Thanks for the advice!
When you say you paid $90 for a half day, were the other guys in your party or they just chartered as well and the guides put you on the same boat?
When I go to Cabo and only have a 3-4 hr flight home we always bring the tuna, dorado, and snapper home with us. We make sure to go fishing the last day for that reason. Since it is about 9 hrs travel time to Kauai, I think I'll let them keep the fish.
Last question, where did you buy this guide you speak of?
I have fished yft in Kauaii. It's pretty cheap, but you have to realize that they keep all the fish to sell. These guides are part-guide and part market fisherman. They will give you one or two filets to keep and have sashimi back at your hotel. It's not like you'd be ready to take a bunch of fish home with you anyways when you're on vacation. If you did want to do this, they will sell you the tuna for about $1.50 per pound, depending upon the market price.
I went in February two years ago. I paid $90 to go for a half-day trip with three other guys. Two of the other guys were sick, so two of us ended up catching a half-dozen or so yft each. The fish were all about 12 to 18 pounds- small football yft. I don't remember the guide's name, but we picked him out of our "Ultimate Guide to Kauaii". You need to get this guidebook- that would be my best suggestion in general for your trip. You won't regret it. It's full of very recent recommendations from local on everything from fishing to restaurants to the best hikes and kayak trips.
One final tip- shell out the money for the helicopter ride. It is well worth it. Some of the best scenery on the planet. Have fun!