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Multiple mechanized ocean vessels, including both surface ships and submerged vehicles, can be simultaneously monitored over instantaneous continental-shelf scale regions >10,000 km 2 via passive ocean acoustic waveguide remote sensing. A large-aperture densely-sampled coherent hydrophone array system is employed in the Norwegian Sea in Spring 2014 to provide directional sensing in 360 degree horizontal azimuth and to significantly enhance the signal-to-noise ratio (SNR) of ship-radiated underwater sound, which improves ship detection ranges by roughly two orders of magnitude over that of a single hydrophone. Here, 30 mechanized ocean vessels spanning ranges from nearby to over 150 km from the coherent hydrophone array, are detected, localized and classified. The vessels are comprised of 20 identified commercial ships and 10 unidentified vehicles present in 8 h/day of Passive Ocean Acoustic Waveguide Remote Sensing (POAWRS) observation for two days. The underwater sounds from each of these ocean vessels received by the coherent hydrophone array are dominated by narrowband signals that are either constant frequency tonals or have frequencies that waver or oscillate slightly in time. The estimated bearing-time trajectory of a sequence of detections obtained from coherent beamforming are employed to determine the horizontal location of each vessel using the Moving Array Triangulation (MAT) technique. For commercial ships present in the region, the estimated horizontal positions obtained from passive acoustic sensing are verified by Global Positioning System (GPS) measurements of the ship locations found in a historical Automatic Identification System (AIS) database. We provide time-frequency characterizations of the underwater sounds radiated from the commercial ships and the unidentified vessels. The time-frequency features along with the bearing-time trajectory of the detected signals are applied to simultaneously track and distinguish these vessels. 

The wide‐area group behaviour of spawning Atlantic cod and herring is investigated. By a combination of Ocean Acoustic Waveguide Remote Sensing (OAWRS) and conventional sensing methods, first‐look images of the instantaneous population density are obtained of entire Atlantic cod spawning groups, stretching for tens of kilometres in the Nordic Seas. This structural information made it possible to quantify the spawning group size distribution of cod over a roughly 30‐year period from conventional line‐transect data acquired annually by vertical echo sounding in the Nordic Seas. The size distribution is found to be consistent with the log‐normal probability density often found in growth processes that depend on many independent parameters. Nordic Seas cod populations are found to distribute into many vast behavioural groups during spawning with relatively stable mean size despite larger variations in total annual population. When sustained at pre‐industrial levels, the total spawning population is found to greatly exceed the mean spawning group size. As an apparent consequence of this large differential, when the total population, or overall scale, declined to within a standard deviation of this mean cod spawning group quantum, or inner‐group‐behavioural scale, return to pre‐industrial levels required decades. Findings for Atlantic herring are similar, where summing the spawning group populations measured in a single instantaneous OAWRS image per day over the 8‐day peak spawning period enabled accurate enumeration of the entire Georges Bank herring spawning population to within 7% of the independent NOAA estimate for 2006. These results may be relevant to other oceanic fish.