Identification of Antarctic minke and killer whales with passive acoustic monitoring in Prydz Bay, Antarctica

Although four species of odontocete and four species of baleen whale have been recorded in Prydz Bay, their vocalizations have been rarely investigated. Underwater vocalizations were recorded during March 2017 in Prydz Bay, Antarctica. Bio-duck sounds, downsweeps, inverted “u” shape signals, whistles, pulsed sounds, and broadband clicks were recorded. Bio-duck sounds and downsweeps were associated with Antarctic minke whales (Balaenoptera bonaerensis) based on visual observations. Similarities between inverted “u” shape signals, biphonic calls, and clicks with vocalizations previously described for killer whales (Orcinus orca) lead us believe the presence of Antarctic killer whales. According to sound structures, signal characteristics, and recording location, Antarctic type C killer whales were the most probable candidates to produce these detected calls. These represent the first detection of inverted “u” shape signals in Antarctic waters, and the first report of Antarctic killer whale in Prydz Bay based on passive acoustic monitoring. The co-existence of Antarctic minke and killer whales may imply that minke whales can detect differences between the sounds of mammal-eating and fish-eating killer whales. Our descriptions of these underwater vocalizations contribute to the limited body of information regarding the distribution and acoustic behavior of cetaceans in Prydz Bay.