MONTAUK, N.Y. — Caterers in Washington tweeted a photo of maroon sashimi appetizers served to 700 guests attending the governor’s inaugural ball last year. They were told the tuna was from Montauk. But it was an illusion. It was the dead of winter and no yellowfin had been landed in the New York town. An Associated Press investigation traced the supply chain of national distributor Sea To Table to other parts of the world, where fishermen described working under slave-like conditions with little regard for marine life. In a global seafood industry plagued by deceit, conscientious consumers will pay top dollar for what they believe is local, sustainably caught seafood.