Seasonal and Diel Vocalization Patterns of Antarctic Blue Whale (Balaenoptera musculus intermedia) in the Southern Indian Ocean: A Multi-Year and Multi-Site Study
Résumé
Passive acoustic monitoring is an efficient way to provide insights on the ecology of large
whales. This approach allows for long-term and species-specific monitoring over large
areas. In this study, we examined six years (2010 to 2015) of continuous acoustic recordings
at up to seven different locations in the Central and Southern Indian Basin to assess
the peak periods of presence, seasonality and migration movements of Antarctic blue
whales (Balaenoptera musculus intermedia). An automated method is used to detect the
Antarctic blue whale stereotyped call, known as Z-call. Detection results are analyzed in
terms of distribution, seasonal presence and diel pattern of emission at each site. Z-calls
are 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 every
site, but varies between sites. Z-calls are mainly detected during autumn and spring at the
subantarctic locations, suggesting that these sites are on the Antarctic blue whale migration
routes, and mostly during winter at the subtropical sites. In addition to these seasonal
trends, there is a significant diel pattern in Z-call emission, with more Z-calls in daytime
than in nighttime. This diel pattern may be related to the blue whale feeding ecology.