Description: Passive acoustic data provide a prime source of information on marine mammal distribution and behaviour. Particularly in the Southern Ocean, where ship-based data collection can be severely hampered by weather and ice conditions, passive acoustic monitoring (PAM) of marine mammals forms an important source of year-round information on acoustic presence. Array data can be used to obtain directional information on the species present in the recordings to derive movement patterns. Acoustic arrays furthermore allow spatial comparisons of marine mammal distribution patterns and habitat affinities when the acoustic presence information is linked to local environmental parameters. Here we present two passive acoustic monitoring arrays that have been implemented by the Alfred Wegener Institute’s Ocean Acoustic Lab and serve the investigation of marine mammals on different spatial scales. During the austral summer season 2012/2013 a local scale array of sea ice-based time-synchronized passive acoustic recorders was deployed in Atka Bay, Antarctica. The PASATA (PASsive Acoustic Tracking of Antarctic marine mammals) project investigates coastal local habitat usage and communication ranges of marine mammals by integrating positional information from triangulation of calling animals and information from environmental parameters. For studies on marine mammals over larger spatial scales, 23 passive acoustic recorders were deployed in oceanographic moorings in the Southern Ocean, reaching from the Greenwich meridian throughout the Weddell Sea to the Western Antarctic Peninsula. The inter-disciplinary nature of this mooring array allows combining in-situ oceanographic measurements with passive acoustic data on marine mammal occurrence. It furthermore forms the first basin-wide, long term array, at least in the Southern Ocean. Here, we describe both arrays, the recorder types used, and technical and logistic requirements for PAM in a polar environment.

Description: Passive acoustic data provide a prime source of information on marine mammal distribution and behaviour. Particularly in the Southern Ocean, where ship-based data collection can be severely hampered by weather and ice conditions, passive acoustic monitoring (PAM) of marine mammals forms an important source of year-round information on acoustic presence. Array data can be used to obtain directional information on the species present in the recordings to derive movement patterns. Acoustic arrays furthermore allow spatial comparisons of marine mammal distribution patterns and habitat affinities when the acoustic presence information is linked to local environmental parameters. Here we present two passive acoustic monitoring arrays that have been implemented by the Alfred Wegener Institute’s Ocean Acoustic Lab and serve the investigation of marine mammals on different spatial scales. During the austral summer season 2012/2013 a local scale array of sea ice-based time-synchronized passive acoustic recorders was deployed in Atka Bay, Antarctica. The PASATA (PASsive Acoustic Tracking of Antarctic marine mammals) project investigates coastal local habitat usage and communication ranges of marine mammals by integrating positional information from triangulation of calling animals and information from environmental parameters. For studies on marine mammals over larger spatial scales, 23 passive acoustic recorders were deployed in oceanographic moorings in the Southern Ocean, reaching from the Greenwich meridian throughout the Weddell Sea to the Western Antarctic Peninsula. The inter-disciplinary nature of this mooring array allows combining in-situ oceanographic measurements with passive acoustic data on marine mammal occurrence. It furthermore forms the first basin-wide, long term array, at least in the Southern Ocean. Here, we describe both arrays, the recorder types used, and technical and logistic requirements for PAM in a polar environment.

Description: Water is an excellent medium for sound transmission and many aquatic animals actively produce sound for communication, orientation or foraging purposes. The underwater environment is filled with abiotic and biotic sounds of variable intensity over a wide range of frequencies and showing high levels of variation in space and time. Evidence is increasing that the passive use of such environmental sounds also provides an important information source for aquatic organisms to orient themselves and obtain information about the environment. All fishes can detect and process acoustic particle motion, including species that do not produce sound, indicating that sound is likely to be of critical importance in the lives of many fish species. Over the last century, human activities in and near the water have increasingly added artificial sounds to the underwater environment. To date, information on the behavioral and ecological implications of increasing underwater sound levels for fish is generally lacking. However, comparative evidence from other vertebrate species suggests that impeding the ability of fish to hear biologically relevant sounds can interfere with critical functions such as acoustic communication, predator avoidance and use of information from underwater soundscapes. Sounds produced by offshore windpower plants comprise loud impulse sounds (construction) and more moderate underwater noises of longer duration (operation and maintenance), which differ substantially in the type of impact and the spatio-temporal scale over which effects may occur. Short impact sounds, such as from pile driving can have dramatic effects on nearby fish, resulting in physical damage and death. However, long-term moderate anthropogenic noise exposure may have a greater impact on fish behaviour and ecology, potentially affecting whole ecosystems. Before noise-exposure criteria and mitigation measures can be established for fish, experimental studies in the field and in the laboratory are needed to investigate if and how fish are impacted behaviorally and physiologically by chronic and impact noise. Comparative evidence from terrestrial studies may provide guidance in experimental design and in taking a more holistic approach to develop a better understanding of the ecological impact of anthropogenic noise.

Description: An understanding of marine mammal distribution patterns forms the basis of the design and implementation of effective management measures. Habitat modeling offers a valuable approach to combine information on species presence (or absence) with local environmental parameters to explore species-specific habitat affinities. Most habitat modeling approaches require marine mammal presence-absence data which can only be obtained during dedicated visual surveys. However, in the Southern Ocean, the collection of visual data is complicated by the region’s remoteness, limited seasonal accessibility and the dependency on favorable light and weather conditions to conduct visual observations. Passive acoustic monitoring, by contrast, is highly suitable for long-term monitoring of marine mammals as they use sound in many behavioural contexts and species can be readily identified by their acoustic signatures. Passive acoustic data provide accurate information on temporal patterns in acoustic presence and time spent in the vicinity of the recorders. Furthermore, knowledge on the behavioral context in which specific sound types are produced can be used to derive information on habitat usage. Here we describe an approach for combining multi-year, year-round marine mammal presence data from passive acoustic recorders with a selected set of relevant environmental parameters to develop species-specific habitat models. Our project comprises multi-year passive acoustic data collected in Antarctic coastal as well as offshore areas throughout the Weddell Sea. Some of the species recorded are sighted only rarely during visual surveys, but are acoustically abundant in our recordings, such as the Antarctic blue whale (Balaenoptera musculus intermedia), humpback whale (Megaptera novaeangliae), fin whale (B. physalus), leopard seal (Hydrurga leptonyx), crabeater seal (Lobodon carcinophaga) and Ross seal (Ommatophoca rossii). The model will incorporate both static environmental variables, such as depth or slope, and dynamic variables, such as sea surface temperature, sea surface height, sea ice concentration and their derivatives. The project aims at furthering our current understanding of marine mammal habitat affinities in the Southern Ocean by constructing species-specific habitat models at yet unprecedented spatial and temporal time scales.

Description: The Southern Ocean provides an important habitat for marine mammals, both residential and migratory, yet long term studies of their habitat usage are hampered by the region’s seasonal inaccessibility. To overcome this problem, two autonomous underwater passive acoustic recorders were deployed in the Weddell Sea in 2008 to collect multiyear passive acoustic data. The recorders were retrieved in 2010 and the acoustic recordings were analyzed in terms of broad- and narrow-band noise. Noise in this context is defined as the acoustic energy not assignable to a specific singular source. It comprises both biotic as well as abiotic components. Noise levels were determined by selecting the quietest 10 s of each 5 min recording to exclude energetic contributions from nearby singular acoustic sources. The respective sound pressure levels (SPL) and spectra were correlated with time series of environmental covariates. The ambient noise levels of both recorders were found to be highly variable in time, ranging from 102 to 115 dB re 1 μPa (broadband SPL 5th and 95th percentile), and were correlated with the sea ice cover and wind speed. The annual variation of the ice cover caused a bimodal distribution of broadband SPL. In winter the SPL mode was 106 dB re 1 μPa. By contrast, storms over the open ocean in summer resulted in an SPL mode of 111 dB dB re 1 μPa. Variation in the ambient noise spectra could be correlated to wind speed and ice coverage. The acoustic presence of several mysticete (Antarctic blue whale, Balaenoptera musculus intermedia, fin whale, Balaenoptera physalus) and pinniped (leopard seal, Hydrurga leptonyx, crabeater seal, Lobodon carcinophaga) species created distinct bands in the spectra that contributed considerably to ambient noise levels. Comparison of the timing of these noise bands between the two acoustic data sets revealed offsets in the occurrence of acoustic activity between both recorders, suggestive of marine mammal latitudinal migration. At 66°S (the northern recorder position) fin whales were acoustically present earlier and longer in summer than at 69°S. Similarly, the blue whale chorus was more intense at 66°S than at 69°S. This might be related to the response of these species to the seasonal variation in the extension and density of sea ice. Seasonal cycles were also detected in the noise band attributed to crabeater seal vocalisations. They were annually present in September and November, followed by the leopard seals noise band, which is discernible between December and January. Results from this latitudinal recorder pair give a first impression on possible marine mammal migration patterns as well as the spatial and temporal distribution of marine mammal acoustic presence in the Southern Ocean. Additional recorders deployed in the basin wide HAFOS array will expand the spatial and temporal resolution of the acoustic dataset and allow conducting detailed multiyear studies of marine mammal acoustic presence and behavior throughout the Weddell Sea.

Description: The Arctic and Antarctic share a strong seasonality of light and temperature extremes that create similar selective pressures for animals living in these two polar and associated sub polar regions. There is significant evidence that Arctic ice conditions are rapidly deteriorating due to global climate change and evidence that Antarctic ice is also changing. Sub polar regions experience a seasonal ice cover with an added dynamic range of environmental conditions often exceeding that at the poles. In polar and sub polar waters, the presence of sea ice dominates the physical environment for an extended period of time. This strongly influences pinniped distribution, reproductive strategies, foraging ecology, and acoustic behavior. In both polar regions, seals have distinctly different underwater vocal repertoires associated with breeding and an airborne repertoire associated with mother and pup communication. In this chapter, a comparative approach is taken to relate the underwater acoustic behavior of polar pinnipeds (phocids and walrus) to their ecology and aspects of their sea ice habitat. Understanding the commonalities and differences in the spatial, spectral, and temporal characteristics of vocalizations from species with comparable biologies relative to local sea ice conditions may provide insights into the acoustic ecology of pinnipeds in polar habitats. Acoustic ecology describes the interaction between an animal and its environment as mediated through sound and is determined by the species' behavioral ecology, but also by biotic and abiotic factors of the environment. Insight into acoustic ecology may therefore provide information on the potential direct and indirect impacts of polar climate change on pinnipeds. Loss of sea ice will likely affect polar pinniped distribution and breeding activities; both of which can be detected through long-term passive acoustic monitoring. One of the secondary effects of sea ice loss is the impact to the polar acoustic soundscape (i.e., the acoustic environment). The communication system of polar pinnipeds, which permeates critical life functions like breeding, evolved in an acoustic environment dominated by ambient noise levels associated with seasonal ice cover. Changes in ice dynamics will likely be accompanied by shifts in habitat use by both marine animals and humans which will lead to a corresponding change in the acoustic soundscape. The combined impacts of these effects is unprecedented, but the knowledge gained from a comparison of pinniped acoustic ecology between the Arctic and the Antarctic will lead to a better understanding of the relationship between ice seals and their changing environment.