Simulation-based daily cohort analysis of Pacific anchovy (Engraulis japonicus) in southern Korean coastal waters

I estimated daily standing stock biomass and potential production of Pacific anchovy, Engraulis japonicus, in the southern coastal areas off the Korean peninsula by a cohort analysis based on the reported estimates of anchovy spawning biomass and the empirically driven allometric relationships of fecundity, growth and mortality. Reported biomass estimate of adult anchovy in the southern coastal area of Korea for the May–July period ranged from 0.14 to 0.56 × 106 mt, but my simulation-based cohort analysis indicated that the biomass level of larval, juvenile and adult anchovy is seasonally variable and could reach 1.9 × 106 mt in early November. Estimated potential production of anchovies of egg to age-2 stages was 8.1 × 106 mt yr−1, which peaked in September. Age-0 anchovies accounted for 84% of the estimated annual mean biomass and 92% of the annual potential production. Comparison of monthly length frequencies of anchovies between the simulation and the samples of fisheries catch suggested that catches from January to May consisted of anchovies spawned in the previous year (the 2nd year anchovy) whereas those from June to December were mostly from young-of-the-year anchovies. Estimated instantaneous fishing mortality derived from the catch statistics (ca. 0.25 × 106 mt in 2006) and the estimated annual production by anchovy >30 mm fork length (ca. 5.9 × 106 mt) was 0.40 yr−1, which was marginal compared with the estimated natural mortality, 11.29 yr−1. The ratio of annual production to mean biomass was 6.7 yr−1. Ongoing acoustic surveys will validate and improve my stock assessment of anchovy, which is critical in possible fisheries management of anchovy in Korea.