I've seen a few ahi over 300# in my time, but not many. For the average tourist on a charter boat, a 100 pounder is challenge. A 150 pound Ahi is considered a trophy catch in Hawaii. Recently, a 40 pound ahi was a lot more than I could handle.... I can't even fathom one weighing over 400 pounds.
See pictures and story...
http://www.pointlomasportfishing.com/
