Stock structure of Japanese anchovy

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1. Reproductive ecology was compared between 4 sub-populations that inhabit off Japan. The spawning activity was commonly controlled by the water temperature higher than 15℃ for anchovies in the coastal waters in Sagami Bay, Wakasa Bay and Osaka Bay. Within this temperature range the spawning period was varied between localities depending on nutritional conditions reflecting food availability. Maturity body lengths differed among the three bays. The anchovy in the offshore east of Honshu spawned under the temperature environment much lower than 15℃. Moreover, the offshore anchovy matured at 10cm in body length, later than that for the coastal anchovy. Fecundity and spawning frequency were positively correlated with temperature for anchovies in every locality. However, the anchovy offshore east of Honshu showed spawning ability equivalent to the coastal anchovy in the lower temperature environment. Anchovies in the different localities exhibited different spawning patterns in accordance with their environment.2. Otolith microstructure was examined with a scanning electron microscope for 6 sites samples from Kyushu to Hokkaido. The early stage growth determined by daily growth rings from hatching to 60 days was different among the sampling sites. The growth rate tended to be higher in the south and lower in the north. In addition, external morphology was examined with 12 body parts measured. The morphological variation tended to increase with geographical distance. This suggests the existence of local populations that have different hatching and distribution areas.3. Stable isotope ratios of delta-15-N delta 13-C was compared between anchovies from Wakasa Bay, Japan Sea and off the Pacific coast of eastern Honshu. The values of delta-15-N and delta-13-C ranged differently between two areas as a whole, though they overlapped and varied among samples considerably. The great variation seemed to make the use of the stable isotope ratio difficult for stock identification.