Tipping on a chartered fishing boat on Lake Michigan in Waukegan, IL.?

We are going on a 5 hour trip on a private charter - there will be myself, my husband, the captain of the boat and he said he would bring one other person along in order for my husband and I to use more fising poles. Our charter costs $520 for the 5 hour trip. Could anyone tell me if a captain expects to be tipped? I believe we should, but I don't want to insult anyone. If so, what amount do you think would be fair...