The Miami Sound Machine, NRL300, and NRL500 sources are confirmed
singing by dangling a hydrophone off the deck of the Knorr
during Voyage 183 (deployment).
A Rutgers Glider towing a URI hydrophone confirms sources are still singing midway through the experiment. (Aug19) Sound file doesn't help too much since sources are in the noise
but spectrogram (pdf file) clearly shows them.