Face off: the great white shark vs the killer whale

Our oceans are full of predators, ranging from tiny carnivorous fish to poisonous snakes; from poisonous snakes to electrocuting eels; from electrocuting eels to murderous dolphins. In short, predators are everywhere and none are more feared than the great white shark and the killer whale. Both of these animals are titans – huge animals that can hunt and kill almost anything they want to (and yes, humans are included). But which of these is the top predator? Which of them would best the other in a fight?

The great white shark, Carcharodon carcharias, is one of the most feared animals in the oceans. The sharks often hunt by taking advantage of their huge strength, ambushing the seals they hunt from underneath while they rest on the surface. Unfortunately, surfers resting on their boards can look very similar to seals from underwater, which is believed to be the main cause of great white shark attacks on humans.

I’m sure many of you are thinking that this would be the great white. And why not? Great whites have been known to kill humans and there is a huge ‘fear culture’ around sharks after Peter Benchley’s Jaws was televised in a film. You would be wrong, however, and there is a case that to show that it is in fact orcas that rule the oceans.

In the first instance, you have to remember that orcas are social and hunt in packs (which has actually earned them the nickname of ‘the wolves of the sea’). Obviously, this provides killer whales with a huge advantage over the solitary great white and orcas can bring down prey much larger than themselves. In fact, orcas have even been known to go after small female sperm whales (which are actually the largest predator alive), so picking off a lone great white shouldn't be too much of a problem for them!

Like humans and other primates, killer whales are extremely social and live most of their lives in tight-knit social groups of close family members. To prevent the inbreeding that this would inevitably lead to, male orcas usually leave their maternal pod once they sexually mature and actively seek another pod to live with for the rest of their adult lives.

Secondly, you have to consider the intelligence of killer whales, which are part of the same family of oceanic dolphins (Delphinidae). All of the members in this family are extremely resourceful and have been seen to use complex, highly sophisticated tactics while hunting their prey. In fact, killer whales have actually been observed practicing to hunt (click here for more information) and it is one such tactic that leaves little doubt that orcas are hierarchically above great whites.

As you may or may not already be aware, orcas have different cultures (in much the same way as humans do) and different pods in various locations around the world specialise in hunting certain animals. Common examples of their sources of prey include fish and water mammals, such as seals. But it is the pods that specialise in hunting sharks that are really relevant for this post. Such orcas have realised and taken advantage of two very simple aspects of shark anatomy:

• Firstly, most species of shark go into a hypnotic state of sleep called tonic immobility when they are turned upside down
• Secondly, sharks have to keep swimming in order to breathe and, as soon as they stop moving, water ceases flowing through their gills and they begin to suffocate

Since great white sharks have to keep swimming in order to breathe, they have developed a remarkable method of sleep where they rest each half of their brain separately. This allows the neurotransmitters in their brain to recover to normal levels after waking activity, while simultaneously allowing the shark to keep moving and remain alert for prey and danger.

By taking advantage of these two simple facts, orcas can kill sharks extremely easily and with very little risk of injury to themselves (i.e. the sharks can’t fight back). To do this, orcas take advantage of their extreme agility and ambush sharks from above. As they near the unassuming shark, they bite it just above their dorsal fin and use their strength and body weight to roll the shark upside down, meaning that it falls asleep and stops struggling. Then, it’s just a simple case of the killer whale holding its breath while it waits for the shark to suffocate and die!

This tactic is merciless and brutal, but it is extremely effective and scientists have actually seen killer whales using it on great whites off the coast of California! What is also interesting, other than orcas being able to kill great whites so easily that is, is that great whites (like many species of shark) release chemicals called ‘death signals’ into the water when they are killed. These signals drive off all other great whites for miles and, for many years, scientists were baffled by why the massive predator suddenly vanished from Californian waters. It was only when they realised that the exodus of great whites coincided with the seasonal arrival of a certain pod of orcas from Antarctica that they put two and two together and began to observe how the two predators interacted. Just imagine their surprise!

Hunting in the depths

The sperm whale, Physeter macrocephalus (previously Physeter catodon), is a fearsome hunter and frequently dives to depths as deep as 3km in search of its main source of food - giant squid. Even though 3km doesn't sound like much, it is so deep that we struggle to build submarines that can withstand the extreme pressures even now; making the whales an amazing feat of evolutionary engineering, being one of the few animals that can survive the radical pressure change between the oceans' surface and its depths. Sperms whales can live for more than 70 years and males, which are more than 40% more massive than females, can grow to over 20 metres in length, weighing up to 57, 000kg. They have the largest brain of any animal and are also the largest living toothed species, although only males actually possess teeth, which can weigh up to a kilogram each.

A male sperm whale breaking up out of the ocean. Note its slender lower jaw, which increases the pressure of its bite (making it more powerful) and the thin, conical teeth that fit into alcoves in the whale's upper jaw - helping to trap anything that it bites in its mouth.

Sperm whales are named due to the large and well developed spermaceti organ that forms most of their head, which at times, can make up a third of an individual's total body length. This gives the whales a distinct body shape, making it difficult to confuse them with another species. Unfortunately, this made them easy targets for whalers in the Industrial Revolution, where they were killed for the whale oil that was harvested from the organ itself and from their blubber. Sadly, their population fell dramatically and, as a result, sperm whales are now protected and the species is classified as 'vulnerable' by the ICUN. Even though the organ has largely brought about the downfall the species, it is critical for their survival. This is fairly obvious really, when you think about the organ's large size compared to the whale's body and the energy that it must take in order to produce and maintain it.

A sperm whale, with its box-like spermaceti organ clearly visible. The whale also has a very powerful, muscular body and thick, triangular flukes that allows it to dive to such extreme depths.

The oldest known function of the spermaceti organ is as a buoyancy aid. At the surface, whales reduce the blood flow to the organ by contracting the diameter all of the blood vessels it contains, in a process known as vasoconstriction. This causes the temperature of the organ to fall and the spermaceti wax solidifies, increasing in density. As the organ is in the whales head, it sinks and pulls the whale downwards head-first; thereby, helping it dive and stay submerged. When the whale wants to rise to the surface, usually to breathe (sperm whales can stay submerged for about 90 minutes at a time), the converse it true and the blood vessels dilate (expand), causing the wax to melt and decrease in density. Thus, the whale is pulled upwards head-first, which allows it to ascend more quickly. This could be potentially life-saving for a whale - imagine running out of breath 3km underwater...

Sperm whales live in small social groups, rather unimaginatively called units, which consist of multiple related females, one unrelated male and calves (both male and female - males leave the group once they sexually mature). In this photo, the unit is sleeping, which is identifiable since the whales always sleep in this vertical position; kept afloat by their spermaceti organs.

However, buoyancy aid is only a secondary function of the spermaceti organ, with it being primarily involved in echolocation. Water is an excellent absorber of light, so that 3km down it is completely dark - no sunlight penetrates to such depths. Interestingly, even if light did reach such depths, sperm whales would be unable to see as they shut their eyes very tightly to protect them against the pressure and cannot open them. Therefore sperm whales are completely blind at these depths, which isn't ideal for a predator. Echolocation, also seen in bats, is an ingenuous adaptation that allows the whales to form an image of their surroundings by generating a series of clicks using the phonic lips at the front of their nose. These clicks then pass into Junk Bodies in the spermaceti organ and are forced out into the water through the Junk's lens-like structure. The whales can then process these clicks as they are reflected back, bouncing off the objects in the water. This allows them to form a 'mental image' of their surroundings, which may be part of the reason why they have such large brains - forming the images requires a large amount of neural processing.

The spermaceti organ also has a third and much more sinister function. The broad-beam clicks that it uses to generate an image of its surroundings can be focused into a much narrower, more intense beam. This beam is used for hunting and is 'fired' at potential prey targets once they have been located. It is so intense that it stuns and completely disorientates its prey, allowing the whale to get close enough to bite it, which normally means game over for the unlucky animal. Further to this, the depths of the ocean are filled with bioluminescent phytoplankton and cyanobacteria, which light up when stressed. Thus, when they are hit by the narrow beam they light up and the sudden surge of flashing light can disorientate the giant squid, which can see at such depths, even more.

A photograph taken by a deep-water submersible that shows a male sperm whale attacking its prey, a giant squid. Giant squid are a formidable killer in their own right, possessing thousands of suckers that each contain razor sharp chitin rings and a great quantity of scars can be seen on the whale, as a result from past encounters.

As said previously, one of the most amazing abilities of sperm whales is their ability to dive down from the relatively low pressure of the surface, to the abyssal depths that are under enormous pressure. So, as you would expect, they have many physiological adaptations that allow them to do this. The main ones are that their entire body, including all of their viscera (internal organs) are designed to be crushed, yet continue to function. Their rib cage is highly flexible and can fold almost flat; their lungs secrete a unique pulmonary surfactant that contains detergents to stop their delicate alveoli sticking together; and their heart virtually stops beating during the dive, which is accomplished by a massive drop in their metabolism. The fact that their metabolism and heart rate slows down so dramatically allows them to hold their breath for much longer than they could have otherwise. However, this still wouldn't allow them to hold their breath for a dive of 90 minutes so, to increase this time, they have an enormous quantity of blood, which therefore, can hold an enormous quantity of oxygen. Sperm whales also have extensive reserves of a pigment in their muscles called myoglobin, which acts as an emergency store of oxygen. Thus, sperm whales are able to dive at great depths for an extended period of time.

Despite still being rare, the population of sperm whales is beginning to rise and it is faring much better than other endangered species of whale. Mainly because its hunting is now banned in almost every country, meaning that commercial whaling of sperm whales has ceased, it has no natural predators and giant squid are not fished by humans, so its food source is not declining. Therefore, it is likely that this truly amazing animal has survived industrial whaling and will grace our oceans for many years to come.