Long distance dispersal of larval and juvenile rockfish, Sebastes thompsoni, with drifting seaweed in the Tohoku area, Northwest Pacific, estimated by analysis of otolith microstructure

The possibility of long distance dispersal of larvae and juveniles of the gold-eye rock-fish, Sebastes thompsoni, which lives in association with drifting seaweed during the early developmental period, was examined in the Tohoku area, northwest Pacific, Japan, by analysis of otolith microstructure. Larvae and juveniles associated with drifting seaweed were caught throughout the region from near the coast seaward to more than 300 km offshore. Analyzing daily otolith increments in larvae and juveniles, two types of otolith microstructure were found, differing in daily increment width in the near-core portion just outside the extrusion check. Individuals having otoliths with wide daily increments were estimated to have been extruded in the south of Inubozaki. These regions have higher water temperatures because of their location on the route of the Kuroshio Extension, and the wide increments were considered to be due to higher growth rates of the larvae. As warm water from the Kuroshio Extension intruded into the northern regions, individuals with wide increments occurred also in off southern Sanriku. Research off Onagawa Bay in 1994 and 1995 showed that about 20% of individuals had been transported from the south of Inubozaki. These results suggest that this fish achieve long distance longitudinal dispersal for at least 400 km from south to north, and individuals extruded in the southern waters contribute to northern local populations.