In 1955, "the first of the great herring fisheries collapsed off the East Anglia coast of England. This herring population had sustained a highly productive fishery for over a thousand years, but it could not survive the onslaught of twentieth-century industrial fishing. In 1966, the total herring catch from the North Sea reached 1.2 million tonnes. Through the late 1960s and early 1970s, herring stock crashed one after another across Europe, and by 1975, North Sea catches came to just 200,000 tonnes. Soon after the final collapse came, it was estimated that fisheries extracted over 70 percent of the herring from the North Sea every year, a take that even the most resilient species cannot withstand for long. In 1977, a moratorium was called on herring fishing in the North Sea and extended to western waters of Europe in 1978."

-- The Unnatural History of the Sea

The New York Times Magazine has published an exceptional piece on bluefin tuna, and the significance of its dwindling stocks:

...bluefin tuna and all species of tuna are the living representation of the very limits of the ocean. Their global decline is a warning that we just might destroy our last wild food.

In prehistoric times, the hunting of fish began close by, in freshwater rivers and lakes and coastal ocean waters. But as human populations grew, easily accessed grounds fell short of demand. By the late Middle Ages, European stocks of freshwater fish and near-shore ocean species proved insufficient. By then, Basque and Viking fisherman had already moved on to the continental shelves off Canada, ushering in the Age of Cod -- an age that escalated until the late 20th century, when some of the largest fishing vessels ever built devastated the once-two-billion-strong stock of cod on the Canadian Grand Banks. But there were still new places to fish. In the 1980s and '90s, virgin fishing grounds were found in the Southern Hemisphere, and supplies of replacement fish like New Zealand hoki and Chilean sea bass helped seafood supplies keep pace with demand.

But appetites continued to outstrip supply. Global seafood consumption has increased consistently to the point where we now remove more wild fish and shellfish from the oceans every year than the weight of the human population of China. This latest surge has taken us past the Age of Cod and landed us squarely in the Age of Tuna. Fishing has expanded over the continental shelves into the international no-man's territory known as the high seas -- the ocean territory that begins outside of national "exclusive economic zones," or E.E.Z.'s, usually 200 nautical miles out from a country's coast, and continues until it hits the E.E.Z. of another country. The high seas are owned by no one and governed by largely feeble multinational agreements. According to the Sea Around Us project of the University of British Columbia's Fisheries Center, catches from the high seas have risen by 700 percent in the last half-century, and much of that increase is tuna. Moreover, because tuna cross so many boundaries, even when tuna do leave the high seas and tarry in any one nation's territorial waters (as Atlantic bluefin usually do), they remain under the foggy international jurisdiction of poorly enforced tuna treaties.

The essentially ownerless nature of tuna has led to the last great wild-fish gold rush the world may ever see.

The idea of the ocean as a place of limitless bounty persists even now. That is folly, as evidenced by a long list of over-fished species -- cod, herring, and now tuna are but three examples -- whose populations have collapsed in locales all over the world. It ought to be the defining environmental issue of our time.

It is not.