Spatio-temporal patterns in Antarctic minke whale (Balaenoptera bonaerensis) vocal behaviour in the Weddell Sea

Antarctic minke whales (Baleanoptera bonaerensis) occur in open as well as ice-covered waters throughout the Southern Ocean. Their low visual detectability and ice-associated habitat makes the species difficult to study using traditional visual methods. The recent identification of vocalizations produced by Antarctic minke whales now allows the use of passive acoustic records to investigate spatio-temporal patterns in occurrence, also in areas that are (seasonally) inaccessible to ships due to extensive ice cover. Here we present preliminary results on Antarctic minke whale occurrence patterns based on part of a multi-year passive acoustic data set collected from 6 locations throughout the Atlantic sector of the Southern Ocean. These comprised four autonomous passive acoustic recorders which collected data along the Greenwich meridian between 2008 and 2011, one passive acoustic recorder in the Weddell Sea that collected data between 2010 and 2012 and long-term recordings from the PALAOA observatory on the Eckström Iceshelf off the Antarctic continent (2006-2016). Analyses were based on daily presence of Antarctic minke whale pulse trains, also referred to as the bio-duck call. The bio-duck signal is characterized by its repetitive nature, consisting of regular down-sweeped pulses, with most energy located in the 50-300 Hz band. Antarctic minke whales were present at all six Antarctic recording locations from June to December, with highest presence occurring between August and November (>80% of days with bioduck calls present). At the southernmost recording locations and the location in the Weddell Sea, the bioduck call was present throughout nine and ten months of the year, respectively. Substantial variation in the seasonal on- and offset period of vocal activity of Antarctic minke whales was observed between years at the different recording positions, possibly corresponding to variation in local ice conditions. Ongoing work aims to further quantify this relationship to better understand year-round Antarctic minke whale habitat preferences. Furthermore, further work will comprise more fine-scale analyses to unravel diel patterns in vocal activity and explore if variation in the acoustic signature of the bioduck call can potentially be attributed to regional differences in Antarctic minke whale vocal behavior, possibly representing subpopulations of the species