Distribution and feeding habits of juvenile herring (Clupea pallasii) in Northern Japan

Distribution and feeding habits of wild and artificially produced juvenile herring are described for the Ishikari subpopulation of Pacific herring on the west coast of Hokkaido in Japan. Herring were collected using a beach seine, larva net, small beam trawl, and fishing efforts at the coast of Atsuta, and with set nets in the Ishikari River, in the summers of 1996-1999. Large numbers of wild juveniles, ranging from about 30 to 50 mm in total length, were collected in the surf zone near the river mouth of the Ishikari River (salinity range 0.03-33.65 psu) in late June-early July. From early to middle July larger wild juveniles (50-70 mm) were found in the Ishikari River. These results suggest that in the Atsuta estuary, herring juveniles gather in the surf zone at about 30 mm in length and move to the river when they grow to about 50 mm in total length. Small coastal and brackish copepods (Paracalanus parvus, Oithona similis, O. atlantica, Clausocalanus pergens, Eurytemora spp.), harpacticoids, and cladocerans composed the majority of food organisms in the guts of juveniles (including some artificially produced herring) up to 60 mm. However, the composition differed between sampling locations and dates and juveniles greater than 80 mm (all artificially produced herring) fed on larger organisms such as mysids, amphipods, and fishes.