Migration of adult Pacific herring, Clupea pallasii, around spawning ground revealed by an automated ultrasonic telemetry system

Pacific herring (Clupea pallasii) spawn in coastal waters of northern Japan in winter and spring. Although Pacific herring are an important target species of coastal fisheries, few studies have reported their migration around their spawning ground. In this study, ultrasonic transmitters were attached to 16 adult herring specimens, which were then released into Miyako Bay, Iwate Prefecture, Japan, in 2015 and 2016. Four automated receivers were deployed around the spawning ground in the inner bay, and the behaviors of four individuals were monitored successfully. Adult herring stayed mainly in deeper waters during the day but moved to shallower spawning areas intermittingly at night. It is likely that the fish did not spawn immediately upon reaching the spawning grounds but rather stayed around the spawning grounds for a certain period of time before spawning.