So, short of following Greenberg's lead and going clamming in the Delaware, what's a locavore to do?
Greenberg, 46, met us at Reading Terminal Market to help us navigate the contents of its fish cases.
First up, Wan's Seafood - which Greenberg says gets points just for being a fish market, an endangered species.
The case is well-stocked with shrimp: raw and precooked, deveined and butterflied. Most of it likely comes from abroad.
It was shrimp that first inspired American Catch. After the publication of his previous book - the James Beard Award-winning Four Fish - coincided with the BP oil spill in 2010, Greenberg had proposed a book about the spill's impact on the Gulf of Mexico. But, after a dozen others beat him to publication, he reconsidered.
Still, he kept the research trips he'd booked with Gulf shrimpers. He learned they were still catching shrimp - but getting rock-bottom returns.
The Asian shrimp flooding the market has driven down the price, they complained.
That's when Greenberg recognized the scope of this strange situation - one that wouldn't be obvious to the typical Wan's shopper.
Though the FDA mandates labels stating country of origin and method of production (farm-raised or wild-caught), most placards in this case offer only the fish's name, such as "croaker" or "spot."
At least those two, Greenberg said, are local (though the spot, it turned out, had been frozen; shoppers should check for freshness, looking for moist skin, clear eyes and red gills). And, of all the offerings, the sacks of Rhode Island mussels are Greenberg's top pick: high in omega-3s, low in toxins, and a deal at $4.49.
But there are also long-distance travelers here, such as branzino and tilapia. As for the squid, it may be local, foreign, or the product of a round-trip journey (it's often processed in China and reimported).
Sea scallops are local: They're a big business in New Jersey.
Ernie Panacek, dock manager at Viking Village in Barnegat Light, said his biggest, freshest sea scallops are distributed to U.S. restaurants and markets.
But about a third of the catch landed at Viking Village is sent abroad. For example, much of his monkfish goes to South Korea. "The market drives it," he said. "There's a lot more demand internationally for U.S.-produced seafood than there is here." He said high demand has driven up international prices, encouraging still more exports.
When it comes to the smaller bay scallops, Greenberg said, about half come from abroad.
A Chinese aquaculturalist in 1982 brought about 120 of them home from Martha's Vineyard. Those that survived became the basis for a multimillion-dollar industry. Some of it is even managed by U.S. companies like Atlantic Capes Fisheries, which, in addition to growing Cape May Salts, works with Chinese scallop farms.
"China has huge food-security issues, so they give a lot of their coast over to making food," Greenberg said. "Whereas we give our coast over to wealthy people who don't want to look at oyster farmers in their viewshed."
Matt Gregg, who runs oyster farms under the brand 40 North in Barnegat Bay and Long Island, can attest to the tough climate here. It took four years to untangle the red tape and get a lease on his 10 acres in Barnegat Bay, in algae-covered, oxygen-starved waters.
"The U.S. is importing their own indigenous fish, things like bay scallops," he said. "You need to question: Why? And my answer is that government makes it really difficult for someone like myself to make a living as a producer of seafood."
The irony, Greenberg said, is that oysters could be a key to cleaning up our coastal waters: A single oyster can filter 50 gallons of water per day.
When Gregg is out diving on his farm, he can see that impact clearly.
"There's areas where I don't have any oysters and there are just dead zones. But then, as I swim up to a cage, it's full of life. It's like a living reef."
Because of that phenomenon, environmentalists are working in parallel with farmers like Gregg.
The New Jersey Department of Environmental Protection and a volunteer-run group called ReClam the Bay founded in 2005, have established an oyster reef at the mouth of the Toms River, and placed 15 million clams and oysters in Barnegat Bay. ReClam the Bay's president, Rick Bushnell, said the bivalves are slowly regenerating - though the best that can be said about the bay itself is that its water quality has stopped declining.
It's still recovering from Hurricane Sandy, which decimated farms like 40 North. Gregg finally has oysters coming to market size; he expects to sell 200,000 this year, to restaurants including the Oyster House in Philadelphia.
But while Jersey oysters may be an easy sell, back at the Reading Market, Greenberg points out something that concerns him.
He peers into the case at Johnny Yi's, where there are tilapia and basa, an Asian catfish, basa, both of them farmed and imported. Absent is Alaska pollock, America's largest catch.
It's an odd swap, he said: We send most of our pollock abroad (though some returns as foods like Filet-O-Fish), and import an equivalent amount of tilapia and basa.
"They serve the same culinary niche," he said - that is, bland and good for frying. "The difference is, one is wild and one isn't." Essentially, we're downgrading our food supply, swapping heart-healthy brain food for an inferior product.
The same trade-off is on view in the salmon case, where farmed fish may come from as far away as New Zealand.
But the case also contains Alaskan sockeye, wild-caught - and, Greenberg noted, in season right now. It doesn't come cheap, though: At Johnny Yi's, it costs $3 per pound more than the cheapest farmed filet, which is about $13 per pound. Alaskan wild king salmon is even pricier, about $20 per pound.
But Greenberg argues that investing in Alaskan-caught salmon - along with other American-produced fish and seafood - is not only a healthy choice, but also critical to turning the tide. "One of the most patriotic things you can do," he said, "is eat American-farmed oysters."
Sea Scallops alla Caprese
2 pounds mixed heirloom tomatoes
24 basil leaves
3 medium red onions, sliced 1 inch thick
Fresh-ground black pepper
5-6 tablespoons extra-virgin olive oil
12 diver scallops (2 ounces each)
Maldon salt or other coarse sea salt
1 lemon, halved
1. Preheat a gas or charcoal grill. Place a flat griddle or stone slab on grill to preheat.
2. Slice tomatoes (leave very small ones whole, or halve them) and lay them on a platter. Tear basil leaves over the tomatoes, and set aside.
3. Season onion slices on both sides with salt and pepper. Place them on the dry cooking surface and cook, unmoved, for 7 to 10 minutes, until well charred on one side. Using tongs, turn and cook for 7 to 10 minutes, until well charred and softened. Transfer to a plate, let cool slightly, separate into rings and scatter over the tomatoes. Drizzle with 3 to 4 tablespoons olive oil.
4. Slice a checkerboard pattern 1/4-inch deep into once side of each scallop. Season with salt and pepper, toss in a bowl with 2 tablespoons oil, and stir to coat.
5. Place scallops on cooking surface, cut-side down, and cook 5 to 7 minutes unmoved, until almost cooked and opaque almost all the way through. Flip over and sear for 30 seconds, then add to tomatoes. Sprinkle with sea salt and lemon and serve.
-From "Italian Grill" by Mario Batali
Per serving: 248 calories; 20 grams protein; 9 grams carbohydrates; 3 grams sugar s; 15 grams fat; 37 milligrams cholesterol; 800 milligrams sodium; 2 grams dietary fiber.
Fire-Roasted Mussels With Wheat Beer
3 pounds large fresh mussels
1 tablespoon coarsely ground smoked salt
2 tablespoons coarsely ground sea salt
1 tablespoon freshly cracked black pepper
2 tablespoons roughly chopped thyme
3 tablespoons roughly chopped rosemary
8 cloves garlic, minced
1 bottle Shock Top or other Belgian-style wheat ale
2 oranges, halved
1/4 cup cold butter cut in 1/2-inch cubes
1. Rinse mussels under cold running water. Remove the beard from each mussel using a damp paper towel or kitchen towel. Cover mussels with damp paper towels and refrigerate until ready to grill.
2. Fire up your grill to 450 to 550 degrees. Set grill topper directly onto grill, close lid and allow to heat.
3. Place mussels in a large bowl. Add smoked salt and sea salt, pepper, thyme, rosemary and garlic, then toss to coat. Drizzle mussels with about a quarter of the beer (4 ounces). Toss to coat evenly.
4. Open grill lid and carefully pour mussels onto grill topper. Close lid and roast until mussels open, about 8 to 10 minutes. About halfway through, open grill lid and squeeze 3 orange halves over mussels, and drizzle with more beer. Close lid and continue to cook until all the shells are open, a couple more minutes.
5. Remove mussels from grill, place in a large bowl, add butter and squeeze the last orange half over top. Discard any unopened shells, drizzle with a little more beer and serve immediately, with toasted baguettes and cold beer.
- From "Gastro Grilling" by Ted Reader
Per serving: 505 calories; 43 grams protein; 33 grams carbohydrates; 9 grams sugars; 20 grams fat; 126 milligrams cholesterol; 5270 milligrams sodium; 4 grams dietary fiber.
Monkfish Wrapped in Parma Ham
2 sprigs rosemary, leaves stripped and chopped
Zest of half an unwaxed lemon
2 monkfish tail filets (6 ounces each)
3 ounces parma ham, thinly sliced
1 tablespoon olive oil
Extra-virgin olive oil
1. Preheat oven to 425 degrees.
2. Scatter rosemary and lemon zest on a cutting board, then roll monkfish filets in the mixture.
3. Wrap monkfish with parma ham, letting pieces overlap.
4. Drizzle oil in a shallow roasting pan, place ham-covered fish in the pan, and roast 15 minutes, or until just cooked.
5. Remove from the oven, transfer fish to a board, and let rest for 2 to 3 minutes while you arrange a bed of radicchio leaves on a serving platter, drizzling a little extra-virgin olive oil and lemon juice over the salad. Cut the fish into chunky diagonal slices, taking care to keep the ham in place around it, place fish atop the radicchio and serve immediately.
- From "Nigellisima"
by Nigella Lawson
Per serving: 309 calories; 40 grams protein; 5 grams carbohydrates; 14 grams fat; 79 milligrams cholesterol; 605 milligrams sodium; 2 grams dietary fiber.