Description: The eastern Atlantic Ocean is considered to provide important breeding and wintering habitats for several migratory cetacean species. The spatio-temporal distributions and migratory behaviors of cetaceans off southern Africa are nevertheless still poorly understood. This study investigated the temporal patterns of acoustic occurrence of baleen whales in a presumed baleen whale breeding area off Namibia using passive acoustic recordings collected between November 2011 and May 2013. Our results show seasonal acoustic presence of humpback whales Megaptera novaeangliae, fin whales Balaenoptera physalus and Antarctic minke whales B. bonaerensis from November to January and from June to August. Their acoustic absence from February to May possibly indicates that most animals migrated to other areas (presumably in higher latitudes) in austral summer to feed. By contrast, Antarctic blue whales B. musculus intermedia were acoustically present throughout the recording period, indicating that part of the population remains at lower latitudes year-round. Our findings support the presumed ecological importance of the oceanic area off Namibia, providing (part of) a suitable cetacean wintering and, possibly, breeding range or migratory corridor. Furthermore, the occurrence of Antarctic blue and minke whales off Namibia, concurrent with their reported acoustic presence in high-latitude feeding areas, adds to growing evidence that baleen whale migration is not obligate but much more dynamic than has long been assumed.

Description: The ocean is crowded with human uses, many of which also introduce underwater sound in the ocean environment. To understand if and how these underwater sound sources impact marine mammals and eventually mitigate against the potential consequences, information on distribution patterns is crucial. Passive acoustic monitoring techniques offer a versatile tool to study marine mammals, particularly in polar ocean environments where ship access is often limited and visual sighting conditions can be compromised by light availability and weather. In this talk I will provide an introduction on passive acoustic techniques, how they can be applied and what type of data they generate. Three case studies serve to illustrate how passive acoustic techniques have contributed to fundamentally improve the knowledge status on cetacean and pinniped species in Antarctic waters.

Description: Distribution and movement patterns of Antarctic blue whales Balaenoptera musculus intermedia at large temporal and spatial scales are still poorly understood. The objective of this study was to explore spatio-temporal distribution patterns of Antarctic blue whales in the Atlantic sector of the Southern Ocean, using passive acoustic monitoring data. Multi-year data were collected between 2008 and 2013 by 11 recorders deployed in the Weddell Sea and along the Greenwich meridian. Antarctic blue whale Z-calls were detected via spectrogram cross-correlation. A Blue Whale Index was developed to quantify the proportion of time during which acoustic energy from Antarctic blue whales dominated over background noise. Our results show that Antarctic blue whales were acoustically present year-round, with most call detections between January and April. During austral summer, the number of detected calls peaked synchronously throughout the study area in most years, and hence, no directed meridional movement pattern was detectable. During austral winter, vocalizations were recorded at latitudes as high as 69°S, with sea ice cover exceeding 90%, suggesting that some Antarctic blue whales overwinter in Antarctic waters. Polynyas likely serve as an important habitat for baleen whales during austral winter, providing food and reliable access to open water for breathing. Overall, our results support increasing evidence of a complex and non-obligatory migratory behavior of Antarctic blue whales, potentially involving temporally and spatially dynamic migration routes and destinations, as well as variable timing of migration to and from the feeding grounds.

Description: 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.

Description: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Endangered Species Research 30 (2016): 239-253, doi:10.3354/esr00739.

Description: Distribution and movement patterns of Antarctic blue whales Balaenoptera musculus intermedia at large temporal and spatial scales are still poorly understood. The objective of this study was to explore spatio-temporal distribution patterns of Antarctic blue whales in the Atlantic sector of the Southern Ocean, using passive acoustic monitoring data. Multi-year data were collected between 2008 and 2013 by 11 recorders deployed in the Weddell Sea and along the Greenwich meridian. Antarctic blue whale Z-calls were detected via spectrogram cross-correlation. A Blue Whale Index was developed to quantify the proportion of time during which acoustic energy from Antarctic blue whales dominated over background noise. Our results show that Antarctic blue whales were acoustically present year-round, with most call detections between January and April. During austral summer, the number of detected calls peaked synchronously throughout the study area in most years, and hence, no directed meridional movement pattern was detectable. During austral winter, vocalizations were recorded at latitudes as high as 69°S, with sea ice cover exceeding 90%, suggesting that some Antarctic blue whales overwinter in Antarctic waters. Polynyas likely serve as an important habitat for baleen whales during austral winter, providing food and reliable access to open water for breathing. Overall, our results support increasing evidence of a complex and non-obligatory migratory behavior of Antarctic blue whales, potentially involving temporally and spatially dynamic migration routes and destinations, as well as variable timing of migration to and from the feeding grounds.