Physical environment at a site suitable for artificial reefs

Abstract

We have to think environmental conditions in waters for a decision of settled site of artificial reefs. Commonly their settled sites have been decided based on fishermen's experience and there is no scientific evidence to design their settled site. We researched an physical environment of fishing grounds of benthic and pelagic fishes in two waters. In case of benthic fishes, we applied an environmental analysis method extracting some restrict factors for object species to a natural reef named “Kakino-se” off Yamaguti Pref. It could make clear for juveniles of Yellow Sea bream that the interval between reefs, water temperature, and silt concentration in the sea bottom became these factors as the fishig ground. In case of pelagic fishes, internal waves as physical environment concims with an ecosystem. We observed an water mass behavior around the natural reef named Hutashima-guri off Yamaguti Pref. An artificial high-rise reef had been settled close to this natural reef and is aggregating many zooplanktons and horse mackerels. This aggregation was suggested for a internal vertical mixing caused by this shoal hydraulically.