Biological characteristics of Ommastrephes bartramii in northwest Pacific Ocean

Abstract:

Based on the samples from Chinese squid jigging vessels in the traditional fishing area (150°-165°E，39°-45°N) of northwest Pacific in 2007, the biological characteristics of squid Ommestrephes bartramii were studied. The results showed that the range of mantle length was from 200 to 436 mm and the average mantle length attained 282 mm, the dominant mantle length ranged from 230 to 320 mm which accounted for 81.6 percent of the total. The monthly mantle length of male squid was smaller than that of female, the growth index of relationship between mantle length and body weight was nearly three. The sex ratio of total number accorded with 1∶1（P>0.05）, but the proportion of mature males was obviously higher than that of females（P<0.05）. The sexual maturity stage dominated Ⅰ and Ⅱ, the average maturity stage of females was less than that of males. The length and weight of nidamental gland of squid increased with the growth of gland maturity. Since the composition of mantle length had two modes in samples and immature and mature individuals both exist, it is concluded that the individuals of the catch could be divided into two populations in the northwest Pacific Ocean, i.e. winterspring cohort with smaller size and autumnspawning cohort with bigger size, in which the winterspring cohort dominated in the catch.