IMPACTS OF ARTIFICIAL REEFS ON FISHERY PRODUCTION IN SHIMAMAKI. JAPAN

The role of artificial reefs as a tool for increasing fishery production rather than just aggregating fish is addressed for two fisheries, octopus, Octopus dofeini, and flatfish, (Pleuronectidae), near Shimamaki, Japan. The time series of catch and effort data examined covers periods before and after two adjacent fishinggrounds received 8,645 and 40,766 m3 ofartificial reef. Octopus catches were increased by 4% per 1,000 m3 of artificial reef or by an average of I .8 kg/m3 of artificial reef. Artificial reefs aggregated flatfishes but did not increase catches in the regions. A survey of fishermen in the two regions revealed that the reefs generally are considered beneficial. Artificial reefs are widely advocated as a tool to enhance fishing. The U.S. Congress established a national policy to promote the use of artificial reefs (Stone, 1985). Japan has a long history of artificial reef usage, and its government currently spends about US$lO million annually on the construction and deployment of artificial reefs in its coastal waters. The Japanese Government has justified this program with reports of annual combined pelagic and demersal catches at the reefs of up to 16-20 kg/m3 of artificial reef (Sato, 1985). However, these catch rates do not measure the extent that artificial reefs increase fishery production in a region because, if the reefs were not present, many of these fishes might have been caught at the surrounding natural habitat instead. Evaluating the extent that artificial reefs can produce a sustainable increase in fishery production in a region, rather than just aggregate fish already present, is an important ecological question as well as a high priority research topic with important consequences for fisheries management (Bohnsack and Sutherland, 1985; Sato, 1985). This study compares annual catches and catch per unit ofeffort (CPUE) between two adjacent fishing grounds. Examining two regions rather than just one separates the effects of artificial reefs on catches from the effects of year-class strength, changes in fishing power, and market factors. Any changes in relative catch and CPUE, corresponding to differences in the magnitude of artificial reefs between the two regions, are likely due to the artificial reefs. This study is believed to be the first to quantify the extent that artificial reefs produce a sustainable increase in fishery production.