Seasonal and Diel Vocalization Patterns ofAntarctic Blue Whale (Balaenopteramusculus intermedia) in the Southern IndianOcean: A Multi-Year and Multi-Site Study

International audiencePassive acoustic monitoring is an efficient way to provide insights on the ecology of largewhales. This approach allows for long-term and species-specific monitoring over largeareas. In this study, we examined six years (2010 to 2015) of continuous acoustic recordingsat up to seven different locations in the Central and Southern Indian Basin to assessthe peak periods of presence, seasonality and migration movements of Antarctic bluewhales (Balaenoptera musculus intermedia). An automated method is used to detect theAntarctic blue whale stereotyped call, known as Z-call. Detection results are analyzed interms of distribution, seasonal presence and diel pattern of emission at each site. Z-callsare detected year-round at each site, except for one located in the equatorial Indian Ocean,and display highly seasonal distribution. This seasonality is stable across years for everysite, but varies between sites. Z-calls are mainly detected during autumn and spring at thesubantarctic locations, suggesting that these sites are on the Antarctic blue whale migrationroutes, and mostly during winter at the subtropical sites. In addition to these seasonaltrends, there is a significant diel pattern in Z-call emission, with more Z-calls in daytimethan in nighttime. This diel pattern may be related to the blue whale feeding ecology