Abstract
The net breakage and predation are a severely damage to the manila clam, Ruditapes philippinarum, farming using the net bags in the Shigetomi tidal flat, located in the northern part of Kagoshima Bay. This study aimed to estimate the cause of net bag breakage by monitoring with interval cameras. The cameras were placed on the seafloor approximately 1 m away from the net bags to record at 5-second intervals from installation until sunset. The images were used to analyze the behavior of the species that approached the net bags. Fish behavior was divided into appearing, contacting, pecking, and pulling the net bag. Blackhead seabream, Acanthopagrus schlegelii, and yellowfin seabream, Acanthopagrus latus appeared, contacted, pecked, pulled at the net bags. There were some tears in the nets bag that were observed to be pecked and pulled by Acanthopagrus sp., and the tears of about 5–10 cm in length were enough large for the mouth of Acanthopagrus sp.to pass through. Shells were observed outside the net bags after Acanthopagrus sp. pecked the net bag. From these results, we estimated that Acanthopagrus sp. broke the net bag and prey on manila clams by removing them from the net bags.
