Arnoux’s beaked whales acoustically misidentified as Type C killer whales in Prydz Bay, Antarctica

Abstract

The Southern Ocean is home to five ecotypes of killer whale, which differ in diet, morphology, behaviour, and vocal repertoire. Recently, fish-eating Type C killer whales were reported in Prydz Bay, Antarctica from sounds recorded in hydrophone data collected in March 2017, on the basis that these sounds bore similarities to acoustic behaviour of Icelandic fish-eating killer whales. Here we re-examine the structure of the sounds identified as Prydz Bay Type C killer whales and we identify the calls to be those of the Arnoux’s beaked whale. The whistles are more structurally similar and fall within the same frequency range as those of the Arnoux’s beaked whale, rather than the killer whale. Of the two killer whale types observed in Prydz Bay, the most common had behaviour and morphology typical of Type B killer whales, while the other had morphology typical of Type A. Although we show that the sounds are not likely to be killer whale Type C calls, this would be the first recorded occurrence of Arnoux’s beaked whales in Prydz Bay. Arnoux’s beaked whales are a rarely seen, cryptic whale species.