Feeding Ecology of Juvenile Masu Salmon Oncorhynchus masou in the Coasts of Hokkaido with Special Reference to Stomach Contents

Abstract

Feeding ecology of juvenile masu salmon, Oncorhynchus masou, collected by commercial set nets, was studied in the coastal waters of Hokkaido between 1991 and 1993. Stomach fullness indices varied among sampling dates and two areas sampled (Japan Sea and Pacific Ocean). The stomach contents of juveniles collected along the coasts of the northern Japan Sea were composed entirely of sand lances (Ammodytes personatus), which were 1/4-1/2 of the body lengths of the juvenile salmon. In contrast, stomach contents of the juveniles collected along the coast of the Pacific Ocean included a variety of organisms, and size ratios of prey to juveniles were lower than those in the northern Japan Sea. The results of comparisons of juvenile stomach contents between the Japan Sea and Pacific Ocean indicate that juvenile masu salmon occupy different ecological niches in the two areas. Production of juveniles in the northern Japan Sea may depend on the abundance of sand lance. © 1995, The Japanese Society of Fisheries Science. All rights reserved.