Occurrence and size distribution of ayu larvae around the surf zones facing Toyama Bay related to habitat shift

Abstract

The Occurrence and distribution of ayu, Plecoglossus altivelis, larvae around the surf zones of a sandy beach were investigated in Toyama Bay, the Sea of Japan, from 1992 to 1998. Larvae appeared at the surf zones of the sandy beach from October through January, with a peak in November. Mean standard length of larvae collected by a surf zone net was 12.1±1.8 mm in October, 18.3±3.0 mm in November, 22.0±4.9 mm in December and 23.3±2.7 mm in January. The standard length of ayu larvae collected at offshore shallow waters from January to February by a beach seine ranged from 21 to 48 mm (Ave. 36.1±3.8 mm) with a mean of 36 mm. Ayu larvae were observed by scuba diving at surf zones and adjacent offshore shallow waters from November to March. These findings of seasonal occurrence and distribution suggested that most ayu larvae inhabited the surf zones from October to December and then migrated to the adjacent offshore shallow waters by February as the larvae grew and the water temperature fell in Toyama Bay.