I know it may not properly work like this all the time, but it seems that some cutters wanting to cross or travel the Styx might learn darks that'll allow the bashers to call a marraenaloth to them wherever they are on the river. For the sake of argument, let's assume any berk can do some kind of ritual or somesuch that'll cause a marraenaloth to answer and come promptly, no matter where you are on the river. These rituals only guarantee the arrival of an oarsman, mind you. They don't guarantee passage.
But anyway, do you have any ideas for what these rituals could entail? What sort of magic or action could merit the immediate attention of one of the mysterious ferrymen?
Throwing something into the River Styx like a small animal would be a start.