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In 1741, the German naturalist Georg Steller wrote of the fur seals and sea lions on Bering Island, "If I were asked to say how many I have seen . . . I can say without lying that it is impossible to make any computation. They are innumerable." Today, the sea lion named after Steller is listed as endangered in the Aleutians, its numbers down 70 percent worldwide since 1960--from roughly 300,000 animals to 85,000, according to the Seal Conservation Society. The reason? Quite likely, overfishing of a staple food source: pollock. Two other species that Steller was the first to describe, the spectacled cormorant and Steller sea cow, are extinct, hunted into oblivion for their meat.

Threatened species, threatened environments. Every week, it seems, more dire news appears about the state of the oceans. Coral reefs are sliming away, turning into dead zones. Inland bays such as the Chesapeake are being drowned in sediment and excess nutrients. Hawksbill turtles struggle at the edge of extinction. Fisheries are collapsing.

And yet many people think all this is, if not normal, then perhaps inevitable. Not the way it's always been, to be sure, but absent any catastrophic changes--such as volcanic eruptions or tsunamis bring--these slow, chronic, hard-to-notice slides become part of reality as we know it.

This phenomenon of acceptance has a name: it's called the shifting baselines syndrome, and it is beginning to drive some new thinking in marine conservation.

The term was coined by Daniel Pauly, a Canadian fisheries scientist who happens also to be an outspoken critic of modern fishing practices. In a 1995 paper in Trends in Ecology and Evolution, Pauly charged that young biologists fail to address the collapse of once-abundant fishing stocks because anecdotes of immense past catches have little meaning for them. "Each generation," wrote Pauly, "accepts as a baseline the stock size and species composition that occurred at the beginning of their careers." The result is an ever-shrinking sense of possibility, which leads to ineffectiveness, and to continued overexploitation--or, as Pauly puts it, a continued "fishing down the food web" that eventually will leave people with a diet of "jellyfish and plankton soup."

In 2001 in an article in Science, Jeremy Jackson, a marine ecologist at Scripps Institution of Oceanography, and 18 co-authors presented a worldwide examination of shifting baselines, exploring the idea that "humans have been disturbing marine ecosystems since they first learned how to fish." Kelp forests, coral reefs, tropical and subtropical seagrass beds, and estuarine oyster beds are all scrutinized, and the short- and long-term effects of overfishing examined. Those effects, the scientists conclude, "are synergistic, so that the whole response is much greater than the sum of individual disturbances." And there is a time lag, typically, between the onset of fishing and a noticeable collapse in stocks or environmental health.

Complexity and, especially, time: these are masks that hide change from view. Baselines, reference points for measuring the health of ecosystems, shift without our noticing. That means that many ecological models, which supposedly relate to "natural" conditions, were almost certainly programmed from erroneous starting points, starting points much closer to present-day conditions than to conditions that held even 100 years ago, much less before Europeans came along with their fancy boats and fishing nets.

Jackson, who has spent over three decades exploring Caribbean coastal waters, says that "every ecosystem I've studied is unrecognizably different from when I started." And that's in only 30-odd years. The turtlegrass beds he first encountered as a young researcher, for instance, flowing meadows of foot-high, emerald-green grass, looked healthy enough from a distance. But one thing missing from the scene was turtles--as many as 40 million of them, Jackson estimates, based on colonial hunting records. "Even the smallest estimate for green turtles" in the 17th and 18th centuries, he notes, "exceeds the highest recorded wildebeest abundances in the Serengeti." And all these turtles chomped away, cropping the turtlegrass to a height of only a few inches. This action kept the grass healthy and the organisms that depend on it thriving.

By the 19th century, however, green turtles had been largely eliminated from the Americas, hunted to excess for food. Today, in the absence of these natural lawn mowers, the turtlegrass grows long and the tops become rotten and covered by encrusting organisms. One of these is a slime mold that, in the 1980s, caused a vast die-off of turtlegrass beds in Florida Bay and the Gulf of Mexico.

Other, similar scenarios have played out in oceans worldwide. The consequences are potentially huge, yet relatively little scientific study of historic processes has been done. "We are," observes Jackson, "more aware of the mass extinction of large vertebrates at the end of the Pleistocene than what happened in coastal seas only a century ago."
Can we bring back millions of sea turtles? No. Can we do anything? Of course.

Part of the answer involves understanding just how far our baselines have shifted--and ceasing, or seriously modifying, destructive practices before we find ourselves eating plankton soup. To continue to believe that wild coastal fisheries are sustainable, for example, is foolhardy, both Jackson and Pauly believe. Rather than perpetuating that myth, Jackson writes, "scientific efforts should be redirected toward evaluating options for restoration of resources. . . . It is hard to imagine how increasingly sophisticated and frequent environmental monitoring and micromanagement could do a fraction of the good of simply stopping fishing."

Stopping fishing is far from simple, though. And taking a single action, in any case, is never sufficient. In addition to overfishing, impacts on the health of ocean waters include pollution, coastal development, and global warming. The web of influences is complex, and remedies must be similarly multifaceted.

The shifting baselines concept feeds into this complexity, giving concerned parties--scientists, conservationists, policymakers, or citizens--new hope (a new baseline, if you will) for what can be done. By understanding what once existed, we can plan better for what might again be possible.

I spoke with Jeremy Jackson by phone recently, and will let his words round out this overview.

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