I have had a hydrophone on the researchboat many times and you can hear all kinds of things. We have heard harbor porpoise a number of times. Absolutely you could hear whales. Their sounds are outside of the human audible frequencies but they are also inside of those frequencies, 20 Hz to 20 kHz, as well.
Can you tow one at 6kts?
Iím in touch with one manufacturer who claims you can, but I was wondering if the water turbulence would make too much noise
Besides being neat to hear them, maybe knowing they are around would be of some value, keep better watch