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A large number of marine mammal vocalizations, most likely from humpback whales, were passively recorded by a towed horizontal receiver array during the ocean acoustic waveguide remote sensing (OAWRS) Gulf of Maine 2006 Experiment. Spectral analyzes show that most of the vocalizations were random broadband signals with short time duration, typically lasting 1–2 s in the 300–600-Hz frequency range. The array invariant method [Lee and Makris, J. Acoust. Soc. Am. (2006)] is applied to localize the whales in bearing and range after conventional plane-wave beamforming and matched filtering of passively recorded vocalizations on the array. The source levels of a sequence of whale calls in a 110-min time period, belonging to a number of individuals, are estimated based on the localization results. The estimation results are consistent with previous studies. We also examine the feasibility of actively detecting and localizing whales with OAWRS at low-to-mid frequencies in a random range-dependent ocean waveguide. A full-field waveguide scattering model is applied to determine the scattered field level from whales, as a function of range and depth location of the whale, and compared to environmental reverberation measured in the Gulf of Maine. The dominant source of scattering from whales at these frequencies is their air-filled lungs.

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