02097nas a2200193 4500008004100000022001400041245011100055210006900166260001600235300001600251490000800267520145600275100002801731700001701759700002601776700002701802700002301829856005101852 2018 eng d a0001-496600aDouble-difference tracking of migrating Bowhead Whales using autonomous vector sensors in the Beaufort Sea0 aDoubledifference tracking of migrating Bowhead Whales using auto cJan-09-2018 a1695 - 16960 v1443 a

Passive acoustic monitoring has become a standard method for detecting bowhead whale (Balaena mysticetus) activity in Arctic waters. Between 2007 and 2014, over 40 autonomous vector sensors, known as DASARs, were deployed in the Beaufort Sea during the bowhead whale migration season. Individual DASARs can estimate azimuth, allowing calls to be localized by triangulation using multiple DASARs. However, these bearings are subject to calibration biases, and individual sensors were not precisely time-synchronized, making relative time-of-arrival information unreliable for standard localization purposes. Double-difference methods have previously been applied in seismology to obtain high-precision relative positions of earthquakes by measuring changes in relative travel-times between multiple events over widely distributed seismic sensors. This same concept has also been used to track fin whales on a seafloor seismic network. Here, the double-difference method is applied to previously localized bowhead whale calls in order to improve their relative positions. The approach uses changes in both relative call travel-times and bearings, detected at multiple DASARs, to determine high-precision relative locations of these calls despite the presence of systemic timing and bearing errors in the measurements. The resulting positions may allow tracking of individual whales, which would provide insight into the function of these calls.

1 aTenorio-Hallé, Ludovic1 aThode, Aaron1 aConrad, Alexander, S.1 aBlackwell, Susanna, B.1 aKim, Katherine, H. uhttp://asa.scitation.org/doi/10.1121/1.506753601961nas a2200181 4500008004100000022001400041245009700055210006900152260001600221300001600237490000800253520137400261100001701635700002701652700002301679700002601702856005101728 2018 eng d a0001-496600aAcoustic response of a migrating bowhead whale population to open-ocean ambient noise levels0 aAcoustic response of a migrating bowhead whale population to ope cJan-09-2018 a1696 - 16960 v1443 a

Automated and manual acoustic localizations of migrating bowhead whale calls in the Beaufort Sea were used to examine their acoustic response to changes in wind-driven, continuous, ambient noise levels. At low noise levels, the population’s source levels and calling rates increased with increasing noise level, with the source level distribution adjusting to maintain a consistent functional detection range, estimated to be between 20 and 60 km. However, once noise levels exceeded the 75thpercentile of their long-term distribution, source level increases failed to keep pace with further increases in noise level, thereby reducing the population’s detection range and associated communication space. Call production rates, on the other hand, continued to increase even up to the highest noise levels. Migrating bowhead whales thus attempted to maintain long-range call detectability by adjusting their source level and calling rate. Beyond a certain noise level, whales cannot increase their source levels, but do continue to increase their calling rate. The results provide context for interpreting the effects of industrial noise on bowhead whale acoustic behavior; for example, distant airgun signals stimulate an increase in mean call production rate equivalent to a 26 dB increase in natural ambient noise levels. [Work sponsored by NPRB.]

1 aThode, Aaron1 aBlackwell, Susanna, B.1 aKim, Katherine, H.1 aConrad, Alexander, S. uhttp://asa.scitation.org/doi/10.1121/1.506753802005nas a2200181 4500008004100000022001400041245015200055210006900207260001600276300001600292490000800308520136300316100001701679700002701696700002301723700002601746856005101772 2018 eng d a0001-496600aMulti-year measurements of the underwater noise field directionality in the shallow Beaufort Sea during open-water and drifting ice flow conditions0 aMultiyear measurements of the underwater noise field directional cJan-09-2018 a1696 - 16970 v1443 a

Between 2007 and 2014, over 35 Directional Autonomous Seafloor Acoustic Recorders (DASARs) were deployed over a 280 km swath of the Beaufort Sea continental shelf (20–55 m depth) during the open-water season, in order to monitor the fall (westward) bowhead whale migration. DASARs have one omnidirectional pressure sensor and two orthogonal particle motion sensors, which permit instantaneous measurements of the azimuths of both transient signals and continuous noise between 20 and 500 Hz. The lack of significant shipping or industrial noise in this region provided a rare opportunity to directly measure the properties of wind-driven noise in expanding ice-free regions. Here, we map the azimuthal directionality of the diffuse Beaufort ambient noise field as a function of frequency and space across seven seasons. The dominant directionality of the diffuse ambient noise field varied strongly with frequency and was highly correlated with the received power spectral density. Certain directional features of the ambient noise field remained stable over seven deployment seasons, suggesting that judicious processing of the ambient noise soundscape could provide underwater navigational information in arctic waters. The influence of local drifting floes and sheets of ice on this directionality is also examined. [Work sponsored by ONR.]

1 aThode, Aaron1 aBlackwell, Susanna, B.1 aKim, Katherine, H.1 aConrad, Alexander, S. uhttp://asa.scitation.org/doi/10.1121/1.506754102069nas a2200217 4500008004100000022001400041245010400055210006900159260001600228300001600244490000800260520139900268100001701667700001901684700002101703700001801724700002101742700001701763700002001780856005101800 2017 eng d a0001-496600aUsing nonlinear time warping to estimate North Pacific right whale calling depths in the Bering Sea0 aUsing nonlinear time warping to estimate North Pacific right wha cJan-05-2017 a3059 - 30690 v1413 a

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.

1 aThode, Aaron1 aBonnel, Julien1 aThieury, Margaux1 aFagan, Aileen1 aVerlinden, Chris1 aWright, Dana1 aCrance, Jessica uhttp://asa.scitation.org/doi/10.1121/1.4982200