Inconsistency between the Per Capita Fecundity and Estimate of the Yearly Egg Production of the Chub Mackerel Scomber japonicus in Japan

抄録

We calculated the stock in number of chub mackerel Scomber japonicus in the Pacific ocean off Japan during 1970-1988 by virtual population analysis (VPA). We also calculated the number of eggs spawned by all adults from estimation of the age-dependent percapita fecundity.Japan Fisheries Agency compiles the yearly egg production estimated by plankton net survey.This project is called the egg production survey. Wecompared the yearly egg production estimated by VPA and the egg production survey. We found that the yearly egg production estimated by the egg production survey fluctuates from year to year much greater than that estimated by VPA.This result suggests that either the per capita fecundity is much smaller than we considered before or the egg production survey underestimates the yearly egg production at least when the stock is rare.We also estimate fluctuation of the natural mortality coefficient of adult and the survival rate of 0 yrold fish.