Abstract
In order to observe of fish behavior to the set net, a radio transmission system for underwater video image
was constructed and tested. This system consists of a transmitting station on the sea and a receiving station on
the land. The transmitting station is composed of an underwater video camera, a video transmitter, a transmitting
antema, lead-acid batteries, a cellular phone and a sound sensor for remote control of power supply. The underwater
video image is transmitted to the receiving station with microwave of l.2 GHz. The receiving station is
composed of a receiving antenna, a video receiver, a monitor and a VCR. The maximum transmission distance of
the system was measured with about 7 km on the sea. The test run of the radio transmission system for underwater video image was conducted on the set net fishing ground in Tateyama Bay, Chiba Prefecture. The underwater video camera was installed in front of a funnel net to observe the fish behavior to the final trap of the set net. The transmitting station was moored near the final trap and the receiving station was set up in the Banda
Marine Laboratory of Tokyo University of Fisheries where is l.5 km away from the set net. The test run lasted
for 23 days in November, 2002. A total of 60 hours of the underwater video image were recorded and the fish
behavior of 18 species were observed clearly during the test run. The inshore fish such as rudderfish Kyphosus
vaigiensis, filefish Stephanolepis cirrhifer and blackfish Girella punctata frequently swam in and out the final
trap through the funnel net. In contrast, yellowtail Seriola quinqueradiata did not escape from the final trap
except for only one fish.
