ALBERT

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: Passive acoustic monitoring (PAM) data were collected by recorder SV1009 of type Sono.Vault (manufactured by develogic GmbH, Hamburg, Germany) at 65°41.79' S, 36°41.012' W, mooring AWI208-8, in Weddell Sea, Atlantic sector of the Southern Ocean. During a deployment period from January 2017 to January 2019, passive acoustic data were collected from January 2017 to May 2018 (recording period) by SV1009 as part of the Hybrid Antarctic Float Observing System (HAFOS) in the Weddell Sea. The recorder was moored at 1032 m depth and scheduled to record continuously at a sample rate of 6,857 Hz. Further details about the data acquisition and processing of this data set can be found in the accompanying metadata file (see Additional metadata) as well as the data processing report (see Data Processing Report). Further information on terminology, data processing, preparation and standardization can be found in the associated Standard Operating Procedure (SOP) Glossary (Thomisch et al. 2023a) and SOP Part 1: Data preparation and standardization (Thomisch et al. 2023b).

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: 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: 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.

Description: Spatio-temporal patterns in Antarctic minke whale (Balaenoptera bonaerensis) vocal behaviour in the Weddell Sea. 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 Antarctic minke whale vocalizations now allows the use of passive acoustic monitoring to investigate year-round spatio-temporal patterns in occurrence in ice-covered areas. Here we present preliminary results on Antarctic minke whale occurrence patterns based on a multi-year passive acoustic data set from 6 locations throughout the Atlantic sector of the Southern Ocean. Analyses were based on daily presence of the bio-duck call, which 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, the bioduck call was present up to ten months of the year. Substantial inter-annual variation in the seasonal on- and offset period of vocal activity was observed at the different recording positions, possibly corresponding to variation in local ice conditions.

Description: Evidence of off-season humpback whale (Megaptera novaeangliae) acoustic presence in high latitude feeding areas is accumulating for Northern Hemisphere waters. To date, however, long-term studies investigating humpback whale vocal behavior in the Southern Ocean were limited to the coastal region. This study provides preliminary baseline data from three recording sites on humpback whale vocal behavior on Antarctic feeding grounds. Passive acoustic recorders were located in a transect along the Greenwich meridian at 59’S (SV0002), at 64’S (SV1000) and 66’S (SV1001). Humpback whales were acoustically present from January to August (SV0002), from January to June (SV1000) and from January until May (SV1001). Acoustic presence was most pronounced (〉60% of recording days containing calls) from May to July (SV0002), and April to May (SV1000 and SV1001), concurring with substantial increases in ice cover (〉90%) at all three sites. During the period of ice formation (February to April) acoustic presence was sparser. Calls were divided into 27 call categories with a maximum of 10 subtypes per category. For all three recorders 4 to 8 call categories made up 〈80% of all calls, 3 call categories of which where the same for all three recorders. The vocal repertoire was more diverse in March, April and May compared to January, February, June, July and August in all three recorders. Furthermore, humpback whale song was present at all 3 recording sites, at SV0002 in May and June, SV1000 in March and SV1001 in April. This study demonstrates that pervasive humpback whale presence in the Southern Ocean is not limited to the coast, but extends to pelagic regions. The presence of social sounds and song during extended periods suggests that whales were not just transiting the area, but roamed the area for some time, possibly to exploit the presence of local food patches and open water.

Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Schall, E., Di Iorio, L., Berchok, C., Filun, D., Bedrinana-Romano, L., Buchan, S. J., Van Opzeeland, I., Sears, R., & Hucke-Gaete, R. Visual and passive acoustic observations of blue whale trios from two distinct populations. Marine Mammal Science, (2019): 1-10, doi:10.1111/mms.12643.

Description: Blue whale populations from both hemispheres are thought to undertake annual migrations between high latitude feeding grounds and low latitude breeding grounds (Mackintosh, 1966). For individuals of some populations these predetermined movements to and from wintering areas where calving occurs have been confirmed through photo‐identification, satellite‐tracking, and passive acoustic monitoring (Burtenshaw et al., 2004; Mate, Lagerquist, & Calambokidis, 1999; Sears & Perrin, 2002; Stafford, Nieukirk, & Fox, 1999a). However, for many blue whale populations no clear migratory behavior has been reported and locations of respective breeding grounds remain unclear (e.g., Hucke‐Gaete, Osman, Moreno, Findlay, & Ljungblad, 2004; Samaran et al., 2013; Stafford, Chapp, Bohnenstiel, & Tolstoy, 2011; Thomisch et al., 2016). On feeding grounds in the Gulf of St. Lawrence and along the coast of California, blue whales have been observed to form female–male pairs during summer, which can remain stable up to over several weeks, with the number of pairs increasing towards the end of summer (Sears & Perrin, 2002; Calambokidis, unpublished data;1 RS, unpublished data). These pairs are sometimes joined by a second male, forming a blue whale trio, which often is observed to engage in surface active behaviors lasting several minutes (Sears & Perrin, 2002; RS, unpublished data). The formation of blue whale trios is probably related to reproductive competition between male escorts and female choice (RS, unpublished data). Blue whale males produce population‐specific songs likely functioning as reproductive advertisement (Edds‐Walton, 1997; Oleson et al. 2007a; Stafford, Fox, & Clark, 1998). Several studies have reported song year‐round in low‐, mid‐, and high‐latitude waters, frequently with high song production rates during summer on the feeding grounds (e.g., Barlow et al., 2018; Buchan, Stafford, & Hucke‐Gaete, 2015; Samaran, Adam, & Guinett, 2010; Širović et al., 2004; Stafford, Nieukirk, & Fox, 1999b; Thomisch et al., 2016). Therefore, breeding activities in blue whales may be more opportunistic, i.e., not restricted to the breeding season or to a specific habitat.

Description: ES thanks Prof. Dr. Per J. Palsbøll for the supervision of the initial Master research project, the Marco Polo fund, and the University Groningen for covering travel expenses. We thank the Melimoyu Ecosystem Research Institute, SNP Patagonia Sur, and the company Teledyne Reson for partially funding the acoustic data collection in southern Chile. RHG is thankful to WWF‐Germany/Chile for partially funding fieldwork through grants to Centro Ballena Azul. CLB thanks the team of the Mingan Island Cetacean Study for their logistical support of boats and lodging, access to the North Atlantic blue whale database, and field assistance; Yvon Bélanger for opening his home to her and RS's field crews; for financial support from the National Science Foundation (Graduate Fellowship), National Defense Industrial Association, American Museum of Natural History (Lerner Gray Fund for Marine Research Grant), Penn State Applied Research Laboratory, and private donors Jeff and Lynn Kraus; and graduate advisors at Penn State University David L. Bradley, Thomas B. Gabrielson, and Diana McCammon. LDI thanks the Croisières du Grand Héron and Center Mériscope for allowing and supporting fieldwork, the Animal Behavior Department of the University of Zurich (Switzerland), the Bioacoustics Research Program at Cornell University (USA) and Prof. M. Manser and C. W. Clark for supervising LDI's Ph.D. The work was supported by grants to LDI for her PhD from the Forschungskommission der Universität Zürich, Züricher Tierschutz, Basler Stiftung für Biologische Forschung, SCNAT, Zangger‐Weber‐Stiftung, SSVA. SJB thanks the Center for Oceanographic Research COPAS Sur‐Austral, CONICYT PIA PFB31, the Office of Naval Research Global (awards N62909‐16‐2214 and N00014‐17‐2606), and a grant to the Centro de Estudios Avanzados en Zonas Áridas from Programa Regional CONICYT R16A10003 for support during manuscript writing. We would like to thank the field crews (F. Viddi, J. Ruiz, A. Carpentier, M. Lessard, A. Liebschner, C. Ramp, S. Angel, K. Aucrenaz, T. Doniol‐Valcroze, J. LeBreus, B. Kot, and J. Puschock) for their immense commitment to blue whale research.

Description: Antarctic minke whales (AMW) have a circum-antarctic distribution and are known to occur in both open and ice-covered waters of the Southern Ocean (SO). They are a pagophilic species and are regularly observed in heavily sea-ice covered areas. Because of this, current knowledge about Antarctic minke whales is scarce and limited to austral summer and ice-free regions where the majority of visual survey data have been collected. Hence, very little is known on their winter distribution in high latitude waters and to what extent the wintering individuals that are occasionally observed in Antarctic waters represent single observations or a structurally present behavioral trait of the species. Likewise, AMW population structure is poorly known. As most baleen whale species, AMWs are known to undertake annual migrations between high latitude feeding areas and low latitude breeding areas. However, available data to date suggest that for AMWs, migrations seem more protracted and complex than in other baleen whale species. The recent identification of vocalizations produced by AMWs (“bio-duck call”) now makes it possible to also use passive acoustic technology to study occurrence patterns and behavior. Passive acoustic monitoring (PAM) offers a versatile technology with which long-term archival data can be collected on sound-producing species using autonomous recording units. Acoustic observation has the additional advantages that it can continue data collection independent of light conditions and under poor weather conditions. Furthermore, it can monitor large areas at the same time, since it collects data omnidirectionally, and it can collect data over extended periods (i.e., multi-year time scales) through the use of autonomous devices. In the scope of this doctoral thesis, I analysed passive acoustic data from high and low latitudes collected in the Atlantic Ocean sector of the Southern Ocean (Weddell Sea) and southern Atlantic Ocean, to investigate spatio-temporal patterns in the acoustic presence and vocal behaviour of AMWs. In Chapter I, I investigate year-round spatial- temporal patterns in AMW occurrence in ice-covered areas. Our analysis was based on a 9-year passive acoustic dataset (2008- 2016) from 21 locations throughout the Weddell Sea (WS). AMW bio-duck calls 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, bio-duck calls were present up to 10 months of the year. We identified a 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. In Chapter II, I used PAM data from 6 positions located along the WS during 2013 as well as three consecutive years of PAM data (2015-2016-2017) recorded at the stationary coastal acoustic observatory PALAOA to study both spatial and inter-annual variability in the acoustic behavior of AMWs. During 2013, between May and December throughout the WS, we detected 11 different bio-duck call types. The comparative analyses of the AMW bio-duck call repertoire throughout the WS showed that these 11 call types can be attributed to four call type groups. Furthermore, multi-year data from PALAOA on AMW repertoire composition showed an inter-annual difference in bio-duck call type usage. The observed patterns in AMW vocal behavior show that AMW vocal behavior matches the definition of song, exhibiting regional differences and highly dynamic revolutions over time. This study provides new information to potentially explore stock structures and movement patterns using passive acoustic methods. In Chapter III, my work addressed the occurrence of the AMW through bio-duck acoustic detections in the Santos Basin, South-Southeastern Brazil (22º and 28º S / 42º and 48º W), recorded between 12 November and 19 December 19, 2015, utilizing advanced passive acoustic technologies, i.e., an autonomous underwater vehicle (SeaGlider), for sampling. AMW calls were detected during 12 days. We detected and classified 9 different bio-duck calls in Brazilian coastal waters, evidencing a highly diverse acoustic behavior on this potential Antarctic minke whale breeding ground. Finally, in Chapter IV, our study investigated the temporal patterns of acoustic occurrence of baleen whales in a presumed baleen whale breeding area off Namibia. Our results show seasonal acoustic presence of humpback whales, fin whales and Antarctic minke whales 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. 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 previously assumed. Overall, this PhD thesis highlights the significance of using long-term and large-scale datasets for the investigation of distribution patterns, habitat preferences, behavior and the effects of environmental variation on AMW distribution. The results present new information about fundamental and ecological knowledge of AMWs that can be implemented for the conservation and management of populations and ecosystems.