With 150 dead zones in our oceans, some the size of Ireland, author Taras Grescoe argues that there's been a massive die out of sea life.

In pictures, on CSI Miami, and to the naked eye the sea looks the same today as it ever did: blue, green or blue-green, rolling in glassy crashing curls, tormented then serene. It will look this way tomorrow, next year, arguably for eternity. No matter what freaks us out on earth, our species takes great comfort in knowing that the sea always looks exactly the same.

From up here.

But not down there. Not underneath. Under the swells and the sparkles and the froth, fathoms down, the globe's oceans have transformed over the last several decades, transforming even as we sit here into wastelands, ghost worlds, desolate deathscapes that could be filmed in situ for sci-fi films about the post-apocalypse. You won't find this out from a day at the beach. The smiling sea captain depicted on the fish-sticks box is keeping mum. But Canadian food journalist Taras Grescoe tells all in his important new book, Bottomfeeder (Bloomsbury, 2008).

"Rather quickly, the oceans are becoming environments unlike any we have ever known," Grescoe agonizes, giving as his first example the North Atlantic, where he watches Nova Scotian fishermen exulting over a new lobster boom while apparently neither knowing nor caring about its probable cause: human greed.

Yes, climate change plays a part but it's marginal compared to the massive overfishing required to supply restaurants and stores in a world that stuffs itself on tuna sandwiches, salmon steaks, shrimp cocktail and sashimi.

"The shallow waters off Nova Scotia used to be full of swordfish and bluefin tuna, as well as untold numbers of hake, halibut, and haddock. Cod in particular were the apex predators in these parts," Grescoe writes. (Later in the book, he quotes early observers describing "cod mountains" off a once-rich Newfoundland coast where the fifteenth-century navigator John Cabot reported cod populations so thick that they actually blocked his ships' passage.) Cod, Grescoe writes, once "prowled the gullies offshore in dense shoals, using their powerful mouths to suck up free-swimming larvae, sea urchins, and even full-grown crustaceans. But the cod were fished to collapse in the early 1990s. With the cod gone, stocks of lobsters and other low-in-the-food-chain species exploded." By wiping out predator species, the fishing industry screws up ecosystems. As sea creatures high on the food chain disappear, their populations more than decimated in the last half-century, a lobster boom "may just be a tiny blip on a slippery slope to oceans filled with jellyfish, bacteria, and slime."

Meanwhile, overfishing has created some 150 "dead zones" -- oxygen-free patches of ocean that can sustain no life -- around the world: Some of these patches, Grescoe tells us forebodingly, "are now as large as Ireland." In search of seafloor-dwelling species such as the trendy monkfish -- long ignored, then popularized singlehandedly by Julia Child in 1979 -- bottom-trawls weighing more than 26,000 pounds each rake and flatten wildlife-rich undersea peaks, leaving a paved-looking flatness in their wake. Oh, and a large percentage of coral reefs worldwide are dying or already dead. Oh, and those bluefin tuna and halibut steaks you like? Say it with me: Mercury. Those jumbo fried shrimp battened on pesticides and antibiotics in bacteria-riddled Chinese farms, their decomposing flesh treated with borax? How's your health insurance?

It is happening right this minute but not quite right before our eyes. This is exactly the sort of thing our species prefers not to think about. What kind of catastrophe is it? Take your pick. Ecological. Medical.

And ethical: Grescoe started this project as a diner, "a fish lover, but ... no fish hugger" who has caught and eaten seafood eagerly all his life. But knowing as he does "that ours might be among the last generations in history able to enjoy the down-to-earth luxury of freshly caught wild fish," his fantasies of sampling Japanese pufferfish and Chinese "drunken shrimp" slam hard against reality:

"I draw the line," he resolves, "where the pursuit or cultivation of my dinner obviously damages the environment, where cruelty is involved, where pollution or adulterants make it unsafe to eat. I would get no pleasure from eating a nearly extinct songbird, wine made from tiger bones, or the last few grams of beluga caviar from the Caspian. For me, a pleasure that diminishes the experience of everybody else on earth is no pleasure at all."

Fair enough. So in this spirit of sad apprehension he set out around the world to report on the state of some of humanity's most celebrated seafoods and the communities surrounding their consumption: from Chesapeake Bay oysters to Japanese sushi to English fish and chips and beyond. Part detective, part adventurer, part whistleblower, he reveals underhanded practices, such as Japan's "scientific" whale fishing, and outright crime, such as tons of cod harvested illegally, exceeding official quotas, during their spawning season by Russian ships that offload their catch to other ships at sea in order to evade detection. (Greenpeace calls this "pirate fishing.") The results end up in myriad English "chippies," doused with salt and vinegar.

And we learn about "finning," the practice of slicing off just-caught sharks' pectoral and dorsal fins -- destined for soup -- with hot metal blades. "Kicked back into the ocean, alive and bleeding," it can take the sharks days to die. Nearly forty million are killed this way annually. Seventeen countries, including the US and Canada, now ban finning, but China and the EU are among the world's remaining avid finners; Grescoe identifies Spain as the most avid of all. Although shark hunting is technically forbidden in Galpagos National Park, a vast marine reserve, some 300,000 sharks are caught there every year. Until the 1960s, whitetip sharks were "the most abundant large animals on earth," Grescoe writes. "Forty years later they have all but disappeared from the Gulf of Mexico," where they once thrived. "Up the length of the Atlantic coast, the story is the same: since 1972, bull, dusky, smooth, and hammerhead shark populations have all been fished to one percent of their former levels." Who cares? Well, it's all about the ecosystems. Sharks eat skates and rays. Sans sharks, skyrocketing skate and ray populations are eating scallops and clams into extinction.

This book is a veritable eulogy. For ecosystems. For the toxic, dead water. For sea creatures. And for many of our fellow human beings, although honestly it's hard to care much at this point about anyone who would eat sharkfins or whale: "Every year, twenty thousand tons of heavy metals and eight hundred tons of cyanide end up in Chinese waters," Grescoe reveals. Unsurprisingly, two years ago cancer has been the leading cause of death in China. Massive quantities of cheap seafood from pesticide-suffused Chinese fish farms is exported worldwide; only a fraction is tested or inspected. Much is infected with salmonella and listeria. Most has lived its life in water thick with fecal bacteria, human and animal: "The fish, in other words, were bathing in shit."

It's also a eulogy for lifestyles, for old-fashioned fisherfolk in those seafaring communities that spent centuries supporting themselves by catching, processing, selling and eating species in the wild: scallops in North Carolina, oysters in Chesapeake, hake in Namibia, shrimp in Tamil Nadu, India. On one hand, you could say, Hey, they did it to themselves: got too greedy, maintained certain tactics that became unsustainable. On the other hand, you could say it's sad -- that these communities fell victim to intrusive large-scale foreign operations, as fishing has gone from local to global: As an example, Grescoe visited a huge Nova Scotia processing plant that used to handle cod from Canadian waters but now gets its cod from Russia, its salmon from Chile, its catfish from Vietnam. The factory outsources labor-intensive tasks, such as skewering salmon, to China. The finished product is labeled "Product of Canada."

You could say too that the residents of these communities are relatively powerless over such government-controlled decisions as the 1.5 billion gallons of urban sewage that pour into Chesapeake Bay every day. Grescoe sympathizes with the Tamil Nadu fisherfolk who, put out of business by industrial shrimp farms, tell him: "Our village is going to die." But an encounter with a Yorkshireman who blusters angrily after being arrested for catching more than his legal share -- and who blames declining salmon and cod populations on "horrible, sliming, stinking, eye-watering bloody seals" -- leaves Grescoe cold:

"This kind of attitude lies at the heart of the problems facing the oceans," he seethes. "It is the ongoing plunder of the seas, done in the name of keeping a boat afloat for another season, and multiplied a hundred thousand times in all the ports of the world .... If this were still the age of inexhaustible cod mountains and endless salmon rivers, such a display of spirit might be admirable. It is the essence of the indomitable, short-sighted, buck-passing Atlantic fisherman: an independent, almost lordly working-class hero, romanticized to death in our culture. As long as there is a single jellyfish left in the ocean, he will be ready to go out and catch it." And jellyfish, down at the foot of the food chain, will be the last edible species out there in a not-too-distant future when our great-grandchildren, Grescoe half-jokes, will eat "peanut butter and jellyfish sandwiches" and "jellyfish and chips."

He agrees with the scientists and activists who now advocate a "slow-fish" movement. It would entail banning destructive fishing methods such as bottom-trawling; "revalorizing" earlier techniques such as hook-and-line; protecting overfished species; and drastically reducing aquaculture -- that is, fish farming -- as well as government subsidies to fishing fleets. And while Grescoe doesn't suggest never eating any seafood again, he now chooses his intelligently: avoiding the farmed, the faraway, the overfished, and those large, long-lived, high-on-the-food-chain species such as halibut, tuna, shark and swordfish whose meat is infused with mercury and other chemicals known to cause eventual nerve damage. Instead, he suggests sardines, sea urchins and squid: In other words: Become a Bottomfeeder -- at least until, and if, the seas stop dying.

Anneli Rufus is the author of several books, including "Party of One: The Loners' Manifesto."