Terror in Black and White - killer whales attacking sperm whales
© Natural History Magazine written by Robert L. Pitman & Susan J. Chivers
Killer whales devastate a pod of sperm whales in
the Pacific off the coast of California.
We sit silently in the galley waiting for the sun to rise on another day at
sea. Vibrations from the ship's engines cause concentric circles to jiggle
in our coffee cups, and we stare at them, mesmerized. Attention is easily
corralled at five in the morning.
Our meditations are interrupted by a phone call from the wheelhouse, with a
report that killer whales are attacking sperm whales in front of the ship.
We hesitate. The crew is sometimes merciless with its practical jokes, and
the scientists on board are easy prey. We are here to study the diving
habits of sperm whales, but we have spent a luckless two weeks off the coast
of central California on the David Starr Jordan, a research vessel of the
National Oceanographic and Atmospheric Administration (NOAA). Late
yesterday, about seventy miles off the coast, we finally sighted a group of
whales; and we are, as the crew knows, eager to relocate them. So it is not
without skepticism that we gather our coffee cups and make our way up to the
flying bridge. Moments later, we are focusing our binoculars on a group of
sperm whales rafting close together at the surface. They are surrounded by a
large slick, the kind that forms when oil from exposed blubber seeps to the
surface. Even in the dim light, we can see a large and widening circle of
blood.
As our eyes adjust to the light, we witness a sight that few who study
whales have ever seen. Nine sperm whales have gathered to form a "rosette,"
their heads pointing to the center, their bodies radiating out like the
spokes of a wheel. Sperm whales, like musk oxen, are known to "circle the
wagons" in the face of imminent danger, but whereas musk oxen always face
outward with their horns toward their attackers, sperm whales form a ring
with their tails out--the tail of a large whale being a formidable weapon.
The reason for the defensive formation quickly becomes apparent: three or
four adult killer whales are rapidly circling just outside the rosette.
From their relatively small,
backward-curving dorsal fins, we can see that the killer whales are females
(the dorsal fins of adult males are giant and triangular). At least two of
the females are accompanied by young calves, which leap alongside their
mothers like frisky pups.
A killer whale in attack mode is a strangely contradictory sight; the
consensus among us is that with its striking black-and-white pattern and
aggressive demeanor, it looks like a shark in a clown costume. But this
group of killer whales is here on business. One of the adults charges into
the rosette, arches, and broadsides a sperm whale, hitting it hard below the
waterline. The wound she inflicts must be serious, because fresh blood wells
up to the surface of the water.
Next, for no apparent reason, the killer whales abruptly dive and leave the
scene. The sperm whales, however, continue to hold their formation. Soon,
four female killer whales come charging in, this time from about a quarter
mile out. At one hundred yards, they lunge high out of the water, shoulder
to shoulder, in the synchrony of practiced pack hunters. Circling rapidly
around the rosette, they stay just beyond the reach of those dangerous
tails. One cuts in and locks her jaws onto the side of a sperm whale. We can
see flashes of white below the surface as she spins around, tail pumping,
trying to wrest a mouthful of flesh. As fresh blood again colors the
surface, two more killer whales join the attack. After a brief flurry, the
attackers again retreat and the sperm whales shore up their formation. From
our vantage point, the sperm whales appear to be holding their own. But the
air is filled with the smell of flesh and oil, and they huddle in a
gathering cloud of their own blood, which hints at the unseen damage below.
Curiously, although killer whales are believed to prey regularly upon larger
whales, only a handful of recorded observations exist. And these eyewitness
accounts are lacking in detail--probably because most of the action takes
place underwater. Consequently, almost nothing is known about how these
attacks are orchestrated, what the responses of the prey are, or even how
prevalent such encounters really are.
Although we are scheduled to move out of the area, this rare opportunity
cannot be ignored. We watch for three hours as the female killer whales and
their excited young return again and again to press their attack. The rest
of the herd, including two or three adult males, are scattered up to a mile
or so away. The strategy of the attackers seems to be to wear down their
much larger prey--to wound them, withdraw and let them bleed for a while,
and then charge again. Whenever the killer whales withdraw for a little
longer than usual, individual sperm whales briefly pull away from the
rosette, roll on their sides, or hang head-up or tail-up in the water,
perhaps looking for signs of the predators' return.
The sperm whales we are observing this morning are probably adult females,
judging by their size. Smaller than males, they are still considerably
larger than their aggressors (about thirty-three feet versus twenty-one
feet) and much heavier (approximately thirteen tons versus four tons). They
can, with a flick of that giant tail, inflict a fatal blow. Even a broken
jaw can cut short the roughly sixty-year life span of a killer whale.
After witnessing some two dozen attacks, we begin to wonder aloud why the
sperm whales don't defend themselves. Old whaling accounts are filled with
graphic descriptions of sperm whales lashing out at whalers who attacked
them, at times destroying longboats with their flailing tails or snapping
jaws, or even ramming whaling vessels with their blunt heads. Sperm whales
can also dive for over than killer whales can. And nothing in our years at
sea working with whales has prepared us for such apparent helplessness.
We also have another question: why aren't the adult male killer whales
participating? Only the adult females and their young have so far been
involved in the raids. Adult males are substantially larger, outweighing
females by as much as a ton and a half. But the only ones we have seen in
the area have stayed out of the action. What are they waiting for?
Killer whales hunt in packs like wolves, and this group may have spent
decades together honing the cooperative skills necessary to bring down large
prey. This morning they seem intent on breaking up the rosette and isolating
individuals. During one of their sorties, a sperm whale is pulled away from
the rosette and immediately set upon by four or five attackers. We can see
several black-and-white shapes beneath the water; the group is charging at
the sperm whale from both sides. Twisting their bodies and violently shaking
their heads like huge hungry sharks, the killer whales try to wrench off
mouthfuls of what must be very tough flesh. The tempo of the attack picks
up, as though the killer whales sense they are gaining the advantage. The
sperm whale cannot survive this punishment for long.
Then, to our astonishment, two sperm whales leave the rosette formation and
approach their isolated companion. One on each side, the two begin to herd
the severely injured whale hack to the rosette. For a time, the killer
whales redirect their attack to the escorts, then retreat once again. We see
this same heroic scenario several times: one or two members of the rosette
invite attack on themselves in an effort to bring one of their own back into
the formation. All who watch are shaken by these acts of apparent altruism.
Eventually the sperm whales become disoriented. They try, but fail to hold
the rosette formation. All appear to be wounded, several severely. The
number of killer whales in the area is building--we now estimate there are
forty to fifty--and the raiding parties are getting larger. Perhaps
emboldened by their success, they attack with increasing intensity. Earlier,
during the actual attacks, the killer whale calves were left swimming
outside the rosette, but now they tug on whale flesh alongside their
mothers. Could this be a training exercise? Or could the area now be safer
because the sperm whales are weaker? The mothers are solicitous of their
young calves, a behavior that starkly contrasts with the carnage of the
hunt, and we are aware of our own tangled emotions as we watch in horror and
fascination.
The battle has reached its peak. Several
sperm whales have been dragged away from the rosette and are being savagely
attacked. One of the largest rolls slowly over on its side like a sinking
ship and appears to be very near death. Then, as if on cue, a bull killer
whale rushes in. He broadsides the isolated sperm whale, pushing it
side-ways through the water. Like an angry dog, he seizes it by the flanks
and shakes it violently from side to side, then swings it around in an arc,
throwing up huge sprays of water. As he jerks his head to tear off chunks of
flesh, his turgid dorsal fin quivers with intensity. The actions of the
female killers have been demure compared with the power exhibited by this
animal.
Just as abruptly as it began, this final assault ends, and a calm sea covers
up the evidence. The bull slips away, dragging the dead sperm whale with
him. Our vessel moves slowly through the area of the kill; we pick up a
forty-pound chunk of floating blubber from the slain whale. Back at the lab,
using molecular genetic techniques, we will confirm that the victim was a
female. Sperm whales are thought to have a matriarchal social system; this
individual may have been mother, daughter, or sister to the others in her
group.
After the coup de grace and exit of the bull, the females and their young
leave the area. We see the dead sperm whale one last time when a group of
four or five killer whales bring it briefly to the surface. Towing it
backward through the water, they quickly distance themselves from the
remaining sperm whales. A giant tail, once lifted out of the water in
majestic arcs at the start of hour-long dives, now dangles awkwardly over
the heads of the victors.
A pod of whales that may have spent decades traveling the North Pacific
together has been devastated. Instead of targeting a specific individual
during the attacks, the killer whales appear to have attacked at random. As
a result, every member of the herd has been injured, and all may die from
wounds received this morning. One has been disemboweled, its intestines
draped over its back and floating alongside. Another rolls over close to our
ship; hanging from its side is a huge, yawning slab of blubber, perhaps
eight inches thick and as trig as a queen-size mattress. The attackers had
been skinning this whale alive. The killer whales killed more this morning
than they could possibly eat: hundreds of tons of flesh are left behind. We
are struck by the tremendous waste. Leaving the remaining sperm whales, we
silently watch them still trying, with little apparent success, to form a
rosette as they disappear in our wake.
A mile or so from the kill site, we rejoin the killer whales and photograph
them for an hour as they dive, presumably feeding on a carcass well below
the surface.
What we have seen is probably the most dramatic killer whale attack on a
large whale species ever witnessed by scientists. Although it has provided
new insights into the dynamics of killer whale predation, it has also left
many unanswered questions. For example, how important has killer whale
predation been in shaping the life-history characteristics of large whales?
Before witnessing this encounter, we--like others in the field--believed
that sperm whales, because of their size, cooperative herd behavior, and
deep-diving proclivities, were largely exempt from the pressures of
predation by killer whales. Also, why were these sperm whales so passive in
the face of attack, and why did they stay together and, in some cases, risk
their lives to come to the aid of others in their group? Many individuals
might have escaped harm by diving and leaving their wounded companions
behind.
Just as many questions remain about killer whales. What is the role of the
adult male in their hunting strategy? Does he wait, like the male lion,
until the females have performed the risky business of killing larger prey,
then step in and use his large size to claim the spoils? Or does he
represent the power hitter who steps up to bat when the bases are loaded?
Interestingly, scientists currently recognize two distinct types of killer
whale: A rather docile type, typically found near shore, preys mainly on
fish and tends to be relatively easy to follow and study. Another, wilder
type is usually found farther offshore, and relatively little is known about
it, except that it preys primarily on marine mammals. The forces of
political correctness and media marketing seem bent on projecting an image
of a more benign form (the Free Willy or Shamu model), and some people urge
exclusive use of the name "orca" for the species, instead of what is
perceived as the more sinister label of "killer whale." But consider, for
example, that by current estimate more than 80,000 killer whales live in the
waters off Antarctica during the summer. There they are well known for their
habit of eating just the fleshy lips and tongues of minke whales, then
leaving their victims to die. The image of the gentle giant may be ingrained
in many people's minds, but the name "killer whale" is an appropriate
reminder that this species consumes huge numbers of marine mammals annually
and that its predatory habits are a significant force in shaping marine
communities.
Both authors are employed by NOAA's National Marine Fisheries Service and
work at the Southwest Fisheries Science Center in La Jolla, California.
Robert L. Pitman, a marine ecologist, has participated in more than fifty
marine bird and mammal survey cruises in oceans throughout the world. Susan
J. Chivers, a marine biologist, specializes in cetaceans. She was chief
scientist on the cruise that witnessed the killer whale attack.
© Natural History Magazine written by Robert L. Pitman & Susan J. Chivers