East Antarctica
East Antarctica
        This project will initiate focused acoustic research into the biology of Southern Ocean cetaceans. Sonobuoys will be used to survey large geographic regions for the presence and relative abundance of cetaceans. In addition, bottom mounted acoustic recording devices will permit continuous acoustic monitoring of targeted locations over long time frames. These techniques will help answer important questions regarding the presence, relative abundance, seasonality, movements, and distribution of Southern Ocean marine mammals that are necessary for effective management.
        This multi-year initiative within the Antarctic Marine Living Resources (AMLR) program aims to implement a focused acoustic research program that will examine Southern Ocean marine mammal population dynamics through the use of technologically advanced acoustic monitoring techniques. In order to achieve the aims of this study an international collaboration has been developed leading to a multi-faceted research program. Long-term autonomous sea-floor recording devices will be utilized to conduct year-round acoustic surveys in targeted locations. Sonobuoys will additionally be used over shorter time frames to conduct strategic vessel-based acoustic surveys over large geographic ranges. These data will be used to assess distribution, movement, relative abundance, seasonality, and behaviour of cetaceans in Southern Ocean waters. These results can then be integrated with concurrently collected data on oceanographic and biological variables from vessel based surveys and remote satellite sensing leading to a larger understanding of the role of marine mammals in the Southern Ocean ecosystem.
        Long-term acoustic records can be valuable for assessing the timing of migrations, peak periods of abundance, and seasonality and overlap of different whale species over vast spatial scales. Previously, such records have not been obtained across the Southern and Indian Ocean waters south of Australia. Here, acoustic datasets of between 1-3 years (2004-2007) were collected from widely spaced sites between Australia and Antarctica utilizing autonomous recording units and data from a cabled hydrophone array. Recording locations included 3 sites spanning 2500km along the Antarctic continental shelf-break, 2 sites 2500km north off the western and eastern Australian continental shelf, and 2'mid'-ocean sites. Power spectral density was calculated for successive 15 minute segments over the entire datasets. Ratios of power at whale (Antarctic & pygmy blue, fin) song frequencies to surrounding frequencies were calculated to determine the relative contribution of whale song to ocean noise.
        Peak 'acoustic presence' of Antarctic blue whales occurred just slightly earlier at Antarctic sites (April-July) compared to Australian sites (May-August), suggesting a combination of seasonal calling behaviour and migratory movement influences the results. While peak fin whale acoustic presence occurred simultaneously with Antarctic blue whales at Australian sites (May-August), they were present over a much shorter period (April-May) in Antarctic data, consistent with the more northerly distribution expected for fin whales. At Australian sites, peak pygmy blue whale acoustic presence was consistently earlier (March-May) than Antarctic blue or fin whales, suggesting these animals are present primarily before Antarctic blue and fin whales migrate north. Considering the limited understanding of large whales and their interactions in these waters, these long term acoustic records are helping reveal the seasonal presence and movement patterns of these animals over vast areas of the Indian and Southern Oceans.
The red stars indicate where we've used the Scripps ARPs, the yellow locations are where we've deployed acoustic loggers (15 min samples/hr @ 4kHz sampling rate) built by Curtin University (Rob McCauley), and the blue locations are part of the Comprehensive Nuclear
Test Ban Treaty Organization (CTBTO) hydroacoustic monitoring network.
        

Accurate information on distribution, abundance, movement, and seasonality of marine mammals is essential for answering targeted management-based questions. Our knowledge of the general biology, feeding ecology and migratory patterns of many Southern Ocean marine
mammals is limited leading to poor understanding or recognition of their role within marine ecosystems (Costa and Crocker, 1996; Bannister et al., 1996). Such information is especially lacking for cetaceans due to their pelagic nature and difficulties involved in studying these
animals. The scientific arguments for the development of improved assessment of distribution, relative abundance, movement, seasonality, and behaviour are compelling.
        Much of our knowledge of Southern Ocean cetaceans comes from the whaling industry and more recently, ship-based platforms of opportunity. Southern Ocean cetacean distribution and relative abundance estimates are traditionally based on visual surveys from vessels. Visual surveys, however, are restricted by the amount of time marine mammals spend on the surface, visibility (daylight, weather), oceanographic conditions (sea state, sea-ice presence), observer subjectivity, and access to observation platforms (Thomas et al., 1986; Leaper and Scheidat, 1998; Gillespie, 1997). In addition, due to the difficulties of working in the Southern Ocean, most Antarctic cetacean observations are made in the spring and summer (Thiele and Gill, 1999). Subsequently, there is little information regarding the winter distribution, abundance and ecology of whales in Antarctic waters despite increasing evidence that some proportion of populations over-winter in the Southern Ocean (Thiel and Gill, 1999; Sirovic et al., 2004; Brown et al., 1995).
        Acoustic study, however, is particularly well suited to overcome many of these difficulties and has enormous potential to help understand the role of cetaceans in the Antarctic ecosystem. Many cetaceans are highly vocal and produce species-specific, and sometimes stock-specific sounds. Underwater sound travels large distances from its source with baleen whale calls often detected to ranges of many 10s of kilometres. Acoustic surveys of cetacean habitats, therefore, are a powerful means of identifying the species present, locating and tracking individuals, identifying stocks from regional dialects, and determining patterns of seasonal distribution and relative abundance (Stafford et al., 1999; Clark and Ellison, 1989; Thompson et al., 1992; Clark et al., 1996; Clark and Fristrup, 1997; Clark and Charif, 1998; Moore et al., 1998).
        Long-term acoustic monitoring techniques enable detection of calling animals when sighting surveys are not feasible and permit year-round acoustic surveys of regions that are normally inaccessible due to weather or ice cover. Already, initial deployment of these instruments on the Antarctic Peninsula has indicated that calling blue whales are present in the Antarctic for much longer periods than was previously suspected (Sirovic et al., 2004). For instruments deployed in a single location for long periods, peaks in detections of each species' call can be used to assess the timing of migrations, period of peak relative abundance, seasonality, and temporal overlap of different species' presence (Sirovic et al., 2004). Comparison of recording packages from different locations can be used to assess variations in relative abundances, times of residence and potentially migratory movements. Finally, comparison of acoustic detections from individual locations over multiple years will permit changes in presence, abundance and timing through seasons to be assessed. These data can then be compared to other biological and oceanographic data collected from vessel-based surveys and remote satellite sensing to correlate whale behaviour with such variables as sea-ice presence, water temperature, and biological productivity.

 

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Credit: Jason Gedamke and John Hildebrand