Development of assessment techniques for pelagic fish stochs: applications of daily egg production method and pelagic trawl in the Northestern Pacific Ocean

Abstract

Biomass estimates of pelagic fishes from both fishery-dependent and independent data are necessary for robust stock assessment and fishery management. The spawning biomass of the chub mackerel Scomber japonicus was estimated for 1996 and 1998 by the daily egg production method (DEPM), though the estimates were smaller than those of the virtual population analysis (VPA) in 1998 when the sampling spatially and temporally mismatched to the actual spawning. Abundance indices of young-of-the-year (YOY) of chub mackerel and Japanese sardine Sardinops melanostictus (30-170mm BL) were obtained by a pelagic trawl survey using a net with a 27m×27m mouth opening in the Kuroshio-Oyashio transition region (36-40°N, 143-170°E) during 1996-2001. The indices fairly agreed with the recruitment levels estimated by VPA, and hence could be used for recruitment forecasts.