Behavioral study of black sea bream Acanthopagrus schlegelii by acoustic telemetry to guide countermeasures against feeding damage to cultivated nori Neopyropia yezoensis off Kobe, Hyogo, Japan

Although feeding damage caused by black sea bream Acanthopagrus schlegelii has become severe in the nori Neopyropia yezoensis cultivation industry, the behavioral ecology of black sea bream in nori farms remains unclear. In this study, we monitored black sea bream around a nori farm using acoustic telemetry in order to understand the behavioral characteristics of this species. Of the 23 fish specimens tagged with acoustic transmitters, 18 fish were traced over periods > 100 days, with 8 fish considered to be feeding on cultivated nori. It is thought that the black sea bream, which were inferred to have been feeding on nori, exhibited periodicity in their behavior, feding on cultivated nori near the water surface during the day and settling on the seafloor or around seabed structures during the night. Furthermore, the feeding on nori gradually lessened when the water temperature in the cultivation grounds fell below 13 °C. Some methods aimed at reducing feeding damage are proposed that take advantage of the diurnal behavior of black sea bream to catch individuals around nori sets with gill nets or set nets during the season when the water temperature exceeds 13 °C.