南太平洋におけるマグロ類とマカジキの体長と体重の関係について

The data were obtained by the Koyo tuna fishing fleet in the Fiji area during the period of four months from August to November, 1958. At present the Fiji ground is restricted roughly to the area extending from 170°E. to 170°W. and from 18°S. to 30°S. The purpose of this report is to estimate the conversion equation between length and weight of albacore, Thunnus alalunga (BONNATERRE) and striped marlin, Makaira audax (PHILIPPI), caught in the Pacific Ocean. Therefore, for converting length-frequency data to weight-frequency data, the length-weight relationships derived from the regression of weight on length can be taken as: albacore ; w=2.257・l-3.198……(1) striped-marlin ; w=3.504・l-6.737……(2) where l is logarithm of length (cm) and w is logarithm of weight ((1) in kg, (2) in kan). The relationships are illustrated in Figs. 1-3 and Table 1. The bodyweight of those with the same body-length differed by locations. The body-weight of albacore and yellowfin tuna caught in the area to the north of the equator showed a trend to increase as the fishing ground proceeded eastward. while, in the area to the south of the equator, yellowfin tuna and bigeye tuna from the intermediate latitude are mostly of body-weight than those from the low latitude. The body-weight of albacore in the Fiji area (18°-30°S) is generally larger than that in the North-Western Pacific Ocean. The body-weight composition of albacore distributed in a location south of the equator is exactly identical with that on the same latitude north of the equator. In the South Pacific Ocean, the catch of the striped-marlin consists of large sized ones. The principal group is composed of mature fishes with the body-weight from 55 to 111 kg. But on the contrary fishes with the body-weight from 23 to 36 kg are the leading group in the North-Western Pacific Ocean. In the area north of the equator, the length-weight relationship of bigeye tuna scarcely varied according to the location and season. Therefore, for the purpose of converting length-frequency samples to weight-frequency samples, it seems that the statistics obtained from the total regressions are not affected by the difference in location or seaons.

南太平洋におけるヒンナカとマカシキの主漁場てあるフィジー漁場とキハダとメバチの主漁場てある南北両赤道海域のカロリン・ソロモン漁場において,それら魚種の体長－体重間の関係を調査した結果,次のような知見を得た. 1)体長(L)と体重(W)の換算式はビンナカ log W=2.257 log L-3.198 マカノキ log W=3.504 log L-6.737 となる. 2)ビンナガ フィジー漁場の魚体は北西部太平洋漁場のそれよりわずかに肥満している.また,ミッドウェー近海の魚体はこの両漁場のそれより著しく肥満している.南北両太平洋のビンナガの分布構造は地理的に同体長-体重の魚群か対象的に生息している点で特異である. 3)マカンキ 南北両太平洋の本種の主漁場における魚群を比較した結果,北西部太平洋漁場(30°N以北)の魚群では23～36Kgの体重級のものによって主群か構成されているのに対して,南太平洋漁場てはその殆んどが成熟群によって占められ,その主群は55～111Kgの体重級のものによって構成されていて著しく大型である. 4)キハダ 南太平洋において,赤道海域の魚体は中緯度海域のそれよりわすかに肥満している一方,北太平洋において東部太平洋の魚体は西部太平洋のそれより肥満している 5)メバチ　本種もキハダと同じく,赤道海域の魚体は以南海域のものに比して肥満している.しかし,北太平洋において,魚体の体長－体重関係はほぼ一様に変化しているので,赤道以北のメバチについて,体長－体重の換算か目的であれは海域差,季節差は考慮しなくてもよいだろうと思われる.