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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.

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.

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.

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.

Funding for the ASAMM project is from Bureau of Ocean Energy Management (BOEM) Interagency Agreements M07RG13260 and M11PG00033 (C. Monnett, R. Denton, and C. Fairfield). Funding for the NOAA mooring and analysis is from BOEM: CHAOZ–M09PG00016 (C. Monnett and H. Crowley) and ARCWEST–M12PG00021 (C. Monnett, J. Denton, and H. Crowley). Funding for the UW mooring and analysis is from National Oceanographic Partnership Program (NOPP) Grant No. N00014-08-1-0311 and National Science Foundation (NSF) Grant Nos. ARC-0856244 and ARC-855828 to K.M.S. from the Office of Polar Programs of the NSF. T.A.M.’s time was covered by the Living Marine Resources (LMR) ACCURATE project (Contract No. N3943019C2176) and partial support by the Center of Statistics and its Applications (CEAUL) (funded by FCT–Fundação para a Ciência e a Tecnologia, Portugal, through Project No. UIDB/00006/2020). 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. Publisher PDF

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., Limited information exists on the distribution and movement patterns for most baleen whale species in the western North Atlantic Ocean. Previously, we conducted a broad‐scale passive acoustic monitoring study to analyze North Atlantic right whale seasonal distribution and shifts therein, based on identified changes in occurrence patterns starting in 2010. This study uses similar acoustic datasets and protocols to understand the seasonal distribution of humpback, sei, fin, and blue whales within the western North Atlantic, and to determine whether any of these species exhibited similar shifts in distribution patterns across time.

Little is known about the winter distribution of the Critically Endangered eastern population of North Pacific right whale Eubalaena japonica (NPRW), but it has been proposed that the eastern Aleutian Islands, specifically Unimak Pass, constitute a plausible migratory route for individuals. This is a major point of concern given the high shipping traffic in this pass. Therefore, a long-term acoustic recorder was deployed in Unimak Pass (2009-2015), and NPRWs were identified using the ‘up’ and ‘gunshot’ call types during manual review of data (8188 recorded hours). Calls were grouped into periods of hypothesized migration (Dec-Feb and Mar-May) and other (Jun-Aug and Sep-Nov). Overall, NPRW calling was intermittent and clustered in time, suggestive of a few individuals transiting the area across seasons. Upcalls (n = 31) were detected on 7 d and occurred most often during Dec-Feb, whereas gunshots (n = 465) were detected on 32 d, occurring in all months except February and October. The majority of individual gunshot calls (n = 306) occurred over 3 d in Dec-Feb 2014-15. Because of this pattern, gunshot calling occurred on more days during Jun-Aug, while more individual calls occurred during Dec-Feb. Diel and seasonal trends in hourly call detection rates were absent. Together, these data confirm that NPRW use Unimak Pass both during and outside of the assumed migratory period. Pervasive vessel noise throughout the study highlights near constant potential for interaction with anthropogenic disturbance. Consistently higher vessel noise during Dec-Feb suggests that this species is most vulnerable during the assumed migratory period.

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 National Oceanic and Atmospheric Administration (NOAA)/National Park Service (NPS) Ocean Noise Reference Station (NRS) Network is an array of currently twelve calibrated autonomous passive acoustic recorders. The first NRS was deployed in June 2014, and eleven additional stations were added to the network during the following two years. The twelve stations record data that can be used to quantify baseline levels and multi-year trends in ocean ambient sound across the continental United States, Alaska, Hawaii, and island territories within and near to the United States Exclusive Economic Zone (U.S. EEZ). The network provides multi-year, continuous observations of low-frequency underwater sound between 10 Hz and 2000 Hz to capture anthropogenic, biological, and geophysical contributions to the marine soundscape at each location. Comparisons over time and among recording sites will provide information on the presence of calling animals and the prevalence of abiotic and anthropogenic activities that contribute to each soundscape. Implementation of the NRS Network advances broad-scale passive acoustic sensing capabilities within NOAA and the NPS and is an important tool for monitoring protected areas and marine species and assessing potential environmental impacts of anthropogenic noise sources. This analysis focuses on the first year of recordings and captures the wide variability of low-frequency sound levels among and within individual NRS sites over time. Continued data collection will provide information on long-term, low-frequency sound level trends within or near the U.S. EEZ and will be used to explore the value of using soundscape analysis to inform management and mitigation strategies.

Killer whales (Orcinus orca) are highly intelligent and versatile predators. Though they have a consistent presence in southern Alaskan waters, they are not known to frequently or consistently venture into the typically ice-covered U.S. Arctic, where they risk ice entrapment. However, with the trend of decreasing sea ice in the Arctic Ocean, these top predators may be venturing into waters that were previously inaccessible to them. To expand our knowledge of killer whale movements in the Arctic, eight years of data (2010–2018) from four AFSC passive acoustic moorings (funded by NOAA S&T, the U.S. Navy, and BOEM) located in the Chukchi, Beaufort, and northern Bering Seas, were manually analyzed for the presence/absence of killer whale signals to examine interannual trends in the acoustic presence of killer whales. Results from our data indicate that killer whales spend more time than previously recorded in the Arctic, as far as the edge of the Chukchi Borderland, directly following the decrease in sea ice in these areas. These results speak to a changing Arctic, both in terms of the presence of killer whales themselves and in terms of the impact that increased killer whale predation could have on Arctic food webs.

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.

During dedicated surveys for the Critically Endangered eastern stock of North Pacific right whales Eubalaena japonica (NPRW) in the Bering Sea, focal follows (FFs) were combined with passive acoustic monitoring to correlate vocal activity with dive behavior. During FFs, impulsive gunshot calls (hereafter ‘gunshots’), similar to those produced by other right whale populations, were localized to male and female NPRWs. The timing of gunshots correlated strongly with diving behavior observed during the FFs. Log survivorship analysis of inter-blow intervals showed a bout criterion interval of 40 s, separating the data into shorter surfacings and longer dives. For both, gunshots were skewed closer to the end of the sequence (modal gunshot to blow times: 5 s for dives, 7 s for surfacings) than the beginning (modal blow to gunshot times: 22 s for dives, 13 s for surfacings). Gunshots were more commonly produced during dives than surfacings. Mean gunshot calling rate during FFs was 133.0 calls h-1 (range: 38.9-425.0). Other NPRW calls, including upcalls, the predominant call used to identify right whales acoustically, were not detected during the FFs. To determine comparative call detection rates, an additional 180 h of non-FF recordings were analyzed. Gunshots were detected ~50 times more frequently than upcalls (mean: 228.3 vs. 4.3 calls h-1, respectively), with a maximum gunshot calling rate of 835.7 calls h-1. This is the first study to definitively attribute gunshots to NPRW, and demonstrates the importance of including gunshots in passive acoustic studies, which will greatly increase NPRW detectability while supporting more accurate determinations of their spatio-temporal distribution.

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.

ECG was supported by a National Research Council-National Academy of Sciences Postdoctoral Fellowship. 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. Postprint

A reliable lower bound is derived for the number of vocalizing bowhead whales and walruses in the Chukchi Sea from ten acoustic receivers deployed during NOAA's CHAOZ experiment in 2011. The lower bound is derived from extremely reliable 100% confidence intervals (CI) of the sound's locations. CI are derived from measurements of the Time Differences of Arrival (TDOA) of sound between receivers. Sequential Bound Estimation (SBE) is used to estimate the CI by assimilating the TDOA. SBE was successfully and independently evaluated by the U.S. Navy. It is a nonlinear non-Bayesian technique capable of explicitly accounting for all errors affecting uncertainty while being computationally efficient. To date, its CI always contain the true location of the source. The CI are affected by uncertainty of sound speed, TDOA, receiver location, and clock time. For two-dimensional models of location, i.e., longitude/latitude, it appears necessary to utilize isodiachrons instead of hyperbolas to obtain reliable CI because of the extreme non-homogeneity of sound speed needed to obtain correct location. [Supported by the North Pacific Research Board and Microsoft.]A reliable lower bound is derived for the number of vocalizing bowhead whales and walruses in the Chukchi Sea from ten acoustic receivers deployed during NOAA's CHAOZ experiment in 2011. The lower bound is derived from extremely reliable 100% confidence intervals (CI) of the sound's locations. CI are derived from measurements of the Time Differences of Arrival (TDOA) of sound between receivers. Sequential Bound Estimation (SBE) is used to estimate the CI by assimilating the TDOA. SBE was successfully and independently evaluated by the U.S. Navy. It is a nonlinear non-Bayesian technique capable of explicitly accounting for all errors affecting uncertainty while being computationally efficient. To date, its CI always contain the true location of the source. The CI are affected by uncertainty of sound speed, TDOA, receiver location, and clock time. For two-dimensional models of location, i.e., longitude/latitude, it appears necessary to utilize isodiachrons instead of hyperbolas to obtain reliable CI because...

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.

International audience; Fin whales (Balaenoptera physalus) in the North Pacific consistently range as far north as the Bering Sea. While occasional sightings of fin whales occur north of the Bering Strait, they are rarely documented north of 67°N. However, a recent increase in passive acoustic monitoring has shown that fin whales are more prevalent in the Chukchi Sea than previously thought. During a 2012 field survey in the Alaskan Chukchi Sea, fin whale calls were detected on a DiFAR sonobuoy deployed at 71.575°N, 157.823°W, 50 km off Barrow near the mouth of Barrow Canyon. On August 27, 2012, approximately 30 fin whale downsweep calls were detected over an hour and a half, at bearings of approximately 270–290° from the sonobuoy. Since only one sonobuoy was deployed, in situ localization of the calls was not possible. Post hoc range estimates using a combination of modal dispersion techniques, nonlinear time-domain warping, and geoacoustic inversion resulted in a source range estimate of less than 5 km. This location is approximately 280 and 365 km northeast of the previous closest acoustic detection and confirmed visual sighting of a fin whale, respectively. These results represent the farthest northeast record of fin whale calls in the Alaskan Arctic and illustrate the importance of continued passive acoustic monitoring in a rapidly changing environment.

Two populations of beluga whales (Delphinapterus leucas) migrate annually between their summering grounds in the eastern Chukchi and eastern Beaufort Seas, and overwintering areas in the Bering Sea. To contribute to the understanding of migratory streams of this highly vocal species, we investigated temporal peaks in acoustic detections from 4-year-long (2010–2011) recorders located in the northeastern Chukchi (inshore and offshore), western Beaufort, and northern Bering Seas. Beluga calls were detected throughout summer (July–August) in the western Beaufort; other studies suggest these animals are likely from the eastern Chukchi population. In autumn (September–November), calls were detected in the western Beaufort and northeastern Chukchi, which were likely from both the eastern Beaufort and eastern Chukchi populations. A strong peak at the inshore northeastern Chukchi site occurred in late-November; this peak is likely to be from the eastern Chukchi population. During spring, beluga calls were detected in the northeastern Chukchi and western Beaufort in two distinct vocal peaks (early- and late-May). The timing was consistent with the hypothesis that both vocal peaks were caused by the eastern Beaufort population. This suggests that migration of populations can be discriminated when temporal differences between vocal peaks are large enough to be identified as independent events. Our study results complement and support the population identity of peaks suggested by satellite telemetry, aerial surveys, and other acoustical studies. Passive acoustic monitoring improves our understanding of the migratory timing of beluga populations for management and conservation in a region undergoing rapid change.

International audience; 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 = 2.9 × 10-5); 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.

Due to the seriously endangered status of North Pacific right whales Eubalaena japonica, an improved understanding of the environmental factors that influence the species' distribution and occurrence is needed to better assess the effects of climate change and industrial activities on the population. Associations among right whales, zooplankton, and the physical envi- ronment were examined in the southeastern Bering Sea during the summers of 2008 and 2009. Sampling with nets, an optical plankton counter, and a video plankton recorder in proximity to whales as well as along cross-isobath surveys indicated that the copepod Calanus marshallae is the primary prey of right whales in this region. Acoustic detections of right whales from sonobuoys deployed during the cross-isobath surveys were strongly associated with C. marshallae abun- dance, and peak abundance estimates of C. marshallae in 2.5 m depth strata near a tagged right whale ranged as high as 10 6 copepods m �3 . The smaller Pseudocalanus spp. was higher in abun- dance than C. marshallae in proximity to right whales, but significantly lower in biomass. High concentrations of C. marshallae occurred in both the surface and bottom layers of the highly stratified water column, but there was no evidence of diel vertical migration. Instead, occurrence of C. marshallae in the bottom layer was associated with elevated near-bottom light attenuance and chlorophyll fluorescence, suggesting C. marshallae may aggregate at depth while feeding on resuspended phytodetritus. Despite the occasional presence of strong horizontal gradients in hydrographic properties, no association was found between C. marshallae and either fronts or phytoplankton distribution.

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.

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 Spitsber- gen population in the North Atlantic, depleted to the point of extinction. Recent sightings of bow- head whales west of Svalbard precipitated an effort to listen for their vocalizations via 2 re - corders deployed in 2008 on oceanographic moor- ings 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 con- centration, 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 mat- ing area — for this Critically Endangered popula- tion of bowhead whales.

Recent expansion in the capabilities of passive acoustic monitoring of sound-producing animals is providing expansive data sets in many locations. These long-termdata sets will allowthe investigation of questions related to the ecology of sound-producing animals on time scales ranging fromdiel and seasonal to inter-annual and decadal. Analyses of these data often span multiple analysts from various research groups over several years of effort and, as a consequence, have begun to generate large amounts of scattered acoustic metadata. It has therefore become imperative to standardize the types of metadata being generated. A critical aspect of being able to learn from such large and varied acoustic data sets is providing consistent and transparent access that can enable the integration of various analysis efforts. This is juxtaposed with the need to include new information for specific research questions that evolve over time. Hence, a method is proposed for organizing acoustic metadata that addresses many of the problems associated with the retention of metadata from large passive acoustic data sets. A structure was developed for organizing acoustic metadata in a consistent manner, specifying required and optional terms to describe acoustic information derived from a recording. A client-server database was created to implement this data representation as a networked data service that can be accessed from several programming languages. Support for data import froma wide variety of sources such as spreadsheets and databases is provided. The implementation was extended to access Internet-available data products, permitting access to a variety of environmental information types (e.g. sea surface temperature, sunrise/sunset, etc.) fromawide range of sources as if they were part of the data service. This metadata service is in use at several institutions and has been used to track and analyze millions of acoustic detections from marine mammals, fish, elephants, and anthropogenic sound sources. Publisher PDF

Calling depth distributions and ranges are estimated for two types of calls produced by critically endangered eastern North Pacific right whales (NPRW) in the Bering Sea, using passive acoustic data collected with bottom-mounted single-hydrophone recorders in 50–90 m water depths. Nonlinear time resampling of 12 NPRW “upcalls” and 20 broadband “gunshots” typically isolated 3 to 4 individual mode arrivals below 200 Hz. Matched-mode processing (MMP) methods were used to remove the unknown source phase and amplitude structure, but incoherently averaging MMP ambiguity surfaces across frequency yielded many local minima when inverting for sediment properties. Instead, the ambiguity surfaces were plotted as a function of range and frequency, which revealed the type and degree of environmental mismatch present in initial waveguide models. This qualitative approach revealed the existence of large sound speed gradients in the sediment, along with downward-refracting sound speed profiles during the summer months. G...

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.

This paper describes unique, stereotyped, gunshot songs produced by the eastern North Pacific right whale (NPRW, Eubalaena japonica). Four unique songs were documented over eight years (2009–2017) and five separate locations in the southeastern Bering Sea. Similar to songs reported for other species, each NPRW song consists of a hierarchical structure of 1-3 different repeating phrases comprised predominantly of gunshot calls (though other call types were occasionally present). Songs were detected every year from July through early January. All four song structures remained consistent over eight years. Two different songs often occurred simultaneously; the same song never occurred simultaneously at the same location. However, the detection of the same song on the same day and time at two locations 310 km apart indicates multiple animals can produce the same song. These songs were localized to individual male NPRWs using directional sonobuoys; it remains unknown if females also sing. We hypothesize that these songs may be a reproductive display similar to song in other mysticetes. Although singing has not been documented in congeneric right whale species, songs presented here fit the classification of song attributed to other cetacean species. Possible functions of these songs and their management implications will be discussed.

Calling depth distributions and ranges are estimated for two types of calls produced by critically endangered eastern North Pacific right whales (NPRW) in the Bering Sea, using passive acoustic data collected with bottom-mounted single-hydrophone recorders at the 50 m isobath. Nonlinear time resampling of 12 NPRW “upcalls” and 20 broadband “gunshots” typically isolated 3 to 4 individual mode arrivals below 200 Hz. Matched-mode processing (MMP) methods were then used to estimate range, depth, and propagation environment. When plotted as a function of range and frequency, MMP ambiguity surfaces reveal the existence of large sound speed gradients in the sediment, along with strongly downward-refracting sound speed profiles during certain summer/fall seasons. Refractive propagation effects from these profiles can induce dramatic changes in signal structure that required new developments in “warping” techniques. Gunshot sounds were generally produced at a few meters depth, while upcall depths clustered between...

The Distributed Biological Observatory (DBO) is a set of eight biological hotspot areas spanning latitudinally from the Northern Bering Sea to the Canadian Beaufort Sea. The DBO is an international collaboration between researchers from the United States, Japan, Canada, China, South Korea, and Russia that work in the Alaskan Bering, Chukchi, and Beaufort Seas; all research vessels passing through one of the DBO regions collect biophysical data (i.e., temperature, salinity, sea ice concentration and thickness, chlorophyll, nutrients, and zooplankton occurrence) along a pre-described line of sampling stations. Since the pilot study in 2010, and with funding from the Bureau of Ocean Energy Management (BOEM), the Marine Mammal Laboratory at the Alaska Fisheries Science Center of NOAA has maintained passive acoustic recorder moorings at two of the DBO regions, colocated with oceanographic moorings from the Pacific Marine Science Center (P. Stabeno). This coverage was expanded to five DBO regions in 2012, again with colocated oceanographic moorings at four of the sites. Here, an interannual comparison of the long-term mooring results from gray, bowhead, beluga, humpback, and killer whales, walrus, ribbon and bearded seals, and vessel and seismic airgun noise will be presented and compared with the sampled biophysical data.

Funding was provided by the Bureau of Ocean Energy Management under InterAgency Agreement M09PG00016. E.C.G. was supported by a National Research Council (National Academy of Sciences) Postdoctoral Fellowship. 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 clas- sification 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 pas- sive 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. Publisher PDF

Killer whales (Orcinus orca) are a highly vocal species that produce three types of vocalizations; pulsed calls, whistles, and clicks. Unlike the Northern and Southern Resident populations of western Canada and the Pacific Northwest, little is known regarding the acoustic behavior of resident and transient killer whale populations north of the Aleutian Islands in the Bering and Chukchi Seas. Acoustic data were analyzed from moored recorders deployed by the Marine Mammal Laboratory at two sites each in the Bering and Chukchi Seas (BOEM-funded). The recorders sampled at 4 kHz on a 7% duty cycle (Bering) or 16 kHz on a 28% duty cycle (Chukchi). Over 1100 calls were identified, and discrete call classification was conducted using an alphanumerical system that distinguished calls by location, general contour, and segment variation. Parameters analyzed included call duration, start/end frequency, and delta frequency/time; periods of call repetition were common. These results will help determine if resident popu...

The Marine Mammal Laboratory has deployed long-term passive acoustic recorders along the 50 m and 70 m isobaths throughout the Bering Sea since 2007. Instruments recorded at either 4 kHz on a ~7-11% duty cycle, or 8 kHz on a 30-45% duty cycle. In addition, directional sonobuoys were deployed during field surveys to allow real-time monitoring for large whale presence. During the 2010 survey, a stereotyped, repetitive gunshot call pattern was acoustically detected on sonobuoys. This same call pattern was then detected on two different long-term moored recorders in two separate years. Since then, six different stereotyped, repetitive patterns have been documented, three of which have been analyzed. Preliminary results show that each pattern has a minimum of 30 iterations repeated over several hours. Furthermore, in several cases, these patterns are repeated throughout the season, in consecutive years, and in one instance, in non-consecutive years. While male North Atlantic right whales produce long gunshot b...

The eastern population of the critically endangered North Pacific right whale (NPRW; Eubalaena japonica) historically ranged in the eastern Bering Sea from the Aleutian Islands to St. Matthew Island (60.4°N), with limited (n < 20) detections further north (which some consider bowhead whale; Balaena mysticetus). Since the 1980s, most NPRW sightings have been isolated to the southeastern Bering Sea. In order to describe the current spatio-temporal distribution of NPRW, long-term passive acoustic recorders throughout the Bering Sea (2012–2016) were analyzed manually (10,204.2 days; 27–29% duty cycle) for the presence of NPRW, which were identified using the “up” and “gunshot” calls. NPRW were consistently detected during ice-free months in the southeastern Bering Sea, and intermittently during the same months northward to 59°N. NPRW were also detected at low calling activity within two eastern Aleutian Passes. Notably, NPRW were detected north of St. Matthew (61.6°N) in summer 2016 (July–Aug.). Up and gunshot calls north of 62°N in ice-free months and north of 58°N in ice-associated months could not be distinguished from bowhead whale. Together, these results indicate that NPRW currently range with certainty from the eastern Aleutian Passes to 61.6°N, but may range as far north as the Bering Strait.The eastern population of the critically endangered North Pacific right whale (NPRW; Eubalaena japonica) historically ranged in the eastern Bering Sea from the Aleutian Islands to St. Matthew Island (60.4°N), with limited (n < 20) detections further north (which some consider bowhead whale; Balaena mysticetus). Since the 1980s, most NPRW sightings have been isolated to the southeastern Bering Sea. In order to describe the current spatio-temporal distribution of NPRW, long-term passive acoustic recorders throughout the Bering Sea (2012–2016) were analyzed manually (10,204.2 days; 27–29% duty cycle) for the presence of NPRW, which were identified using the “up” and “gunshot” calls. NPRW were consistently detected during ice-free months in the southeastern Bering Sea, and intermittently during the same months northward to 59°N. NPRW were also detected at low calling activity within two eastern Aleutian Passes. Notably, NPRW were detected north of St. Matthew (61.6°N) in summer 2016 (July–Aug.). Up and gunsho...

The acoustic ecology of Arctic marine mammals is driven by anthropogenic, biotic, and abiotic factors each of which may influence the behavioral ecology of each species. The acoustic environment of bowhead (Balaena mysticetus) and beluga (Delphinapterus leucas) whales in three core-use regions of the Pacific Arctic was examined during the months in which both species occur in these regions. The Anadyr Strait region in winter was dominated by the signals of bowhead whales, walrus and bearded seals. In Bering Strait in late fall and winter, wind noise predominated in November but once the region was ice-covered, bowhead and walrus were the main sources of noise. Barrow Canyon in late summer and fall was the only region in which anthropogenic sources overlapped with both whale species. Overall, ambient noise levels were low in the Pacific Arctic when compared to other ocean basins in which anthropogenic noise dominates low frequencies. However, climate change-driven increases in open water are leading to ris...

Fin whales are common throughout the North Pacific region, particularly in the Gulf of Alaska and the Bering Sea, even though these areas were heavily depleted by decades of whaling. Whalers also took fin whales in the southwestern Chukchi Sea, but only five sightings have been reported for the entire Chukchi Sea in the past 30 years. Large-scale arrays consisting of 26 – 44 bottom-mounted acoustic recorders were deployed in the northeastern Chukchi Sea from July to October in 2007 to 2010. Fin whales were detected off Cape Lisburne and Point Lay in 2007, 2009, and 2010. Large interannual variations in the number of acoustic detections may be related to environmental conditions. Calls detected during summer months consisted primarily of irregular sequences. Stereotyped sequences, called songs, were also detected at the end of the recording period in 2007 and 2010. Their structure matched that of one of the songs recorded in the Bering Sea, suggesting that only one of the stocks occurring in the Bering Sea extends its range into the northeastern Chukchi Sea. These detections currently represent the northernmost fin whale records in the North Pacific region.

The Marine Mammal Laboratory has deployed long-term, moored, passive acoustic recorders at numerous locations in the Alaskan Arctic since the BOEM-funded Chukchi Acoustics, Oceanography, and Zooplankton (CHAOZ) study began in 2010. These instruments, often collocated with oceanographic instruments, collect year-round passive acoustic data (16 kHz sampling rate, ~30% duty cycle). All acoustic recordings (100%) were analyzed using an in-house Matlab-based manual analysis program for 12 different Arctic and sub-Arctic cetacean and pinniped species, as well as for vessel, seismic airgun, and ice noise. Bowhead and beluga distributions showed similar patterns, with bimodal temporal distributions representing the fall and spring migrations. Infrequent gray whale detections (isolated on nearshore recorders) followed a similar, albeit less defined, bimodal distribution. Walrus and bearded seal calls were detected almost year-round, with peak bearded seal calling from April through June. Detections of sub-Arctic s...

Passive acoustic monitoring (PAM) of sound-producing animals (e.g. marine mammals) is producing multi-year data sets in many locations. Such long-term data sets allow the investigation of questions related to the effects of environmental processes and anthropogenic activities on these animals at varying temporal-spatial scales. Preservation of acoustic metadata in a standardized format can prevent the loss of detailed information that is not captured in scientific publications and permits the analysis of decadal-scale data sets and beyond. The need for standardization is juxtaposed with the need to include new information for specific research questions that evolve over time. This work proposes a schema for organizing acoustic metadata that addresses many of the problems associated with the retention of metadata from long-term passive acoustic data sets and enables the incorporation of research-question specific details without the need for changes to the schema or its implementation. The long-term goals of this effort are to produce community data standards and software capable of organizing and archiving acoustic metadata associated with passive acoustic monitoring of marine mammals. The software provides a reference implementation of the community standards in a scientific workbench setting. The workbench enables researchers to integrate queries for both biological and physical data by providing mediation services to support the retrieval of Internet-available data sets in a manner similar to those used for querying the acoustic data. The data are accessible from a variety of languages used by the scientific community for analysis and modeling. The Tethys server at Scripps now has data sets that cover over nine years, and published and submitted articles are demonstrating the benefits to the preservation of consistent metadata from long time-series data.

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.

A growing number of passive acoustic monitoring systems have resulted in a wealth of annotation information, or metadata, for recordings. These metadata are semi-structured. Some parameters are essentially mandatory (e.g., time of detection and what was detected) while others are highly dependent upon the question that a researcher is asking. Tethys is a metadata system for spatial-temporal acoustic data that provides structure where it is appropriate and flexibility where it is needed. Networked metadata are stored in an extended markup language (XML) database, and served to workstations over a network. The ability to export summary data to OBIS-SEAMAP is in development. The second purpose of Tethys is to serve as a scientific workbench. Interfaces are provided to networked databases, permitting the import of data from a wide variety of sources, such as lunar illumination or sea ice coverage. Interfaces currently exist for Matlab, Java, and Python. Writing data driven queries using a single interface ena...

The National Marine Mammal Laboratory has been collecting passive acoustic recordings of vocalizing marine mammals through much of the southeastern Bering Sea since 2000. The present analysis combines these recordings with those obtained in 2007 from a North Pacific Research Board-funded study (Stafford and Mellinger) to determine the long-term spatio-temporal distribution of fin whales throughout the Bering Sea shelf. A total of 28 moorings (19 Autonomous Underwater Recorders for Acoustic Listening (AURALs); 9 Ecological Acoustic Recorders (EARs)) were deployed year-round from October 2007 to September 2011 at varying depths and locations along the Bering Sea shelf, from Umnak Pass to just south of St. Lawrence Island. Preliminary analyses show an annual southward movement of calling fin whales in winter, seemingly associated with the expanding ice edge; these results will be compared with 1-day composite ice cover measured by the Advanced Microwave Scanning radiometer for the Earth Observing System (NOA...

Beluga whales (Delphinapterus leucas) are highly vocal animals which make them ideal candidates for passive acoustic monitoring. Alaskan belugas overwinter in the Bering Sea, and in spring, two subpopulations migrate to their predictable summering grounds in the eastern Chukchi and eastern Beaufort Seas. In autumn, these subpopulations complete their annual migration by returning south to the Bering Sea. Additional information is required on the timing and migration routes in spring and autumn to assist in detecting these subpopulations as they transit between the two regions. Preliminary results are presented on the temporal distribution of Alaskan beluga based on acoustic detection (September 2010 to May 2011) from a passive acoustic recorder located 30 miles off Icy Cape, AK, in the eastern Chukchi Sea. Belugas were sporadically detected in autumn from mid-September to the start of December, with a peak in detections in late November. In spring, belugas were detected from mid-April to the end of May, w...

The Bering Sea is an important area for many cetaceans. It functions as both summer feeding grounds for some species like humpback and right whales, and wintering grounds for more northern species such as bowhead and beluga whales. Passive acoustics is an important tool for monitoring the presence of these and other species in the Bering Sea, although similarities in call characteristics among species can create confusion. For example, gunshot calls are produced by both right and bowhead whales. Recordings made in the Bering Sea (2007-2011) have been analyzed for the presence of gunshot calls. The spatio-temporal distribution of these calls is compared to that of more ‘standard’ bowhead and right whale calls. With the inclusion of information on historical range, migration patterns, and ice coverage, a tentative separation of the two species is proposed. Call characteristics and contextual information from the resulting subsets of data are then examined and compared with data confidently attributed to each species. Whether right and bowhead whale gunshot calls can be discriminated with sufficient reliability to include in spatio-temporal distribution analyses, and what added value this call type gives over using only ‘standard’ call types, will be discussed.