Description: Passive acoustic monitoring (PAM) has emerged as a highly efficient technology to conduct long-term monitoring of marine mammals at species dependent, local to basin scales, providing valuable new insights into species distributions and migration patterns. To study Antarctic mammals, we deployed up to ten moored, autonomous acoustic recorders in the Atlantic sector of the Southern Ocean. Due to this region’s remoteness, challenging accessibility, and ensuing logistic constraints, especially during winter, recording devices were/are deployed for two years or longer, resulting in high demands on their power efficiency and storage capability. Two types of recorders, AURAL and MARU, which were deployed in March 2008 and December 2008, respectively, were recovered in December 2010. More recently, a set of eight, newly developed recorders (SONOVAULT), were deployed in December 2010, and are scheduled for recovery in December 2012. While in-situ recordings are hence available for AURAL and MARU, for SONOVAULTs extensive laboratory tests have been performed. Based on these recordings, this paper provides a user-based comparison of these three types of acoustic recorders, discussing their technical specifications and limitations (including recent enhancements) along with their actual performance and data quality. The paper concludes with a discussion of future needs for long-term monitoring applications along with each instrument’s potential to meet such requirements.

Description: Although Antarctic blue whales (Balaenoptera musculus intermedia) are known to occur throughout the Southern Ocean, undertaking seasonal migrations between their breeding and feeding grounds, knowledge on spatio-temporal patterns in their distribution is limited. Here, passive acoustic recordings collected over three years from four locations at different latitudes along the Greenwich meridian south of 59°S, provided data on patterns in occurrence of stereotyped 3-unit vocalizations of Antarctic blue whales in the Weddell Sea. Highest vocalization rates occurred during austral summer at all recording locations, with calls detectable during 10 months in recordings from 59°S and 66°S, over 11 months in recordings from 69°S and year-round in recordings from coastal waters off the Antarctic continent at 70°S. Antarctic blue whale acoustic activity showed seasonal maxima that differed in timing between recorders, but were consistently present between years. Onset of increased acoustic presence occurred in November-December in the northernmost recorder at 59°S, in January in the recorders at 66°S and 69°S and in February in the southernmost recorder at 70°S. These results are consistent with a southbound migration of vocalizing Antarctic blue whales with at least some individuals migrating as far south as the Antarctic coastal waters during austral summer. A secondary increase in acoustic activity occurred during March and April in the recorders at 59°S and 66°S, respectively, supporting previous suggestions that migration of Antarctic blue whales is segregated in time. The absence of a corresponding secondary maximum at 69°S hints towards not all individuals migrating this far south, and that migratory destinations (or alternatively, vocal activity) may hence be spatially segregated. The year-round presence of Antarctic blue whale calls off the Antarctic continent suggests that Antarcticas’ coastal polynyas, i.e. patches of open water where animals can surface to breathe, may provide important habitats for animals to overwinter in high latitude waters.