Juvenile Fishes and Halfbeak Hyporhamphus sajori Eggs Removed by the Marine Environment-improving Ship with Floating Subjects in the Central Seto Inland Sea

Abstract

To understand juvenile fishes and halfbeak Hyporhamphus sajori eggs removed by the marine environment-improving ship in the central Seto Inland Sea, we examined the quantity and composition of floating objects. The annual amount of floating objects removed by the ship was about 1, 300 m³ from April 1995 to March 1999. The volume increased in spring, peaked in July, and decreased in autumn and winter. The major items of the floating objects were seaweeds and sea-grass in spring and sea-grass and reed Phragmites australis in summer. Juvenile fishes were hardly removed by the ship. The halfbeak eggs clung to floating seaweeds appeared from April to June. The number of eggs per kg of marine-algae was 500-16, 000. The weight of marine-algae removed from April to May was about 41, 000kg. These results suggested that about 320 million halfbeak eggs per year can be removed by the ship.