Stealthy radio controlled lobster trap?

The waters around long island ny are loaded with lobsters, To catch them the lobster trap has to sit on the bottom at least over night.Commercial lobster men use personalized floats ,witch everybody knows you damn well do not touch period.However when the lobster pirates see a non commercial float there pulling it up every time. So Im thinking of trying this but I need to know how deep a radio signal will go in salt water, if at all. I have a transmitter and servos from a model airplane. The idea is to attach a string to a tennis ball ,the string then attached to the rope from the lobster trap. make a radio controlled latch witch will release the tennis ball, bringing up the rope to the trap. No one knows its there and a grappling hook is not needed. what do you think?