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Small pelagic fishes such as the Japanese sardine Sardinops melanostictus and the chub mackerel Scomber japonicus are important fishery stocks in Japan. Stock abundances of these species are subject to both low and high frequency variability. With the ratification of the United Nations Conference on the Law of the SEA (UN 1983), the Japanese government introduced a Total Allowable Catch (TAC) system in 1997. Currently, eight species are managed under the TAC system, and five of them have been assessed by virtual population analysis (VPA). For robust stock assessments and fishery management, fishery-independent biomass estimation is indispensable, because of the potential biases in fishery data and great uncertainties in the VIA estimates of abundance in terminal years and their proximity. In recent years, the stock abundances and catches of both species remain at low levels, and 0 and 1 year old fishes account for the majority of annual andings (after Fisheries Agency and NRIFS, Japan). Therefore, this situation strongly requires alternative assessment techniques to VPA. Also, forecasting the level of number of recruits before their exploitation is very important for the management of these species. As a fishery-independent index for the spawning stock biomass (SSB), the egg census had been performed since 1978 for mackerels Scomber japonicus and Scomber australasicus, the Japanese anchovy Englaulis japonicus, and the Japanese sardine.1 These species are multiple spawners and their spawning ecology (e.g., spawning frequency, batch fecundity, spawning area and spawning season) varied from year to year,2 which are required to be incorporated into the current egg production method.2 We investigated the spawning ecology of chub mackerel around Izu Islands, the major spawning grounds, in 1996 1998 and estimated the spawning biomass using the daily egg production method (DEPM).2 We also performed a pelagic trawl survey in the Kuroshio extension (KE) and Kuroshio Oyashio transition region (KR) from May to June during 1996 2001 and estimated the abundance of small pelagic fishes. Finally, the applicability of these techniques for stock assessments was discussed.

fisheries science

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