Monitoring behavioral characteristics of the rockfish Sebastescheni inhabitinga seawall using LBL acoustic positioning system

Abstract

Many members of the genus Sebastes exhibit homing behavior. Specifically, these species will return to the site where they have been captured after being released. In addition, Sebastes spp. exhibit site fidelity and diel migration in their home territories and foraging areas. The aim of this study was to use a high-precision ultrasonic biotelemetry system to accurately clarify the horizontal distribution patterns and the diurnal vertical movements of Sebastescheni inhabiting a seawall. Field experiments were conducted in Uraga Bay, Japan. The small bay is enclosed by seawalls and the sea floor of the area is smooth and approximately 10m deep. In 2011, experimental fish was captured using a hook and line and a transmitter with built-in a depth sensor was implanted into the peritoneal cavity of each fish. To reduce anomalous readings, the locality data were filtered using swimming speed, HDOP and excluded landing. Movement patterns were then monitored using a radio-linked acoustic positioning system after release at a site 40 m distant from the capture site. Tagged fish were observed to return to the site where they were captured, remaining in a relatively small area for the duration of the monitoring period. Tagged fish utilized three core areas in their home range, one was used during the day and the others were used between sunset and sunrise. Tagged fish remained at approximately 5m below the surface during the daytime, exhibiting more extensive vertical movements at night.