Temporal-spatial, spectral, and source level distributions of fin whale vocalizations in the Norwegian Sea observed with a coherent hydrophone array

To better understand fin whale vocalization behaviour in the Norwegian and Barents Seas, a large-aperture densely sampled coherent hydrophone array was deployed in late winter 2014 to monitor their vocalizations instantaneously over wide areas via passive ocean acoustic waveguide remote sensing (POAWRS). Here, we (i) provide a time-frequency characterization for different call types observed (20Hz pulses, 130Hz upsweeps, 30-100Hz downsweep chirps, and 18-19Hz backbeats); (ii) compare their relative abundances in three different coastal regions off Alesund, Lofoten, and Northern Finnmark; (iii) estimate the temporal and spatial distributions; (iv) source level distributions; and (v) probability of detection (PoD) regions for the more abundant 20Hz pulse and 130Hz upsweep call types. The fin whale vocalizations received over the diel cycle (24h) were significantly more abundant by a factor of roughly seven off Northern Finnmark than the other two regions, associated with fish feeding activities. The source levels are estimated to be 190.5 +/- 7.4 dB for the fin whale 20Hz pulses and 170.3 +/- 5.2dB for the 130Hz upsweeps. We find that fin whales are capable of producing each vocalization type either independently or simultaneously with other types, and the 20Hz sound production in the fin whales involves a mechanism that generates a significantly less-intense second-order harmonic of the fundamental.