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Description:
In order to elucidate the stock structure and growth of neon flying squid, seasonal variations in dorsal mantle length, sex ratio, gonad weight and degree of sexual maturity of this species are presented here on the basis of the results of biological measurements of the samples taken by squid gillnetters during June and December in 1983-1985. The majority of the sampled squid were immature and not copulated females, while the proportion of males in number was only 2.4% in the 3-year average, and about half of the males were semi-mature (11%) or mature (36%). The principal modal mantle length in females shifted from 37cm level in June to 45cm level in September, then backed again to a smaller modal size within the range of 35-41cm in October-November. The ovary weights showed a general tendency to gradually increase between June and August, but this was followed by an abrupt decrease in September. Judging from these results, it is presumed that Japanese squid squid gillnetters mainly catch “extra-large sized” group of neon flying squid in June-September and “large sized” one in October-December, selectively out of four different size groups in the northern North Pacific.