If you like salmon, I would recommend checking out the Coho (aka silver) salmon at Whole Foods. The price is decent considering fishermen in Canada and Alaska only get paid about $.25 a pound if they are lucky. Coho and pink salmon are still making runs through September in Alaska and Canada.
I should warn people that there are fish mongers who are trying to rip people off with King Salmon. Most king salmon runs are finished by late June and grow increasingly rare in July. Late runs in September are possible. I won't mention names but I have seen "king salmon" that looks terrible in some reputable fish joints. Individually quick frozen king salmon is great and available year round but you shouldn't be expected to pay a "Fresh price". King salmon is also caught in California year round on troll line but this is incredibly fresh and expensive. It rarely makes it to the East coast.
I should also point out that there is very little fish actually landed at the pier in Boston. Eastern seaboard fish is primarily landed in New Bedford (#1 landing last year), Gloucester, Point Judith, Cape May and Point Pleasant. Frankly because of all the environmental lawsuits courtesy of Pew Charitable Trust money, there is less and less seafood actually being landed in the Northeast. Perhaps this will increase the availability in the 10 - 20 years but it will result in increased imports, higher prices and less fresh fish available to the consumer.
What you will find at the pier is container loads of fish trucked or air freighted in from points afar - that can mean Canada, Europe, Latin America, Africa, etc.. Most of our farmed salmon comes from Chile in containers, sea bream from Med fish farms, tuna and swordfish from Africa, Latin America and Canada, shrimp from Latin America and Asia, etc...
I should add that this is applies for the Fulton Market and the new Hunt's Point location.
I still believe that buying at the Pier is the freshest option for Bostonians. Pigeon Cove (Whole Foods) buys fish from the wholesalers and importers and simply labels it "Pigeon Cove". It's not like Whole Foods owns fleets of boats that are plying the oceans just for their stores. That said, Whole Foods consistently has some of the best looking seafood in the Boston area. I believe that they have high turn over which means that the fish is most likely to on display for a few days.
I recently visited Wulf's and found the owners to be knowledgeable and skilled. They can tell you where they bought their fish from. They won't buy bad fish from the wholesalers. Unfortunately I don't think they move enough volume so some of the fillets were already breaking down when I visited the store.
More and more people are discovering the virtues of fresh fish. Unfortunately there is a whole lot of bad information and improper handling going on.
Look for coho salmon and enjoy while it lasts. I recommend lightly oiling a fillet with olive oil, give the flesh side a small sprinkling of pepper and placing on a hot grill for 6-7 minutes skin side down, cover on. Don't over cook because coho has up to 5% less fat than farmed salmon or king salmon.