駿河湾湾奥におけるシラス地曳網で採集された稚仔魚の食性

抄録

Gut-contents of fish larvae and juveniles distributed in a shirasu (whitebait) fishing-ground were investigated on the basis of samples collected by a shore seine at the inner part of Suruga Bay, central Japan, from April to June 1975. Among 12 fish species with sufficient data on the gut content, eight (Japanese sardine Sardinops melanostictus, Japanese anchovy Engraulis japonicus, round herring Etrumeus teres, ayu Plecoglossus altivelis, black rockfish Sebastes inermis, bluefish Scombrops boops, horse mackerel Trachurus japonicus, Gobiidae sp.) formed a feeding guild that utilized planktonic copepods such as Paracalanus and Calanus. In the guild, S. melanostictus, E. japonicus and P. altivelis preyed mainly on smaller copepod (Paracalanus); on the other hand, E. teres, S. boops, S. inermis and T. japonicus preyed also on larger copepod (Calanus). Among these species, S. boops shifted from a planktivor to a piscivor at 30 mm in standard length. Of the remaining four species, Scomber sp. and red sea bream Pagrus major utilized various preys including tunicates such as appendicularians and doliolids. Japanese barracuda Sphyraena japonica was completely piscivorous. Black scraper Thamnaconus modestus had a unique gut-content signal with prey items mostly being oncaeid copepods, which is known to forage in appendicularian houses. The guild that utilizes planktonic copepods seems to be supported mainly by herbivorous copepods formed after the spring bloom in Suruga Bay, and being preyed upon not only by fish but also by carnivorous zooplankton (e.g. chaetognaths). The dominance of Scomber sp. in the late study-period when doliolid increased after a peak in the copepod population may be caused by its wide-ranging feeding habit. A possible change in the food resources for juveniles of Scomber sp. between before and after the climatic regime-shift in 1976/77 was also discussed.