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: This study investigates the relevance of the Elephant Island (EI) region for Southern Hemisphere fin whales (Balaenoptera physalus) in their annual life cycle. We collected 3 years of passive acoustic recordings (January 2013 to February 2016) northwest of EI to calculate time series of fin whale acoustic indices, daily acoustic occurrence, spectrograms, as well as the abundance of their 20-Hz pulses. Acoustic backscatter strength, sea ice concentration and chlorophyll-a composites provided concurrent environmental information for graphic comparisons. Acoustic interannual, seasonal and diel patterns together with visual information and literature resources were used to define the period of occupancy and to infer potential drivers for their behaviour. Spectral results suggest that these fin whales migrate annually to and from offshore central Chile. Acoustic data and visual information reveal their arrival at EI in December to feed without producing their typical 20-Hz pulse. For all 3 years, acoustic activity commences in February, peaks in May and decreases in August, in phase with the onset of their breeding season. Our results emphasize the importance of EI for fin whales throughout most of the year. Our recommendation is to consider EI for establishing a marine protected area to expedite the recovery of this vulnerable species.

Description: The recent identification of the bio-duck call as Antarctic minke whale (AMW) vocalization allows the use of passive acoustic monitoring to retrospectively investigate year-round spatial-temporal patterns in minke whale occurrence in ice-covered areas. Here, we present an analysis of AMW occurrence patterns based on a 9-year passive acoustic dataset (2008–2016) from 21 locations throughout the Atlantic sector of the Southern Ocean (Weddell Sea). AMWs were detected acoustically at all mooring locations from May to December, with the highest presence between August and November (bio-duck calls present at more than 80% of days). At the southernmost recording locations, the bio-duck call was present up to 10 months of the year. Substantial inter-annual variation in the seasonality of vocal activity correlated to variation in local ice concentration. Our analysis indicates that part of the AMW population stays in the Weddell Sea during austral winter. The period with the highest acoustic presence in the Weddell Sea (September–October) coincides with the timing of the breeding season of AMW in lower latitudes. The bio-duck call could therefore play a role in mating, although other behavioural functions of the call cannot be excluded to date.

Description: Bowhead whales (Balaena mysticetus) of the East Greenland-Svalbard-Barents Sea (Spitsbergen) population have been depleted close to the point of extinction by commercial whaling and are still considered as endangered. Due to their low abundance and the remoteness of their habitat, baseline knowledge on spatio-temporal distribution patterns and behavioural aspects are scarce, yet crucial for the conservation of this population. Long-term passive acoustic recordings were collected at different locations in eastern Fram Strait (78-79°N, 0-7°E) as part of the Ocean Observing System FRAM (Frontiers in Arctic Marine Monitoring). Data recorded in 2012 and 2016/2017 were analysed for the acoustic occurrence of bowhead whales at an hourly resolution using an automated detector. Bowhead whales were acoustically present from autumn throughout the winter months (October-February) and occasionally in spring (March-June), supporting hypotheses that Fram Strait is an important overwintering area. Acoustic presence peaked between mid-November and mid-December when bowhead whales were recorded almost daily, often hourly for several days in a row. The observed peak in acoustic presence coincided with the presumed mating period of bowhead whales, starting in late winter, indicating that Fram Strait may also serve as a mating area. Detailed analyses of recordings of a single year and location revealed eight distinct bowhead whale song types comprising simple songs and call sequences. No bowhead whales were recorded in summer (July-September), indicating that they either were vocally inactive or had migrated to summering areas. Compared to previous studies in western Fram Strait, bowhead whale detections in our recordings were less frequent and less complex. The observed regional differences in bowhead whale acoustic behaviour across Fram Strait suggest that our mooring locations in eastern Fram Strait may represent the eastern distribution boundary of the bowhead whale overwintering area.

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.