1The Japanese Institute of Technology on Fishing Ports, Grounds and Communities, Chiyoda, Tokyo 101-0047, 2Chateau Marine Survey Co., Ltd., Miyakojima, Osaka 534-0025, Japan
To investigate behavioral properties of the Jack mackerel Trachurus japonicus, an ultrasonic biotelemeter (V9P-1H, VEMCO) was externally attached to 30 cm-long Jack mackerel principally in an artificial reef put in place at a depth of 45 meters in the Sea of Japan, off the coast of Hamochi, Sado Island. Each fish was tracked seven times from June to July in 2008. Their circadian behaviors are quite clear. The Jack mackerel stays in an area within 10 meters from the top of the reef during the daytime and swims in the reef near the sea surface at depths of 5 to 10 meters during the nighttime.