Implications of meso-scale eddies caused by frontal disturbances of the Kuroshio Current for anchovy recruitment

Abstract

This paper discusses the implications of the meso-scale eddies, which are caused by frontal disturbances of the Kuroshio Current, for larval transport, distribution and food availability for Japanese anchovy, Engraulis japonicus (Houttuyn). It is a ubiquitous feature of the Kuroshio Front that wave-like meanders, with wavelengths of 100–400 km, generate cyclonic frontal eddies off the Pacific coast of the island of Japan. These eddies are likely to affect larval transport and the survival of the coastal spawning fish such as anchovy in the Kuroshio region by possibly moving coastal water offshore to the frontal region. With this in mind, a frontal eddy was tracked from 18–23 May 1994 in the Enshu-nada Sea, where one of large spawning grounds of anchovy was found. Intensive transect surveys across the eddy were made to collect anchovy eggs and larvae simultaneously with prey organisms e.g. naupliar and copepodite copepods. These surveys showed that anchovy eggs and larvae hatched in the coastal water of the Enshu-nada Sea were entrained into the frontal eddy and transported along the Kuroshio Front, possibly recruiting to coastal nurseries in the Enshu-nada Sea. In addition, the upwelling of nutrient-rich water in the vicinity of this cyclonic eddy enhanced primary production and subsequent copepod production, providing potentially favourable conditions for the feeding and growth of the anchovy larvae entrained in the eddy.