No sound from a machine can come close to 235dB naval sonar pulses. Cetaceans voices can reach 180dB, 40dB more than a jet taking off. A machine may be annoying to cetaceans but it isn't going to kill them. Silt and tailing plumes made by mining aren't going to come close to the silt dumped into the ocean by rivers or disturbed by submarine landslides.
I say forge ahead and make corrections as we learn more.
The ocean was always a desert, right? No animals ever known to live there, even before we set about industrial scale mining in the name of ecology, so no harm done.
I say forge ahead and make corrections as we learn more.