Dispersal of larvae and juveniles of Japanese anchovy Engraulis japonicus in the Kuroshio Extension and Kuroshio–Oyashio transition regions, western North Pacific Ocean

Abstract

A sampling survey for Japanese anchovy Engraulis japonicus larvae and juveniles was carried out using two types of sampling gear for capturing a wide size range of fish in the Kuroshio Extension and Kuroshio–Oyashio transition regions in August 1996. Anchovy larvae were found widely far offshore. Total lengths (TLs) of the fish ranged mostly from 6 to 40 mm, which corresponded to 5–50 days after their hatching in July. The number of anchovy collected varied with sampling sites, but it was not clear what factors accounted for the variation. While the mean lengths of larvae taken in the Kuroshio Extension area tended to be smaller offshore, those in the transition area significantly increased in size as the distance offshore increased, perhaps because larger larvae migrated northward into the transition region. The mean growth rate of otolith-aged larvae was 0.63 mm per day, which was similar to those previously reported in the coastal waters. The daily mortality coefficient, which was estimated based on age–frequency distribution converted from length–frequency distribution, ranged from 0.362 to 0.136 per day. The mortality rates decreased with growth, being lowest for larger larvae offshore.