Abstract
Abstract. The sei whale (Balaenoptera borealis) is one of the least known whale species. Information on sei whale distributions and its regional variability in the south-eastern Pacific Ocean are even more scarce than that from other areas. Vocalizations of sei whales from this region are not described yet. This research presents the first characterization of sei whale sounds recorded in Chile during the austral autumn of 2016 and 2017. Recordings were done opportunistically. A total of 41 calls were identified to be sei whale downsweeps. In 2016, calls ranged from an average maximum frequency of 105.3 Hz down to an average minimum of 35.6 Hz over 1.6 s with a peak frequency of 65.4 Hz. During 2017, calls ranged from an average maximum frequency of 93.3 down to 42.2 Hz (over 1.6 s) with a peak frequency of 68.3 Hz. The absolute minimum frequency recorded was 30 Hz and the absolute maximum frequency was 129.4 Hz. Calls generally occurred in pairs, but triplets or singles were also registered. These low-frequency sounds share characteristics with recordings of sei whales near the Hawai'ian Islands but with differences in the maximum frequencies and duration. These calls distinctly differ from sounds previously described for sei whales in the Southern Ocean and are the first documented sei whale calls in the south-eastern Pacific.
Highlights
The sei whale (Balaenoptera borealis; Lesson 1828) is the third largest rorqual in the Balaenopteridae family, after the blue whale (B. musculus) and the fin whale (B. physalus)
The aim of this work is to describe sei whale vocalizations based on opportunistic recordings at the Penas Gulf, Chile, and to obtain a framework baseline regarding the characterizes of sei whales populations in the south-eastern Pacific Ocean
Low and high frequency (Hz), frequency range (Hz), peak frequencies, and duration (s) for all calls found and attributed to sei whales were analysed from spectrograms and waveform plots created in Raven Pro 1.5 (Hann window; 50 % overlap; window size 14 563 samples; DFT 16 384 samples)
Summary
The sei whale (Balaenoptera borealis; Lesson 1828) is the third largest rorqual in the Balaenopteridae family, after the blue whale (B. musculus) and the fin whale (B. physalus) It is one of the least known whales. The sei whale is a cosmopolitan species found in temperate oceans and subpolar areas (Mackintosh, 1942; Gambell, 1968; Rice, 1998; Horwood, 2002; Reeves et al, 2002; Jefferson et al, 2008). It prefers deep offshore waters with temperatures below 20 ◦C and avoids semi-enclosed bodies of water (Omura and Nemoto, 1955; Gambell, 1985).
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