Behavioral patterns of Antarctic fishes revealed by ultrasonic biotelemetry under the fast ice

The ecological roles of fishes as intermediate predators in the Antarctic Ocean remain understudied. Understanding their behavioral patterns provides valuable insights into the structure of the Antarctic ecosystem. However, sea ice covering Antarctic coastal waters makes it difficult to collect fish with nets or conduct acoustic surveys using sonar. We conducted a behavioral investigation of Antarctic fishes using an ultrasonic biotelemetry system with receivers installed beneath fast ice. We investigated in Kita-no-ura Cove, Lützow-Holm Bay, East Antarctica, and focused on three species abundant in this area: the emerald rockcod (Trematomus bernacchii), the sharp-spined notothenia (T. pennellii), and the striped rockcod (T. hansoni). A total of 28 individuals were surgically implanted with ultrasonic transmitters and released. Data were successfully collected over 26 cumulative days. We observed a distinctive behavioral pattern in the emerald rockcod. It stayed at a specific location on the seafloor for several days, then moved to another area and remained there again, exhibiting repeated intermittent transitions. On average, it spent 81% of the total time on the seafloor (SD = 11%). Notably, the emerald rockcod is recognized as the dominant species in the study area. Such characteristic behavior may be attributed to site fidelity, territoriality, or feeding strategies.