Variations in food abundance for Japanese sardine larvae related to the Kuroshio meander

Long-term fluctuations of chlorophyll a concentration, and abundance of herbivorous or omnivorous small copepods during the spawning season of the Japanese sardine, Sardinops melanosticta , were examined in relation to the types of Kuroshio meander. The purpose was to clarify the influence of the meander on the production of food organisms for the sardine larvae and their survival in the Pacific coastal region of central Japan. During an A-type meander of the Kuroshio, when the offshore and inshore movements of the Kuroshio path were small except at the beginning of the meander, the surface chlorophyll a concentration in the coastal region was lower than that during a non-A-type meander with frequent and prompt fluctuations of the Kuroshio path. The abundance of small copepods was also low during the A-type meander except in the subsequent spring just after the beginning of an A-type meander, but often high during the non-A-type meander. Prompt fluctuations of the Kuroshio path during the non-A-type meander probably cause local upwellings which stimulate primary and secondary production near the Kuroshio, and may enhance the survival of the sardine larvae. On the contrary, the quasi-stationary state of an A-type meander may be unfavourable for the production of phytoplankton and nauplii of herbivorous or omnivorous small copepods, and therefore the survival of the sardine larvae becomes poor.