Estes and Palmisano had inadvertently added another brick to the infamous green world hypothesis of Hairston, Smith, and Slobodkin, whose paper had sensitized—if not irritated—so many ecologists to the notion of predators having so much to do with the state of the planet. The sea otter’s kelp forests were in fact brown, but the analogy was apt. At least from a coastal Aleutian perspective, the world was brown because sea urchins don’t eat all the kelp, because sea otters eat sea urchins. The sea otter had triggered a chain reaction across two links in the food web, the most compelling example since Pisaster of what Paine himself would later famously coin as a “trophic cascade.”
Do predators matter in the web of life? They certainly did on the rocky shores of outer Washington state; and now, across a continent’s breadth of North Pacific kelp forests, there was a compelling case for an urchin-eating carnivore whose presence could flip an ecosystem like a switch.
The Science paper was soon succeeded by a string of correspondences from the Aleutians, lauding the kelp forests’ furry new patron saint of biological diversity. In 1978, Estes, along with his doctoral adviser, Norm Smith, and colleague Palmisano, emphatically reaffirmed the sea otter’s top-heavy ecological influence with a paper in the journal Ecology. In it they painted an even more compelling picture of life with otters on the Aleutian reefs. Where there were otters, there were forests of kelp, and where there was kelp, there were extraordinary gatherings of fish. There were fish feeding on kelp, hiding in kelp, chasing smaller fish in kelp. On the tails of the fish came harbor seals, in numbers conspicuously elevated beyond those in the urchin barrens of Shemya and Attu. Bald eagles, feeding largely on fish and seabirds as well the occasional baby seal and sea otter pup, were abundant at Amchitka and nearby islands, absent on Shemya and Attu. The life energy flowing from the gardens of kelp was forever tracing back to this one adorable little carnivore.
Estes’s otter had become the new textbook example of a keystone predator, eclipsing Paine’s less cuddly Pisaster. It had emerged—as Paine himself would come to praise it—as “the poster child of marine near-shore ecology.” It rang all the right bells—charming, charismatic animal hero with the tale of the comeback kid, bearing great ecological powers and a vital conservation lesson: Save the sea otter, save the forest. It was the stuff of instant legend. And it would have made for a much happier story had it ended right there.
FOUR
The Whale Killer
Novelty ordinarily emerges only for the man who, knowing with precision what he should expect, is able to recognize that something has gone wrong.
—Thomas S. Kuhn
Hatfield’s Observation
On June 10, 1993, an assistant of Jim Estes’s was training his telescope upon the coastal waters off the island of Amchitka. The sky was standard Aleutian gray, the bay water blessedly calm for the purpose of observing wildlife. Gulls cried and eagles chittered overhead. Into the viewfinder appeared the black dorsal fins of a pod of killer whales. And completing the Bering Sea diorama, a furry-faced sea otter lay floating amid the canopy of kelp.
These were good times to be a sea otter. Or one who studied them. In the twenty years since Estes and his crews had started taking measure of the Aleutian coastal ecosystem, the otter population had prospered, filling in the fur hunters’ century-old gaps to the point of overflowing. The Amchitka otters in particular had reached that mystical pivot point in ecological theory known as carrying capacity —the point of saturated abundance beyond which starvation and sickness would be expected to begin weeding the surplus. Here, thought the ecologist Estes, by then a professor at the University of California at Santa Cruz, was a rare opportunity to observe a top predator at the height of its profession, unbound from persecution, operating at the limits of its food supply.
On this afternoon, it was Brian Hatfield’s turn at the watch, glassing the goings-on of the Amchitka kelp beds. The otters were mixing work and leisure as usual, gliding through the smooth water, fastidiously grooming the plushest fur in the animal kingdom, reclining with lunch on the chest. And there in the background swam those killer whales, four black-and-white behemoths filling the scope, one with the towering dorsal fin of a grown male. It was not unusual to see killer whales in these waters. Moreover, in recent years they’d become especially commonplace to Estes and his crews, who would see them two to three times a day in their otter surveys, often up close and lolling along the edge of the kelp beds. It was a curious new wrinkle of killer whale behavior to which nobody had given much thought.
At 1400 hours, as noted in his journal, Hatfield startled to a resounding splash about two hundred yards out. He scanned to find the big male, and at the leading edge of its wake, racing for the kelp bed, a sea otter. There was something strange about the otter, even as it reached the safety of the kelp. Back and forth the otter swam in spastic disarray, its hind flippers flailing the air. Hatfield, in his thousands of hours behind the spotting scope, had never seen such behavior. He had never seen what he could only surmise was the tortured writhings of a sea otter wounded by a killer whale.
Hatfield continued watching the queerly swimming otter, but now with another eye tracking the killer whales as they cased another bed of kelp. He noted, at 1430 hours, about three hundred yards from the scene of the attack, the dorsal fin of a whale slowly cutting toward a sea otter. The otter lay until the whale was twenty feet away and then dove. As it surfaced, the killer whale was waiting.
Into the kelp the killer whale charged. The otter doubled back and dove, resurfacing behind the whale. The whale turned about; the otter dodged again. Hatfield recognized the otter’s tactic as one commonly used on him while he tried to capture them from his skiff. The otter made a final lifesaving dash for refuge in the rocky shallows, where the whale gave up the chase.
That night at the Amchitka mess hall, Hatfield relayed the events to his boss. Estes knew Hatfield as a keen and dependable observer, but this had Estes thinking twice. “I don’t know, Brian,” said Estes. “I’ve been watching these things for years. And I’ve never seen a killer whale attack them.”
Little more than a year later, another of Estes’s team came to him with a similar story. On yet another stretch of Amchitka shoreline, Tim Tinker had noticed three dorsal fins circling an otter before one of the whales lunged out of the water and came smashing down. Whale and otter disappeared; only the whale resurfaced. Still blinking over what he had just seen, Tinker followed the whales as they approached a second otter. Again the dorsal fins circled, and again a killer whale came crashing upon an otter that Tinker never saw again.
Estes didn’t know what to imagine. After two decades among the Aleutian otters, he had come to believe he could trace their food chain as easily as his way to the Amchitka mess hall. Suddenly there’s a six-ton killer whale lying broadside across his path.
It was a phenomenon weird enough to wonder about, but by that time there was a more worrisome anomaly that begged more immediate attention. There were hints that the Aleutian otters, now half a century into their celebrated recovery from the brink, might in fact be crashing once again.
Collapse
In 1994, work on the Amchitka otters was coming to a close. The grant money had expired, the navy had pulled out (taking along its logistical support), and the otter research team was preparing to trade the ghost island of Amchitka for another windy gray outpost to the east called Adak. Before leaving, they conducted one last census of Amchitka’s otters, scanning the island’s entire 120-mile perimeter, as Estes had done more than twenty years ago in his inaugural explorations. Estes had counted upward of seven thousand otters in the early seventies. Now the count came back three thousand short. Upon looking around, the decline appeared to have legs. A more extensive, Aleutian-wide aerial census conducted just two years earlier by the U.S. Fish and Wildlife Service had tallied a 50 percent drop in otters since 1965. The numbers at first surprised Estes, though not stunningly so. It was still possible, he thought, that the shor
tfalls lay within the range of experimental error, or the realm of natural fluctuations.
It was hard to imagine otherwise. By then the otter’s legend had been securely enshrined in the textbooks of ecology, thanks to Jim Estes. With the fur hunters long departed, it seemed the only question left was how many of these benevolent predators the system could hold. The idea that the Aleutians should be anything but a full house of sea otters just didn’t want to enter the mind.
The trouble followed Estes to Adak, where in Kuluk Bay two of every three sea otters disappeared in their first year under watch. Now the paltry census from Amchitka, along with the falling aerial counts across the Aleutians that Estes had initially soft-pedaled, began to strike a more serious chord. Estes had been watching these otters long enough to understand that something was fundamentally wrong. But when it came to recognizing what that something was, perhaps he’d been watching too long.
His assistant Tim Tinker was not yet so encumbered by the prejudice of experience. Tinker had just begun observing the otters of Adak in intensive spells, recording their feeding habits, tracking their movements. Every month or so, he would also note a pod of killer whales come by. And a day or so later a couple more of his tagged otters would be missing. The coincidences began to click. Tinker had also been the one watching in Amchitka a year earlier, when the two otters were body slammed and presumably swallowed in order. When in November 1995, four more of the otter team stood and watched as a killer whale dispatched an otter —this time at Adak —Tinker could no longer deny the conclusion that for Estes was still unthinkable.
Tinker phoned his boss with his killer whale theory for the missing Aleutian otters.
My god, thought Estes. He’s been up there too long.
But how else to reconcile the evidence? They had run the blood tests, measured the body fat —there were no signs of disease, contaminants, or starvation to explain the diving numbers. The otters of Adak were pumping out pups at healthy rates. Most confounding of all, there were no bodies. As a general rule, dead otters do not sink. Every winter during their years at Amchitka, Estes and the otter crews would walk the beaches, ten to fifteen miles at a stretch, crossing dozens of carcasses and skeletons washed ashore —the sort of natural attrition to be expected for a population too crowded for their own well-being. But after two years of walking the beaches of Adak, they found not a single carcass. What in hell, wondered Estes.
What finally convinced him of Tinker’s sanity was Clam Lagoon. Clam Lagoon lay adjacent to Kuluk Bay, where the otters were vanishing in droves. Yet the counts at Clam Lagoon remained uncannily steady, straightlining merrily across the charts. The pivotal difference between the two could be traced to an act of Ice Age geology. Across the mouth of Clam Lagoon lay a natural breakwater of glacial rubble, creating a shallow channel all but land-locking the lagoon. Kuluk Bay, on the other hand, was wide open to the ocean. More to the point, the shallow entrance to Clam Lagoon was a barrier to killer whales.
In retrospect, it suddenly made all the sense in the world, and none at all: the sudden appearance of killer whales skulking among the kelp beds in the early nineties; the subsequent spate of eyewitness attacks —a rash of nine in a four-year span (with more on the way) —compared with a handful of vague references and speculations from the previous two centuries; the free-falling censuses of otters; the utter absence of bodies.
But it was one thing to finger killer whales for a few hundred deaths at Adak, and another to indict them for an ocean-wide massacre. Across the Aleutians there were by now some forty thousand missing otters to account for, and maybe several hundred killer whales as potential suspects. So few killer whales could never eat so many otters … could they?
Estes turned to a fellow professor at Santa Cruz namedTerrie Williams, who, besides being his wife, was a marine mammal physiologist. Williams determined that it took somewhere between 160,000 and 240,000 calories each day to power a killer whale. She then had several dead sea otters ground to hamburger, burned in a bomb calorimeter, and measured for the heat generated. It turned out a single swallowed sea otter in the belly of whale would provide 40,000 to 60,000 calories, or about the same as a baby sea lion.
From there it was a simple exercise in math. On a hypothetically strict diet of sea otters, a killer whale would need on average four to five a day. At that rate, Williams concluded, every one of those forty thousand sea otters gone missing over the last six years could have been accounted for by the appetites of as few as 3.7 killer whales.
“Uh uh,” replied Estes. “Go back and run that again.”
Williams returned. “Three-point-seven killer whales,” she confirmed.
The blurred picture of the Aleutians had finally refocused in Estes’s mind, if now a much grayer image than the one he had thought he knew. Sea otters were disappearing en masse, kelp forests were being clear-cut by urchins. It was like stepping back to the bloody days of the promyshlennik. Only this time, the suspected demon was no swarthy seaman with a club, but a national icon, performing star of marine parks and Hollywood films, carrying stage names such as Willy and Shamu.
With due trepidation, Estes, along with Williams, Tinker, and Dan Doak, a fellow ecologist at the University of California at Santa Cruz, submitted their death-by-killer-whale hypothesis to the journal Science. And with its publication in October 1998, the sea otter once again shone in the public light, albeit this time partly obscured by the menacing, sickle-shaped shadow of a great black dorsal fin.
The Brewing Storm
The Science paper landed with a splash. Major dailies on both coasts ran headlines: ORCAS GOBBLING ALASKAN OTTERS. KILLER WHALES PUT ALASKA SEA OTTERS AT RISK. Science itself lauded the findings in its news of the week: “Experts call the study a vivid example of an ecological cascade operating on a vast scale.” Among those experts was the godfather of ecological cascades, Robert T. Paine, who said: “It’s a heroic effort, and it’s a terrific find.”
It was an unsettling find as well. If true, this cascade had spanned a sea. It had reached from open ocean to coastal kelp, from the apex of the oceanic food pyramid down to one of its most fertile foundations. Along the way, it had exposed a dark potential of the ocean’s topmost predator when tipped just a little off kilter.
But why? Why —after centuries of presumably peaceful coexistence — might the killer whales have so suddenly taken to chasing sea otters? Why would a whale-chasing, seal-swallowing killer whale switch, as one ecologist put it, “from eating steaks to eating popcorn?”
It was a question that concerned more than sea otters. It turned out the missing otters and their aberrant killers were only the latest in a succession of ecological phenomena sweeping across the northern seas since the 1970s. By the time anyone had recognized the sea otters failing, harbor seals, northern fur seals, and Steller sea lions were already a decade or two on the skids. The Steller sea lion, a buff-colored behemoth weighing as much as a ton, had by 1997 fallen so drastically as to land on the federal endangered species list.
Conservationists and the mainstream of marine biologists had come to believe that the answer was fish. Over the decades, the waters of the North Pacific had undergone cyclic swings in temperature, sending tremors through the oceanic food chain, flipping and flopping the stocks of fish that fed the masses. And shifting climate or no, there for anyone who cared to view it floated that omnipresent fleet of factory trawlers, some longer than a football field, mining fish by the megaton from the Aleutian waters. By the twenty-first century, the Alaskan fishery was accounting for more than half the total weight of the entire country’s landings, with an annual catch in groundfish worth $1.5 billion. The trawlers and fickle temperatures, acting alone or in tandem, had to many minds become the de facto culprits in the collapse of the northern seas’ fish-eating seals.
At the time, Estes had no quarrel with the fishy logic for the pinniped collapses. What mattered was that their disappearance could explain his missing otters: For want of seals, reasoned
Estes, the killer whales had taken to eating otters.
But soon the stock explanations began to unravel under a barrage of scrutiny. One of the consequences of listing the Steller sea lion as legally endangered was the legal threat of closing those fisheries suspected of endangering it. Which led to the sudden appearance of a bargeload of federal research money, which in turn spawned a welter of competing hypotheses as to whom or what to blame. Another was an order from Congress for the National Academy of Sciences to sort through those hypotheses. The academy’s blue-ribbon panel was chaired by Robert T. Paine and included eleven other ecologists, zoologists, oceanographers, and marine biologists, James Estes among them. By the time they had finished, they had unveiled a new prime suspect in the sea lion’s demise.
Paine and his committee just couldn’t explain the sea mammals’ free fall on account of poor nutrition. It was possible that toxins or plague were involved, though evidence was slim. Whatever was killing the sea lions, it was killing them quickly. “Bottom-up hypotheses invoking nutritional stress are unlikely to represent the primary threat to recovery,” the panel determined. Or in simpler terms, “The question shifts away from ‘Is it food?’ to ‘Were they food?’”
It was the sort of scenario that repeatedly brought to suspicion a more violent sort of death, as by a bullet. Or, say, a very large set of jaws.
It was no secret that despite legal protection (allowing for subsistence hunting), Steller sea lions were still being shot as a habit by Aleut islanders and hateful fisherman. As for other predators, the committee deemed the resident sharks as lacking in both sufficient abundances and seal-eating tendencies to qualify as a smoking gun. But there was a third candidate with the pedigree and the appetite to potentially supply all the firepower necessary. Killer whales were indeed common in sea lion waters, in numbers enough to at least warrant theoretical concerns. (Terrie Williams’s analysis of killer whales requiring around 200,000 calories per day had made that possibility quite plausible.) Moreover, killer whales had a deep history as sea lion gourmands. A biological survey from 1887 reported that the Steller sea lions “have a dreaded enemy in the Killer Whale, which pursues and captures them at sea and about their rocky resorts. The native hunters when at sea frequently see them leaping high out of the water in useless endeavor to escape their pursuers. At such times they say it is dangerous for an umiak or other small boat to be in the vicinity, as the animal, in its terror, will sometimes leap into and wreck the boat.”
Where the Wild Things Were Page 8