I captained out of port A every summer years ago, mostly kingfish trips off my 26 foot center console. I was usually very fortunate on getting my customers nice fish. Back then my trips were usually around 4 hours and $400. Gas was cheap and my Yamahas were great on using fuel. I think 10% is usually fine and 20% extremely generous. Today I would say $50 is nice, especially if you fish with the guide often and you book him for his slower weekdays. Being able to go with short notice is also great. Nothing like being loaded up and waiting to go and they no show 🤬

To answer your question directly, 20% is standard. A guide is a server, entertainer, educator, helper, and does all the dirty work so you can relax. If he does all of those things well, then he deserves a tip. Keep in mind that a guide was on the water 3 - 4 hours before you arrived to catch bait and get things ready for you. After you leave he has another hour of work cleaning up your mess, washing the boat, etc.