Niaz Dorry rolls her eyes, grins and says she had forgotten how hard collecting signatures can be. She is a big, wide, powerful woman with an amiable, unfooled expression and a finger-in-the-light-socket aurora of curly brown hair. She helped organize Greenpeace's Fish Bus Tour '98, a 30-city caravan that left Seattle in July and crossed the heartland toward a September finish on Cape Cod. Middle Americans may not harvest the ocean's bounty, but they are hearty eaters of the catch.