they cost me nothing as they are paid off.
Not true. You could sell them if you wanted to. The money from that sale could be used for other purposes--investments, leisure, home, etc. Foregoing those other purposes is the cost of owning the boat. From an accounting/cost determination standpoint, the boat is an investment, and the cost of that investment needs to be accounted for in the cost of the product (fish)--both the depreciation cost of the boat (depreciation), and the lost potential revenue from the investments you could make if that money wasn't tied up in the boat. If/when you donate it, the remaining value of the boat can be treated as a charitable contribution, as that donation has actual value.
Again, I fully agree with you that you're taking the right approach on it, and that the memories are priceless. But when assessing the actual cost of the fish, it's necessary to get more clinical in the evaluation.
OK, that said--can you ship me some fresh dolphin? The stuff in the stores here in Minnesota is plenty old, and, simply put, is crap. When I lived in Miami, the fresh stuff I had after a day on the Atlantic was to die for. If it's at all a realistic possibility (yes I am serious), e-mail me at biggbill at hotmail dot com, and let me know what it would cost you.