  Recording the undersea three-dimensional bioacoustic sound field in real-time
promises major benefits to marine behavior studies. We describe a novel
hydrophone array -- the hydroambiphone (HAP) -- that adapts ambisonic
spatial-audio theory to sound propagation in ocean waters to realize many of
these benefits through spatial localization and acoustic immersion. Deploying
it to monitor the humpback whales (Megaptera novaeangliae) of southeast Alaska
demonstrates that HAP recording provides a qualitatively-improved experience of
their undersea behaviors; revealing, for example, new aspects of social
coordination during bubble-net feeding. On the practical side, spatialized
hydrophone recording greatly reduces post-field analytical and computational
challenges -- such as the "cocktail party problem" of distinguishing single
sources in a complicated and crowded auditory environment -- that are common to
field recordings. On the scientific side, comparing the HAP's capabilities to
single-hydrophone and nonspatialized recordings yields new insights into the
spatial information that allows animals to thrive in complex acoustic
environments. Spatialized bioacoustics markedly improves access to the
humpbacks' undersea acoustic environment and expands our appreciation of their
rich vocal lives.
