Effects of frontal eddies on the distribution and food availability of anchovy larvae in the Kuroshio Extension

Abstract

The frontal area of the Kuroshio Extension was observed in June 1997 and May 1999. In 1997, anchovy larvae were most abundant in a frontal region of the eddy generated in association with a northward intrusion of warm water from the Kuroshio Extension. High nutrient concentrations apparently overlapped with the larval aggregation, while chlorophyll-a concentration was rather low all over the region. In 1999, observations were made along a two-day trajectory of a drifter released from the eddy centre, which was recognized by a satellite image. Chlorophyll-a concentration was high in the eddy centre but decreased with time. By contrast, abundance of copepod nauplii in the eddy increased with time, and eventually doubled. These results suggest that the frontal eddy contributes to both copepod production and horizontal entrainment or aggregation of anchovy larvae in the frontal region. The frontal eddy possibly benefits the growth and survival of fish larvae in the oligotrophic oceanic water of the Kuroshio Extension region.