It happens because of the vibrations of the motor. It makes them think they are in danger from the sound waves and they try and jump out of the water.
I heard this last week while flipping through channels
sadly this is old news those fish kill of most life in rivers breed and move fast.
you would think we could figure out the right sound wave to heard them fish into nets, if its the sound waves from the prop that makes them jump out
of water. heck one could start a circus with those ugly monsters.