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Clark C.W.,Cornell University | Berchok C.L.,National Oceanic and Atmospheric Administration | Blackwell S.B.,Greeneridge science Inc. | Hannay D.E.,JASCO Applied science | And 3 more authors.
Progress in Oceanography | Year: 2015

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. © 2015 Elsevier Ltd.


Bonnel J.,ENSTA Bretagne | Thode A.M.,University of California at San Diego | Blackwell S.B.,Greeneridge science Inc. | Kim K.,Greeneridge science Inc. | Michael Macrander A.,Royal Dutch Shell
Journal of the Acoustical Society of America | Year: 2014

Bowhead whales generate low-frequency calls in shallow-water Arctic environments, whose dispersive propagation characteristics are well modeled by normal mode theory. As each mode propagates with a different group speed, a call's range can be inferred by the relative time-frequency dispersion of the modal arrivals. Traditionally, at close ranges modal arrivals are separated using synchronized hydrophone arrays. Here a nonlinear signal processing method called "warping" is used to filter the modes on just a single hydrophone. The filtering works even at relatively short source ranges, where distinct modal arrivals are not separable in a conventional spectrogram. However, this warping technique is limited to signals with monotonically increasing or decreasing frequency modulations, a relatively common situation for bowhead calls. Once modal arrivals have been separated, the source range can be estimated using conventional modal dispersion techniques, with the original source signal structure being recovered as a by-product. Twelve bowhead whale vocalizations recorded near Kaktovik (Alaska) in 2010, with signal-to-noise ratios between 6 and 23 dB, are analyzed, and the resulting single-receiver range estimates are consistent with those obtained independently via triangulation from widely-distributed vector sensor arrays. Geoacoustic inversions for each call are necessary in order to obtain the correct ranges. © 2014 Acoustical Society of America.


PubMed | Royal Dutch Shell, University of California at San Diego, University of New Hampshire and Greeneridge science Incorporated
Type: Journal Article | Journal: The Journal of the Acoustical Society of America | Year: 2017

Automated and manual acoustic localizations of migrating bowhead whales were used to estimate source level and calling depth distributions of their frequency-modulated-modulated calls over seven years between 2008 and 2014. Whale positions were initially triangulated using directional autonomous seafloor acoustic recorders, deployed between 25 and 55m water depth near Kaktovik, Alaska, during the fall westward migration. Calling depths were estimated by minimizing the discrepancy between source level estimates from at least three recorders detecting the same call. Applying a detailed waveguide propagation model to the data yielded broadband source levels of 1619dB re 1Pa


Blackwell S.B.,Greeneridge science Inc. | Nations C.S.,Western EcoSystems Technology Inc. | McDonald T.L.,Western EcoSystems Technology Inc. | Thode A.M.,University of California at San Diego | And 5 more authors.
PLoS ONE | Year: 2015

In proximity to seismic operations, bowhead whales (Balaena mysticetus) decrease their calling rates. Here, we investigate the transition from normal calling behavior to decreased calling and identify two threshold levels of received sound from airgun pulses at which calling behavior changes. Data were collected in August-October 2007-2010, during the westward autumn migration in the Alaskan Beaufort Sea. Up to 40 directional acoustic recorders (DASARs) were deployed at five sites offshore of the Alaskan North Slope. Using triangulation, whale calls localized within 2 km of each DASAR were identified and tallied every 10 minutes each season, so that the detected call rate could be interpreted as the actual call production rate. Moreover, airgun pulses were identified on each DASAR, analyzed, and a cumulative sound exposure level was computed for each 10-min period each season (CSEL10-min). A Poisson regression model was used to examine the relationship between the received CSEL10-min from airguns and the number of detected bowhead calls. Calling rates increased as soon as airgun pulses were detectable, compared to calling rates in the absence of airgun pulses. After the initial increase, calling rates leveled off at a received CSEL10-min of ∼94 dB re 1 μPa2-s (the lower threshold). In contrast, once CSEL10-min exceeded ∼127 dB re 1 μPa2-s (the upper threshold), whale calling rates began decreasing, and when CSEL10-min values were above ∼160 dB re 1 μPa2-s, the whales were virtually silent. © 2015 Blackwell et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.


Abadi S.H.,University of Michigan | Thode A.M.,University of California at San Diego | Blackwell S.B.,Greeneridge science Inc. | Dowling D.R.,University of Michigan
Journal of the Acoustical Society of America | Year: 2014

This paper presents the performance of three methods for estimating the range of broadband (50-500 Hz) bowhead whale calls in a nominally 55-m-deep waveguide: Conventional mode filtering (CMF), synthetic time reversal (STR), and triangulation. The first two methods use a linear vertical array to exploit dispersive propagation effects in the underwater sound channel. The triangulation technique used here, while requiring no knowledge about the propagation environment, relies on a distributed array of directional autonomous seafloor acoustics recorders (DASARs) arranged in triangular grid with 7 km spacing. This study uses simulations and acoustic data collected in 2010 from coastal waters near Kaktovik, Alaska. At that time, a 12-element vertical array, spanning the bottom 63% of the water column, was deployed alongside a distributed array of seven DASARs. The estimated call location-to-array ranges determined from CMF and STR are compared with DASAR triangulation results for 19 whale calls. The vertical-array ranging results are generally within ±10% of the DASAR results with the STR results providing slightly better agreement. The results also indicate that the vertical array can range calls over larger ranges and with greater precision than the particular distributed array discussed here, whenever the call locations are beyond the distributed array boundaries. © 2014 Acoustical Society of America.


Blackwell S.B.,Greeneridge science Inc. | Nations C.S.,Western EcoSystems Technology Inc. | Mcdonald T.L.,Western EcoSystems Technology Inc. | Greene C.R.,Greeneridge science Inc. | And 3 more authors.
Marine Mammal Science | Year: 2013

This study assesses effects of airgun sounds on bowhead calling behavior during the autumn migration. In August-October 2007, 35 directional acoustic recorders (DASARs) were deployed at five sites in the Alaskan Beaufort Sea. Location estimates were obtained for >137,500 individual calls; a subsample of locations with high detection probability was used in the analyses. Call localization rates (CLRs) were compared before, during, and after periods of airgun use between sites near seismic activities (median distance 41-45 km) and sites relatively distant from seismic activities (median distance >104 km). At the onset of airgun use, CLRs dropped significantly at sites near the airguns, where median received levels from airgun pulses (SPL) were 116-129 dB re 1 μPa (10-450 Hz). CLRs remained unchanged at sites distant from the airguns, where median received levels were 99-108 dB re 1 μPa. This drop could result from a cessation of calling, deflection of whales around seismic activities, or both combined, but call locations alone were insufficient to differentiate between these possibilities. Reverberation from airgun pulses could have masked a small number of calls near the airguns, but even if masking did take place, the analysis results remain unchanged. © 2013 by the Society for Marine Mammalogy.


Guerra M.,University of California at San Diego | Thode A.M.,University of California at San Diego | Blackwell S.B.,Greeneridge science Incorporated | Michael MacRander A.,Royal Dutch Shell
Journal of the Acoustical Society of America | Year: 2011

Shallow-water airgun survey activities off the North Slope of Alaska generate impulsive sounds that are the focus of much regulatory attention. Reverberation from repetitive airgun shots, however, can also increase background noise levels, which can decrease the detection range of nearby passive acoustic monitoring (PAM) systems. Typical acoustic metrics for impulsive signals provide no quantitative information about reverberation or its relative effect on the ambient acoustic environment. Here, two conservative metrics are defined for quantifying reverberation: a minimum level metric measures reverberation levels that exist between airgun pulse arrivals, while a reverberation metric estimates the relative magnitude of reverberation vs expected ambient levels in the hypothetical absence of airgun activity, using satellite-measured wind data. The metrics are applied to acoustic data measured by autonomous recorders in the Alaskan Beaufort Sea in 2008 and demonstrate how seismic surveys can increase the background noise over natural ambient levels by 30-45 dB within 1 km of the activity, by 10-25 dB within 15 km of the activity, and by a few dB at 128 km range. These results suggest that shallow-water reverberation would reduce the performance of nearby PAM systems when monitoring for marine mammals within a few kilometers of shallow-water seismic surveys. © 2011 Acoustical Society of America.


PubMed | University of California at San Diego and Greeneridge science Inc.
Type: Journal Article | Journal: The Journal of the Acoustical Society of America | Year: 2016

Masking from industrial noise can hamper the ability to detect marine mammal sounds near industrial operations, whenever conventional (pressure sensor) hydrophones are used for passive acoustic monitoring. Using data collected from an autonomous recorder with directional capabilities (Directional Autonomous Seafloor Acoustic Recorder), deployed 4.1km from an arctic drilling site in 2012, the authors demonstrate how conventional beamforming on an acoustic vector sensor can be used to suppress noise arriving from a narrow sector of geographic azimuths. Improvements in signal-to-noise ratio of up to 15dB are demonstrated on bowhead whale calls, which were otherwise undetectable using conventional hydrophones.


PubMed | Royal Dutch Shell, Greeneridge science Inc., Western EcoSystems Technology Inc. and University of California at San Diego
Type: Journal Article | Journal: PloS one | Year: 2015

In proximity to seismic operations, bowhead whales (Balaena mysticetus) decrease their calling rates. Here, we investigate the transition from normal calling behavior to decreased calling and identify two threshold levels of received sound from airgun pulses at which calling behavior changes. Data were collected in August-October 2007-2010, during the westward autumn migration in the Alaskan Beaufort Sea. Up to 40 directional acoustic recorders (DASARs) were deployed at five sites offshore of the Alaskan North Slope. Using triangulation, whale calls localized within 2 km of each DASAR were identified and tallied every 10 minutes each season, so that the detected call rate could be interpreted as the actual call production rate. Moreover, airgun pulses were identified on each DASAR, analyzed, and a cumulative sound exposure level was computed for each 10-min period each season (CSEL10-min). A Poisson regression model was used to examine the relationship between the received CSEL10-min from airguns and the number of detected bowhead calls. Calling rates increased as soon as airgun pulses were detectable, compared to calling rates in the absence of airgun pulses. After the initial increase, calling rates leveled off at a received CSEL10-min of ~94 dB re 1 Pa2-s (the lower threshold). In contrast, once CSEL10-min exceeded ~127 dB re 1 Pa2-s (the upper threshold), whale calling rates began decreasing, and when CSEL10-min values were above ~160 dB re 1 Pa2-s, the whales were virtually silent.


PubMed | University of Michigan, Greeneridge science Inc. and University of California at San Diego
Type: Journal Article | Journal: The Journal of the Acoustical Society of America | Year: 2014

This paper presents the performance of three methods for estimating the range of broadband (50-500Hz) bowhead whale calls in a nominally 55-m-deep waveguide: Conventional mode filtering (CMF), synthetic time reversal (STR), and triangulation. The first two methods use a linear vertical array to exploit dispersive propagation effects in the underwater sound channel. The triangulation technique used here, while requiring no knowledge about the propagation environment, relies on a distributed array of directional autonomous seafloor acoustics recorders (DASARs) arranged in triangular grid with 7km spacing. This study uses simulations and acoustic data collected in 2010 from coastal waters near Kaktovik, Alaska. At that time, a 12-element vertical array, spanning the bottom 63% of the water column, was deployed alongside a distributed array of seven DASARs. The estimated call location-to-array ranges determined from CMF and STR are compared with DASAR triangulation results for 19 whale calls. The vertical-array ranging results are generally within 10% of the DASAR results with the STR results providing slightly better agreement. The results also indicate that the vertical array can range calls over larger ranges and with greater precision than the particular distributed array discussed here, whenever the call locations are beyond the distributed array boundaries.

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