Highlights
• This study couples passive and active acoustic time series data.
• Our aim is to examine the drivers of blue whale presence over time.
• Seasonal and submonthly blue whale presence was associated with euphausiid biomass.
• Blue whale song calls followed a seasonal cycle; D-calls varied over submonthly cycles.
• Spring tides may increase prey aggregation and/or transport into the Corcovado Gulf.
• Short-lived storms may also contribute to the aggregation of prey.

Highlights

• Less sea ice and increasing storminess are making Arctic waters louder during the open water
season due to increased wind and wave noise.
• Arctic marine mammals are changing their migratory patterns and subarctic visitors are heard
for more of the year and further north as sea ice loss opens habitat for them.
• Arctic shipping traffic between the Pacific and Atlantic Oceans continues to increase and with it, ambient noise levels are increasing in the frequency bands used by marine mammals.

Blue whales (Balaenoptera musculus spp.), an endangered species globally, are found throughout the Indian Ocean, including the northern Indian Ocean (NIO) and Arabian Sea. Blue whales track productive habitats where primary productivity is high and dense aggregations of prey occur. The island mass effect, associated upwelling, and nutrient discharge increase productivity near mid‐oceanic islands. In the NIO, where seasonal monsoons shape ocean life, mid‐oceanic islands may act as predictable hotspots for baleen whale prey.

Northern Hemisphere blue and fin whales are regular summer migrants to Arctic waters. Given the profound changes the Arctic is currently undergoing due to global warming, changes in habitat use and distribution of these migratory species are predicted. In this study, 3 passive acoustic recorders, 2 in Fram Strait about 95 km apart and 1 north of the Svalbard Archipelago (Atwain), were used to investigate the spatial and temporal vocal occurrence of these species in the Northeast Atlantic High Arctic. Acoustic data were available for 7 years for western Fram Strait (WFS), 2.5 years for central Fram Strait (CFS) and 3 years for Atwain. At both Fram Strait locations, most blue whale call detections occurred from August through October, though recently (2015–2018) in WFS a clear increase in blue whale call rates was detected in June/July, suggesting an expansion of the seasonal occurrence of blue whales. In WFS, fin whale calls were detected intermittently, at low levels, almost year-round. In CFS, fin whale calls were more frequent but occurred mainly from July through December. At Atwain, blue whale detections commenced in July, both species were recorded in September/October and fin whale calls extended into November. Results from this study provide novel long-term baseline information about the occurrence of blue and fin whales at extreme northerly locations, where traditional ship-based survey methods are seasonally limited. Continued sampling will support investigation of how environmental change influences cetacean distribution and habitat use.

The Distributed Biological Observatory (DBO) was established to detect environmental changes in the Pacific Arctic by regular monitoring of biophysical responses in each of 8 DBO regions. Here we examine the occurrence of bowhead and beluga whale vocalizations in the western Beaufort Sea acquired by acoustic instruments deployed from September 2008 – July 2014 and September 2016 – October 2018 to examine inter-annual variability of these Arctic endemic species in DBO Region 6. Acoustic data were collected on an oceanographic mooring deployed in the Beaufort shelfbreak jet at ~71.4°N, 152.0°W. Spectrograms of acoustic data files were visually examined for the presence or absence of known signals of bowhead and beluga whales. Weekly averages of whale occurrence were compared with outputs of zooplankton, temperature and sea ice from the BIOMAS model to determine if any of these variables influenced whale occurrence. In addition, the dates of acoustic whale passage in the spring and fall were compared to annual sea ice melt-out and freeze-up dates to examine changes in phenology. Neither bowhead nor beluga whale migration times changed significantly in spring, but bowhead whales migrated significantly later in fall from 2008–2018. There were no clear relationships between bowhead whales and the environmental variables, suggesting that the DBO 6 region is a migratory corridor, but not a feeding hotspot, for this species. Surprisingly, beluga whale acoustic presence was related to zooplankton biomass near the mooring, but this is unlikely to be a direct relationship: there are likely interactions of environmental drivers that result in higher occurrence of both modeled zooplankton and belugas in the DBO 6 region. The environmental triggers that drive the migratory phenology of the two Arctic endemic cetacean species likely extend from Bering Sea transport of heat, nutrients and plankton through the Chukchi and into the Beaufort Sea.

Eight years of passive acoustic data (2007–2014) from the Beaufort Sea were used to estimate the mean cue rate (calling rate) of individual bowhead whales (Balaena mysticetus) during their fall migration along the North Slope of Alaska. Calls detected on directional acoustic recorders (DASARs) were triangulated to provide estimates of locations at times of call production, which were then translated into call densities (calls/h/km²). Various assumptions were used to convert call density into animal cue rates, including the time for whales to cross the arrays of acoustic recorders, the population size, the fraction of the migration corridor missed by the localizing array system, and the fraction of the seasonal migration missed because recorders were retrieved before the end of the migration. Taking these uncertainties into account in various combinations yielded up to 351 cue rate estimates, which summarize to a median of 1.3 calls/whale/h and an interquartile range of 0.5–5.4 calls/whale/h.

The goal of this project is to use acoustic signatures to detect, classify, and count the calls of four acoustic populations of blue whales so that, ultimately, the conservation status of each population can be better assessed. We used manual annotations from 350 h of audio recordings from the underwater hydrophones in the Indian Ocean to build a deep learning model to detect, classify, and count the calls from four acoustic song types. The method we used was Siamese neural networks (SNN), a class of neural network architectures that are used to find the similarity of the inputs by comparing their feature vectors, finding that they outperformed the more widely used convolutional neural networks (CNN). Specifically, the SNN outperform a CNN with 2% accuracy improvement in population classification and 1.7%–6.4% accuracy improvement in call count estimation for each blue whale population. In addition, even though we treat the call count estimation problem as a classification task and encode the number of calls in each spectrogram as a categorical variable, SNN surprisingly learned the ordinal relationship among them. SNN are robust and are shown here to be an effective way to automatically mine large acoustic datasets for blue whale calls.

Since 2001, hundreds of thousands of hours of underwater acoustic recordings have been made throughout the Southern Ocean south of 60° S. Detailed analysis of the occurrence of marine mammal sounds in these circumpolar recordings could provide novel insights into their ecology, but manual inspection of the entirety of all recordings would be prohibitively time consuming and expensive. Automated signal processing methods have now developed to the point that they can be applied to these data in a cost-effective manner. However training and evaluating the efficacy of these automated signal processing methods still requires a representative annotated library of sounds to identify the true presence and absence of different sound types. This work presents such a library of annotated recordings for the purpose of training and evaluating automated detectors of Antarctic blue and fin whale calls. Creation of the library has focused on the annotation of a representative sample of recordings to ensure that automated algorithms can be developed and tested across a broad range of instruments, locations, environmental conditions, and years. To demonstrate the utility of the library, we characterise the performance of two automated detection algorithms that have been commonly used to detect stereotyped calls of blue and fin whales. The availability of this library will facilitate development of improved detectors for the acoustic presence of Southern Ocean blue and fin whales. It can also be expanded upon to facilitate standardization of subsequent analysis of spatiotemporal trends in call-density of these circumpolar species.

This volume covers bowhead biology from their anatomy and behavior, to conservation, distribution, ecology and evolution. The book also discusses the biological and physical aspects of the Arctic ecosystem in which these whales live, with careful attention paid to the dramatic changes taking place. A special section of the book describes the interactions of humans with bowheads in past and present, focusing on their importance to Indigenous communities and the challenges regarding entanglement in fishing gear, industrial noise and ship strikes.

This volume brings together the knowledge of bowheads in one place for easy reference for scientists that study the species, marine mammal biologists, but, equally important, for everyone who is interested in the Arctic.

Globally, the Indian Ocean appears to have the greatest blue whale (Balaenoptera musculus ssp) acoustic diversity, with at least four acoustic populations from three defined sub-species. To understand how these different populations use this region as habitat, we first need to characterize their spatial and seasonal distributions. Here, we build on previous passive acoustic monitoring studies and analyze a passive acoustic dataset spanning large temporal (9 years) and spatial (3–9 sites covering more than 12 million km² of potential acoustic habitat in the southwest Indian Ocean) scales. A novel detection algorithm was employed to investigate the long-term presence of Antarctic blue whale and SEIO and SWIO pygmy blue whale calls. We found that Antarctic and pygmy blue whales have completely different spatial and seasonal distribution in the southern Indian Ocean. Antarctic blue whales are heard almost year-round on the whole array, with great inter-annual variability. The two pygmy blue whales share a highly stable seasonal acoustic presence, but their geographical distributions overlap at only a few central Indian Ocean sites. However, Antarctic and pygmy blue whale acoustic co-occurrence is common, especially in sub-tropical waters. These temporal and spatial distributions strengthen our understanding of seasonal occurrence and habitat use of distinct populations of blue whales in the southern Indian Ocean. A better comprehension of the ecology of Indian Ocean blue whales will require interdisciplinary studies to examine the drivers of the variability seen from passive acoustic studies.

The southeast Pacific (SEP) contains the home ranges of several migratory large whale species, determined largely based on research in coastal waters. These whales’ pelagic seasonal residency is unknown. The Juan Fernández Archipelago (JFA) is an offshore island in the SEP where passive acoustic monitoring (PAM) data collection is ongoing at the HA03 hydroacoustic station (sample rate of 250 Hz) maintained by the Preparatory Comprehensive Nuclear-Test-Ban Treaty Organization. Six years (2007–2009 and 2014–2016) of PAM data from HA03 were examined for the acoustic presence of Antarctic, Chilean (southeast Pacific 1, southeast Pacific 2), and southeast Indian Ocean blue whale song types; the fin whale 20-Hz song; and minke whale vocalizations. The weekly presence or absence of these six vocalization types was annotated manually by an expert analyst and then averaged across all years. For each vocalization type, the number of weeks per month with presence was averaged over all years. Consistently, we found austral wintertime presence of Antarctic blue, fin, and minke whales; and the year-round presence of Chilean blue whales. Southeast Indian Ocean blue whales were also detected, but very rarely. We discuss the possible seasonal movements of each species or acoustic group in the offshore SEP. This is the first year-round multispecies study of baleen whale in the offshore SEP and provides valuable information for understanding the migrations of endangered baleen whales in this region, highlighting the importance of offshore areas as hotspots for baleen whale biodiversity.

There is limited information about the biology and seasonal distribution of bearded seals (Erignathus barbatus) in Greenland. The species is highly ice-associated and depends on sea ice for hauling out and giving birth, making it vulnerable to climate change. We investigated the seasonality and distribution of bearded seal vocalizations at seven different locations across southern Baffin Bay and Davis Strait, West Greenland. Aural M2 and HARUphone recorders were deployed on the sea bottom during 2006–2007 and 2011–2013. Recordings were analyzed for presence/absence of bearded seal calls relative to location (including distance to shore and depth), mean sea ice concentration and diel patterns. Calling occurred between November and late June with most intense calling during the mating season at all sites. There was a clear effect of depth and distance to shore on the number of detections, and the Greenland shelf (< 300 m) appeared to be the preferred habitat for bearded seals during the mating season. These results suggest that bearded seals may retreat with the receding sea ice to Canada during summer or possibly spend the summer along the West Greenland coast. It is also possible that, due to seasonal changes in bearded seal vocal behavior, animals may have been present in our study area in summer, but silent. The number of detections was affected by the timing of sea ice formation but not sea ice concentration. Diel patterns were consistent with patterns found in other parts of the Arctic, with a peak during early morning (0400 local) and a minimum during late afternoon (1600 local). While vocalization studies have been conducted on bearded seals in Norwegian, Canadian, northwest Greenland, and Alaskan territories, this study fills the gap between these areas.

We measured spatial and temporal patterns of ambient noise in dynamic, relatively pristine Arctic marine habitats and evaluate the contributions of environmental and human noise sources. Long-term acoustic recorders were deployed around St. Lawrence Island and the Bering Strait region within key feeding and migratory corridors for protected species that are inherently important to Native Alaskan cultures. Over 3000 h of data from 14 recorders at nine sites were obtained from October 2014 to June 2017. Spatial and temporal ambient noise patterns were quantified with percentile statistics in 1/3rd-octave bands (0.02–8 kHz). Ice presence strongly influenced ambient noise by influencing the physical environment and presence of marine mammals. High variability in noise was observed within and between sites, largely as a function of ice presence and associated factors. Acute contributions of biological and anthropogenic sources to local ambient noise are compared to monthly averages, demonstrating how they influence Arctic soundscapes.

Arctic marine ecosystems are experiencing substantial changes associated with sea ice loss and surface warming. The most obvious and dramatic changes include earlier ice retreat and a longer ice-free season, particularly on Arctic inflow shelves, including the Barents Sea in the Atlantic Arctic and the northern Bering Sea and Chukchi Sea in the Pacific Arctic. The extreme variability observed in recent years in the Pacific Arctic is unparalleled in recorded history. This volume is devoted to studies that integrate research across various components of the Arctic marine ecosystem to better characterize these changes. The intent of this integrated approach is to better understand the linkages and interactions that shape ecosystem processes, influence timing and phenology of events, and inform predictions of future conditions. The studies presented in this Special Issue investigate processes in the Bering Sea, Chukchi Sea, and Beaufort Sea. The data derive from remote sensing, ship-based surveys, and integrated data products. The research presented includes time-series analyses on environmental change across the greater Pacific Arctic, heat flux, stratification and mixing dynamics, vertical structure, and wind and current patterns. It explores the influence of physical processes on, and seasonal and annual variability in, primary production, nutrient distribution, and the export of biogenic matter. It also examines the effects of oceanographic variability on zooplankton taxa, the distribution of larval fishes, age and growth in Arctic fishes, responses of salmon to warming, and variability in cetacean occurrence. These studies are designed to provide new insights on integrated ecosystem research in the Pacific Arctic, with a focus on improving understanding of ecosystem processes, timing and change. This volume marks the first in a series of research volumes supported by the North Pacific Research Board to integrate ecosystem research in the Pacific Arctic and to inform our collective understanding of the rapid transformation in this region.

Six baleen whale species are found in the temperate western North Atlantic Ocean, with limited information existing on the distribution and movement patterns for most. There is mounting evidence of distributional shifts in many species, including marine mammals, likely because of climate‐driven changes in ocean temperature and circulation. Previous acoustic studies examined the occurrence of minke (Balaenoptera acutorostrata) and North Atlantic right whales (NARW; Eubalaena glacialis). This study assesses the acoustic presence of humpback (Megaptera novaeangliae), sei (B. borealis), fin (B. physalus), and blue whales (B. musculus) over a decade, based on daily detections of their vocalizations. Data collected from 2004 to 2014 on 281 bottom‐mounted recorders, totaling 35,033 days, were processed using automated detection software and screened for each species’ presence. A published study on NARW acoustics revealed significant changes in occurrence patterns between the periods of 2004–2010 and 2011–2014; therefore, these same time periods were examined here. All four species were present from the Southeast United States to Greenland; humpback whales were also present in the Caribbean. All species occurred throughout all regions in the winter, suggesting that baleen whales are widely distributed during these months. Each of the species showed significant changes in acoustic occurrence after 2010. Similar to NARWs, sei whales had higher acoustic occurrence in mid‐Atlantic regions after 2010. Fin, blue, and sei whales were more frequently detected in the northern latitudes of the study area after 2010. Despite this general northward shift, all four species were detected less on the Scotian Shelf area after 2010, matching documented shifts in prey availability in this region. A decade of acoustic observations have shown important distributional changes over the range of baleen whales, mirroring known climatic shifts and identifying new habitats that will require further protection from anthropogenic threats like fixed fishing gear, shipping, and noise pollution.

A decrease in the frequency of two southeast Pacific blue whale song types was examined over decades, using acoustic data from several different sources in the eastern Pacific Ocean ranging between the Equator and Chilean Patagonia. The pulse rate of the song units as well as their peak frequency were measured using two different methods (summed auto-correlation and Fourier transform). The sources of error associated with each measurement were assessed. There was a linear decline in both parameters for the more common song type (southeast Pacific song type n.2) between 1997 to 2017. An abbreviated analysis, also showed a frequency decline in the scarcer southeast Pacific song type n.1 between 1970 to 2014, revealing that both song types are declining at similar rates. We discussed the use of measuring both pulse rate and peak frequency to examine the frequency decline. Finally, a comparison of the rates of frequency decline with other song types reported in the literature and a discussion on the reasons of the frequency shift are presented.

The International Whaling Commission (IWC) carried out blue whale research within its annual austral summer Southern Ocean Whale and Ecosystem Research (SOWER) cruises between 1996 and 2010. Over 700 sonobuoys were deployed to record blue whale vocalisations during 11 Antarctic and three low latitude blue whale cruises off Australia, Madagascar and Chile. The recorded acoustic files from these deployments were collated and reviewed to develop a database of both the digital acoustic files and the associated deployment station metadata of 7,486 acoustic files from 484 stations. Acoustic files were analysed using the automated detection template and visual verification method. We found a significant difference between the total number of acoustic recording hours (2,481) reported for these cruises (in the associated cruise reports) and the currently available number of acoustic recording hours (1,541). Antarctic blue whale vocalisations (9,315 D-calls and 24,902 Z-calls) were detected on 4,183 of the 7,486 acoustic files. December had the lowest call rates whilst January and February yielded high call rates. Although the majority (63%) of the sonobuoys were deployed between 1800hrs and 0600hrs the following day, most calls (62%) were detected during observation periods between 0600hrs and 1800hrs. The recently described southeastern Pacific 2 song of the Chilean pygmy blue whale was also found in Chilean blue whale cruise acoustic data. The difference between the available and reported data is of concern and a reconciliation of these and any future IWC acoustic data is strongly recommended.

Fin whales (Balaenoptera physalus) are common summer visitors to the Pacific Arctic, migrating through the Bering Strait and into the southern Chukchi Sea to feed on seasonally-abundant prey. The abundance and distribution of fin whales in the Chukchi Sea varies from year-to-year, possibly reflecting fluctuating environmental conditions. We hypothesized that fin whale calls were most likely to be detected in years and at sites where productive water masses were present, indicated by low temperatures and high salinities, and where strong northward water and wind velocities, resulting in increased prey advection, were prevalent. Using acoustic recordings from three moored hydrophones in the Bering Strait region from 2009–2015, we identified fin whale calls during the open-water season (July–November) and investigated potential environmental drivers of interannual variability in fin whale presence. We examined near-surface and near-bottom temperatures (T) and salinities (S), wind and water velocities through the strait, water mass presence as estimated using published T/S boundaries, and satellite-derived sea surface temperatures and sea-ice concentrations. Our results show significant interannual variability in the acoustic presence of fin whales with the greatest detections of calls in years with contrasting environmental conditions (2012 and 2015). Colder temperatures, lower salinities, slower water velocities, and weak southward winds prevailed in 2012 while warmer temperatures, higher salinities, faster water velocities, and moderate southward winds prevailed in 2015. Most detections (96%) were recorded at the mooring site nearest the confluence of the nutrient-rich Anadyr and Bering Shelf water masses, ~35 km north of Bering Strait, indicating that productive water masses may influence the occurrence of fin whales. The disparity in environmental conditions between 2012 and 2015 suggests there may be multiple combinations of environmental factors or other unexamined variables that draw fin whales into the Pacific Arctic.

Seasonal occurrence, diel‐vocalizing patterns, and call‐types of Antarctic minke whales are described using bio‐acoustic recordings from the west coast of South Africa and the Maud Rise, Antarctica. In Antarctica, minke whale bioduck calls were detected in seven of nine months of hydrophone deployment (peaking in May and September) while downsweeps were only detected in June. Bioduck calls were sporadically detected in South African waters with peak calling in September/October, and no bioducks were detected from March through August. Bioduck call occurrence was high during daytime in Antarctica but there was no diel‐vocalizing pattern in South African waters. We split bioduck B call‐type into two subtypes: B1 with 13 ± 1 pulses and B2 with 9 ± 1 pulses. Bioduck B2 was detected both in Antarctic and South African waters, with harmonics up to 2 kHz. Similar bioduck call‐types were detected in Antarctic and South African waters, with bioduck A2 being the most common. Month of the year was the most important predictor of bioduck occurrence both in Antarctic and South African waters. This is the first study to describe the seasonal occurrence, diel‐vocalizing behavior and call‐types of Antarctic minke whales off the South African west coast and eastern Weddell Sea.

Declines in Arctic sea ice cover are influencing the distribution of protected endemic marine mammals, many of which are important for local Indigenous Peoples, and increasing the presence of potentially disruptive industrial activities. Due to increasing conservation concerns, we conducted the first year‐round acoustic monitoring of waters off Gambell and Savoonga (St. Lawrence Island, Alaska), and in the Bering Strait to quantify vocalizing presence of bowhead whales, belugas, walruses, bearded seals, and ribbon seals. Bottom‐mounted archival acoustic recorders collected data for up to 10 months per deployment between 2012 and 2016. Spectrograms were analyzed for species‐typical vocalizations, and daily detection rates and presence/absence were calculated. Generalized additive models were used to model call presence as a function of time‐of‐year, sea surface temperature, and sea ice concentration. We identified seasonality in call presence for all species, corroborating previous acoustic and distribution studies, and identified finer‐scale spatiotemporal distribution via occurrence of call presence between different monitoring sites. Time‐of‐year was the strongest significant effect on call presence for all species. These data provide important information on Arctic endemic species' spatiotemporal distributions in biologically and culturally important areas within a rapidly changing Arctic region.

The highly productive northern Bering and Chukchi marine shelf ecosystem has long been dominated by strong seasonality in sea-ice and water temperatures. Extremely warm conditions from 2017 into 2019 — including loss of ice cover across portions of the region in all three winters — were a marked change even from other recent warm years. Biological indicators suggest that this change of state could alter ecosystem structure and function. Here, we report observations of key physical drivers, biological responses and consequences for humans, including subsistence hunting, commercial fishing and industrial shipping. We consider whether observed state changes are indicative of future norms, whether an ecosystem transformation is already underway and, if so, whether shifts are synchronously functional and system wide or reveal a slower cascade of changes from the physical environment through the food web to human society. Understanding of this observed process of ecosystem reorganization may shed light on transformations occurring elsewhere.

The 2019 ENRICH Voyage (Euphausiids and Nutrient Recycling in Cetacean Hotspots), was conducted from 19 January – 5 March 2019, aboard the RV Investigator. The voyage departed from and returned to Hobart, Tasmania, Australia, and conducted most marine science operations in the area between 60°S – 67°S and 138°E – 152°E. As part of the multidisciplinary research programme, a passive acoustic survey for marine mammals was undertaken for the duration of the voyage, with the main goal to monitor for and locate groups of calling Antarctic blue whales (Balaenoptera musculus intermedia). Directional sonobuoys were used at 295 listening stations, which resulted in 828 hours of acoustic recordings. Monitoring also took place for pygmy blue, (B. m. brevicauda), fin, (B. physalus), sperm (Physeter macrocephalus), humpback (Megaptera novaeangliae), sei (B. borealis), and Antarctic minke whales (B. bonarensis); for leopard (Hydrurga leptonyx), crabeater (Lobodon carcinophaga), Ross (Ommatophoca rossii), and Weddell seals (Leptonychotes weddellii), and for odontocete (low frequency whistles) vocalisations during each listening station. Calibrated measurements of the bearing and intensity of the majority of calls from blue and fin whales were obtained in real time. 33,435 calls from Antarctic blue whales were detected at 238 listening stations throughout the voyage, most of them south of 60°S. Southeast Indian Ocean blue whale song was detected primarily between 47° and 55°S while the southwest Pacific blue whale song was recorded between 44° and 48°S. Most baleen whale and seal calls were detected along the continental shelf break in the study region but some were also detected in deeper waters. Marine mammal calls were uncommon on the shelf, which did not have any ice cover during the survey. Calling Antarctic blue whales were tracked and located on multiple occasions to enable closer study of their fine-scale movements and calling behaviour as well as enabling collection of photo ID, behavioural, and photogrammetry data. The passive acoustic data collected during this voyage will allow investigation of the distribution of Antarctic blue whales in relation to environmental correlates measured during ENRICH, with a focus on blue whale prey.

Prior stranding records suggest that at least 12 cetacean species occur within the Lakshadweep archipelago off the southwest coast of India. These islands consist of coral atolls and form the northern part of the undersea Chagos–Laccadive ridge. Distinct oceanographic features, seasonal monsoon cycles, and high productivity make this region a potentially rich cetacean habitat. In this article, we report findings from the first systematic visual cetacean surveys, which were conducted from high-speed passenger ferries that sail between nine Lakshadweep islands. The surveys were carried out between October 2015 and April 2016 during both the northeast monsoon (October to December) and inter-monsoon (January to April) seasons. We used a line-transect survey framework to record sightings as well as group size estimates. We documented 139 sightings over 3,880 km of which 78 sightings were during systematic survey effort. Eight odontocete species were confirmed from these sightings: Stenella longirostris, S. attenuata, S. coeruleoalba, Tursiops spp., Globicephala macrorhynchus, Pseudorca crassidens, Grampus griseus, and Feresa attenuata. One Balaenoptera sp. was also encountered during this survey. S. longirostris was sighted the most often (n = 22) followed by Tursiops spp. (n = 18) and G. macrorhynchus (n = 13). We documented significantly higher sightings in the northeast monsoon season compared to the inter-monsoon season. Along ferry routes, cetacean species differed significantly from each other with respect to their associations with seafloor slope gradients and distances to nearest landmass. We encountered mixed species assemblages of G. macrorhynchus with Tursiops sp. and S. attenuata with Tursiops sp. Given the confirmed high cetacean diversity and occurrence in this region, there is a need for in-depth, long-term studies on biogeography, ecology, and population status of cetaceans here.

In order to help develop hypotheses of connectivity among North Pacific fin whales, we examine recordings from 10 regions collected in the spring and fall. We develop a Random Forest model to classify fin whale note types that avoids manual note classification errors. We also present a method that objectively quantifies the note and pattern composition of recordings. We find that fin whale recordings near Hawaii have distinctive patterns, similar to those found in other regions in the central North Pacific, suggesting potential migration pathways. Our results are consistent with previous studies that suggest there may be two different populations utilizing the Chukchi Sea and central Aleutians in the fall and mix to some degree in the southern Bering Sea. Conversely, we found little difference between spring and fall recordings in the eastern Gulf of Alaska, suggesting some residency of whales in this region. This is likely due to fine scale similarities of calls among the inshore regions of British Columbia, while offshore areas are being utilized by whales traveling from various distant areas. This study shows how our novel approach to characterize recordings is an objective and informative way to standardize spatial and temporal comparisons of fin whale recordings.

Declines in Arctic sea ice cover are influencing the distribution of protected endemic marine mammals, many of which are important for local Indigenous Peoples, and increasing the presence of potentially disruptive industrial activities. Due to increasing conservation concerns, we conducted the first year‐round acoustic monitoring of waters off Gambell and Savoonga (St. Lawrence Island, Alaska), and in the Bering Strait to quantify vocalizing presence of bowhead whales, belugas, walruses, bearded seals, and ribbon seals. Bottom‐mounted archival acoustic recorders collected data for up to 10 months per deployment between 2012 and 2016. Spectrograms were analyzed for species‐typical vocalizations, and daily detection rates and presence/absence were calculated. Generalized additive models were used to model call presence as a function of time‐of‐year, sea surface temperature, and sea ice concentration. We identified seasonality in call presence for all species, corroborating previous acoustic and distribution studies, and identified finer‐scale spatiotemporal distribution via occurrence of call presence between different monitoring sites. Time‐of‐year was the strongest significant effect on call presence for all species. These data provide important information on Arctic endemic species' spatiotemporal distributions in biologically and culturally important areas within a rapidly changing Arctic region.

Fin whales Balaenoptera physalus were the species of baleen whale most widely caught by commercial whaling fleets off the Chilean coast and are globally classified as Endangered. However, very little is known about the present distribution and seasonal movements of fin whales off the coast of Chile. Passive acoustic data collected at the HA03 station of the Preparatory Commission for the Comprehensive Nuclear Test Ban Treaty Organization off the Juan Fernandez Archipelago (JFA) between 2007 and 2016 were analyzed. The temporal occurrence of fin whale song was examined using automatic detection via spectrogram cross-correlation of song notes and by calculating the average acoustic power in the frequency bands of fin whale song. Fin whale song off JFA was composed of regular 17 Hz notes associated with high-frequency components at 85 Hz, with singlet phrasing at a dominant primary inter-note interval of 14.4 s and a secondary interval of 30.8 s. There was a clear seasonal pattern in acoustic presence that was consistent across all years: low or no song during the austral summer and a peak in song occurrence in austral winter. A propagation loss model estimated the detection range at this site to be 186 km. Where the fin whales that are heard off JFA spend the summer months remains an open question. Possible locations include the Western Antarctic Peninsula and/or off northern-central mainland Chile. Further studies should be pursued to better understand the distribution and seasonal movements and to support the conservation of this Endangered species.

Passive acoustic monitoring (PAM) has proven to be an efficient method for studying vocally active marine mammals in areas that are difficult to access on a year-round basis. In this study, a PAM recorder was deployed on an oceanographic mooring in western Fram Strait (78°50'N, 5°W) to record the acoustic presence of narwhals (Monodon monoceros) over a 3-yr period. Acoustic data were recorded for 14–17 min at the start of each hour from 25 September 2010 to 26 August 2011, from 2 September 2012 to 11 April 2013 and from 8 September 2013 to 27 April 2014. Pulsed and tonal signals, as well as echolocation clicks, were detected throughout the recording periods, demonstrating that this species is present in this region throughout the year. Generalized linear mixed-effect models showed a negative correlation between the acoustic presence of narwhals and very dense sea-ice cover (≥90%). Surprisingly, a positive correlation was found between the acoustic presence of narwhals and the presence of warm Atlantic Water in the area. Available data suggest that there might be a unique stock of narwhals in the Eurasian sector of the Atlantic Arctic that do not exhibit the "traditional" narwhal pattern of seasonal migration between coastal summering areas and offshore wintering grounds, but rather remain resident year-round in deep, offshore waters.

Due to the difficulty of studying ice seals in their natural environment, distribution and movement patterns of ribbon seals (Histriophoca fasciata) over large spatio-temporal scales are poorly understood. In this study, we analyzed their distribution patterns in the Bering, Chukchi, and Beaufort seas, using passive acoustic data collected between August 2012 and July 2013 at 53 recording sites. Ribbon seal downsweeps were found using spectrogram correlation autodetection, at 30 of these recording sites. These detections were further manually analyzed to investigate the vocal repertoire and quantify the diel pattern in acoustic presence. We found that the Beaufort Sea shelf and the northern Bering Strait/southern Chukchi Sea are ecologically important for ribbon seals during the open-water season. Our results suggest that the northeastern Chukchi Sea serves as part of a migration corridor to and from the Chukchi Plateau and/or Beaufort Sea. In the Bering Sea, most detections occurred from February to June. Vocal activity was higher at nighttime than during the daytime prior to the peak calling period, while during the peak calling period, diel rhythm became less pronounced. The number of calls, proportional use of downsweeps, and bandwidth of downsweeps (estimated broadband source level 170–178 dB re 1 μPa-m) increased during the breeding period, from March to June, peaking in May. An additional call type, the "shuffle", was identified in this study. These results improve our understanding of the migration, occurrence, and acoustic behavior of ribbon seals in the Bering, Chukchi, and Beaufort seas.

Passive acoustic monitoring was used to detect the sounds of rarely sighted Antarctic blue and fin whales to investigate their seasonal occurrence (as presence or absence of whale calls) and behaviour (as determined from call rates) in the Benguela ecosystem. Data were collected using autonomous acoustic recorders deployed on oceanographic moorings for 16.26 months off the west coast of South Africa in 2014 and 2015. Satellite derived environmental variables were used as predictors of whale acoustic occurrence and behaviour. Migratory Antarctic blue and fin whales were acoustically present in South African waters between May and August with call occurrence peaks in July whereas some fin whales extended their presence to November. No whale calls were recorded in summer for either species, suggesting whales use the Benguela ecosystem as an overwintering ground and migration route. Antarctic blue whales produced both their characteristic Z-call and their feeding associated D-call. Fin whales produced calls characteristic of animals from the eastern Antarctic fin whale acoustic population. Random forest models identified environmental variables such as sea surface temperature anomaly, sea surface height, wind speed, months of the year, Ekman upwelling index and log-transformed chlorophyll-a as the most important predictors of call occurrence and call rates of blue and fin whales. Here we present the first acoustic recordings of Antarctic blue and fin whales in the Benguela ecosystem, and provide preliminary information to investigate seasonal abundance and distribution of these large baleen whale populations. This work demonstrates the feasibility of cost-effectively monitoring Antarctic top-consumer baleen whales in the Benguela ecosystem.

The southern Indian Ocean is believed to be a natural territory for blue and fin whales. However, decades after commercial and illegal whaling decimated these populations, little is known about their current status, seasonal habitat or movements. Recent passive acoustic studies have described the presence of 4 acoustic populations of blue whales (Antarctic and 3 'pygmy' types), but are generally limited temporally and geographically. Here, we examine up to 7 yr of continuous acoustic recordings (2010–2016) from a hydrophone network of 6 widely spaced sites in the southern Indian Ocean, looking for the presence of Antarctic and pygmy blue and fin whales. Power spectral density analyses of characteristic and distinct frequency bands of these species show seasonal and geographic differences among the different populations, and the overall patterns for each display interannual consistencies in timing and occurrence. Antarctic blue and fin whales are recorded across the hydrophone network, mainly from austral autumn to spring, with peak intensity in winter. Pygmy blue whales show spatial variation: Madagascan pygmy blue whales are mainly present in the west of the network, while the Australian call type is heard at the eastern sites. Both populations share a common seasonality, with a presence from January to June. Finally, the Sri Lankan call type is recorded only on a single site in the northeast. These results confirm the importance of the southern Indian Ocean for several populations of endangered large whales and present the first long-term assessment of fin whales in the southern Indian Ocean.

Although Arctic marine ecosystems are changing rapidly, year-round monitoring is currently very limited and presents multiple challenges unique to this region. The Chukchi Ecosystem Observatory (CEO) described here uses new sensor technologies to meet needs for continuous, high-resolution, and year-round observations across all levels of the ecosystem in the biologically productive and seasonally ice-covered Chukchi Sea off the northwest coast of Alaska. This mooring array records a broad suite of variables that facilitate observations, yielding better understanding of physical, chemical, and biological couplings, phenologies, and the overall state of this Arctic shelf marine ecosystem. While cold temperatures and 8 months of sea ice cover present challenging conditions for the operation of the CEO, this extreme environment also serves as a rigorous test bed for innovative ecosystem monitoring strategies. Here, we present data from the 2015–2016 CEO deployments that provide new perspectives on the seasonal evolution of sea ice, water column structure, and physical properties, annual cycles in nitrate, dissolved oxygen, phytoplankton blooms, and export, zooplankton abundance and vertical migration, the occurrence of Arctic cod, and vocalizations of marine mammals such as bearded seals. These integrated ecosystem observations are being combined with ship-based observations and modeling to produce a time series that documents biological community responses to changing seasonal sea ice and water temperatures while establishing a scientific basis for ecosystem management.

The acoustic environment of two focal Arctic species, bowhead (Balaena mysticetus) and beluga (Delphinapterus leucas) whales, varied among the three core-use regions of the Pacific Arctic examined during the months in which both species occur: (1) January–March in the St. Lawrence Island/Anadyr Strait region, (2) November–January in the Bering Strait region, and (3) August–October in the Barrow Canyon region. Biological noise (consisting of the signals of bowhead whales, walrus and bearded seals) dominated the acoustic environment for the focal species in the St. Lawrence Island/Anadyr Strait region, which was covered with ice throughout the months studied. In the Bering Strait region whales were exposed primarily to environmental noise (in the form of wind noise) during November, before the region was ice-covered in December, and biological noise (from bowhead and walrus) again was prevalent. Anthropogenic noise dominated the Barrow Canyon region for the focal species in late summer and fall (August through October); this was also the only region in which the two species did not overlap with sea ice. Under open water conditions both near Barrow Canyon and in Bering Strait, noise levels were tightly correlated with wind. However, with climate-change driven increases in open water leading to rising noise levels across multiple fronts (atmospheric, biological, anthropogenic), the relatively pristine acoustic environment of Arctic cetaceans is changing rapidly. Characterizing the acoustic habitat of these regions before they are further altered should be considered a management and conservation priority in the Arctic.

The seasonal and geographic patterns in the distribution, residency, and density of two populations (Chukchi and Beaufort) of beluga whales (Delphinapterus leucas) were examined using data from aerial surveys, passive acoustic recordings, and satellite telemetry to better understand this arctic species in the oceanographically complex and changing western Beaufort Sea. An aerial survey data-based model of beluga density highlights the Beaufort Sea slope as important habitat for belugas, with westerly regions becoming more important as summer progresses into fall. The Barrow Canyon region always had the highest relative densities of belugas from July–October. Passive acoustic data showed that beluga whales occupied the Beaufort slope and Beaufort Sea from early April until early November and passed each hydrophone location in three broad pulses during this time. These pulses likely represent the migrations of the two beluga populations: the first pulse in spring being from Beaufort animals, the second spring pulse Chukchi belugas, with the third, fall pulse a combination of both populations. Core-use and home range analyses of satellite-tagged belugas showed similar use of habitats as the aerial survey data, but also showed that it is predominantly the Chukchi population of belugas that uses the western Beaufort, with the exception of September when both populations overlap. Finally, an examination of these beluga datasets in the context of wind-driven changes in the local currents and water masses suggests that belugas are highly capable of adapting to oceanographic changes that may drive the distribution of their prey.

Almost all mammals communicate using sound, but few species produce complex songs. Two baleen whales sing complex songs that change annually, though only the humpback whale (Megaptera novaeangliae) has received much research attention. This study focuses on the other baleen whale singer, the bowhead whale (Balaena mysticetus). Members of the Spitsbergen bowhead whale population produced 184 different song types over a 3-year period, based on duty-cycled recordings from a site in Fram Strait in the northeast Atlantic. Distinct song types were recorded over short periods, lasting at most some months. This song diversity could be the result of population expansion, or immigration of animals from other populations that are no longer isolated from each other by heavy sea ice. However, this explanation does not account for the within season and annual shifting of song types. Other possible explanations for the extraordinary diversity in songs could be that it results either from weak selection pressure for interspecific identification or for maintenance of song characteristics or, alternatively, from strong pressure for novelty in a small population.

Climate-related shifts in marine mammal range and distribution have been observed in some populations; however, the nature and magnitude of future responses are uncertain in novel environments projected under climate change. This poses a challenge for agencies charged with management and conservation of these species. Specialized diets, restricted ranges, or reliance on specific substrates or sites (e.g., for pupping) make many marine mammal populations particularly vulnerable to climate change. High-latitude, predominantly ice-obligate, species have experienced some of the largest changes in habitat and distribution and these are expected to continue. Efforts to predict and project marine mammal distributions to date have emphasized data-driven statistical habitat models. These have proven successful for short time-scale (e.g., seasonal) management activities, but confidence that such relationships will hold for multi-decade projections and novel environments is limited. Recent advances in mechanistic modeling of marine mammals (i.e., models that rely on robust physiological and ecological principles expected to hold under climate change) may address this limitation. The success of such approaches rests on continued advances in marine mammal ecology, behavior, and physiology together with improved regional climate projections. The broad scope of this challenge suggests initial priorities be placed on vulnerable species or populations (those already experiencing declines or projected to undergo ecological shifts resulting from climate changes that are consistent across climate projections) and species or populations for which ample data already exist (with the hope that these may inform climate change sensitivities in less well observed species or populations elsewhere). The sustained monitoring networks, novel observations, and modeling advances required to more confidently project marine mammal distributions in a changing climate will ultimately benefit management decisions across time-scales, further promoting the resilience of marine mammal populations.

In order to study the long-term stability of fin whale (Balaenoptera physalus) singing behavior, the frequency and inter-pulse interval of fin whale 20 Hz vocalizations were observed over 10 years from 2003–2013 from bottom mounted hydrophones and seismometers in the northeast Pacific Ocean. The instrument locations extended from 40°N to 48°N and 130°W to 125°W with water depths ranging from 1500–4000 m. The inter-pulse interval (IPI) of fin whale song sequences was observed to increase at a rate of 0.54 seconds/year over the decade of observation. During the same time period, peak frequency decreased at a rate of 0.17 Hz/year. Two primary call patterns were observed. During the earlier years, the more commonly observed pattern had a single frequency and single IPI. In later years, a doublet pattern emerged, with two dominant frequencies and IPIs. Many call sequences in the intervening years appeared to represent a transitional state between the two patterns. The overall trend was consistent across the entire geographical span, although some regional differences exist. Understanding changes in acoustic behavior over long time periods is needed to help establish whether acoustic characteristics can be used to help determine population identity in a widely distributed, difficult to study species such as the fin whale.

Given new distribution patterns of the endangered North Atlantic right whale (NARW; Eubalaena glacialis) population in recent years, an improved understanding of spatio-temporal movements are imperative for the conservation of this species. While so far visual data have provided most information on NARW movements, passive acoustic monitoring (PAM) was used in this study in order to better capture year-round NARW presence. This project used PAM data from 2004 to 2014 collected by 19 organizations throughout the western North Atlantic Ocean. Overall, data from 324 recorders (35,600 days) were processed and analyzed using a classification and detection system. Results highlight almost year-round habitat use of the western North Atlantic Ocean, with a decrease in detections in waters off Cape Hatteras, North Carolina in summer and fall. Data collected post 2010 showed an increased NARW presence in the mid-Atlantic region and a simultaneous decrease in the northern Gulf of Maine. In addition, NARWs were widely distributed across most regions throughout winter months. This study demonstrates that a large-scale analysis of PAM data provides significant value to understanding and tracking shifts in large whale movements over long time scales.

Highlights

- At present, underwater sound levels in western Fram Strait are low to moderate (< 60 dB).
- Shipping activity is low, but seismic surveys occur nearby in summer/autumn.
- Critically endangered bowhead whales are present in the area throughout most of the year.
- Currently, little human activity overlaps with bowhead winter occurrence.

Migrations are often influenced by seasonal environmental gradients that are increasingly being altered by climate change. The consequences of rapid changes in Arctic sea ice have the potential to affect migrations of a number of marine species whose timing is temporally matched to seasonal sea ice cover. This topic has not been investigated for Pacific Arctic beluga whales (Delphinapterus leucas) that follow matrilineally maintained autumn migrations in the waters around Alaska and Russia. For the sympatric Eastern Chukchi Sea ('Chukchi') and Eastern Beaufort Sea ('Beaufort') beluga populations, we examined changes in autumn migration timing as related to delayed regional sea ice freeze-up since the 1990s, using two independent data sources (satellite telemetry data and passive acoustics) for both populations. We compared dates of migration between 'early' (1993–2002) and 'late' (2004–2012) tagging periods. During the late tagging period, Chukchi belugas had significantly delayed migrations (by 2 to >4 weeks, depending on location) from the Beaufort and Chukchi seas. Spatial analyses also revealed that departure from Beaufort Sea foraging regions by Chukchi whales was postponed in the late period. Chukchi beluga autumn migration timing occurred significantly later as regional sea ice freeze-up timing became later in the Beaufort, Chukchi, and Bering seas. In contrast, Beaufort belugas did not shift migration timing between periods, nor was migration timing related to freeze-up timing, other than for southward migration at the Bering Strait. Passive acoustic data from 2008 to 2014 provided independent and supplementary support for delayed migration from the Beaufort Sea (4 day yr) by Chukchi belugas. Here, we report the first phenological study examining beluga whale migrations within the context of their rapidly transforming Pacific Arctic ecosystem, suggesting flexible responses that may enable their persistence yet also complicate predictions of how belugas may fare in the future.

Harvested to perilously low numbers by commercial whaling during the past century, the large scale response of Antarctic blue whales Balaenoptera musculus intermedia to environmental variability is poorly understood. This study uses acoustic data collected from 586 sonobuoys deployed in the austral summers of 1997 through 2009, south of 38°S, coupled with visual observations of blue whales during the IWC SOWER line-transect surveys. The characteristic Z-call and D-call of Antarctic blue whales were detected using an automated detection template and visual verification method. Using a random forest model, we showed the environmental preferences pattern, spatial occurrence and acoustic behaviour of Antarctic blue whales. Distance to the southern boundary of the Antarctic Circumpolar Current (SBACC), latitude and distance from the nearest Antarctic shores were the main geographic predictors of blue whale call occurrence. Satellite-derived sea surface height, sea surface temperature, and productivity (chlorophyll-a) were the most important environmental predictors of blue whale call occurrence. Call rates of D-calls were strongly predicted by the location of the SBACC, latitude and visually detected number of whales in an area while call rates of Z-call were predicted by the SBACC, latitude and longitude. Satellite-derived sea surface height, wind stress, wind direction, water depth, sea surface temperatures, chlorophyll-a and wind speed were important environmental predictors of blue whale call rates in the Southern Ocean. Blue whale call occurrence and call rates varied significantly in response to inter-annual and long term variability of those environmental predictors. Our results identify the response of Antarctic blue whales to inter-annual variability in environmental conditions and highlighted potential suitable habitats for this population. Such emerging knowledge about the acoustic behaviour, environmental and habitat preferences of Antarctic blue whales is important in improving the management and conservation of this highly depleted species.

The seasonal and geographic patterns in the distribution, residency, and density of two populations (Chukchi and Beaufort) of beluga whales (Delphinapterus leucas) were examined using data from aerial surveys, passive acoustic recordings, and satellite telemetry to better understand this arctic species in the oceanographically complex and changing western Beaufort Sea. An aerial survey data-based model of beluga density highlights the Beaufort Sea slope as important habitat for belugas, with westerly regions becoming more important as summer progresses into fall. The Barrow Canyon region always had the highest relative densities of belugas from July–October. Passive acoustic data showed that beluga whales occupied the Beaufort slope and Beaufort Sea from early April until early November and passed each hydrophone location in three broad pulses during this time. These pulses likely represent the migrations of the two beluga populations: the first pulse in spring being from Beaufort animals, the second spring pulse Chukchi belugas, with the third, fall pulse a combination of both populations. Core-use and home range analyses of satellite-tagged belugas showed similar use of habitats as the aerial survey data, but also showed that it is predominantly the Chukchi population of belugas that uses the western Beaufort, with the exception of September when both populations overlap. Finally, an examination of these beluga datasets in the context of wind-driven changes in the local currents and water masses suggests that belugas are highly capable of adapting to oceanographic changes that may drive the distribution of their prey.

Using mooring timeseries from September 2008 to August 2012, together with ancillary atmospheric and satellite data sets, we quantify the seasonal variations of the shelfbreak jet in the Alaskan Beaufort Sea and explore connections to the occurrences of bowhead and beluga whales. Wind patterns during the four-year study period are different than the long-term climatological conditions in that the springtime peak in easterly winds shifted from May to June, and the autumn peak was limited to October instead of extending farther into the fall. These changes were primarily due to the behavior of the two regional atmospheric centers of action, the Aleutian Low and Beaufort High. The volume transport of the shelfbreak jet, which peaks in the summer, was decomposed into a background (weak wind) component and a wind-driven component. The wind-driven component is correlated to the Pt. Barrow, AK alongcoast windspeed record, although a more accurate prediction is obtained when considering the ice thickness at the mooring site. An upwelling index reveals that wind-driven upwelling is enhanced in June and October when storms are stronger and longer-lasting. The seasonal variation of Arctic cetacean occurrence is dominated by the eastward migration in spring, dictated by pack-ice patterns, and westward migration in fall, coincident with the autumn peak in shelfbreak upwelling intensity.

Highlights

- Wind stress influences beluga whale dive depths.
- Wind stress influences the geographical distribution of belugas in Barrow Canyon.
- The subsurface layer of Atlantic Water in the Pacific Arctic may represent an important front for belugas and their prey.

Air–Sea Interactions in the Northern Indian Ocean (ASIRI) is an international research effort (2013–17) aimed at understanding and quantifying coupled atmosphere–ocean dynamics of the Bay of Bengal (BoB) with relevance to Indian Ocean monsoons. Working collaboratively, more than 20 research institutions are acquiring field observations coupled with operational and high-resolution models to address scientific issues that have stymied the monsoon predictability. ASIRI combines new and mature observational technologies to resolve submesoscale to regional-scale currents and hydrophysical fields. These data reveal BoB’s sharp frontal features, submesoscale variability, low-salinity lenses and filaments, and shallow mixed layers, with relatively weak turbulent mixing. Observed physical features include energetic high-frequency internal waves in the southern BoB, energetic mesoscale and submesoscale features including an intrathermocline eddy in the central BoB, and a high-resolution view of the exchange along the periphery of Sri Lanka, which includes the 100-km-wide East India Coastal Current (EICC) carrying low-salinity water out of the BoB and an adjacent, broad northward flow (~300 km wide) that carries high-salinity water into BoB during the northeast monsoon. Atmospheric boundary layer (ABL) observations during the decaying phase of the Madden–Julian oscillation (MJO) permit the study of multiscale atmospheric processes associated with non-MJO phenomena and their impacts on the marine boundary layer. Underway analyses that integrate observations and numerical simulations shed light on how air–sea interactions control the ABL and upper-ocean processes.

The Bay of Bengal (BoB) is strongly density stratified due to large freshwater input from various rivers and heavy precipitation. This strong vertical stratification, along with physical processes, regulates the transport and vertical exchange of surface and subsurface water, concentrating nutrients and intensifying the oxygen minimum zone (OMZ). Here, we use basinwide measurements to describe the spatial distributions of nutrients, oxygen, and phytoplankton within the BoB during the 2013 northeast monsoon (November–December). By the time riverine water reaches the interior bay, it is depleted in the nutrients nitrate and phosphate, but not silicate. Layering of freshwater in the northern BoB depresses isopycnals, leading to a deepening of the nutricline and oxycline. Oxygen concentrations in the OMZ are lowest in the north (<5 µM). Weak along-isopycnal nutrient gradients reflect along-isopycnal stirring between ventilated surface water and deep nutrient-replenished water. Picoplankton dominate the phytoplankton population in the north, presumably outcompeting larger phytoplankton species due to their low nutrient requirements. Micro- and nanoplankton numbers are enhanced in regions with deeper mixed layers and weaker stratification, where nutrient replenishment from subsurface waters is more feasible. These are also the regions where marine mammals were sighted. Physical processes and the temperature-salinity structure in the BoB directly influence the OMZ and the depth of the oxycline and nutricline, thereby affecting the phytoplankton and marine mammal communities.

Because the monsoon strongly affects India, there is a clear need for indigenous expertise in advancing the science that underlies monsoon prediction. The safety of marine transport in the tropics relies on accurate atmospheric and ocean environment predictions on weekly and longer time scales in the Indian Ocean. This need to better forecast the monsoon motivates the United States to advance basic research and support training of early career US scientists in tropical oceanography. Earlier Indian field campaigns and modeling studies indicated that an improved understanding of the interactions between the upper ocean and the atmosphere in the Bay of Bengal at finer spatial and temporal scales could lead to improved intraseasonal monsoon forecasts. The joint US Air-Sea Interactions Regional Initiative (ASIRI) and the Indian Ocean Mixing and Monsoon (OMM) program studied these interactions, resulting in scientific advances described by articles in this special issue of Oceanography. In addition to these scientific advances, and while also developing long-lasting collaborations and building indigenous Indian capability, a key component of these programs is training early career scientists from India and the United States. Training has been focusing on fine-scale and mixing studies of the upper ocean, air-sea interactions, and marine mammal research. Advanced methods in instrumentation, autonomous robotic platforms, experimental design, data analysis, and modeling have been emphasized. Students and scientists from India and the United States at all levels have been participating in joint cruises on Indian and US research vessels and in training participants in modern tools and methods at summer schools, at focused research workshops, and during research visits. Such activities are building new indigenous capability in India, training a new cadre of US scientists well versed in monsoon air-sea interaction, and forging strong links between Indian and US oceanographic institutions.

The earliest long-term monitoring of low-frequency signals of large whales was via cabled military arrays. These arrays provided valuable new data but were restricted in the locations that were monitored and there was no open access to the data collected. In order to monitor the low-frequency signals of large whales in different areas and over shorter time scales, Haruphones, single hydrophone, autonomous recording packages, were developed by the Pacific Marine Environmental Laboratory of the US National Oceanic and Atmospheric Administration and deployed in the Gulf of Alaska and the eastern tropical Pacific. By integrating the acoustic data from these broadly spaced deployments with other data streams, new discoveries about blue whales in the eastern Pacific Ocean were made. These included establishing the geographic range and migratory patterns of eastern north Pacific blue whales; establishing that the eastern tropical Pacific appears to be a blue whale "hot spot" where as many as four, but primarily three, acoustic populations of blue whales occur; determining that the Gulf of Alaska is a region where eastern and western North Pacific blue whales overlap in space and time; and showing that blue whale calling behavior has a diel pattern whereby animals produce more sounds at night than during the day. In aggregate, these data show that passive acoustic monitoring is a valuable tool for establishing blue whale population identity, determining habitat range, and studying behavioral ecology over long time periods and in remote regions of the ocean.

The flow through the Bering Strait, the only Pacific-Arctic oceanic gateway, has dramatic local, regional, and global impacts. Advanced year-round moored technology quantifies challengingly large temporal (subdaily, seasonal, and interannual) and spatial variability in the ~85 km wide, two-channel strait. The typically northward flow, intensified seasonally in the ~10–20 km wide, warm, fresh, nutrient-poor Alaskan Coastal Current (ACC) in the east, is otherwise generally homogeneous in velocity throughout the strait, although with higher salinities and nutrients and lower temperatures in the west. Velocity and water properties respond rapidly (including flow reversals) to local wind, likely causing most of the strait's approximately two-layer summer structure (by "spilling" the ACC) and winter water-column homogenization. We identify island-trapped eddy zones in the central strait; changes in sea-ice properties (season mean thicknesses from <1 m to >2 m); and increases in annual mean volume, heat, and freshwater fluxes from 2001 to present (2013). Tantalizing first results from year-round bio-optics, nitrate, and ocean acidification sensors indicate significant seasonal and spatial change, possibly driven by the spring bloom. Moored acoustic recorders show large interannual variability in sub-Arctic whale occurrence, related perhaps to water property changes. Substantial daily variability demonstrates the dangers of interpreting section data and the necessity for year-round interdisciplinary time-series measurements.

Bowhead whales, Balaena mysticetus, in the Bering-Chukchi-Beaufort (BCB) population, experience a variable acoustic environment among the regions they inhabit throughout the year. A total of 41,698 hours of acoustic data were recorded from 1 August 2009 through 4 October 2010 at 20 sites spread along a 2300 km transect from the Bering Sea to the southeast Beaufort Sea. These data represent the combined output from six research teams using four recorder types. Recorders sampled areas in which bowheads occur and in which there are natural and anthropogenic sources producing varying amounts of underwater noise. We describe and quantify the occurrence of bowheads throughout their range in the Bering, Chukchi, and Beaufort seas over a 14-month period by aggregating our acoustic detections of bowhead whale sounds. We also describe the spatial-temporal variability in the bowhead acoustic environment using sound level measurements within a frequency band in which their sounds occur, by dividing a year into three, 4-month seasons (Summer-Fall 2009, August - November 2009: Winter 2009-2010, December 2009 - March 2010: and Spring-Summer 2010, April - July 2010) and their home range into five zones. Statistical analyses revealed no significant relationship between acoustic occurrence, distance offshore, and water depth during Summer-Fall 2009, but there was a significant relationship during Spring-Summer 2010. A continuous period with elevated broadband sound levels lasting ca. 38 days occurred in the Bering Sea during the Winter 2009-2010 season as a result of singing bowheads, while a second period of elevated levels lasting at least 30 days occurred during the early spring-summer season as a result of singing bearded seals. The lowest noise levels occurred in the Chukchi Sea from the latter part of November into May. In late summer 2009 very faint sounds from a seismic airgun survey approximately 700 km away in the eastern Beaufort Sea were detected on Chukchi recorders. Throughout the year, but most obviously during this same November into May period, clusters of intermittent, nearly synchronized, high-level events were evident on multiple recorders hundreds of miles apart. In some cases, these clusters occurred over 2-5 day periods and appear to be associated with high wind conditions.

Little is known about the ecology of beluga whales, Delphinapterus leucas, and harbor porpoises, Phocoena phocoena, inhabiting Yakutat Bay, Alaska. Using passive, acoustic monitoring techniques, their year-round presence was monitored during June 2012–Mar. 2013 off the mouths of two glacial rivers: Esker Creek and Grand Wash. Fishery trawl transects were run in both areas during Mar.–Aug. 2013 to assess fish and invertebrate diversity and to identify potential beluga and harbor porpoise prey. Results supported year-round presence for both species, with restricted home range for beluga and a wider distribution for porpoise. Opposite diel patterns in beluga and harbor porpoise presence suggest potential competitive overlap in prey between species. Based on trawl abundance and ubiquity, several fish and crustacean species were identifi ed as potential prey for beluga and harbor porpoise. Results support the belief that shrimp, crab, and mysids may be an important part of beluga and porpoise diet in Yakutat. Both river mouth areas are used by harbor porpoises but their seasonality might not be driven solely by prey diversity or abundance. Beluga detection results during a coho salmon, Oncorhynchus kisutch, run were indicative of predation by belugas on this species during their spawning migration. This pilot study demonstrates the utility of remote, passive acoustic monitoring technology to better understand the seasonal distribution patterns and prey association of beluga and harbor porpoise in Yakutat Bay.

Bowhead whales (Balaena mysticetus) of the Bering-Chukchi-Beaufort population migrate in nearshore leads through the Chukchi Sea each spring to summering grounds in the Beaufort Sea. As part of a population abundance study, hydrophones were deployed in the Chukchi Sea off Point Barrow, (12 April to 27 May 2011) and in the Beaufort Sea (12 April to 30 June 2011). Data from these sites were analyzed for the presence of bowhead whale song. We identified 12 unique song types sung by at least 32 individuals during ~95 h of recordings off Point Barrow. Six of these songs were detected at the Beaufort MARU site as well as six additional song types that were not analyzed. These results suggest a shared song repertoire among some individuals. This report represents the greatest number of songs to date during the spring migration for this population. We attribute this greater variety to population growth over the 30 yr since acoustic monitoring began in the early 1980s. Singing during early to mid-spring is consistent with the hypothesis that song is a reproductive display, but further research is necessary to understand the exact function of this complex vocal behavior.

A total of 76 confirmed sighting events of beluga whales, Delphinapterus leucas, were gathered from 1938 to 2013 in Yakutat Bay, Alaska. The sightings were a mix of incidental observations from airplane pilots and commercial fishermen as well as directed ground and aerial surveys. The earliest sightings are anecdotal, with the fi rst known observation recalled from the summer of 1938. Throughout the observation period the average group sighting
was 6 whales with a low of 1 animal and an estimated high of 26 animals. Overall, there is little traditional or historical knowledge about the Yakutat Bay belugas, including whether they were a hunted species. However, the study revealed the existence of the local name for belugas %u201CKuyeedaayee%u201D (skin under the stars), which was either of Tlingit origin or, possibly, from the now extinct Eyak language. The fact that there is a Tlingit/Eyak name for the animals supports the theory, and the genetic evidence, that they have inhabited Yakutat Bay for longer than the sighting record indicates. This report includes four summaries of observations from local residents who are most knowledgeable about Yakutat Bay.

Bearded seals (Erignathus barbatus) are widely distributed in the Arctic and sub-Arctic; the Beringia population is found throughout the Bering, Chukchi and Beaufort Seas (BCB). Bearded seals are highly vocal, using underwater calls to advertise their breeding condition and maintain aquatic territories. They are also closely associated with pack ice for reproductive activities, molting, and resting. Sea ice habitat for this species varies spatially and temporally throughout the year due to differences in underlying physical and oceanographic features across its range. To test the hypothesis that the vocal activity of bearded seals is related to variations in sea ice, passive acoustic data were collected from nine locations throughout the BCB from 2008 to 2011. Recording instruments sampled on varying duty cycles ranging from 20% to 100% of each hour, and recorded frequencies up to 8192 Hz. Spectrograms of acoustic data were analyzed manually to calculate the daily proportion of hours with bearded seal calls at each sampling location, and these call activity proportions were correlated with daily satellite-derived estimates of sea ice concentration. Bearded seals were vocally active nearly year-round in the Beaufort and Chukchi Seas with peak activity occurring from mid-March to late June during the mating season. The duration of call activity in the Bering Sea was shorter, lasting typically only five months, and peaked from mid-March to May at the northernmost recorders. In all areas, call activity was significantly correlated with higher sea ice concentrations (p < 0.01). These results suggest that losses in ice cover may negatively impact bearded seals, not just by loss of habitat but also by altering the behavioral ecology of the BCB population.

Arrays of hydrophones were deployed within the Bransfield Strait and Scotia Sea (Antarctic Peninsula region) from 2005 to 2009 to record ambient ocean sound at frequencies of up to 125 and 500 Hz. Icequakes, which are broadband, short duration signals derived from fracturing of large free-floating icebergs, are a prominent feature of the ocean soundscape. Icequake activity peaks during austral summer and is minimum during winter, likely following freeze-thaw cycles. Iceberg grounding and rapid disintegration also releases significant acoustic energy, equivalent to large-scale geophysical events. Overall ambient sound levels can be as much as ~10–20 dB higher in the open, deep ocean of the Scotia Sea compared to the relatively shallow Bransfield Strait. Noise levels become lowest during the austral winter, as sea-ice cover suppresses wind and wave noise. Ambient noise levels are highest during austral spring and summer, as surface noise, ice cracking and biological activity intensifies. Vocalizations of blue (Balaenoptera musculus) and fin (B. physalus) whales also dominate the long-term spectra records in the 15–28 and 89 Hz bands. Blue whale call energy is a maximum during austral summer-fall in the Drake Passage and Bransfield Strait when ambient noise levels are a maximum and sea-ice cover is a minimum. Fin whale vocalizations were also most common during austral summer-early fall months in both the Bransfield Strait and Scotia Sea. The hydrophone data overall do not show sustained anthropogenic sources (ships and airguns), likely due to low coastal traffic and the typically rough weather and sea conditions of the Southern Ocean.

Passive acoustic data were collected January 2012 to April 2013 at four sites in the Chiloense Ecoregion (CER) in southern Chile (~43°S – 44°S, 71°W – 73°W) and 1996–2002 from one site in the eastern tropical Pacific (ETP) (8°S, 95°W). Automatic detectors were used to detect the two songs (SEP1 and SEP2) described for southeast Pacific (SEP) blue whales. There was a strong seasonal pattern of occurrence of SEP songs in the CER from December to August, peaking March to May. In the ETP, the occurrence of songs was an order of magnitude lower but songs were present year-round, with a peak around June. These findings support austral summer/autumn seasonal residency in the CER and a seasonal movement of blue whales towards the ETP during June/July, returning in December. Interannual differences in the ETP were possibly linked to the 1997 – 1998 El Nino event. At both study sites, SEP2 was significantly more common than SEP1; both songs largely followed the same temporal trends. These findings contribute to our understanding of the seasonal movements of endangered SEP blue whales and can inform conservation strategies, particularly in the CER coastal feeding ground. We recommend future year-round passive acoustic studies in the CER and the ETP (e.g., near the Galapagos Islands), ideally coupled with oceanographic data.

The dramatic reduction of sea ice in the Arctic Ocean will increase human activities in the coming years. This activity will be driven by increased demand for energy and the marine resources of an Arctic Ocean accessible to ships. Oil and gas exploration, fisheries, mineral extraction, marine transportation, research and development, tourism, and search and rescue will increase the pressure on the vulnerable Arctic environment. Technologies that allow synoptic in situ observations year-round are needed to monitor and forecast changes in the Arctic atmosphere-ice-ocean system at daily, seasonal, annual, and decadal scales. These data can inform and enable both sustainable development and enforcement of international Arctic agreements and treaties, while protecting this critical environment. In this paper, we discuss multipurpose acoustic networks, including subsea cable components, in the Arctic. These networks provide communication, power, underwater and under-ice navigation, passive monitoring of ambient sound (ice, seismic, biologic, and anthropogenic), and acoustic remote sensing (tomography and thermometry), supporting and complementing data collection from platforms, moorings, and vehicles. We support the development and implementation of regional to basin-wide acoustic networks as an integral component of a multidisciplinary in situ Arctic Ocean observatory.

Little is known about migration patterns and seasonal distribution away from coastal summer feeding habitats of many pelagic baleen whales. Recently, large-scale passive acoustic monitoring networks have become available to explore migration patterns and identify critical habitats of these species. North Atlantic minke whales (Balaenoptera acutorostrata) perform seasonal migrations between high latitude summer feeding and low latitude winter breeding grounds. While the distribution and abundance of the species has been studied across their summer range, data on migration and winter habitat are virtually missing.

Acoustic recordings, from 16 different sites from across the North Atlantic, were analyzed to examine the seasonal and geographic variation in minke whale pulse train occurrence, infer information about migration routes and timing, and to identify possible winter habitats.

Acoustic detections show that minke whales leave their winter grounds south of 30°N from March through early April. On their southward migration in autumn, minke whales leave waters north of 40°N from mid-October through early November. In the western North Atlantic spring migrants appear to track the warmer waters of the Gulf Stream along the continental shelf, while whales travel farther offshore in autumn. Abundant detections were found off the southeastern US and the Caribbean during winter. Minke whale pulse trains showed evidence of geographic variation, with longer pulse trains recorded south of 40°N. Very few pulse trains were recorded during summer in any of the datasets.

This study highlights the feasibility of using acoustic monitoring networks to explore migration patterns of pelagic marine mammals. Results confirm the presence of minke whales off the southeastern US and the Caribbean during winter months. The absence of pulse train detections during summer suggests either that minke whales switch their vocal behaviour at this time of year, are absent from available recording sites or that variation in signal structure influenced automated detection. Alternatively, if pulse trains are produced in a reproductive context by males, these data may indicate their absence from the selected recording sites. Evidence of geographic variation in pulse train duration suggests different behavioural functions or use of these calls at different latitudes.

Persistently poor weather in the Arctic makes traditional marine mammal research from aircraft and ships difficult, yet collecting information on marine mammal distribution and habitat utilization is vital for understanding the impact of climate change on Arctic ecosystems. Moreover, as industrial use of the Arctic increases with the expansion of the open-water summer season, there is an urgent need to monitor the effects of noise from oil and gas exploration and commercial shipping on marine mammals. During September 2013, we deployed a single Slocum glider equipped with a digital acoustic monitoring (DMON) instrument to record and process in situ low-frequency (<5 kHz) audio to characterize marine mammal occurrence and habitat as well as ambient noise in the Chukchi Sea off the northwest coast of Alaska, USA. The DMON was programmed with the low-frequency detection and classification system (LFDCS) to autonomously detect and classify sounds of a variety of Arctic and sub-Arctic marine mammal species. The DMON/LFDCS reported regularly in near real time via Iridium satellite detailed detection data, summary classification information, and spectra of background noise. The spatial distributions of bowhead whale, bearded seal, and walrus call rates were correlated with surface salinity measured by the glider. Bowhead whale and walrus call rates were strongly associated with a warmand salty watermass of Bering Sea origin. With a passive acoustic capability that allows both archival recording and near real-time reporting,we envision ocean gliderswill become a standard tool for marine mammal and ocean noise research and monitoring in the Arctic.

Blue whales (Balaenoptera musculus) were exploited extensively around the world and remain endangered. In the North Pacific their population structure is unclear and current status unknown, with the exception of a well-studied eastern North Pacific (ENP) population. Despite existing abundance estimates for the ENP population, it is difficult to estimate pre-exploitation abundance levels and gauge their recovery because historical catches of the ENP population are difficult to separate from catches of other populations in the North Pacific. We collated previously unreported Soviet catches and combined these with known catches to form the most current estimates of North Pacific blue whale catches. We split these conflated catches using recorded acoustic calls from throughout the North Pacific, the knowledge that the ENP population produces a different call than blue whales in the western North Pacific (WNP). The catches were split by estimating spatiotemporal occurrence of blue whales with generalized additive models fitted to acoustic call patterns, which predict the probability a catch belonged to the ENP population based on the proportion of calls of each population recorded by latitude, longitude, and month. When applied to the conflated historical catches, which totaled 9,773, we estimate that ENP blue whale catches totaled 3,411 (95% range 2,593 to 4,114) from 1905–1971, and amounted to 35% (95% range 27% to 42%) of all catches in the North Pacific. Thus most catches in the North Pacific were for WNP blue whales, totaling 6,362 (95% range 5,659 to 7,180). The uncertainty in the acoustic data influence the results substantially more than uncertainty in catch locations and dates, but the results are fairly insensitive to the ecological assumptions made in the analysis. The results of this study provide information for future studies investigating the recovery of these populations and the impact of continuing and future sources of anthropogenic mortality.

The tools and methods used to study marine mammals should be dictated by the research and conservation questions that need to be answered and the resources available to do so (from funding to ship time). Where very little is known about the community composition within a country's exclusive economic zone, a series of shipboard based visual surveys might be the best way to obtain baseline information on geographic and seasonal abundance of multiple species.

The identity, distribution and movements of blue whales Balaenoptera musculus that forage in the Chiloense Ecoregion in Southern Chile remain unclear. Studies of blue whale songs have identified acoustic populations with distinct song types, geographic ranges, migration routes and seasonal residencies%u2014information that is relevant to the conservation of this endangered species. Here, we characterized the song sequences of blue whales that use the Corcovado Gulf based on dipping hydrophone recordings from 3 austral summer field seasons (2008, 2009, 2011), and compare these data to previously described song types for the Southeast Pacific (SEP) in order to better understand meso-scale (versus basin-scale) variation in blue whale song. Two distinct songs, SEP1 and SEP2, emerged from our analysis. Neither of these songs is used by Antarctic blue whales. Although SEP1 was the first song recorded in the Corcovado Gulf area in 1970, we found SEP2 to be the more common song, despite never having been reported previously in this area. Our report of SEP2 adds a new song to the current description of the SEP blue whale repertoire. Our recording of SEP1 reaffirms the acoustic link already established between Chile and the Eastern Tropical Pacific (ETP); our recording of SEP2 establishes a new acoustic link for this song between Chile and the ETP. These findings provide the basis for future passive acoustic studies on the temporal and spatial distributions of endangered SEP blue whales and for understanding how these songs relate to the population structure.

Very-low-frequency sounds between 1 and 100 Hz propagate large distances in the ocean sound channel. Weather conditions, earthquakes, marine mammals, and anthropogenic activities influence sound levels in this band. Weather-related sounds result from interactions between waves, bubbles entrained by breaking waves, and the deformation of sea ice. Earthquakes generate sound in geologically active regions, and earthquake T waves propagate throughout the oceans. Blue and fin whales generate long bouts of sounds near 20 Hz that can dominate regional ambient noise levels seasonally. Anthropogenic sound sources include ship propellers, energy extraction, and seismic air guns and have been growing steadily. The increasing availability of long-term records of ocean sound will provide new opportunities for a deeper understanding of natural and anthropogenic sound sources and potential interactions between them.

The southern Chukchi Sea is one of the most productive areas in the world ocean. Over the past decade, there have been dramatic changes in this region in sea ice cover and in Bering Strait inflow, and it is now in the path of transpolar shipping and destinational ship traffic, including vessels supporting Arctic offshore oil and gas development and tourism, all of which are anticipated to increase with decreasing seasonal sea ice cover. Little research on cetaceans has been conducted in the southern Chukchi Sea, and most information on the occurrence of subarctic species (humpback whale Megaptera novaeangliae, fin whale Balaenoptera physalus, minke whale B. acutorostrata, and killer whale Orcinus orca) comes from the ships' logs of commercial whalers in the mid to late twentieth century and from observers stationed along the Chukotka Peninsula. Information on cetacean seasonal occurrence east of the International Date Line (IDL) in US waters is particularly scarce.

To address this information gap, we compiled visual sightings and acoustic detections of subarctic cetaceans in the southern Chukchi Sea during summer and early autumn from 2009 to 2012. Humpback whales were common on both sides of the IDL in August and September. Fin and minke whales were widely distributed east of the IDL from July to September, and killer whales were seen sporadically but were the most widely dispersed of the four species. Comparisons of our results with historical records indicate that the incidence of subarctic cetaceans may be increasing in the southern Chukchi Sea. An increase in occurrence may simply be a post-commercial whaling recovery of whale numbers and seasonal range by each species, or it may reflect responses to ongoing climate change. Understanding current stock identity, spatial and temporal distribution, habitat preference, relative abundance, and potential impacts of climate change on these species will require cetacean-focused research in this region of the Arctic.

The Southern Ocean Research Partnership (SORP) is an international research program initiated within the International Whaling Commission (IWC) in 2009 to promote collaborative cetacean research, develop novel research techniques, and conduct non-lethal research on whales in the Southern Ocean (CHILDERHOUSE 2009). One of the original research projects of the SORP is the Blue and Fin Whale Acoustic Trends Project, which aims to implement a long term passive acoustic research program to examine trends in Antarctic blue (Balaenoptera musculus intermedia) and fin whale (B. physalus) abundance, distribution, and seasonal presence in the Southern Ocean through the use of a network of passive acoustic recorders: the Southern Ocean Hydrophone Network (SOHN).

Understanding the seasonal movements and distribution patterns of migratory species over ocean basin scales is vital for appropriate conservation and management measures. However, assessing populations over remote regions is challenging, particularly if they are rare. Blue whales (Balaenoptera musculus spp) are an endangered species found in the Southern and Indian Oceans. Here two recognized subspecies of blue whales and, based on passive acoustic monitoring, four "acoustic populations" occur. Three of these are pygmy blue whale (B.m. brevicauda) populations while the fourth is the Antarctic blue whale (B.m. intermedia). Past whaling catches have dramatically reduced their numbers but recent acoustic recordings show that these oceans are still important habitat for blue whales. Presently little is known about the seasonal movements and degree of overlap of these four populations, particularly in the central Indian Ocean. We examined the geographic and seasonal occurrence of different blue whale acoustic populations using one year of passive acoustic recording from three sites located at different latitudes in the Indian Ocean. The vocalizations of the different blue whale subspecies and acoustic populations were recorded seasonally in different regions. For some call types and locations, there was spatial and temporal overlap, particularly between Antarctic and different pygmy blue whale acoustic populations. Except on the southernmost hydrophone, all three pygmy blue whale acoustic populations were found at different sites or during different seasons, which further suggests that these populations are generally geographically distinct. This unusual blue whale diversity in sub-Antarctic and sub-tropical waters indicates the importance of the area for blue whales in these former whaling grounds.

Bearded seals (Erignathus barbatus) are pan-Arctic pinnipeds that are often seen in association with pack ice, and are known for their long, loud trills, produced underwater primarily in the spring. Acoustic recordings were collected from August 2008 to August 2010 at two locations and a single year (2008–2009) at a third location, in the western Beaufort Sea. Three recorders in 2008–2009 had a 30% duty cycle and a bandwidth of 10–4,096 Hz. One recorder in 2009–2010 had a 45% duty cycle and a bandwidth of 10–4,096 Hz and the second had a 20% duty cycle and bandwidth of 10–8,192 Hz. Spectrograms of acoustic data were examined for characteristic patterns of bearded seal vocalizations. For each recorder, the number of hours per day with vocalizations was compared with in situ water temperature and satellite-derived daily sea ice concentrations. At all sites, bearded seals were vocally active year-round. Call activity escalated with the formation of pack ice in the winter and the peak occurred in the spring, coinciding with mating season and preceding breakup of the sea ice. There was a change in the timing of seasonal sea ice formation and retreat between the two consecutive years that was reflected in the timing of peak bearded seal call activity. This study provides new information on fall and winter bearded seal vocal behavior and the relationship between year-round vocal activity and changes in annual sea ice coverage and in situ water temperature.

Monitoring programmes for white whales (Delphinapterus leucas) have been called for repeatedly in recent years because this species is likely to be negatively impacted by climate change, but also because such a broadly dispersed, high trophic feeder can serve as an effective ecosystem sentinel. Arctic ecosystems are difficult to monitor because of the extensive winter ice coverage and extreme environmental conditions in addition to low human population densities. However, passive acoustic monitoring has proved to be a reliable method to remotely survey the presence of some marine mammals in the Arctic. In this study, we evaluate the potential use of echolocation loggers (T-POD and C-POD, Chelonia Ltd.) for remote monitoring of white whales. Captive experiments and open water surveys in three arctic/subarctic habitats (ice-noise-dominated environment, ice-free environment and low-turbidity waters) were used to document detection performance and to explore the use of logger angle and inter-click interval data to look at activity patterns and tidal influences on space use. When acoustic results were compared to concurrent visual observations, echolocation detection was only attributed to periods of white whale presence near the recorder deployment sites. Both T-PODs and C-PODs effectively detected echolocation, even under noisy ice. Diel and tidal behavioural patterns were identified. Acoustically identified movement patterns between sites were visually confirmed. This study demonstrates the feasibility of monitoring white whales using echolocation loggers and describes some important features of their behaviour as examples of the potential application of this passive acoustic monitoring method in Arctic and subarctic regions.

Oceanographic features and physical processes in the ocean can create regions where prey, and therefore predators, may accumulate. Beluga whales Delphinapterus leucas are the most numerous cetacean in the Arctic. In the Alaskan Beaufort Sea, they prefer continental slope habitat in summer and autumn, presumably because such areas provide enhanced foraging opportunities. Passive acoustic detections of beluga whale calls, current velocity measurements, historical wind records, and 29 yr of beluga whale observations from aerial surveys were used to explore the hypothesis that the foraging success of beluga whales in Barrow Canyon and along the western Beaufort Sea slope is enhanced when the Alaska Coastal Current (ACC) is well-developed and flows east-northeastward and is diminished when the flow of the ACC and its shelf break extension are reversed. Aerial sightings of beluga whales, average observed beluga whale group size, and hours with whale vocalizations were more common when the ACC was well-developed and flowed east-northeastward. When the ACC flow is strong, it is separated from Arctic basin waters by a well-defined front that promotes aggregation of prey species. We speculate that the greater numbers of animals per group sighted and hours with recorded vocalizations may be indicative of enhanced foraging opportunities for beluga whales.

Bowhead whales Balaena mysticetus are long-lived cetaceans, uniquely adapted among the baleen whales to live year-round in the Arctic. All bowhead whale populations were greatly reduced by commercial whaling from the 1600s through the 1800s, with the largest, the Spitsbergen population in the North Atlantic, depleted to the point of extinction. Recent sightings of bowhead whales west of Svalbard precipitated an effort to listen for their vocalizations via 2 recorders deployed in 2008 on oceanographic moorings spaced 95 km apart at 78.8° N latitude in the Fram Strait. Year-round acoustic records were examined for the occurrence of bowhead whale sounds. Simple calls, call sequences, and complex songs were recorded. Repeated call sequences or bowhead whale songs were detected nearly every hour from early November 2008 through late April 2009 on the western Fram Strait recorder. More than 60 unique songs were recorded from October 2008 to April 2009. In contrast, simple calls and call sequences were the most common signals recorded on the central Fram Strait instrument. Peak levels of song production coincided with the period of lowest water temperature, dense ice concentration, and almost complete darkness. Given the diversity, loudness, and period over which songs were recorded, western Fram Strait appears to be a wintering ground — and potentially a mating area — for this critically endangered population of bowhead whales.

During the International Polar Year (IPY), acoustic recorders were deployed on oceanographic moorings in Fram Strait and on the Chukchi Plateau, representing the first coordinated year-round sampling of underwater acoustic habitats at two sites in the High Arctic. Examination of species-specific marine mammal calls recorded from autumn 2008–2009 revealed distinctly different acoustic habitats at each site. Overall, the Fram Strait site was acoustically complex compared with the Chukchi Plateau site.

In Fram Strait, calls from bowhead whales (Balaena mysticetus) and a variety of toothed whales (odontocetes) were recorded year-round, as were airgun pulses from seismic surveys. In addition, calls from blue whales (Balaenoptera musculus) and fin whales (B. physalus) were recorded from June to October and August to March, respectively. Conversely, at the Chukchi Plateau site, beluga (Delphinapterus leucas) and bowhead whale calls were recorded primarily from May to August, with airgun signals detected only in September–October. Ribbon seal (Phoca fasciata) calls were detected in October–November, with no marine mammals calls at all recorded from December to February. Of note, ice-adapted bearded seals (Erignathus barbatus) were recorded at both sites, primarily in spring and summer, corresponding with the mating season for that species.

Differences in acoustic habitats between the two sites were related to contrasts in sea ice cover, temperature, patterns of ocean circulation and contributions from anthropogenic noise sources. These data provide a provisional baseline for the comparison of underwater acoustic habitats between Pacific and Atlantic sectors of the High Arctic.

The successful use of SOSUS to track broad-scale occurrence patterns in whale calls during the second half of the 20th century fostered the development of autonomous recorders that can be deployed virtually anywhere in the world ocean. Over the past decade, data from these recorders have provided dramatic insights to marine mammal ecology. Patterns of call reception have demonstrated the near year-round occurrence of some baleen whale species in Arctic and Antarctic waters, a discovery that challenges long-held assumptions about the phenology of seasonal migrations. Integration of year-long calling records with physical oceanographic measures at mooring-based ocean observatories provides a means to include large whales in ecosystem-based models. The reception of anthropogenic sounds on nearly all recorders, whether deployed in coastal or remote areas, emphasizes the need to develop regional "soundscapes" based upon integrative sampling and analytical protocols. Examples from several long-term research programs will be provided as the basis for the strong assertion that passive acoustic observation of marine mammals is a vital component of any ocean observing system. Opportunities for future collaborations and the challenges of data management and access will be discussed.

Most baleen whales undertake migrations between low-latitude breeding grounds and high-latitude feeding grounds. Though little is known about the timing of their migration from the Arctic, fin whales are assumed to undertake a similar migratory pattern. To address questions about habitat use and migrations, the acoustic activity of fin whales in Davis Strait, between Greenland and Canada, was monitored continuously for two years using three bottom-moored acoustic recorders.

The acoustic power in the fin whale call frequencies peaked in November–December, showing that fin whales are present in Davis Strait much later in the year than previously expected. The closely timed peaks in song activity and conception time imply that not all fin whales migrate south to mate, but rather start mating at high latitudes rather than or before migrating. Singing activity was strongly linked to daylight hours, suggesting that fin whales might feed during the few daylight hours of the late fall and early Arctic winter. A negative correlation between the advancing sea ice front and power in fin whale frequencies indicates that future changes in sea ice conditions from global warming might change the distribution and migratory patterns of fin whales near the poles.

Over the past decade, long-term deployments of passive acoustic recorders have provided a new baseline on the seasonal occurrence of large whale species in remote regions of the world ocean. In the Arctic, passive acoustic sampling has identified both whale calls and sounds from anthropogenic sources (ships and seismic profiling), activities that are expected to increase with diminished sea ice cover. In 2008, NOAA capitalized on an opportunity to join on-going IPY projects by inclusion of recorders at three High Arctic mooring sites: one on the Chukchi Plateau and two on either side of Fram Strait. The recorders (AURAL–M2) provided a year of sub-sampled (9 min on/11 min off) recordings at 0.1 Hz to 4 kHz (8192 sampling rate), which encompasses the bandwidth of whale and ice seal calls. Data from the recorders were complemented by a suite of standard oceanographic measures from other instruments on the mooring line.

Provisional results show novel occurrence of both marine mammal and anthropogenic signals in the High Arctic. To realize the vision of a Global Ocean Acoustic Observing Network [Dushaw et al. (2009)], passive acoustic technology must become a standard sampling component, especially in the Arctic during this time of rapid climate change.

Fin whales are common throughout the North Pacific and have recently been detected acoustically as far north as the northeastern Chukchi Sea. Non-acoustic evidence suggests that North Pacific fin whales are segregated into two populations wintering along the Asian and North American coast with at least some animals intermingling in the summer in the Bering Sea–Aleutian Islands area. Male fin whales produce regionally distinctive songs which are likely indicative of population structure. In this study we evaluated the relationship of fin whales recorded in the northeastern Chukchi (2007 and 2009) and southeastern Bering (2007–2008) seas by comparing the structure of their song. Additionally, we investigated whether fin whales detected in these areas could be part of an Asian population by comparing their songs to those recorded near the Emperor Seamounts in the western North Pacific (2007). The results will be discussed in light of the current knowledge on North Pacific fin whale population structure.

Integrated ocean observation, from physical and atmospheric forcing mechanisms to the distribution and abundance of top-level predators, is critical to the investigation of marine ecosystems and the impact of climate change on them. We integrated data from a biophysical mooring in the southeast Bering Sea to create a one-year snapshot of ocean dynamics in this remote large marine ecosystem.

Distinct patterns in production (chlorophyll), zooplankton biovolume (copepods and euphausiids) and the occurrence of zooplankton predators (fin and right whales) were defined and related to discrete features in the annual physical cycle. Peaks in prey and predator cycles were linked to spikes in fluorescence that occurred at the onset of water column stratification in late spring 2006 and the appearance of sea ice in late winter 2007. These data illustrate the capability and potential of integrated ocean observing systems (IOOS) to describe seasonal variability and linkages in a remote marine ecosystem.

Two types of passive-acoustic survey were conducted to investigate the seasonal occurrence of bowhead whales (Balaena mysticetus) in the western Beaufort and far northeastern Chukchi seas: (1) an over-winter (2003–04) survey using autonomous recorders deployed northeast of Barrow, Alaska, and (2) a summertime dipping-hydrophone survey along the 2005 NOAA Ocean Exploration (OE) cruise track northwest of Barrow. The longest continuous sampling period from the over-winter survey was 3 October 2003 to 12 May 2004. During that period, bowhead whale calls were recorded from 3 to 23 October, intermittently on 6–7 and 22–23 November, then not again until 25 March 2004. Bowhead calls were recorded almost every hour from 19 April to 12 May 2004, with a call rate peak on 30 April (ca. 9400 calls) and a few instances of patterned calling (or, "song") detected in early May. Bowhead whale calls were never detected during the NOAA OE cruise, but calls of beluga whales (Delphinapterus leucas) were recorded at 3 of 16 acoustic stations. Opportunistic visual surveys for marine mammals were also conducted during the NOAA OE cruise from the ship (65 h) and helicopter (7.8 h), resulting in single sightings of bowhead whales (3–5 whales), beluga (16–20 whales), walrus (1), polar bear (2=sow/cub), and 17 sightings of 87 ringed seals from the ship and 15 sightings of 67 ringed seals from the helicopter.

As climate change is driving rapid, unprecedented warming of the Arctic, there is increasing interest in how such change will impact Arctic marine mammals. Impacts are anticipated from habitat alteration, including increasing ambient noise levels from shipping, seismic exploration for oil and gas and geophysical research, and (potentially) commercial fishing. In order to monitor natural and anthropogenic sources of noise, four autonomous recorders were deployed along the 100-m isobath between Cape Halkett and Barrow and recorded data from July 2007–March 2008. The instruments sampled at 8192 Hz on a schedule of 10 min on, 20 min off.

Marine mammal sounds recorded included pinnipeds (walrus and bearded seals) and cetaceans (bowhead and beluga whales), while anthropogenic sources included shipping and air gun sounds. Seasonal and geographic patterns for these sounds will be presented. These data form part of a broader-scale international, year-round monitoring program in the Arctic that we hope will eventually span the entire Arctic and provide a basin-wide acoustic observatory.

A 6 yr time series of blue whale Balaenoptera musculus and fin whale B. physalus call detections in the North Pacific Ocean was correlated with 3 oceanographic variables (sea-surface temperature, chlorophyll a concentration, and mixed layer depth), to investigate the broad-scale calling behavior of these species. Monthly values for satellite-derived oceanographic data and whale call data were compared for 4 regions (30° longitude by 15° of latitude) encompassing the whole subarctic North Pacific and an area in the temperate northeastern Pacific.

To determine predictive models for whale call occurrence, generalized linear models were used to determine which, if any, oceanographic variables might influence whale calling behavior over such broad space and time scales. Sea-surface temperature was the best oceanographic variable for predicting whale call detections for both species and all regions.

Three songs were recorded from bowhead whales (Balaena mysticetus) in Disko Bay, West Greenland, during 59 h of recordings via sonobuoys deployed on seven days between 5 and 14 April 2007. Song elements were defined by units following the protocol of previous description of bowhead whale song. The two most prominent songs were loud, complex, and repeated in long bouts on multiple recording days while the third song was much simpler and recorded on only one day.

Bowhead whale simple calls and faint song elements were also recorded using digital audio tape recorders and a dipping hydrophone deployed from the sea ice approximately 100–150 km southwest of Disko Bay on three separate days suggesting that song is also produced in the central portion of Baffin Bay in winter. Songs recorded in Disko Bay are from an area where approximately 85% of the whales have been determined to be adult females. Although it is not known which sex was singing, we speculate that, as in humpback whales (Megaptera novaeangliae), male bowhead whales may sing to mediate sexual competition or mate selection behaviors. This is the first detailed description of springtime songs for bowhead whales in the eastern Arctic.

Cetaceans are increasingly being included as top trophic-level predators in models of ecosystem dynamics (Baumgartner and Mate, 2003; Tynan, 2004; Redfern et al., 2006). Traditional visual survey methods for cetaceans detect only a fraction of the animals present, both because visual observers can see them only during the very short period when they are at the surface, and because visual surveys can be undertaken only during daylight hours in relatively good weather (Mellinger and Barlow, 2003). Perhaps more importantly, visual survey results can be highly variable, due both to clumping of cetaceans into large groups and to their relatively limited spatial and temporal scales. Surveys are typically performed using a small number of observation points—one or a few vessels—for a few weeks to a few months of the year.

Over the past decade, fixed recorders have come into increasing use for long-term sampling of whale calls in remote ocean regions. Concurrently, the development of several types of autonomous underwater vehicles has demonstrated measurement capabilities that promise to revolutionize ocean science. These two lines of technical development were merged with the addition of broadband (5 Hz to 30 kHz) omni-directional hydrophones to seagliders. In August 2006, the capability of three Acoustic Seagliders (ASGs) to detect whale calls was tested in an experiment offshore Monterey, California. In total, 401 dives were completed and over 107 hours of acoustic data recorded. Blue whale calls were detected on all but two of the 76 dives where acoustic data were analyzed in detail, while humpback and sperm whale calls were detected on roughly 20% of those dives. Various whistles, clicks and burst calls, similar to those produced by dolphins and small whales, were also detected, suggesting that the capability of ASGs can be expanded to sample a broad range of marine mammal species. The potential to include whale call detection in the suite of standard oceanographic measures is unprecedented and provides a foundation for mobile sampling strategies at scales that better match the vertical and horizontal movements of the whales themselves. This capability opens new doors for investigation of cetacean habitats and their role in marine ecosystems, as envisioned in future ocean observing systems.

Five species of large whales, including the blue (Balaenoptera musculus), fin (B. physalus), sei (B. borealis), humpback (Megaptera novaeangliae), and North Pacific right (Eubalaena japonica), were the target of commercial harvests in the Gulf of Alaska (GoA) during the 19th through mid-20th centuries. Since this time, there have been a few summer time visual surveys for these species, but no overview of year-round use of these waters by endangered whales primarily because standard visual survey data are difficult and costly.

From October 1999–May 2002, moored hydrophones were deployed in six locations in the GoA to record whale calls. Reception of calls from fin, humpback, and blue whales and an unknown source, called Watkins' whale, showed seasonal and geographic variation. Calls were detected more often during the winter than during the summer, suggesting that animals inhabit the GoA year-round. To estimate the distance at which species-diagnostic calls could be heard, parabolic equation propagation loss models for frequencies characteristic of each of each call type were run. Maximum detection ranges in the subarctic North Pacific ranged from 45 to 250 km among three species (fin, humpback, blue), although modeled detection ranges varied greatly with input parameters and choice of ambient noise level.

Since the mid-1990s, gray whales (Eschrichtius robustus) have been reported with increasing frequency near Barrow, Alaska, during summer and autumn months. In collaboration with a broad-scale oceanographic study, three autonomous acoustic recorders were moored northeast of Barrow in October 2003 to provide capability for year-round detection of calls. Two recorders were recovered in September 2004, one from the continental slope (water depth = 316 m) and one from near the base of the slope (water depth = 1258 m). The shallow instrument recorded for roughly 3 months (87 days), and the deeper instrument for roughly 7.3 months (222 days). Gray whale calls were recorded on both instruments throughout their periods of operation. The calling rate at the shallower instrument was higher than at the deeper recorder, but surprisingly, the deeper instrument detected calls throughout the 2003–04 winter, though the calling rate diminished as winter progressed. Low-frequency N1/S1 pulses, the most common of the calls produced by gray whales, were recorded from deployment through December 2003 on the shallower of the two instruments and from deployment through May 2004 on the deeper instrument. Because this is the first-ever winterlong acoustic study, we cannot be certain that gray whales have not overwintered in the Beaufort Sea in the past. However, a combination of increasing population size and habitat alteration associated with sea ice reduction and warming in the Alaskan Arctic may be responsible for the extra-seasonal gray whale occurrence near Barrow.

In 1999, the first phase of a multiyear program was initiated at the National Oceanic and Atmospheric Administration's National Marine Mammal Laboratory and Pacific Marine Environmental Laboratory to advance the use of passive acoustics for the detection and assessment of large whales in offshore Alaskan waters. To date, autonomous recorders have been successfully deployed in the Gulf of Alaska (1999–2001), the southeastern Bering Sea (2000–present), and the western Beaufort Sea (2003–2004). Seasonal occurrences of six endangered species (blue, fin, humpback, North Pacific right, bowhead, and sperm whales) have been documented on the basis of call receptions in these remote ocean regions. In addition, eastern North Pacific gray whale calls were detected in the western Beaufort Sea from October 2003 through May 2004. Here we provide an overview of this suite of research projects and suggest the next steps for applying acoustic data from long-term recorders to the assessment of large whale populations.

Worldwide, calls from blue whales share the characteristics of being long (>20 s), low-frequency (<100 Hz) signals that often exhibit amplitude and frequency modulation. Despite sharing these basic features, the calls of blue whales recorded in different ocean basins are distinct from one another, leading to the suggestion that populations and/or subspecies may be identified based on call characteristics. An example of anomalous calling behavior by a blue whale in the Gulf of Alaska is reported that may complicate this approach, and that suggests that blue whales can mimic each other's calls.