Diel and Spatial Dependence of Humpback Song and Non-Song Vocalizations in Fish Spawning Ground

Abstract

Abstract:The vocalization behavior of humpback whales was monitored over vast areas of the Gulf of Maine using the passive ocean acoustic waveguide remote sensing technique (POAWRS) over multiple diel cycles in Fall 2006. The humpback vocalizations comprised of both song and non-song are analyzed. The song vocalizations, composed of highly structured and repeatable set of phrases, are characterized by inter-pulse intervals of 3.5 ± 1.8 s. Songs were detected throughout the diel cycle, occuring roughly 40% during the day and 60% during the night. The humpback non-song vocalizations, dominated by shorter duration (≤3 s) downsweep and bow-shaped moans, as well as a small fraction of longer duration (∼5 s) cries, have significantly larger mean and more variable inter-pulse intervals of 14.2 ± 11 s. The non-song vocalizations were detected at night with negligible detections during the day, implying they probably function as nighttime communication signals. The humpback song and non-song vocalizations are separately localized using the moving array triangulation and array invariant techniques. The humpback song and non-song moan calls are both consistently localized to a dense area on northeastern Georges Bank and a less dense region extended from Franklin Basin to the Great South Channel. Humpback cries occur exclusively on northeastern Georges Bank and during nights with coincident dense Atlantic herring shoaling populations, implying the cries are feeding-related.

Angular Resolution Enhancement Provided by Nonuniformly-Spaced Linear Hydrophone Arrays in Ocean Acoustic Waveguide Remote Sensing

“…The Atlantic herring areal population densities were monitored over instantaneous wide areas using active OAWRS imaging [1,2,8,12,13] and calibrated with coincident conventional ultrasonic fisheries echo sounding measurements [2,8,13] with fish species identification and physiological parameters extracted from trawl samples collected over the course of the experiment [52,54]. In addition to echo returns of the transmitted source signal, vocalizations from more than eight distinct marine mammal species including fin, humpback, sei, minke, orca, pilot, sperm, and other unidentified baleen and toothed whale species were also passively recorded by the coherent hydrophone array [1,4,5,12]. The ecosystem-wide spatial distributions of vocal marine mammals from multiple cetacean species were simultaneously mapped by the POAWRS technique [1,[4][5][6].…”

“…In contrast, several of these population centers were previously blurred together when beamformed with the array's uniformly-spaced single subaperture. In passive OAWRS (POAWRS) of marine mammal vocalizations and ship-radiated underwater sound, the nonuniformly-spaced subarrays improve angular resolution, bearing estimation, and provide SNR enhancement for whale call and ship-radiated sound in the beamformed spectrograms when compared to that obtained with the uniformly-spaced subapertures [1,[4][5][6].…”

“…We provide an analysis of the Office of Naval Research Five Octave Research Array (ONR-FORA) [26]. The ONR-FORA is a primary receiver array for long range ocean acoustics research of the US academic community, widely employed in field experiments for ocean acoustic propagation, scattering, remote sensing and communications studies [1][2][3][4][5][6][11][12][13]15,16]. The ONR-FORA is a linear oil-filled array consisting of four nested subapertures, each uniformly spaced, designed for beamforming signals without spatial aliasing over frequencies spanning from below 250 Hz up to 2000 Hz.…”

“…These results are compared to those of the uniformly-spaced single subaperture counterparts. The ONR-FORA has been employed as the primary receiver implementing the ocean acoustic waveguide remote sensing (OAWRS) technology [1][2][3][4][5][6][12][13][14], providing real-time or near real-time instantaneous wide-area sensing of the ocean environment in field experiments. Here, we provide illustrative examples showing enhancements in both passive and active OAWRS achieved via beamforming with the nonuniformly-spaced subarrays of the ONR-FORA over that of its uniformly-spaced individual subaperture counterparts using data acquired during the Gulf of Maine 2006 Experiment (GOME06) [1,2,[4][5][6][7][8][11][12][13]24,50,51].…”

“…Large aperture densely-sampled arrays of sensors are employed in remote sensing and communication applications [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] to enhance signal-to-noise ratio (SNR) via coherent beamforming [17][18][19][20][21][22], which reduces noise coming from directions outside the signal beam. Coherent beamforming also provides an estimate of signal bearing, required for direct spatial localization of a signal [11,12,[23][24][25].…”