春季の黒潮親潮移行域および黒潮続流域におけるフウライカマスNealotus tripesの分布と食性

抄録

We examined distribution and feeding habits of adults (150-216mm SL) and subadults (70-149mm SL) and distribution of larvae and juveniles (9-69mm SL) of Nealotus tripes in the Kuroshio-Oyashio Transition Zone (KOTZ) and Kuroshio Extension (KE) in spring obtained by a midwater trawl survey at night. Adults and subadults rarely occurred in KE but were abundant in KOTZ with the concentrated area north of KE axis with sen surface temperature of about 17°C and 100m depth temperature of 12-14°C. Larvae and juveniles had slightly wider distribution in KOTZ. Stomach content index (SCI-stomach content weight per body weight) was not statistically different by time of day or by body size of adults and subadults. According to the index of relative importance (IRI), euphausiids (IRI-2.399) were most important prey of adults followed by myctophids (1,767), unidentified fishes (1,699), miscellaneous (702) and anchovy larvae (543). In subadults, unidentified fishes (mainly mesopelagics excluding myctophids, (1,862) and euphausiids (1,826) were major prey followed by miscellaneous (1,009), squids (209) and myctophids (164). These diet compositions were distinct from those reported for larvae and juveniles of N. tripes which heavily preyed upon anchovy larvae in KOTZ. The ontogenetic descent and diel vertical migration of N. tripes suggest a diet shift from anchovy larvae to micronektons.