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: ABSTRACT: To date, the majority of studies investigating marine mammal distribution and behavior take a single-species perspective, which is often driven by the logistic difficulties of collecting appropriate data at sea. Passive acoustic monitoring, provided recording tools exhibit sufficient bandwidth, has the potential to provide insights into community structure as devices operate autonomously simultaneously collecting data on baleen, pinniped and toothed whale acoustic presence. Data can provide information on local species diversity, residency times and co-occurrence. Here, we used multi-year passive acoustic data from 6 sites in the Weddell Sea, Southern Ocean, to explore how local marine mammal community compositions develop over time and in relation to sea-ice. Diversity peaked in austral late spring and early summer, shortly before seasonal sea-ice break-up. The effective number of species exhibited little variation over time, reflecting that species remain in Antarctic waters throughout austral winter. Community composition showed almost complete seasonal overturn, indicating that species replace each other throughout the year. For all 6 sites, community dissimilarity increased with increasing temporal distance, reflecting temporal trends in community composition beyond seasonality. Several species exhibited significant positive or negative co-occurrence patterns over time. These seasonal associations were consistent across all 5 oceanic sites, but partly inversed at the Western Antarctic Peninsula recording site. This study shows that the application of biodiversity metrics to passive acoustic monitoring data can foster insights into the timing of behaviors and community composition, which can boost the interpretation of responses in the light of ongoing environmental changes.

Description: The Southern Ocean around the Antarctic continent provides some of the most extreme environmental conditions on earth which shape also the unique underwater soundscape. The area probably contains the most quiet locations within the world's oceans but is also stage for some of the loudest natural events. It is still relatively void of anthropogenic noise and is one of the most important feeding grounds for great whales. However, comparatively little acoustic data exists from this region so far because the collection of acoustic recordings is hindered by logistic constraints associated with this remote region. Very Quiet The large cavities below the giant floating ice shelves of Antarctica are amongst the most isolated areas in the world - but with a window to the open sea. Neither local surface noise nor biological sources are present within hundreds of kilometers radius. Sound levels here should reflect unbiased readings of the long-range acoustic energy field - and yield a lower boundary of how quiet the ocean can get. During much of the year large parts of the polar oceans are covered by sea ice, which has a significant impact on the underwater acoustics. Sea ice isolates the water from the air, impeding the generation of waves, while the snow layer absorbs acoustic energy efficiently, creating an "anechoic chamber" which may serve as a natural lab to test and verify sound propagation models. Very Loud But ice is also a major source of noise. Table icebergs, calved from the shelf, are the largest moving objects on earth, spanning areas of 1000 square kilometers with a thickness of several hundred meters. Driven by the ocean currents, billions of tons of ice can gain terajoules of kinetic energy, equaling that of a nuclear bomb. This energy can be released within a brief period of time when the iceberg touches ground or collides with other bergs or the ice shelf. These events produce some of the loudest natural broadband sounds in the ocean, rivaled only by earthquakes and can be recorded in distances as far as other continents. They would probably make perfect test signals to measure long range broadband sound propagation. However, their occurrence is relatively sparse, we detect about one or two such events in the vicinity of our Antarctic observatory per year. Additionally, smaller but frequent iceberg calving events, reaming of ice floes, exploding little bubbles of high pressure gas occlusions in melting glacier ice combine to a most diverse abiotic soundscape. Relevant Biology However, it is the biology that produces the major contribution to the overall sound budget here. Despite the reduction of the blue whale population to a small fraction of their pre whaling size, the chorus of blue whales is the predominant acoustic source in the Southern Ocean, present on 365 days per year. Together with about ten other marine mammal species occupying this ocean area, they fill the whole audible frequency range with relatively little spatio-temporal overlap, suggesting that acoustic bandwidth is an important natural resource that different species compete for. Here we have the unique chance to study the acoustic ecology of a large ecosystem which is not yet significantly influenced by anthropogenic sound and resides in an extremely rich natural soundscape. And as many of its acoustic ingredients compare to anthropogenic emissions in other areas of the world, one could derive reference models of the interaction of sound and biology from here. Data Acquisition All this is based on long term, wide area and high quality passive acoustic data. Our current effort builds on an established network of oceanographic moorings in the Weddell sea, which is fitted with long term acoustic recorders capable of recording broad band audio continuously for several years. Along with the permanent acoustic observatory on the ice shelf, PALAOA, which features a hydrophone array protected under a 100 m thick ice shield, this covers a significant part of the Weddell basin from the shore to the deep sea. Sea ice coverage and ice berg movement is captured by high resolution satellite images and local ship traffic is monitored by AIS receivers. Our acoustic record spans 6 years by now will be continued to be able to characterize typical annual fluctuations and long term trends in both the acoustic background and animal behavior and set them in relation to abiotic factors. We believe that this dataset will serve as a valuable reference for many ocean noise related questions and encourage to set up a similar networks in other polar seas.

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.

Description: 〈jats:p〉Abstract. Systematic long-term studies on ecosystem dynamics are largely lacking from the East Antarctic Southern Ocean, although it is well recognized that they are indispensable to identify the ecological impacts and risks of environmental change. Here, we present a framework for establishing a long-term cross-disciplinary study on decadal timescales. We argue that the eastern Weddell Sea and the adjacent sea to the east, off Dronning Maud Land, is a particularly well suited area for such a study, since it is based on findings from previous expeditions to this region. Moreover, since climate and environmental change have so far been comparatively muted in this area, as in the eastern Antarctic in general, a systematic long-term study of its environmental and ecological state can provide a baseline of the current situation, which will be important for an assessment of future changes from their very onset, with consistent and comparable time series data underpinning and testing models and their projections. By establishing an Integrated East Antarctic Marine Research (IEAMaR) observatory, long-term changes in ocean dynamics, geochemistry, biodiversity, and ecosystem functions and services will be systematically explored and mapped through regular autonomous and ship-based synoptic surveys. An associated long-term ecological research (LTER) programme, including experimental and modelling work, will allow for studying climate-driven ecosystem changes and interactions with impacts arising from other anthropogenic activities. This integrative approach will provide a level of long-term data availability and ecosystem understanding that are imperative to determine, understand, and project the consequences of climate change and support a sound science-informed management of future conservation efforts in the Southern Ocean. 〈/jats:p〉