Good question. When my uncle started taking my brother and I fishing on the boats as kids, the first thing he did was talk about this. He said minimum 50% to the the crew. If it's a big pot, pay off your tab, fish cleaning, and cost of ticket, the rest goes back. Now as a deckhand myself I understand why he taught us this. This is a job done because of a love for fishing, not the money, yet we still have bills to pay. Our wages are less than minimum wage, we make 80% of our money from June to August, and the days are really long. Think about how tired you are after fishing a 3/4 day trip and imagine 2-3hrs of prep and scrubbing on top of this. Many nights I've fallen asleep during dinner. But, I love my job. I've been in the middle of some incredible bites, it just hurts to watch others fishing them. From the customer side, Jp (good tips in general) does help to insure good deckhands are around, because if you can't pay your bills then you find a new job. Any person who gives Jp on our boat will usually have no galley tab or fish cleaning at the end of the day, and free trip will probably be offered. Regulars who do so get even more benefits, namely some of the previously listed stuff w/out winning JP, and also free sacks, sweet huh. Someone who gives half will be treated well especially if you're nice and listen to advice. These two things can't be stressed enough, this alone can keep a bad day from being horrible for all. Any ways, if you get JP judge for yourself what is right. But, whatever you do don't insult the crew with something like $5. If they are a bad crew (keeping in mind that crews have bad days just like you) it'd be better to give nothing and give an explanation than to give almost nothing. At the very least gaffing the JP fish is worth more than that.
Sorry for the long post,
Amish Ed