To make broad use of underwater space for mariculture, a mid-layer floating “Artificial Sea Floor” structure was developed and placed at a depth of 40 meters in Funagoshi bay in Iwate Prefecture in February 1996. The structure was constructed of welded steel (36.4×20.0m) and floated seven meters below the ocean surface. An operational deck projected above surface at the center of the structure. Six months after the facility had been anchored, the dstribution of fish around the structure during the daytime and nighttime was investigated by echo sounder.
A weak stratified fish echo (TS -54.5--51.5dB) and cloud-like fish echo (TS -41--38dB) were identified. Weak stratified fish echoes were estimated to be pelagic animals and were not close to the facility. During the day, cloud-like fish echoes from juveniles of Scomber japonicus were distributed around the facility in small schools, and at night dispersed in the surface layer over entire survey area. The floating reef was concluded to act as a aggregation device for Scomber japonicus in the daytime.
