大槌湾におけるシロザケ稚魚の食性

抄録

Feeding habits of chum salmon fry was studied, using the samples collected from 7 locations in the Otsuchi Bay during the period from 1978 to 1980. Amphipoda, Appendicularia, Chaeto-gnatha, Cladocera, Copepoda, Euphausiacea, Polychaeta, crab and shrimp larvae, fish eggs and larvae, and land insects were found in stomachs of chum salmon fly. Chum salmon fly generally consumed food organisms that were abundant in their habitats. Epibenthic crustaceans were their important food organisms in the inner part of the bay but zooplankton near the mouth of the bay. The mean feeding rate was 1-4%. Feeding rate of chum salmon fry captured near the mouth was larger than that of fry collected from the inner part of the bay. A remarkable difference was recognized in the feeding rate between day and night. Chum salmon fry did not actively feed during the night. Condition factors of released chum salmon fry was about 0.7 and they increased during their stay in the Otsuchi Bay. Large-sized chum salmon fry living near the mouth of the bay had condition factors of more than 0.9. This suggests that chum salmon fry had good environmental conditions during their stay in the Ostsuchi Bay after the seaward migration.