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The low-frequency impulsive gunshot vocalizations of baleen whales exhibit dispersive propagation in shallow-water channels which is well-modeled by normal mode theory. Typically, underwater acoustic source range estimation requires multiple time-synchronized hydrophone arrays which can be difficult and expensive to achieve. However, single-hydrophone modal dispersion has been used to range baleen whale vocalizations and estimate shallow-water geoacoustic properties. Although convenient when compared to sensor arrays, these algorithms require preliminary signal detection and human labor to estimate the modal dispersion. In this paper, we apply a temporal convolutional network (TCN) to spectrograms from single-hydrophone acoustic data for simultaneous gunshot detection and ranging. The TCN learns ranging and detection jointly using gunshots simulated across multiple environments and ranges along with experimental noise. The synthetic data are informed by only the water column depth, sound speed, and density of the experimental environment, while other parameters span empirically observed bounds. The method is experimentally verified on North Pacific right whale gunshot data collected in the Bering Sea. To do so, 50 dispersive gunshots were manually ranged using the state-of-the-art time-warping inversion method. The TCN detected these gunshots among 50 noise-only examples with high precision and estimated ranges which closely matched those of the physics-based approach.

A convolutional neural network (CNN) was trained to identify multi-modal gunshots (impulse calls) within large acoustic datasets in shallow-water environments. South Atlantic right whale gunshots were used to train the CNN, and North Pacific right whale (NPRW) gunshots, to which the network was naive, were used for testing. The classifier generalizes to new gunshots from the NPRW and is shown to identify calls which can be used to invert for source range and/or environmental parameters. This can save human analysts hours of manually screening large passive acoustic monitoring datasets.

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.

To understand mysticete acoustic-based detection of ships, radiated noise from high-speed craft, cruise ships, catamarans and fishing vessels was recorded June-September 2009. Calibrated acoustic data (<2500 Hz) from a vertical hydrophone array was combined with ship passage information. A cruise ship had the highest broadband source level, while a fishing vessel had the lowest. Ship noise radiated asymmetrically and varied with depth. Bow null-effect acoustic shadow zones were observed for all ship classes and were correlated with ship-length-to-draft-ratios. These shadow zones may reduce ship detection by near-surface mysticetes.

The eastern North Pacific right whale (NPRW) is the most endangered population of whale and has been observed north of its core feeding ground in recent years with low sea ice extent. Sea ice and water temperature are important drivers for zooplankton dynamics within the whale's core feeding ground in the southeastern Bering Sea, seasonally forming stable fronts along the shelf that give rise to distinct zooplankton communities. A northward shift in NPRW distribution driven by changing distribution of prey resources could put this species at increased risk of entanglement and vessel strikes. We modeled the abundance of NPRW prey, Calanus glacialis, Neocalanus, and Thysanoessa species, using a dynamic biophysical food web model of nine zooplankton guilds in the Bering shelf zooplankton community during a period of warming (2006–2016). This model is unique among prior zooplankton studies from the region in that it includes density dependence, thereby allowing us to ask whether species interactions influence zooplankton dynamics. Modeling confirmed the importance of sea ice and ocean temperature to zooplankton dynamics in the region. Density‐independent growth drove community dynamics, while dependent factors were comparatively minimal. Overall, Calanus responded to environment terms, with the strength and direction of response driven by copepodite stage. Neocalanus and Thysanoessa responses were weaker, likely due to their primary occurrence on the outer shelf. We also modeled the steady‐state (equilibrium) abundance of Calanus in conditions with and without wind gusts to test whether advection of outer shelf species might disrupt the steady‐state dynamics of Calanus abundance; the results did not support disruption. Given the annual fall sampling design, we interpret our results as follows: low‐ice‐extent winters induced stronger spring winds and weakened fronts on the shelf, thereby advecting some outer shelf species into the study region; increased development rates in these warm conditions influenced the proportion of C. glacialis copepodite stages over the season. Residual correlation suggests missing drivers, possibly predators, and phytoplankton bloom composition. Given the continued loss of sea ice in the region and projected continued warming, our findings suggest that C. glacialis will move northward, and thus, whales may move northward to continue targeting them. [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]

On the North Pacific feeding grounds, humpback whales (Megaptera novaeangliae) are recovering from commercial whaling at a rapid rate (6.8%). The potential effect that this recovery will have on trophic dynamics involving these predators is currently unknown. To better elucidate complex trophic dynamics, variability in diet composition of apex predators on their respective feeding grounds needs to be understood. Thus, we explored the diet composition of two defined subaggregations of humpback whales of the Kodiak Archipelago population ("North," "South") using stable carbon (δ13C) and nitrogen (δ15N) isotope ratios of humpback whale skin and regional prey samples in Bayesian dietary mixing models. Humpback whales in the "North" region consumed proportionally more fish, dominated by capelin (Mallotus villosus), whereas, whales in the "South" region consumed predominantly krill. The difference in diet composition appears to reflect regional differences in prey availability. Thus, regional variability in diet composition by humpback whales may have disproportionate impacts on prey resources of sympatric predators depending on available prey biomass. As a result, we suggest fine-scale studies of apex predator diets are needed to better model trophic dynamics with accuracy. [ABSTRACT FROM AUTHOR]