POPULATION ESTIMATES WITH VARIANCES OF SPANISH SARDINE ALONG THE SOUTHERN FUJIAN COAST, CHINA, FROM LENGTH-BASED COHORT ANALYSIS

Population size and fishing mortality rate and their variances were es timated for the Spanish sardine Sardinella aurita along the southern F ujian coast, China, in 1971-1983 and 1986-1989 by Jones's length-based cohort analysis. Population abundance and biomass varied among differ ent periods, whereas exploitation patterns were consistent within peri ods from 1971 to 1983 but differed significantly from those in 1986-19 89. The approximate variance estimators for this method were developed in general form by the delta method. Errors in the estimates caused b y the input parameters were examined, and we conclude that correlation between the estimates of asymptotic length L(infinity) and the growth coefficient K tends to reduce errors in the population estimates from length-based cohort analysis. Risk of misestimating population size i ncreases when length-based cohort analysis is used for stocks with hig h natural mortality. A comparison of the population biology and fisher ies of the Spanish sardine around the world shows that the population along the southern Fujian coast is much smaller than that off northwes tern Africa.