The evidence at the public landing at Port Clyde on the Gulf of Maine is that there are a lot of mackerel in the sea. And a hook with an eel on it will tell you the same in the East River about the striped bass, and a shiny jig about bluefish. But what about the others? The Times has invited specialists who study the matter to comment here. Among those on the good list: haddock, east coast scallops, and Alaska wild salmon - at record levels now.