There are locations where big marlin roam in unforgiving sea conditions, such as Cape Verde, Ghana, Australia’s Great Barrier Reef, Madeira and Brazil. And there are hot spots where vast numbers of billfish can be found, but you’re forced deal with winds that rarely lie down and seas that are less than cordial during the prime months of the season. St. Thomas, Puerto Rico, the Dominican Republic and Isla Mujeres, Mexico, come to mind. But you don’t have to leave the continental United States to find plenty of rough-water fishing either. The canyons off the mid-Atlantic, Oregon Inlet, North Carolina, the winter sailfish run in Florida and the distant offshore fishing in the Gulf of Mexico all offer plenty of days when you’d better take off the flip-flops, put on your dancing shoes and keep a firm grip on something solid.