スケトウダラの年齡組成(豫報I)

概要

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20, 600 individuals of Theragra chaigogramma (Pallas) were•angled in the waters 8 miles NW of Iwanai Harbour, Hokkaidô and 10 miles off Teradomari Harbour, Niigata Pref. from Dec. 1935 to Mar. 1936. With regard to 525 samples out of them, the body lengths and weights were measured, the age was determined counting the winter rings on vertebra, and the sex and mat rity were also determined (Table 1, 2 and Fig. 1). Following results are obtained. (1) Sex ratio is nearly the same for both of the fishing grounds, namely male 40% and female 60% (2) In the opening fishing season, the shoals are mainly consisted from immature fishes, while, in the closing season the percentage of spent fishes markedly increases. (3) Shoals are composed of the 6 age groups of 3 to 8 years old. (4) On the both fishing grounds investigated, is the growth rate nearly the same.