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: 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: Natural ambient noise in the ocean is generated by the interaction of wind, waves, ice and biological sound sources. This thesis investigates ambient noise and its dynamics at selected locations in the Atlantic sector of the Southern Ocean. The Southern Ocean provides an important habitat for marine mammals. Rising noise levels might negatively affect marine mammals, which rely on their acoustic senses for foraging, orientation and communication. Two autonomous underwater recorders were deployed on moorings at 66° S and 69° S along the zero meridian, they provided a quasi 3-year acoustic dataset which was analysed using Matlab TM . A set of good environmental status descriptors, as proposed under the European Union marine strategy framework directive, was used to evaluate low frequency continuous noise. The recorded ambient noise, varying strongly over time and frequency, was correlated to ice coverage, wind speed and solar radiation. Seasonal sound pressure level change of 4.25 dB re 1 µPa was caused by the annual change in sea ice coverage. On a Weekly to sub-diurnal scale, sound pressure level variation is caused mainly by changes in wind speed. Marine mammal choruses influence distinct parts of the noise spectrum. The low frequency chorus generated by blue whales is the loudest frequency band in the ambient noise. During Antarctic winter, signals of unknown origin dominate the mid frequency part of the spectrum. The chorus of this signals exhibits a circadian rhythm at the beginning of winter. Over the 3-year recording period, a low frequency noise increase of 0.36 db re 1 µPa 2 s −1 at 40 hz per was detected. These findings can be used as baseline for future passive acoustic monitoring in the Southern Ocean.

Description: This paper describes the natural variability of ambient sound in the Southern Ocean, an acoustically pristine marine mammal habitat. Over a 3-year period, two autonomous recorders were moored along the Greenwich meridian to collect underwater passive acoustic data. Ambient sound levels were strongly affected by the annual variation of the sea ice cover, which decouples local wind speed and sound levels during austral winter. With increasing sea ice concentration, area and thickness, sound levels decreased while the contribution of distant sources increased. Marine mammal sounds formed a substantial part of the overall acoustic environment, comprising calls produced by Antarctic blue whales (Balaenoptera musculus intermedia), fin whales (Balaenoptera physalus), Antarctic minke whales (Balaenoptera bonaerensis) and leopard seals (Hydrurga leptonyx). The combined sound energy of a group or population vocalizing during extended periods contributed species specific peaks to the ambient sound spectra. The temporal and spatial variation in the contribution of marine mammals to ambient sound suggests annual patterns in migration and behaviour. The Antarctic blue and fin whale contributions were loudest in austral autumn, whereas the Antarctic minke whale contribution was loudest during austral winter and repeatedly showed a diel pattern that coincided with the diel vertical migration of zooplankton.

Description: Sebastian Menze, AWI Bremerhaven: „Walisch für Anfänger – Unterwasserradio aus der Antarktis“ Im Südpolarmeer ist es alles andere als still. Unterwasser erwartet uns dort eine Geräuschkulisse unerhörter Vielfalt von kollidierenden Eisbergen bis zu stöhnenden Blauwalen. Wale und Robben erzeugen diverse Laute um zu kommunizieren, zu jagen und sich zu orientieren. Wir nehmen diese Geräusche mit Unterwasserrecordern und einer „Horchstation“ auf und nutzen diese Daten um das Vorkommen und Verhalten der Meeressäuger im Südpolarmeer erforschen. Wer wissen möchte, wie das Südpolarmeer klingt, wer dort alles ruft und warum es einen Chor der Blauwale gibt, sollte die Ohren spitzen.

Description: Sebastian Menze, AWI Bremerhaven: „Walisch für Anfänger – Unterwasserradio aus der Antarktis“ Im Südpolarmeer ist es alles andere als still. Unterwasser erwartet uns dort eine Geräuschkulisse unerhörter Vielfalt von kollidierenden Eisbergen bis zu stöhnenden Blauwalen. Wale und Robben erzeugen diverse Laute um zu kommunizieren, zu jagen und sich zu orientieren. Wir nehmen diese Geräusche mit Unterwasserrecordern und einer „Horchstation“ auf und nutzen diese Daten um das Vorkommen und Verhalten der Meeressäuger im Südpolarmeer erforschen. Wer wissen möchte, wie das Südpolarmeer klingt, wer dort alles ruft und warum es einen Chor der Blauwale gibt, sollte die Ohren spitzen.

Description: With increasing marine traffic, the global level of anthropogenic noise is likely to rise. This might induce further stress to already endangered marine mammals, which rely on their acoustic senses for foraging, orientation and communication. The Southern Ocean provides an important habitat for marine mammals, both residential and migratory. To study its cetacean and pinniped populations as well as the ambient soundscape, autonomous underwater recorders were deployed on moorings in the Atlantic section of the Southern Ocean. Natural ambient noise is generated by the interaction of wind, waves, ice, biological and geological sources and subject to seasonal variations. Transient sounds such as whale and seal vocalisations strongly influence the acoustic spectra. Due to limited marine traffic and industrial activity the Southern Ocean contrasts regions with anthropogenic noise pollution on the northern hemisphere. This rather uninfluenced soundscape is analysed according to indicators as proposed under the European Union marine strategy frameworks directive. In this way a useful reference to the northern hemisphere oceans is given. The scope of anthropogenic and natural noise as well as sound examples will be presented.

Description: Passive acoustic monitoring (PAM) has emerged as a highly efficient technology to conduct long-term monitoring of marine mammals at species dependent, local to basin scales, providing valuable new insights into species distributions and migration patterns. To study Antarctic mammals, we deployed up to ten moored, autonomous acoustic recorders in the Atlantic sector of the Southern Ocean. Due to this region’s remoteness, challenging accessibility, and ensuing logistic constraints, especially during winter, recording devices were/are deployed for two years or longer, resulting in high demands on their power efficiency and storage capability. Two types of recorders, AURAL and MARU, which were deployed in March 2008 and December 2008, respectively, were recovered in December 2010. More recently, a set of eight, newly developed recorders (SONOVAULT), were deployed in December 2010, and are scheduled for recovery in December 2012. While in-situ recordings are hence available for AURAL and MARU, for SONOVAULTs extensive laboratory tests have been performed. Based on these recordings, this paper provides a user-based comparison of these three types of acoustic recorders, discussing their technical specifications and limitations (including recent enhancements) along with their actual performance and data quality. The paper concludes with a discussion of future needs for long-term monitoring applications along with each instrument’s potential to meet such requirements.

Description: Concerns regarding the acoustic quality of habitats have increased over the past years. Within the EU Marine Strategy Framework Directive, this has led to the proposal of environmental status indicators for underwater noise levels. One indicator, based on 1/3- octave band levels at 63- and 125-Hz, intends to monitor anthropogenic noise, particularly from shipping. In this context, ambient noise is defined as the acoustic energy not assignable to a specific source. We applied this indicator to passive acoustic underwater recordings from the Southern Ocean, which represents an environment relatively void of anthropogenic noise. To collect multi-year passive acoustic data, two autonomous underwater recorders were deployed in the Weddell Sea at 0°W/E 66°S and 0°W/E 69°S between March 2008 and December 2010. The analysis of the data revealed three caveats in the current implementation of this indicator: 1.) Usually, band noise calculations are based on temporal averages over all available data at the temporal resolution desired. However, this approach will bias towards transient, single loud and nearby acoustic events rather than representing the typical ambient noise. We propose to calculate ambient noise levels on the basis of the quietest 10 s each e.g. 5-min recording. 2.) Ambient noise levels in the 125-Hz band were strongly influenced by biotic sources. We propose that definitions of noise bands suitable for monitoring of anthropogenic noise need to be tuned as to avoid region-specific biotic interference. 3.) Our recordings reveal a substantial seasonal variability of ambient noise levels (102- 115 dBrms re 1 μPa, broadband sound pressure level 5th and 95th percentile), even if selected outside biotic bands, primarily due to sea state and ice cover. This implies that detecting gradual changes in ambient noise (e.g. the frequently reported 0.3dB/a) on the basis of annual averages is rather challenging if statistical significance is required.