Feasibility of Acoustic Remote Sensing of Large Herring Shoals and Seafloor by Baleen Whales

Abstract

Recent research has found a high spatial and temporal correlation between certain baleen whale vocalizations and peak herring spawning processes in the Gulf of Maine. These vocalizations are apparently related to feeding activities with suggested functions that include communication, prey manipulation, and echolocation. Here, the feasibility of the echolocation function is investigated. Physical limitations on the ability to detect large herring shoals and the seafloor by acoustic remote sensing are determined with ocean acoustic propagation, scattering, and statistical theories given baleen whale auditory parameters. Detection is found to be highly dependent on ambient noise conditions, herring shoal distributions, baleen whale time-frequency vocalization spectra, and geophysical parameters of the ocean waveguide. Detections of large herring shoals are found to be physically feasible in common Gulf of Maine herring spawning scenarios at up to 10 ± 6 km in range for humpback parameters and 1 ± 1 km for minke parameters but not for blue and fin parameters even at zero horizontal range. Detections of the seafloor are found to be feasible up to 2 ± 1 km for blue and humpback parameters and roughly 1 km for fin and minke parameters, suggesting that the whales share a common acoustic sensation of rudimentary features of the geophysical environment.

Instantaneous 3D Continental-Shelf Scale Imaging of Oceanic Fish by Multi-Spectral Resonance Sensing Reveals Group Behavior during Spawning Migration

“…The analysis is done for shoal segments that sub-divide the herring high-density area into a number of annular sectors ( Figure 2) such that the spatial variation in the herring groups' spatial structure is investigated in an efficient manner (Section 2.4). The measured frequency response of herring scattering at each horizontal position is obtained from the instantaneous multi-spectral OAWRS scattering strength images (Section 2.2), whereas the modeled frequency response is obtained from a swimbladder resonance model [17,18] as described in Section 2.5. …”

“…The expected scattering strength SS model of herring in a uniformly-distributed vertical layer with mean shoal depth z 0 , shoal thickness H, neutral buoyancy depth z nb , and areal population density n A at frequency f is determined [17,18] as…”

“…where S is the far-field scatter function [20] of a single herring, k is the acoustic wavenumber, l is the fork length of herring, g(l) is the truncated Gaussian probability density function [18] to ensure positiveness of the parameter l, and z is the herring depth. Here, the backscattering cross section of herring is determined as…”

Vocalization Source Level Distributions and Pulse Compression Gains of Diverse Baleen Whale Species in the Gulf of Maine

“…Baleen whales are not known to produce sounds for echolocation or navigation, which is a capability in toothed whales. Some studies have suggested a potential for echolocation [25,83] or navigation [25,84] in some select baleen whale species, but is highly dependent on vocalization type [83], environmental and prey conditions [25], and they do not consider pulse compression gains since this ability is not known to be present in baleen whales. Here, the pulse compression gains are quantified for passive acoustic marine mammal sensing systems that use pulse compressions to enhance whale vocalization signal detection or bearing-time estimation for whale localization.…”

“…The whale locations for each species were previously determined using the moving array triangulation [2,22,23], the bearings-migration minimum mean square error and the array invariant techniques [2,[22][23][24] from the measured bearing versus time trajectories of sequences of vocalizations from that species [1]. The marine mammal species-dependent vocalization source level is an important parameter for estimating the marine mammal detection region for a given species in any passive underwater acoustic sensing system [1,2,25]. It is also employed in distance sampling estimates of marine mammal call density and abundance estimation [26][27][28][29][30].…”