In the 1990s, a riddle began to play out off the southwest coast of Alaska. Sea otters, which had rebounded from the fur trade so successfully that in places they may have equalled their historical abundance, suddenly began to disappear. Over the next ten years, the otter population plummeted by 90 percent.
To explain the vanishing otters, researchers eventually found themselves looking at a completely different era and completely different species. Whaling in the North Pacific from the mid-1800s onward gradually reduced stocks of the great whales—humpback, blue, right, grey and the wondrous bowhead, which can live two hundred years or more. After World War II, industrial whaling hit even harder, drawing down the still-abundant fin, sei and sperm whales. On average worldwide, whalers killed the equivalent of one hundred whales every day of the last half of the twentieth century.
In the 1970s, after the U.S. had banned all whaling in its waters, harbour seals began a steep and inexplicable decline. Then fur seals. Through the 1980s, sea lion rookeries collapsed. At last, in the 1990s, the sea otters began their own downward spiral. The culprit, several scientists finally proposed, was the killer whale. The name is not as apt as it sounds: not all killer whales kill whales, but some specialize in doing so. Whaling left them an ocean almost empty of whales, and, in the same way that people do, they soon began eating their way down the food chain. By the time they focused on otters, they were dealing with snack foods—it would take more than 1,800 otters a year to keep a single killer whale properly fed. At that rate, just four dedicated killer whales could have crashed the otter population.
The otters were not the end of the cascade. As they disappeared, another chain reaction started. Otters are predators too, and among their favourite foods are sea urchins, those bottom-dwelling creatures, usually in shades of green, purple and red, that look like balls of knitting needles. Urchins, in turn, are plant-eaters with a special fondness for the long, banner-like seaweeds that are the “trees” in the underwater kelp forests along North Pacific shores. Remove otters from the food chain, and the booming population of urchins soon grazes the kelp down to stubble. Even that is not the end of it. Change a kelp forest into an urchin barrens and you alter everything from the diets of bald eagles to the growth rates of barnacles to the height of the waves that strike the shore.
As with most mysteries, the case of the missing otters seemed simple enough once it had been solved. In reality, it took more than a decade to put the puzzle pieces together, and the solution remains contentious and hypothetical—one zoologist describes the science of ecological cascades as “the discovery of pattern and order against a backdrop of noise.” It is the realm of the counterintuitive. For example, common sense might tell us that if you eliminate large predators, then the animals they usually eat will increase. Yet in the West African nation of Ghana, the opposite took place when the killing of lions, leopards, hyenas and wild dogs unexpectedly caused olive baboons to switch from being mainly gentle vegetarians to being intelligent, organized and voracious meat-eaters, devastating prey animals. Who would imagine that the introduction of deer to a landscape might also end up wiping out black bears? On Anticosti Island, Quebec, exactly that occurred: the deer population exploded and browsed the island’s berry bushes so severely that the bears starved to death.
How much of the world around us has been transformed to these extremes? I put the question to James Estes, a University of Santa Cruz ecologist and pioneer of cascade theory. It was Estes who, with marine biologist John Palmisano, first sorted out how a kelp forest could turn into an urchin barrens. But even the kelp forests themselves, Estes said, might have been the end results of even earlier human impacts. Centuries before the sea otter became the gold standard of the maritime fur trade, a huge but almost totally forgotten animal, the Steller’s sea cow, was moving through the kelp in herds. Sea cows were related to the dugongs and manatees that today are found only in tropical waters—placid and bewhiskered, they resembled walruses without the tusks. Sea cows had once been widespread on both the Asian and North American coasts of the North Pacific, but disappeared from most of their range in prehistory, probably at the hands of human hunters. By 1741, when the species was first recorded in scientific literature, Steller’s sea cows could be found only around the isolated Commander Islands of the Russian Far East. Twenty-seven years later, they’d been hunted to extinction. What a kelp forest might look like with hungry sea cows browsing through—the way herds of African elephants browse through savannah woodlands today—can only be imagined.
Big herbivores like the sea cow and elephant, and big predators like lions and sharks, rank among species that have endured the most severe declines since the emergence of modern human beings. Based on what he has learned about contemporary cascades, Estes estimates that human actions over time have altered the natural evolution of ecosystems on more than 90 percent of the globe. The cascading impacts of those losses over the millennia were probably gradual and essentially invisible, and today are mostly unknown and possibly unknowable. When Estes travels in wild places today, such as Yellowstone National Park, which is typically seen as a fragment of near-original American wilderness, he says that he no longer thinks to himself, This must be the way things used to be. Instead, he finds himself thinking, I’ll bet this is a hell of a lot different from the way it was.
“So we’re really talking about a different world,” I say to him.
“A very different world,” Estes replies. “A very different world.”
There is at least one more horizon of transformation to explore—a more personal horizon, if it’s possible to say such things about non-human life.
We will need to revisit the elephants, this time in apartheid-era South Africa. In the early 1980s, the elephant population was swelling in Kruger National Park, and wildlife managers decided to dart numbers of adult elephants from the air and then shoot them to death on the ground. The killing often took place in plain view of juvenile elephants, which were then rounded up and sent to other parks and preserves, with about forty ending up a few hundred kilometres to the southwest in Pilanesberg National Park. It must have seemed like a logical if gruesome act of conservation: reduce overpopulation in one place and spread the wealth of the species to others.
More than a decade later, field biologists in Pilanesberg noted what they termed a “novel situation” emerging. Elephants were, for the first time in history, killing white rhinoceroses, which had been bred back from the brink of extinction. Between 1992 and 1998, elephants were suspected in the deaths of forty-nine rhinos—a massacre. The culprits turned out to be the orphaned young males from Kruger. The obvious conclusion to leap to would be that the elephants’ berserk behaviour was rooted in the trauma they’d endured as calves. Ultimately, however, the investigation turned to a question of the animals’ culture.
As they approach maturity, male elephants enter a rutting condition known as musth, during which testosterone floods their systems so fiercely that even their posture is changed. The adolescent males in Pilanesberg were entering musth too young and staying in it too long; one suspected rhino killer was finally culled after remaining in musth for as many as five months, a length of time that would be unusual even for a male twice its age. Under more natural circumstances—that is, in an elephant herd not comprised of transplanted orphans—the adolescent musth periods are cut short by apparently withering encounters with larger, older males. After standing down to a dominant bull, the rush of hormones in the younger male stops, in some cases in a matter of minutes. As a test, six older male elephants were introduced to Pilanesberg, and the killing of rhinoceroses stopped. The outbreak of elephantine violence was blamed on a lack of elders.
Africa’s “behemoths”—the name given to the continent’s huge, old elephants—were mostly wiped out decades ago. Elephant tusks grow throughout their lifetimes, and the largest tusks ever recorded, with a combined weight of two hundred kilograms of ivory, were cut from a bull that was shot on the slopes of Mou
nt Kilimanjaro in the 1890s. In fact, evidence that human hunters target older animals as a general rule—they tend to be less alert and less dangerous than animals in their prime—stretches back at least to the Middle Stone Age. The trend continues: harvesting by human beings is the leading cause of adult mortality for a long and growing list of species.
We’ve brought an end to old age as a normal part of life in the natural world, and the effect could be so great that Anne Innis Dagg, one of the few zoologists to have written on the subject of elderly animals, argues that it may no longer be possible to know whether or not we are looking at “natural behaviour” when we observe the social order of animals. Elephants are one of the few species in which the importance of aging is slowly being acknowledged. During a 1993 drought in Tanzania, the elephant clans led by the oldest females suffered far fewer deaths than those with younger matriarchs—the herds needed leaders old enough to remember the distant waterholes that their own elders had led them to during droughts in the past. To maintain a mental map of those life-saving pools requires the continuous presence through the centuries not only of adult elephants, but elderly ones—severe drought strikes Tanzania only every five decades or so, and elephants’ maximum lifespan is about sixty-five years.
Such impacts may not be limited only to big-brained, long-lived species. In the early 1990s, the fisheries scientist George Rose headed for the Grand Banks of Newfoundland to attempt to record, for the first time, the migration routes of cod in the northwest Atlantic. The knowledge was suddenly urgent: the fishery, long a symbol of the baroque abundance of which nature is capable, appeared to be failing. Rose predicted the likely migratory path based on water temperatures and sea bottom topography, and echo sounders proved his forecast was largely correct. The fish were there. But he also made an observation he had not expected.
As with the elephants, the last “behemoth” cod disappeared long ago; an Atlantic cod over ninety kilograms hasn’t been caught since the 1890s. Still, it was the largest, oldest fish that seized Rose’s attention on the echo sounder readouts. He could see them distinctly, individual black smudges at the head of every school. “Scouts,” his team called them. In most of the schools, there were only a few such leaders left. Rose came ashore with many questions. What signposts did these scout cod follow through the vast, undifferentiated space of the sea? How did they determine where and when the schools would spawn? Was he really watching fish that had the wisdom and memory of years, that were keepers of knowledge passed down through generations?
Answers would not be forthcoming. In 1992, after centuries of overfishing, the cod stocks collapsed. You could still find cod on the Grand Banks, says Rose, but they were little things, few of them more than five years old. The elders were gone. And for the first time in five hundred years of written history, the ancient cod migration failed to take place.
* Vegetarianism was in fashion in 1620s Netherlands, and one Snyders scholar has argued that this may have influenced the artist’s sympathetic portrayal of fish, which he often shows twisted in death throes or staring with accusing eyes.
* One theory for why some whales strand themselves is to avoid drowning. They are air-breathing mammals, and when sick, wounded or near death from old age, may beach themselves rather than die inhaling water.
* Porpoise was once a much-loved meat, to the extent that a writer in the Transcripts of the American Fisheries Society in 1885, having eaten broiled meat from a porpoise caught off Cape Hatteras, wondered why it had been forgotten. “The golden age of gastronomy was long ago, and in that time kings and other great persons looked upon porpoise as a delicacy of delicacies,” writes the correspondent.
* Small woolly mammoths still existed on Wrangel Island when the Egyptians were building their first pyramids, disappearing only about 4,000 years ago.
Chapter 8.
WHAT NATURE LOOKS LIKE
One of the most memorable scenes in the novel Moby-Dick takes place along what sailors once called the Line—the Equator—in the Pacific Ocean. There, late at night among unnamed islands, the crew of the Pequod kills a sperm whale and lashes it to the ship’s side to wait until morning to cut up the carcass. In most places, this is a reasonable practice. Scavenging sharks will come—so many, in fact, that the sea will seem as “one huge cheese, and those sharks the maggots in it,” as Herman Melville writes—but these can be driven away with whaling spades, which look like sharpened, flattened shovels on the ends of long wooden poles. On the faraway islands of the Line, however, “incalculable hosts” of sharks appear, beyond anything the whalers have ever known, their frenzy so wild that a shark disembowelled with a whaling spade might eat its own entrails, only to have them pass back out the hole that they spilled from in the first place. Even the dignified chief harpooner of the Pequod—the character Queequeg, who shaves with his harpoon, is covered in “unearthly tatooings,” and is descended from the cannibalistic royalty of the imaginary island of Kokovoko—is rattled by the maelstrom. Lowered by lantern light to hack at the monsters from the ship’s cutting platform, he finally climbs back on deck only to nearly lose a hand to a shark that has been hoisted aboard as dead. “Queequeg no care what god made him shark, wedder Fejee god or Nantucket god,” he says, “but de god wat made shark must be one dam Ingin.”
To those who know today’s oceans, the scene seems to say more about Melville’s writerly imagination than the true life of a sailor. Sharks are an uncommon sight on most of the world’s coral reefs, which are scattered like pearls from the Red Sea in the Mideast, through the Indian and South Pacific Oceans, and onward to the coasts of Central America, the Gulf of Mexico and the Caribbean. Taken together, the oceans’ reefs cover an area only as large as Italy, or about half the size of Manitoba. Three quarters of them can be found within fifty kilometres of human settlements, where sharks infesting the water like maggots would be sure to attract some attention.
For most of history since Melville’s day, the world largely forgot about the distant reefs visited by nineteenth-century whaling crews. Ten years ago, marine biologists in search of the world’s most pristine reefs began exploring what are today known as the Line Islands, a raft of remote South Pacific atolls mainly under the flag of Kiribati, along with three that are U.S. possessions. The most isolated of these islands, Kingman, is as near to being an ocean wilderness as there is today. To begin with, the atoll’s thin strips of treeless beach, barely above the tide line, are uninhabitable, while its reef-protected harbour has never seen any heavier use than as a way station for Pan American World Airway’s “flying boats” in the 1930s. Today, Kingman and its waters are a U.S. national wildlife refuge.
Enric Sala, now an explorer-in-residence with the National Geographic Society, was on one of the expeditions that revisited the Line Islands. The scientists knew the most remote atolls were different even as they approached them by boat, he says, because the air was full of the sight and sound of seabirds. “You go to inhabited islands in the tropics and the birds are gone, because people ate the birds or the eggs, or rats ate the chicks,” says Sala. The team dove at more and more remote reefs, and were excited to be seeing sharks on every dive, so the first person to roll off the boat when they reached Kingman was the expedition photographer, hoping to shoot images of the reef in its most undisturbed condition. Instead, he quickly hauled himself back out of the water. “We can’t dive here!” he shouted. “There are too many sharks, and they’re too curious!”
In the end, they did dive at Kingman Reef. Everyone jumped in together, scattering the sharks, then waited for them to return, check out the divers, and finally move on to their ordinary routines. Only then could the scientists begin their work of surveying the reef’s species. This time, the photographer would return to the boat with images that in some cases captured thirty sharks in a single frame. They had found sharks as they were known from the South Pacific of history, from Moby-Dick and seamen’s logbooks recalling “sharks innumerable, and so voracious that they bit ou
r oars and rudder,” lagoons “infested with sharks,” where one sailor was bitten on the heel in three feet of water and barely made it to shore as “a shoal of ravenous monsters” rushed toward the scent of his blood. One of the Kingman dive team later described his experience at the reef as a transfiguration into “a born-again biologist”—his eyes finally opened to what a natural reef really looks like.
“I don’t think I would swim at a pristine coral reef,” says Sala. “Underwater with our black wetsuits, now, that’s different. But if you’re swimming, like chop, chop, chop, and they see all your white belly—I wouldn’t do that. It’s a different world. A landscape of fear.”
The last, best hope to understand nature without the human imprint is in the sea. The hazards and technological difficulties involved in reaching the points most distant from land or farthest below the surface made the open ocean the last place on earth to be affected by our actions. We have no written record of the continents ahead of human settlement, but history is filled with accounts of briny waters that had rarely if ever before seen men. It’s remarkable, then, that these reports describe a world beyond our current understanding.
In 2002, fisheries scientists at the University of British Columbia in Vancouver attempted to develop a computer model of past states of nature in Hecate Strait, a body of water off Canada’s west coast that is famous for winter swells that roll in at heights of ten to twenty metres even without a storm blowing. The researchers divided the strait’s known sea life, from whales to plankton, into fifty-one categories, and followed the data for each one back through time. In more than 80 percent of cases, those sea creatures were more abundant in 1750—earlier than any confirmed contact between the local native population and European or Asian explorers—than they are today. In fact, more than 40 percent of the categories were at least twice as plentiful in the past.
The Once and Future World Page 11