Spatial and Temporal Variation of the Fish Assemblage on a Large Artificial Reef Assessed Using Multiple-Point Stationary Observations

Abstract

Over the past decade, the sizes of artificial reefs in Japan have increased, with heights reaching 30 m or more. However, there are few studies about the efficiency of the high-rise artificial reefs, and it is not clear how effectively these reefs gather and nurse fish resources. In these large artificial reefs, it is difficult for divers to view entire schools of fish. We developed a stationary observation system called FISCHOM (fish school monitoring system) to replace or complement visual censuses conducted by divers. FISCHOM consists of a stereo camera, a programmable timer, and a battery in a stainless steel pressure-resistant housing with transparent acrylic glass rated to a depth of 80 m. FISCHOM takes periodic underwater stereo images, and its maximum duration of operation is approximately 2 months when the photographing interval is set to 1 h. By using multiple FISCHOM systems around an artificial reef, researchers can obtain quantitative data on fauna and body size compositions of the reef fish assemblages and their trends. In this study, we will try to describe the possibilities offered by FISCHOM to study the artificial reef fish assemblages. Then, we will show the survey results conducted at a high-rise artificial reef in the Sea of Japan. We describe the advantages and limitations of FISCHOM for observing artificial reef fish assemblages based on the results of the survey.