Tamarindo in the spring time (March, April, May), is known for marlin because of its proximity to the outer most edge of Costa Rica, right on the drop offs. While you can definitely catch billfish in other locations during these months, it is not uncommon for good boats to pull 8-10 billfish into the boat in a day. There is a bit more wind to contend with when fishing in this area. Tamarindo is a great place to go fishing, inshore is ok too, but if I were going fishing in Costa Rica, I would not choose Tamarindo. If I were going on a family vacation and wanted the white sand beaches Tamarindo is known for, ok then, let's get some fishing in while you're here in Costa Rica; otherwise, fish to the south.