Seafood sustainability is becoming a major issue in the Restaurant World, with subtle and not-so-subtle agitation on the part of the dining public in favor of more responsible seafood choices among chefs, some of whom think it's morally OK to drain the vitality of the oceans for their own picayune culinary glorification. At the forefront of the sustainability seafood movement has been Harbour, a new restaurant west of Soho on Hudson Street, which ransacks the sustainable fisheries up and down the East Coast, and goes to the Mediterranean for certain farmed species. No Thai-grown shrimp or bluefin tuna here. The result is a pleasing menu with smaller quantities of fish featured in pleasing balance with fruits, vegetables, and herbs, in entirely scrumptious compositions.