The Art of Bullying
As violent as life in a northern fur seal colony can be, even this territorial contest between males is really all about social harmony
Yva Momatiuk and Jason Baker
A rickety wooden catwalk suspended a mere 10 feet above a rocky beach is one of the prime locations on Alaska´s St. Paul Island for scientists to study northern fur seals. So that´s where some field biologists go in summer to observe a breeding colony of the marine mammals, often evading territorial bulls with sharp teeth on the way to the ladder. Once on the catwalk, researchers are surrounded by the fur seals jam-packed around the structure. "If you fall, no one can help you," Colorado State University pathologist Terry Spraker warns newcomers to the site, which is strictly off-limits to the public. "The bulls will tear you apart."
It is mid-July, the peak of the breeding season in the Pribilof Islands, 500 miles west of the Alaska mainland. Cold, dusky fog rolls in from the Bering Sea and shrouds the rookery. Barnyard noises emanate from thousands of dark, wet humps. Occasionally the chorus of bleats, barks and roars suddenly swells, whirlpools of movement spread with explosive energy and the rookery goes on full alert.
A sleek female emerges from the sea and runs a gauntlet of menacing jaws to reunite with her bleating pup. Other pups engage in free-for-all combat, lunging to nip folds of skin or flippers. A large bull rushes into the thicket of bodies, invading the established territories of breeding males. Enraged, several of them blast through masses of cowering females, trampling inattentive pups under their giant foreflippers, to sink their canines into the interloper´s 500-pound bulk. His eyes wild, he endures punitive bites until he can scoot away, blood oozing from the lacerations. A bull grabs an escaping female one-fifth his size and throws her back into his territory: Stay put! Her torn skin exposes shredded muscle.
As all of this activity indicates, nearly all relationships among northern fur seals include aggression, fueled by the surging hormones of breeding season and made all the more potent by the size and athletic abilities of the combatants. Yet biologists studying the boistrous life of fur seal colonies have been discovering order rather than chaos, and economy of aggression rather than senseless bloodletting.
Callorhinus ursinus--which roughly means "bear with a beautiful nose"--has been studied for more than a century, by scores of researchers. German naturalist Georg Wilhelm Steller first described the seals as "sea apes" when he observed them in 1741 off the coast of what would become Alaska. Swedish naturalist Carolus Linnaeus praised their "flesh succulent and tender; fat and skin useful."
The animals´ long-sought breeding grounds in the Bering Sea were found by Russian navigator Gerasim Pribilof in 1786. The Russians soon relocated enslaved Native hunters from their homes on the Aleutian Islands chain well south of the Pribilofs to St. Paul and St. George Islands and put them to work killing the animals for their exquisite fur. After Russia sold Alaska, Pribilof residents continued the work as wards of the U.S. government.
Millions of harvested pelts, with 300,000 soft hairs per square inch, filled first Russian and then American coffers with enormous profits. Russian and U.S. government scientists who spent summer months on the Pribilofs focused on the seals´ population dynamics and life cycle to make sure the herds thrived. When the United States called a halt to its commercial seal harvest in the early 1980s, scientists were already studying many aspects of the animals´ biology, including seal-on-seal violence.
Northern fur seals spend most of the year at sea, distributed sparsely over a vast area of the Pacific Ocean. Their range includes the Bering Sea in the north, offshore waters south to California and Japan and all points between. In winter and spring, the seals have been seen traveling singly or, more rarely, in pairs. This solitary life-style changes dramatically in summer and autumn, when the animals crowd onto a few oceanic islands. Approximately 70 percent of all northern fur seals migrate to the Pribilofs, located within one of the world´s most productive marine ecosystems.
St. Paul Island, the largest in the archipelago, is home to nearly one million of the animals. The Bering Sea provides vast quantities of small schooling fishes and squid eaten by the seals. Fur seals of all ages use the island´s shoreline for everything from mating, to rearing young, to simply surviving unscathed. All of that means aggressive interactions among seals with competing interests. Yet more violence does not beget greater success. Bluffs, threats, ritualized displays and mock duels turn out to be the rule; outbursts of grievous violence are the exception.
Adult males arrive on the rookeries in late spring to establish territories before the females appear. Powerful and robust, they are clad in a thick layer of blubber that nourishes them while they protect their domain and fast during the next two months. The breeding bulls defend resources critical to the females: birth sites on prime real estate.
Breeding occurs on crowded beaches, mainly during a few weeks in July, and the success of a male fur seal is largely related to the number of times he mates. Since the opportunities are so condensed in space and time, the disparity between the "haves" and "have nots" is immense. A male that can defend several square yards of boulder-strewn beachfront at the right time of year might couple with as many as 50 females. A hundred yards away, on the periphery of the rookery, the same male could fail entirely, spurned by females that don´t like the location.
This disparity leads to intense competition. Most males fight to obtain their territories and then remain vigilant to the machinations of their neighbors and intruders. Any photographer who tries to capture the head movement of fighting seals on film finds that a shutter speed of a five-hundredth of a second is too slow: The twitch muscles of the neck make an attack seem as fast as that of a striking snake. Typically the largest and most experienced males prevail, and since larger bodies are metabolically more efficient, bigger bulls can fast longer before exhausting their fat reserves.
For the past six years, biologist Masashi Kiyota of the National Research Institute of Far Seas Fisheries in Shimizu, Japan, has studied the social structure of a small colony of northern fur seals on St. Paul. The seals occupy a rocky cove where roughly 100 pups are born each year on perhaps 10 male territories, and Kiyota has focused on how males achieve territorial status and what behavior patterns make them successful.
According to Kiyota, juvenile male seals are simply curious, trying to make contact with females and pups. Excluded from the rookeries by territorial bulls guarding their turf, these nonbreeding males congregate by the thousands in adjacent haul outs, dividing their time between sleep and play, and developing their social skills. As they mature, the young adults become more ambitious and attempt to take over territories, but in a cautious manner. Loitering on the periphery of the breeding area, they pace, snooze and watch senior males for weeks, often during several seasons, and wait for a chance to jump into the breeding arena.
And mature bulls? They seem to know that fights may cause serious, even fatal wounds, while an indignant sideways glance or threatening bellow usually stifles impudent activities at the frontier. Each male regularly performs ritualized boundary displays that entail lumbering up to the invisible edge of a property, dropping to his chest and directing a series of coughlike warnings, called chest puffs, toward the adjacent sovereign. The behemoth recipient of this blast reciprocates with an identical display. Both males may end up with their heads inches apart, but usually no contact is made.
In July, after male territories are well established, most of the females arrive. They tend to choose pupping sites located near where they were born, while the reigning males on those sites often vary from year to year. Still, even on a good site a bull can lose females, and being the meanest bull around is not necessarily the key to success. Maintaining stability is more important. "A newly established bull spends too much time and energy responding to every intruding male and every movement of his females," says Kiyota. As a result, the animal´s territory is always in an uproar, and females tend to move away. Adds Kiyota, "Many females prefer to stay in less stressful territories held by old boys."
Having secured their territories, males regularly inspect the females therein, eagerly checking wheth-er each is in estrus and therefore receptive to sexual advances. Keeping unmated females within their domain is almost as important to them as retaining a territory itself. Any movement by a female suggesting that she is trying to leave his territory provokes an immediate response from the male, which threatens, bites and shoves her back into the fold.
Mature bulls seldom manage to hold territories for more than a year or two, but territorial acquisition and maintenance is a lifelong pursuit. And it is never too early for a young fur seal to begin practicing and honing the necessary skills. Tiny black pups strike comical poses and awkwardly skirmish with one another, playing endless rounds of "king of the mountain" over a 10-inch-high cobblestone. Rarely is an animal seriously hurt in this baby play, yet the pups display the characteristic body language and fighting techniques applied with serious consequences by adults.
A mother and her single newborn pup rapidly imprint upon each other´s calls and scents. Approximately a week after the birth, the female begins a series of several-day-long foraging trips far out to sea, interspersed with brief visits to shore to deliver several quarts of rich, warm milk to her hungry pup.
Adult female fur seals, though 4 to 10 times smaller than mature males, are every bit as scrappy and can be extremely aggressive as they guard their offspring. All mothers are stingy with milk, the costliest component of producing viable youngsters. Newborns that stray too close to a strange female often find themselves bitten and flung several yards through the air. That can prove fatal if thin skulls crack against stone or tooth punctures become infected, and pups soon learn that their mother´s breast is the only safe haven in a perilous world.
How perilous can it be? One misty morning, University of California researcher Mary Donohue noticed that a lone male on the rookery´s periphery had acquired a female, obviously by stealing her. Employed mainly during the peak of breeding season, the strategy of abduction involves the kidnapper dashing into the territory of another male, seizing a female in his jaws and carrying her back to his dominion. The female is often injured but not fatally, and if the abductor is fast enough the other bull cannot retaliate without risking a chaotic fracas and losing even more females.
Yet this time, something had gone terribly wrong, and the injured female lay scarcely moving. "It was remarkable she could move at all, with the gaping breach of skin and muscle on her back," recalls Donohue. "She was split deeply from shoulder to shoulder and could barely respond to her pup."
Donohue thinks that during the assault both bulls grabbed the female, and the ensuing tug-of-war nearly tore her in two. Even after she died, her abductor continued to threaten and prod her putrefying corpse. Donohue helplessly watched the starving pup for more than a week until he finally died too, by his mother´s side. All around them, the rookery resounded with a chorus of threatening roars, rhythmic warbles and raucous bellows.
Yva Momatiuk and John Eastcott spent three summers on St. Paul Island. Their most recent book is Mustang (Rufus Publications, 1996). National Marine Fisheries Service zoologist Jason Baker studied marine mammals in Alaska and the Russian Far East for more than a decade. He now works for the conservation of endangered Hawaiian monk seals.