ABSTRACT

This study examines seasonal bowhead whale vocalization using passive acoustic monitoring (PAM) in the Western Nansen Basin from mid-September, 2019 to late July 2020. Data were collected with an autonomous recorder as part of the INTegrated ARctic Observation System (INTAROS). Bowhead whales were acoustically present from autumn throughout winter (October/November-February) and occasionally in spring (March-June), but acoustically absent in summer (July-September), revealing that bowhead whales exhibit highly seasonal behavior. Peak activity occurred from November 2019 to January 2020, suggesting this site may be a migration route from the Fram Strait to Franz Josef Land or a wintering ground. No whales were detected in summer, implying migration elsewhere. Repeated call sequences of specific S-type were observed from late December 2019 to February 2020.

INTRODUCTION

Bowhead whales (Balaena mysticetus) are cetaceans with an impressive lifespan, specially evolved to inhabit the Arctic throughout the entire year. These highly vocal animals exhibit detailed acoustic displays during the coldest and darkest winter months (Würsig et al., 1993). Bowhead whales are exclusively found in the Arctic waters of the Northern Hemisphere (Moore and Reeves, 1993).

Bowhead whales possess a rich and diverse acoustic repertoire that includes simple calls, call sequences, and complex songs (Ljungblad et al., 1982; Würsig & Clark, 1993). Simple calls, which are either frequency-modulated (FM) or amplitude-modulated (AM), contain most of their acoustic energy below 500 Hz and lack any specific pattern in their occurrence. Call sequences consist of repeated simple FM calls, typically occurring in bouts of 3 to 25 similar calls (Ljungblad et al., 1982; Würsig & Clark, 1993; Stafford et al., 2008; Delarue et al., 2009). These call sequences were sometimes repeated and similarities in these calling patterns among different populations of bowhead whales (Fig. 1b) have been found. The patterns called ‘simple song’ were also the very same with regard to their behavior, and they will be discussed under the name of the call sequences in the arrangement that Würsig & Clark (1993) have used. In contrast, songs consist of a combined acoustical exhibit that is highly structured and very stereotypical of loud, raucous FM and AM calls, known as notes, with little or no pause between them (Fig. 1c). Simple calls are much shorter in duration and are featured in an almost 5 kHz bandwidth while phrases contain the energy of the longer notes (Chapin & Ferral, 1992). In addition, the bowhead whale exhibits the unique ability to sing with ‘two voices’, simultaneously producing high and low frequencies as well as FM-AM sounds (Würsig & Clark, 1993; Tervo et al., 2011). Their songs are generally repeated for hours and vary across populations and age groups (Cummings & Holliday, 1987; Würsig & Clark, 1993; Stafford et al., 2008; Delarue et al., 2009).

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