96-102; 1961
Abstract: The sample of tunas treated in this report were obtained from the catcheres of 3 Tenyo tuna-fishing fleet in the Western South Pacific Ocean during period of four months from May to August 1960. Findings from the study are: (1) Local difference of the length frequency distributions of tunas. The yellowfin tuna and the albacore, proceed to go southward, this group of the larger mode was dominant, but the bigeye tuna. the tendency was quite opposite. The folk length of the yellowfin tuna seemed to become smaller gradually toward the east. (2) Seasonal changes of the length frequency distributions of tunas. In regard to the tuna, the modal size of the principal catch became smaller in accordance with the seasons progress. Especially, in the yellowfin tuna and the bigeye tuna, this phenomenon acoording to my observation and the albacore was not so remarkable. Therefore, the catcher of the yellowfin tuna and of the bigeye tuna are generally composed of the middle size of fish. But, on the contrary, the seasonal change of the bigeye tuna in the South Equatorial Pacific Ocean was not distinct. The seasonal changes of the size compositions of the southern bluefin tuna had not been variable. That of the yellowfin tuna was supposed to be caused by growth of small fish-less than 100cm in length-and migration of the modal size principal catch to low latitude area. (3) In regard to the tuna, as I reported before, the difference in size of male and female was quite evident and this tendency was also the same in this area. In the sex-ratio of tunas this season, the percentage in female were larger than that of the males. Especially, north of 10°S, this tendency was most conspicuous. / 母船式鮪第20次3天洋船団操業を通じて,南太平洋における鮪類の魚体組成について次のような傾向を認めた. 1. 海区別体長組成 (1) キハダ……赤道より南緯する程大きい型の体長群増加の傾向が認められる.又,東方へ向う程,魚体小型化の傾向がうかがわれる. (2) ビンナガ……南緯する程魚体は大きくなっているもののようであるが,キハダのように明瞭な差を見出すことは出来なかった. (3) メバチ……キハダにみられる傾向と逆に,高緯度に向う程,魚体小型化の傾向が認められる. 2. 季節別体長組成の変化 (1) フィジー海域 キハダ……前年度と異った組成を示して中型群の顕著な増加,大,小型群の顕著な減少傾向が認められた.この現象は前年度秋期の100cm以下のModal groupの成長に加えて,この期の主群が低緯度海域へ移動したことに起因するものと考えられる. メバチ……季節の経過に伴い魚体小型化の傾向が認められた.特に本船団時期において,急激な大型群の減少,顕著な中型群の増加傾向が特色として挙げられる. ビンナガ……季節の経過に伴って,魚体小型化の傾向がうかがわれる. 濠州マグロ……一年毎に増減の周期変動を示すもののようである. (2) 南太平洋赤道海域 キハダ……フィジー海域と同様に魚体小型化の傾向がうかがわれる. メバチ……一年毎に主体長群の入れ変る周期変動を示すもののようである. 3. マグロ類は性による魚体差が顕著で,雄は雌より大きい.本期における性の組成においては雌の占める割合が多く,特に10°S以北海区はこの傾向が顕著であつた.
URI: http://hdl.handle.net/10069/31693
ISSN: 05471427
Type: Departmental Bulletin Paper
Text Version: publisher
Appears in Collections:第11号

Citable URI : http://hdl.handle.net/10069/31693

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