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When n animal calls are passively detected at n different times, the number of animals producing the sounds is anywhere between one and n unless more information is available. When extremely reliable confidence intervals of location are also available for each call, the upper bound is still n, but a lower bound can be derived. The lower bound exceeds one when it is physically impossible for an animal to travel quickly enough to go from one reliable location to another within the temporal call interval. When many calls are detected, it may be too complicated or numerically prohibitive to determine the minimum number of animals responsible for the calls in space and time by inspection or brute force methods. Instead, it is advantageous to use graph theory. The lower bound for the number of calling animals can be derived using 100% confidence intervals of each call's location. Mathematical theorems guarantee the lower bound is correct: a lesser value is impossible to obtain. Guaranteed bounds for the abundance of calling animals are useful for conservation in the presence of environmental stress and studying behavior. [ABSTRACT FROM AUTHOR]

This paper describes song production by the eastern North Pacific right whale (NPRW, Eubalaena japonica) in the southeastern Bering Sea. Songs were localized in real-time to individuals using sonobuoys. Singers whose sex could be determined were all males. Autonomous recorder data from 17 year-long deployments were analyzed to document and characterize song types. Four distinct song types were documented over eight years (2009–2017) at five distinct locations. Each song type consists of a hierarchical structure of 1–3 different repeating phrases comprised predominantly of gunshot sounds; three of the four songs contained additional sound types (downsweep, moan, and low-frequency pulsive call). Songs were detected annually (July–January); all song types remained consistent over eight years. Two different songs often occurred simultaneously, produced by different individuals; the same song was never detected simultaneously at the same location. The same song type was detected on the same day and time at two distant locations, indicating multiple individuals can produce the same song. These findings provide support that males produce song; it remains unknown if females also sing. NPRW is the first right whale species documented to produce song. Based on current knowledge about song in mysticetes, it is hypothesized that these songs are reproductive displays. [ABSTRACT FROM AUTHOR]

In a rapidly changing Arctic, multiple lines of evidence suggest that bowhead whale migration is changing. To explore these changes further, we used passive acoustic data to examine bowhead whale presence in the western Beaufort Sea (12 years) and Chukchi Plateau (11 years) spanning 2008 to 2022. Departure from the western Beaufort Sea shifted 45 days later over the 12‐year period. Summer presence increased at both sites, suggesting feeding areas within the Chukchi Sea are becoming more favorable. Likewise, findings from the Bering Strait suggest that some whales are remaining north of the Bering Strait for the winter instead of in the Bering Sea. These Pacific Arctic‐wide changes to migration have occurred over only one decade. Questions remain about prey availability in the Chukchi Sea, implications of migratory changes, such as a northward shift in the core overwintering area, and impact to communities south of the Bering Strait. Plain Language Summary: Bowhead whales are an important top predator in the Pacific Arctic. With increasing temperatures and decreasing sea ice, changes are occurring in the migration patterns of this "ecosystem sentinel" throughout the Pacific Arctic. We analyzed passive acoustic data from the western Beaufort Sea and Chukchi Plateau from 2008 to 2022. Whales are delaying their fall departure from the western Beaufort Sea and spending more time in the western Beaufort Sea and Chukchi Plateau, which, along with increased habitat use on the Chukchi Shelf, suggests that conditions there are becoming more favorable for feeding. Combined with previous data from the Bering Strait, which showed that some whales are spending winter in the southern Chukchi Sea rather than in the northern Bering Sea, these findings suggests that changes are occurring over a short period of time throughout the Pacific Arctic. A northward shift could put bowhead whales in the direct path of ships, especially along the western side of the Chukchi Sea, and impact whaling communities south of the Bering Strait. Key Points: Acoustic data reinforce known delay in bowhead fall departure from the western Beaufort Sea and overwintering in the southern Chukchi SeaIncreased presence in the western Beaufort Sea and Chukchi Plateau suggests these regions are becoming more favorable for bowhead feedingWhales are adapting to a rapidly changing Arctic, but changes and emerging threats may impact them and communities south of Bering Strait [ABSTRACT FROM AUTHOR]

In 1995, the first of a nearly continuous sequence of biophysical moorings was deployed at a site (M2) on the southeastern Bering Sea shelf. Over the next 15 years, 10 additional mooring sites were initiated. The resultant long-term biophysical mooring array extends over 1,800 km from the southern Bering Sea to the northern Chukchi Sea, covering most of the US Arctic. It provides a full range of oceanographic data for researchers, stakeholders, and managers. In addition, these data sets have been critical for the validation of regional ocean models. The ocean temperature data have quantified regional warming and formed the basis for understanding how warmer temperatures and loss of sea ice are modifying these high-latitude marine ecosystems. Changes observed in the context of observations from the mooring program include delayed spring bloom, low abundances of large crustacean zooplankton and crab species, seabird die-offs, changes in ocean acidification, northward expansion of subarctic fish species, and shifts in the ranges of marine mammal species. [ABSTRACT FROM AUTHOR]

Bearded seals are pan-Arctic ice-obligate phocids; for the threatened Beringia population, the majority of the population feeds in the summer in the Chukchi Sea, then migrates south to overwinter in the northern Bering Sea. Contemporary information on the impact of rapidly changing climatic conditions on bearded seal distribution is essential for effective management. To monitor for marine mammals, passive acoustic recorders were deployed throughout the eastern Chukchi and northern Bering seas (64° N to 72° N), sampling at a rate of 16 kHz on a duty cycle of either 80 or 85 min every 5 h. Data from year-long deployments at nine sites over four years (2012–2016) were manually analyzed, totaling 13,275 days (∼75,000 h). Bearded seal calling activity was present at every site in every year. Calling activity increased from September through February and reached sustained and saturated levels from March through June, at which point calling ceased abruptly regardless of ice cover. The timing of calling and its abrupt cessation correspond with the known breeding season of bearded seals. However, the timing of the cessation of calling occurred earlier each year, corresponding with an earlier sea ice retreat. The sustained calling detected overwinter at all locations suggests that this is more than just a few animals that are remaining in the Chukchi Sea. Preceding this main pulse was a smaller peak in calling that progressed southward, corresponding with the fall migration of bearded seals to the Bering Sea. These results increase our knowledge on the year-round spatio-temporal distribution and migration patterns of this pagophilic species, and the relationship between calling activity and sea ice concentration. [ABSTRACT FROM AUTHOR]

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 h 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 the 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. [ABSTRACT FROM AUTHOR]

From 1998 to 2001, 115 h of acoustic recordings were made in the presence of the well-studied St. Lawrence population of blue whales, using a calibrated omnidirectional hydrophone [flat (±3 dB) response from 5 to 800 Hz] suspended at 50 m depth from a surface isolation buoy. The primary field site for this study was the estuary region of the St. Lawrence River (Québec, Canada), with most recordings made between mid-August and late October. During the recordings, detailed field notes were taken on all cetaceans within sight. Characterization of the more than 1000 blue whale calls detected during this study revealed that the St. Lawrence repertoire is much more extensive than previously reported. Three infrasonic (<20 Hz) and three audible range (30–200 Hz) call types were detected, with much time/frequency variation seen within each type. Further variation is seen in the form of call segmentation, which appears (through examination of Lloyd’s Mirror interference effects) to be controlled at least partially by the whales. Although St. Lawrence blue whale call characteristics are similar to those of the North Atlantic, comparisons of phrase composition and spacing among studies suggest the possibility of population dialects within the North Atlantic. [ABSTRACT FROM AUTHOR]

Killer whales occur in the Arctic but few data exist regarding the ecotypes present. The calling behavior differs among ecotypes, which can be distinguished based on pulsed call type, call rate, and bandwidth. In this study, a passive acoustic recorder was deployed 75 km off Point Hope, Alaska, in the southeastern Chukchi Sea to identify which ecotypes were present. A total of 1323 killer whale pulsed calls were detected on 38 of 276 days during the summers (June–August) of 2013–2015. The majority of calls (n = 804, 61%) were recorded in 2013 with the most calls recorded in July (76% of total calls). The calls were manually grouped into six categories: multipart, downsweep, upsweep, modulated, single modulation, and flat. Most detections were flat (n = 485, 37%) or multipart calls (n = 479, 36%), which contained both high and low frequency components. Call comparisons with those reported in the published literature showed similarities with other transient populations in fundamental frequency contour point distribution and median frequency. This study provides the first comprehensive catalog of transient killer whale calls in this region as well as reports on previously undescribed calls. [ABSTRACT FROM AUTHOR]

Ongoing scientific programs that monitor marine environmental and ecological systems and changes comprise an informal but collaborative, informationrich, and spatially extensive network for the Alaskan Arctic continental shelves. Such programs reflect contributions and priorities of regional, national, and international funding agencies, as well as private donors and communities. These science programs are operated by a variety of local, regional, state, and national agencies, and academic, Tribal, for-profit, and nongovernmental nonprofit entities. Efforts include research ship and autonomous vehicle surveys, year-long mooring deployments, and observations from coastal communities. Inter-program coordination allows cost-effective leveraging of field logistics and collected data into value-added information that fosters new insights unattainable by any single program operating alone. Coordination occurs at many levels, from discussions at marine mammal co-management meetings and interagency meetings to scientific symposia and data workshops. Together, the efforts represented by this collection of loosely linked long-term monitoring programs enable a biologically focused scientific foundation for understanding ecosystem responses to warming water temperatures and declining Arctic sea ice. Here, we introduce a variety of currently active monitoring efforts in the Alaskan Arctic marine realm that exemplify the above attributes. [ABSTRACT FROM AUTHOR]

Beluga whales, Delphinapterus leucas, have a graded call system; call types exist on a continuum making classification challenging. A description of vocalizations from the eastern Beaufort Sea beluga population during its spring migration are presented here, using both a non-parametric classification tree analysis (CART), and a Random Forest analysis. Twelve frequency and duration measurements were made on 1019 calls recorded over 14 days off Icy Cape, Alaska, resulting in 34 identifiable call types with 83% agreement in classification for both CART and Random Forest analyses. This high level of agreement in classification, with an initial subjective classification of calls into 36 categories, demonstrates that the methods applied here provide a quantitative analysis of a graded call dataset. Further, as calls cannot be attributed to individuals using single sensor passive acoustic monitoring efforts, these methods provide a comprehensive analysis of data where the influence of pseudo-replication of calls from individuals is unknown. This study is the first to describe the vocal repertoire of a beluga population using a robust and repeatable methodology. A baseline eastern Beaufort Sea beluga population repertoire is presented here, against which the call repertoire of other seasonally sympatric Alaskan beluga populations can be compared. [ABSTRACT FROM AUTHOR]

Changes in gray whale (Eschrichtius robustus) phenology and distribution are related to observed and hypothesized prey availability, bottom water temperature, salinity, sea ice persistence, integrated water column and sediment chlorophyll a, and patterns of wind-driven biophysical forcing in the northern Bering and eastern Chukchi seas. This portion of the Pacific Arctic includes four Distributed Biological Observatory (DBO) sampling regions. In the Bering Strait area, passive acoustic data showed marked declines in gray whale calling activity coincident with unprecedented wintertime sea ice loss there in 2017–2019, although some whales were seen there during DBO cruises in those years. In the northern Bering Sea, sightings during DBO cruises show changes in gray whale distribution coincident with a shrinking field of infaunal amphipods, with a significant decrease in prey abundance (r = -0.314, p<0.05) observed in the DBO 2 region over the 2010–2019 period. In the eastern Chukchi Sea, sightings during broad scale aerial surveys show that gray whale distribution is associated with localized areas of high infaunal crustacean abundance. Although infaunal crustacean prey abundance was unchanged in DBO regions 3, 4 and 5, a mid-decade shift in gray whale distribution corresponded to both: (i) a localized increase in infaunal prey abundance in DBO regions 4 and 5, and (ii) a correlation of whale relative abundance with wind patterns that can influence epi-benthic and pelagic prey availability. Specifically, in the northeastern Chukchi Sea, increased sighting rates (whales/km) associated with an ~110 km (60 nm) offshore shift in distribution was positively correlated with large scale and local wind patterns conducive to increased availability of krill. In the southern Chukchi Sea, gray whale distribution clustered in all years near an amphipod-krill 'hotspot' associated with a 50-60m deep trough. We discuss potential impacts of observed and inferred prey shifts on gray whale nutrition in the context of an ongoing unusual gray whale mortality event. To conclude, we use the conceptual Arctic Marine Pulses (AMP) model to frame hypotheses that may guide future research on whales in the Pacific Arctic marine ecosystem. [ABSTRACT FROM AUTHOR]

The Arctic Ice Monitoring (AIM) observatory has been maintained on the Chukchi Plateau at 75.1° N 168.0° W nearly continuously since 2003. The AIM site consists of a submerged mooring that, since October 2008, has been instrumented with a passive acoustic recorder to sample ambient sound, with a focus on marine mammal detections in the High Arctic. Year-long data sets for 2009, 2012, and 2014–2020 were analyzed for the presence of signals from Arctic species including bowhead and beluga whales, bearded seals, and walrus. Calls from subarctic ribbon seals were commonly detected in autumn months, suggesting they have expanded their distribution much further northward. Killer whale calls were detected in recent years providing evidence that they have moved further north into the Pacific Arctic. No other subarctic cetaceans were heard. Year-round passive acoustic sampling of sounds produced by marine mammals over a decadal timescale has enhanced our understanding of how climate-driven changes in biodiversity are affecting even the very High Arctic. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Twenty-four repeat hydrographic transects occupied across Barrow Canyon from 2010 to 2013 are used to study the seasonal evolution of water masses in the canyon from July–October as well as the occurrence of upwelling. The mean sections revealed that the Alaskan coastal water is mainly confined to the eastern flank of the canyon, corresponding to a region of sloped isopycnals indicative of the surface-intensified Alaskan Coastal Current which advects the water. The Pacific-origin winter water is found at depth, banked against the western flank of the canyon. Its isopycnal structure is consistent with a bottom-intensified flow of this dense water mass out of the canyon. For the months that were sampled, the Alaskan coastal water is most prevalent in August and September, while the coldest winter water is observed in the month of August. It is argued that this newly ventilated winter water is delivered to the canyon via pathways on the central Chukchi Shelf, as opposed to the coastal pathway. Roughly a third of the hydrographic sections were preceded by significant up-canyon winds and hence were deemed to be under the influence of upwelling. During these periods, anomalously salty water is found throughout the eastern flank of the canyon, and, on occasion, Atlantic water fills the deepest part of the section. Using atmospheric reanalysis data, it is shown that upwelling occurs when the Beaufort High is strengthened and the Aleutian Low is deepened. Two modes of storm tracks were identified: northward progressing storms (mode 1) and eastward progressing storms (mode 2), both of which can drive upwelling. Mode 1 is prevalent in July–August, while mode 2 is more common in September–October. These seasonal patterns appear to be dictated by regional variations in blocking highs. [ABSTRACT FROM AUTHOR]

• The two pathways of Pacific water on the eastern Chukchi shelf are investigated. • In the mean, mass is balanced for both pathways outside of upwelling periods. • The seasonal signal diminishes to the north, where an ice-melt signature is dominant. • Mesoscale variability of the two pathways is diagnosed in the southern Chukchi Sea. The flow of Pacific-origin water across the Chukchi Sea shelf impacts the regional ecosystem in profound ways, yet the two current branches on the eastern shelf that carry the water from Bering Strait to Barrow Canyon – the Alaskan Coastal Current (ACC) and Central Channel (CC) Branch – have not been clearly distinguished or quantified. In this study we use an extensive collection of repeat hydrographic sections occupied at three locations on the Chukchi shelf, together with data from a climatology of shipboard velocity data, to accomplish this. The data were collected predominantly between 2010 and 2020 during the warm months of the year as part of the Distributed Biological Observatory and Arctic Observing Network. The mean sections show that mass is balanced for both currents at the three locations: Bering Strait, Point Hope, and Barrow Canyon. The overall mean ACC transport is 0.34 ± 0.04 Sv, and that of the CC Branch is 0.86 ± 0.11 Sv. The dominant hydrographic variability at Bering Strait is seasonal, but this becomes less evident to the north. At Barrow Canyon, the dominant hydrographic signal is associated with year-to-year variations in sea-ice melt. Farther south there is pronounced mesoscale variability: an empirical orthogonal function analysis at Bering Strait and Point Hope reveals a distinct ACC mode and CC Branch mode in hydrography and baroclinic transport, where the former is wind-driven. Finally, the northward evolution in properties of the two currents is investigated. The poleward increase in salinity of the ACC can be explained by lateral mixing alone, but solar heating together with wind mixing play a large role in the temperature evolution. This same atmospheric forcing also impacts the northward evolution of the CC Branch. [ABSTRACT FROM AUTHOR]

Abstract 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. [ABSTRACT FROM AUTHOR]

Abstract 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. [ABSTRACT FROM AUTHOR]

Calling depth distributions are estimated for two types of calls produced by critically endangered eastern North Pacific right whales (NPRWs) in the Bering Sea, using passive acoustic data collected with bottom-mounted hydrophone recorders. Nonlinear time resampling of 12 NPRW “upcalls” and 20 “gunshots” recorded in a critical NPRW habitat isolated individual normal mode arrivals from each call. The relative modal arrival times permitted range estimates between 1 and 40 km, while the relative modal amplitudes permitted call depth estimates, provided that environmental inversions were obtained from high signal-to-noise ratio calls. Gunshot sounds were generally only produced at a few meters depth, while upcall depths clustered between 10 and 25 m, consistent with previously published bioacoustic tagging results from North Atlantic right whales. A Wilcoxon rank sum test rejected the null hypothesis that the mean calling depths of the two call types were the same (p=2.9x10-5); the null hypothesis was still rejected if the sample set was restricted to one call per acoustic encounter (p=0.02). Propagation modeling demonstrates that deeper depths enhance acoustic propagation and that source depth estimates impact both NPRW upcall source level and detection range estimates. [ABSTRACT FROM AUTHOR]