Characteristics of vocalisations recorded from free-ranging Shepherd's beaked whales, Tasmacetus shepherdi

Beaked whales (family Ziphiidae) are among the least studied of all the large mammals. This is especially true of Shepherd's beaked whale (Tasmacetus shepherdi), which until recently had been very rarely sighted alive, with nothing known about the species' acoustic behaviour. Vocalisations of Shepherd's beaked whales were recorded using a hydrophone array on two separate days during marine mammal surveys of the Otago submarine canyons in New Zealand. After carefully screening the recordings, two distinct call types were found; broadband echolocation clicks, and burst pulses. Broadband echolocation clicks (n = 476) had a median inter-click-interval (ICI) of 0.46 s and median peak frequency of 19.2 kHz. The burst pulses (n = 33) had a median peak frequency of constituent clicks (n = 1741) of 14.7 kHz, and median ICI of 11 ms. These results should be interpreted with caution due to the limited bandwidth used to record the signals. To the authors' knowledge, this study presents the first analysis of the characteristics of Shepherd's beaked whale sounds. It will help with identification of the species in passive acoustic monitoring records, and future efforts to further analyse this species' vocalisations.