|Biologists have a different problem to solve when it comes to re-populating
endangered sea lions because the threat does not come from a degradation of their
environment as is the case with most endangered species.
Why Sea Lions Are Endangered
The biggest cause of sea lion mortality occurs because the infants are killed while
young. The largest threat to sea lion pups comes from those within their own group.
Sea lion bulls may inadvertently sit on and squash baby sea lions.
While female sea lions bask on the beach with their babies, younger males sneak up
and take the baby sea lions. They use them to practice herding and harem keeping,
and sometimes kill them. Steller's sea lion cows can be fierce toward pups other than
their own; they bite, shake, and toss "alien" pups that come too near.
And Australian sea lion bulls attack pups with concentrated, lethal fury, biting and
shaking them as a terrier shakes a rat, and leaving them mangled on the beach. In
this species, about 20 percent of pup mortality is due to attacks by adult males.
The Hooker's is the rarest and probably the most mild-mannered of all sea lions
(seal scientists refer to them fondly as "the gentle Hookers"). Most breed in the
Auckland Islands, 300 miles south of New Zealand. Biologists observed them for
several months on Enderby, the northernmost island of this group where, during the
austral summer, about 600 sea lions mass on the broad, half-mile-long breeding
The males arrive in early November and after some violent fights, the strongest bulls
divide the beach among themselves. For nearly a month they all are males-inwaiting,
each jealously guarding his empty circle of sand. The females come to the beach in
early December, settle upon the territories of the waiting bulls, and a few days
later give birth to pups that were conceived the previous year.
Shortly after the birthing season, with many females about to reenter estrus, the
bulls are most excitable and the just-born pups most vulnerable. Biologists watched
bulls and found that they were not actively hostile to pups and never attacked them.
They completely ignored them; for all they cared, the pups might have been lumps of
sand upon the beach. In their jealousy-prodded charges, however, the bulls simply
trampled any pups that got in their way. While the females did their best to shield
the youngsters, they were rarely fast enough or strong enough to deflect a charging
The sand is soft, and the pups are amazingly resilient; most survived being
steamrollered by the great bulls. The greatest danger to pups was not a passing bull,
but one that halted abruptly right on top of the pup. It would sit there, a massive
hulk, totally oblivious of the tiny creature squirming beneath it.
Most females tried frantically but ineffectually to free their pinned pups: if a small
flipper protruded from beneath the bull, they pulled it, usually without success. They
never bite the bulls, but some experts watched a female use a shrewd stratagem to
free her pup. She moved provocatively in front of the bull and presented herself for
mounting. The bull moved instantly to the female, who repelled him, nuzzled her
freed pup, and led it to safety.
Three percent of all pups born on Enderby Island are accidentally crushed to death
by rampaging bulls. The pups are quick and precocious, however. Within three or four
days of birth they know the danger of a big bull and quickly scramble out of the way
when one comes barging along. Within ten days, the surviving youngsters leave the
dangerous regions of the beach and gather in safer areas.
Female pinnipeds (sea lions, seals, and walruses) usually nurse only their own pups and
repel all others. The placid Hooker's sea lion cows generally adhere to this rule, but
with certain exceptions. When females go to sea to feed, for instance, their pups,
hungry after a day or two, shuffle off in search of milk.
Typically, a hungry pup sidles up to another suckling pup to drink quietly from a
sleeping mother's teat. When the female awakes, she growls at the intruder, the
pup backs off, the cow goes back to sleep, and the pup resumes its interrupted meal.
Cows snarl and snap but do not hurt the milk moocher; the youngster's risk is minimal
and the reward worth it.
Immature Hooker's sea lion bulls are a nuisance to the pups, but they do not attack
them. These three to five-year-old males are the restless ruffians of the beach,
constantly play-fighting with one another. Sometimes they try to mount adult cows,
are noisily repelled, and have to flee from charging territorial males--thereby
endangering any pups in their path. Young males may also use pups as female
substitutes: they herd them, try to form and keep pup "harems," and occasionally
attempt to mate with squirming, protesting pups. But they are not brutal, and when
pups are really fed up, they quickly escape.
Southern sea lion pups are less fortunate. During a four-year study conducted at
Peninsula Valde’ s in Argentina, by Claudio Campagna, of the University of California,
and his colleagues, immature male sea lions seized pups on 285 occasions. Some were
individual kidnappings, while other incidents were raids carried out by several subadult
males acting together.
While adult male and female southern sea lions do not injure pups, the subadult males
appear to use pups as female substitutes to redirect their frustrated sexual and
aggressive motivations," according to Campagna. During the study, 5.6 percent of the
abducted pups and 1.3 percent of the pups born each year died from injuries caused
by subadult males.
Among Steller's, or northern, sea lions, the female is a threat to pups. Biologists
studied the behavior of this species during two seasons in the early 1980s on Marmot
Island, off Kodiak Island in Alaska.
The largest of all sea lions, adult males grow up to twelve feet in length and weigh
more than 2,000 pounds, and adult females can be nine feet long and weigh nearly
800 pounds. Sadly, the Steller's sea lion populations have drastically declined in
Alaska. In 1961, the total Steller's sea lion population was thought to be between
240,000 and 300,000. Thirty years later, in 1991, only an estimated 40,000 were
left. Lack of food fish due to overfishing by humans seems to be a major reason for
this rapid decline.
During field studies at Marmot Island a decade ago, more than 10,000 sea lions
crowded the seven rookeries and each season about 5,000 pups were born. Now many
beaches are empty; fewer than 3,000 sea lions were counted during recent summer
breeding seasons there.
At Marmot Island the bulls arrive in May and after many fights divide the beaches
among themselves, top territories going to "beachmasters"--eightto tenyear-old
males in their prime. Their choice of sites seems to accurately anticipate where the
females will cluster. The females arrive about two weeks later, and also claim spaces
according to their places in the social hierarchy, with the most sought-after spots
going to the older cows.
A few days after their arrival at the rookeries, the females bear pups that face a
rough initiation into the world. The moment a pup is born, its mother raises it a few
feet above the beach and drops it onto the rocks--the sea lion version of a slap on
the bottom. She repeats this behavior (one scientist observed a female picking up and
dropping her newborn pup fiftytwo times in a row) until the pup is crying and crawling.
Then the female sniffs her pup and listens intently to its voice; from this moment on
she can pick out her baby from all others on the beach. The hardy, forty-pound pups
easily survive this rough handling, but some face another danger. At times, the
previous year's pups overwhelm the mother with their importunate nuzzling and crying
for attention. Distracted, she may fail to bond properly with the newborn, and might
even attack it as if it were a stranger. In some cases, where 150-pound yearlings
monopolized a mother's attentions, the newborn pup died in a day or two.
The main danger to Steller's sea lion pups, however, is not from their mothers, which
are intensely maternal and protective, but from other, unrelated cows. Most females
are fiercely hostile to all pups that are not their own. During its first week of life, a
pup does not recognize its mother's voice and may crawl hopefully toward any calling
cow on the crowded beach--a move that can be fatal. If a female, upon sniffing the
pup, decides it is not hers, she snarls and tosses it yards away.
Landing in the private space of another cow, the pup may be grabbed and flung again,
then thrown back and forth by hostile females, like a screaming, flippered rag doll.
Most survive this brutal treatment and learn to recognize their mother's voice, for
there is no milk-mooching in this species.
Even more dangerous for a pup than a run-in with the wrong mother is an encounter
with a female that has lost her own youngster. On Marmot Island, biologists watched
several cows seeking and calling for their lost offspring. Such a female rushes
eagerly toward any pup that responds and sniffs it hopefully. If it turns out to be
the "wrong" pup, the frustrated female bites and flings the pup, rushes after it and
bites it again, and may maul it until it is dead.
In size and appearance, Hooker's sea lion, of subantarctic and New Zealand waters,
and the neighboring Australian sea lion are similar. In temperament, however, they
are totally different. Hooker's are placid and pacific, while Australian sea lions are
excitable and belligerent. Australian sea lions differ in another, vital way from other
pinnipeds. Most pinniped species have a twelve-month reproductive cycle, during which
adults return to their ancestral breeding grounds at a specific time of the year.
Females give birth shortly after arrival and mate again a few days later. Within
weeks, adults and young leave the rookery sites and return to the sea to follow their
Only the Australian sea lion has an asynchronous, eighteen-month breeding cycle.
Females can come to breeding beaches and give birth at any time of the year. In a
recent paper, Australian scientists Nicholas J. Gales, Peter D. Shaughnessy, and
Terry R. Dennis speculate that the Australian sea lion's irregular reproductive cycle
is an adaptation to an equitable climate and a depauperate sea. By staggering births,
the lactating females' demands on the local seas' limited food resources is spread
over the entire year.
Among other sea lions, top bulls have harems, while each high-ranking Australian male
usually keeps only one female. If a subordinate male approaches, the guardian bull
quickly chases him away and then, huffing and snorting, returns to his post near the
female. When an equal sized male encroaches on the female, a violent, often bloody
fight ensues. The huge males face each other, hacking and parrying. Often one may
grab a thick fold of skin on the neck or flank of his adversary, jerk and heave and--
like a sumo wrestler--try to lift the opponent off the ground.
Fights last until the lighter, weaker animal turns and flees. Wrestling and
intimidation among mature males is normal sea lion behavior. But biologists are
puzzled by what seem to be aberrant attacks by bulls upon pups. Australian sea lion
females, unlike females of other sea lion species, will bite bulls that come
dangerously close to their pups. As biologists has observed, however, this defense is
usually ineffectual. Some females may even attempt to defend pups that are not
their own from rampaging bulls.
Australian sea lion pups have come to fear all adults, except their mothers, and flee
at their approach. Before a female goes to sea to feed, usually ten days to two
weeks after parturition, she hides her pup in a niche or crevice or beneath piled
boulders where a bull cannot reach it. Biologists observed in 1975, this strategy
favors meek pups that obediently remain concealed, while the curious, venturesome
pup that comes out and explores is most likely to be caught and killed by a bull. It is
difficult to visualize the adaptive advantage of a social system which causes high pup
mortality from adult aggression and which would appear to favor timid and
nonexploratory behavior in pups.
Before the season at Seal Bay on Kangaroo Island off southern Australia, there were
scattered reports about such attacks, but nothing in the dry, detached scientific
literature had prepared me for the malefic ferocity of a bull intent on killing a pup.
Here is one sequence of behavior was witnessed during the austral summer of 1992-
A female about to give birth had come from the sea and picked a spot near the cliff
that rose at the back of the beach. Another female, now at sea, had hidden her
three-week-old pup among the boulders at the base of this cliff. Within a few hours
of her arrival, a top bull had found the pregnant female, guarded her with possessive
vigilance, and fended off the attentions of several encroaching males. Three days
later, a young male tentatively crossed into the exclusive sphere of the resident bull,
only to be attacked. For a moment the rivals faced each other, then the young bull
turned and fled. The huge bull, seething with unspent fighting spirit, his mouth wide
open and vibrissae abristle, waddled back to his post.
At this moment, the long-hidden pup emerged from its refuge among the boulders.
Probably hungry, it may have mistaken the pregnant female for its mother. When the
bull saw the movement, he immediately lunged forward and grabbed the pup before it
could flee. The pregnant female attacked and bit the bull, but to no avail. He shook
the pup, flung it ten feet, rushed after it, grabbed it, and shook and tossed it again.
Each movement of the desperate youngster incited the bull to new attacks, until the
pup lay dead.
Eventually, the beach's resident Rosenberg's goanna, a five-foot-long monitor lizard
that patrolled the area for carrion, fed on the carcass. Leslie V. Higgins, of the
University of California, who studied Australian sea lions at Seal Bay, recorded eight
attacks by bulls on pups, four of which were fatal, and felt that "misdirected
aggression" by bored bulls is the most likely explanation for the behavior.
Harem bulls of other sea lion species defend extensive territories, fight frequently
with rival males, and mate often. In contrast, the Australian sea lion male has a
much smaller territory to defend, and it is occupied by only a single female. Days
may pass without a fight, until anything that moves--and that is usually a pup--
becomes a target and victim of the bull's pent-up aggression.
Other attacks on pups followed a similar pattern but not all resulted in death.
Biologists observed one large male that came upon an older pup playing in a shallow
rock pool. He pounced on it and bit it, but as he tried to get a firmer hold, the pup
twisted free and escaped.
Interestingly, the "ferocious" Australian sea lion males kill about 3 percent of the
pups born in their rookeries--the same percentage destroyed by the "gentle"
Hooker's bulls, with their proclivity for accidental tramplings.
Corwin, J. 100 Heartbeats: The Race to Save Earth's Most Endangered Species.
Steams, P. Stellar Sea Lions (Eye to Eye With Endangered Species). 2011.