Killer+Whale

//Extinct animal: Basilosaurous// //Modern animal: Killer Whales// //Future animal: Speckled Whale//

The killer whale, also known as orca or //orcinus orca//, is a large marine mammal in the order of cetacean. It is part of the suborder of toothed whales (odonteceti) and the family of Delphinidae, along with other dolphin species found in the open seas. However it is the only species belonging to the orcinus genus which remains extant. Killer whales are the largest dolphin and one of the most powerful predators in the world.

It is also important to note that different types of killer whales have evolved, which may then be categorized into different subspecies or even species. One of the ways they have been separated is into the categories of resident, transient and offshore killer whales. Each, though similar in overall appearance and behaviour, generally live in different areas, eat a different diet and stick to their own kind. This is the reason for the wide range of habitats and prey this large marine mammal dominates.

Classification :
 * ** Kingdom ** || Animalia ||
 * ** Phylum ** || Chordata ||
 * ** Class ** || Mammalia ||
 * ** Order ** || Cetacea ||
 * ** Suborder ** || Odontoceti ||
 * ** Family ** || Delphinidae ||
 * ** Genus ** || Orcinus ||
 * ** Species ** || O. orca ||

**Habitat**

Killer whales are the world’s most widely distributed mammals, after humans (fig. 1). Though they are usually found around the colder, coastal regions, they are adapted to a wide range of oceans, from the freezing oceans to the warmer tropical waters. Occasionally, killer whales have been seen swimming into freshwater rivers, sighted in the Colombia River (United States), Fraser River (Canada) and Horikawa River (Japan). Sightings indicate that killer whales can be found in almost all water temperatures, and that though they are difficult to compare due to their wide range, killer whales prefer areas of higher latitudes and coastal areas over pelagic environments.

Killer whale populations can be found along the Alaskan coast, in the waterways of British Columbia and Washington, off the coast of Baja California, near Newfoundland and Labrador to Iceland, Norway, and the British Isles, off the coasts of Argentina, South Africa, New Zealand and Galapagos Islands. Although it is true that killer whales are spread widely across the world, the largest population remains in the Antarctic waters, with about 25 000 living in the Antarctic out of a total of about 50 000, ranging up to the very edge of the pack ice, and can even venture into the denser pack ice.

Killer whales prey on a large range of fish, birds, marine animals and even the occasional swimming terrestrial mammal. This includes herring, penguins, cormorants, gulls, seals (fig 2), sea lions, fur seals, walruses, sea otters, deer, moose, great white shark, and even whales (minke whales, grey whales, sperm whales and blue whales). However, as killing larger prey may take several hours, killer whales prefer to eat smaller, weaker animals. Its diverse diet is in fact specialized depending on individual populations. For example, resident killer whales mainly eat fish and squid, transient killer whales eat mainly marine mammals while offshore killer whales primarily eat schooling fish, but also eat ma mmals and sharks. Since killer whales eat about 227 kilograms of food each day, their presence creates concerns for the population in the area, despite the wide diversity of prey.

Migration patterns of killer whales are poorly understood. Some may travel as much as 160km in a single day, but may remain there for a month or so. Sometimes, the seasonal movements of killer whales are heavily influenced by the migration patterns of their prey. For example, populations living in the Norwegian and Greenland Seas which specialize in hunting herring follow their migration pattern.

Killer whales are at the top of the food chain, and are considered as apex predators, which mean that they have no predators. However, humans are a threat to killer whales as they are responsible for oil spills, pollution and habitat disturbances. Moreover, the declination of prey such as salmon, seals and sea lions is also a growing concern for killer whales.

**Adaptations**

Ever since the ancestors of killer whales have began to spend more and more time in the water about 50 million years ago, they have gradually developed extensive adaptations (fig. 3) which allow then to live more efficiently in the oceans as mammals. What's intriguing is how they are going through somewhat of a "reverse" evolution, as all other mammals have evolved to get out of the water and live on the land. Nevertheless, killer whales have evolved to be extremely well adapted to their current habitats, and are now so ferocious they have earned the title of "wolves of the sea".



**Teeth**

Unlike humans, he number of teeth varies between killer whales, with about 40-56 in total. Their long teeth which measure about 7.6cm in length and 2.5cm in diameter allow them to dig into the flesh of their prey.
 * Adaptation ** : These long conical and interlocking teeth and a strong jaw (fig. 4) to allow them to grasp, rip and tear a wide range of prey from small herring to large sharks and whales. And since they don’t chew, they need to be able to rip prey into chunks so that they can swallow easily. whose teeth are composed mostly of enamel on the outer part of the tooth which covers the dentine, killer whales have teeth coated with cementum that overlies the dentine. Cementum is found covering the root of human teeth.


 * How it helped the animal survive ** : With their lethal teeth, killer whales are able to hunt down large variety of preys which are needed the higher caloric content in order to live as marine mammals. Not only is this set of powerful teeth used for hunting, they help killer whales fight for the right to reproduce.


 * Environmental pressure ** : As killer whales were once land mammals which were either carnivores or omnivores, they have retained their strong, lethal teeth (unlike today’s artiodactyls and prissodactyls which became herbivores) and their carnivorous diet due to the fact that more prey was available

**Blowholes**


 * Adaptation ** : Like all other cetaceans, killer whales have evolved to have a blowhole on the top of their heads through which they can breathe air. In order to open up the blowhole, the killer whale contracts the muscular flap, forcing it to open .These blowholes work in the same way the nostrils of other mammal. The killer whale holds its breath under water, but when it surfaces to breathe, they can forcefully expel (fig. 5) not only air through the blowhole, but also mucus and nitrogen, a result of the whale’s metabolism, which was stored inside the killer whale while diving. As it is released into the atmosphere which has a relatively lower pressure and colder atmosphere, the water vapour condenses, and, along with any water on top of the blowhole, is seen as a white splash. When it is relaxed in a closed position, the flap becomes a water-tight seal, preventing water from seeping through.


 * How it helped the animal survive ** : The blowhole allows the killer whale to survive by allowing it to breathe conveniently. Without it, killer whales will die from suffocation as they cannot breath through their mouth.


 * Environmental pressure ** : As the land mammals which killer whales had originally evolved from spent more time in the water, what was once the nasal opening located at the tip of a long snout shifted up higher and higher, until it reached the position of the blowhole in modern cetaceans, allowing them to reach the surface, inhale, and then submerge with convenience.

**Social Structure**


 * Adaptation ** : Killer whales are noted for their complex social structures. They form what is called matrilineality (fig. 6), where the eldest female killer whale leads a line of her descendants. As females can reach up to the age of about 90, up to four generations of killer whales may travel together. The bonds between these matrilines are extremely close, and killer whales leave the group only to mate or give birth. From these matrilines form closely related groups called pods. They consist of about one to four matriline, and are not as tightly bound as relationships in the matrilines; pods may separate for weeks or months at a time.

Since offspring of resident killer whales stick to their mothers their entire lives, their bonds are much stronger. Not only do they tend to the offspring’s needs, they discipline them, and teach them how to hunt and communicate starting from the second day of birth.

Another feature of killer whales’ social structure is the way the hunt in groups. For example, one may tip the ice back and forth so that the seals on it slide into the mouth of another. Another example is how they hunt down herring. A killer whale can detect herring with its sonar, and dives down, forcing them to swim upwards. The killer whale follows them, while others wait near the surface. Next, the killer whales orbit the herring, keeping them in a group. Another flicks its tail, killing up to twenty herring at once.


 * media type="custom" key="9875579" align="right"How it helped the animal survive ** : If killer whales did not live in martrilines or pods, they may find it much more difficult to hunt, as hunting in groups prevent prey from escaping. Killer whale calves, the sick or the wounded may be at risk to predators such as large sharks, which may attack them when alone, but are well protected by the group. In addition, when a killer whale gives birth to an offspring her mother pushes up the newborn to the surface to take its first breath, enabling it to survive.


 * Environmental pressure ** : The reason for these groups may have been due to hunting benefits, as ancestors of cetaceans mainly fed on molluscs and slow fish. However, as the population grew and competition for food increased, they needed to develop the reflexes, teeth and hunting techniques for catching fast fish.

**Vocalization**


 * [[image:echolocation.gif align="left" caption="Fig. 7: Animation of how echolocation works"]]Adaptation ** : Vocalization is one of the most important behavioural adaptations, as killer whales rely heavily on it to navigate, feed and communicate. Killer whales produce three main sounds: clicks, whistles and pulsed calls. Vocalization is a form of echolocation, which Killer whales use to hunt and navigate. This works by the killer whale emitting a series of clicks, then listening to the echoes that return from surrounding objects, and with this they are able to determine to location, range and identify the object (fig. 7).

Their vocalization varies with each type of killer whales. Resident killer whales which eat fish in the Northeast Pacific are much more vocal compared to transient groups living in the same areas. This difference is most likely caused by the different hearing abilities of their prey; resident killer whales hunt on fish which have poor underwater hearing, thus makes it harder for them to detect the killer whale calls. On the other hand, transient killer whales generally prey on marine mammals, which, unlike fish, have excellent underwater hearing abilities, and so the reason the keep silent is to hide their presence from their prey. For this reason, all killer whales which feed on mammals tend to use a single click occasionally, called a cryptic click, rather the more distinctive series of clicks.


 * How it helped the animal survive ** : Vocalization helps the killer whale survive in many ways. In the dark, murky seas, they are able to hunt thanks to echolocation. It also helps killer whales communicate to one another, which is also important when hunting in groups and mating.


 * Environmental pressure ** : It developed in killer whales due to the aquatic environment they live in, as the murky waters make vision extremely limited while use of sound is much more favourable. It may have begun by adapting to the migration of cephalopods, a marine animal which was likely to have been a prey of killer whale ancestors.

**Thermoregulation**


 * Adaptation ** : The killer whale’s circulatory system helps maintain a constant regular temperature by adjusting it to conserve or dissipate heat. Some of the arteries in extremities including the flippers, flukes and dorsal fin are surrounded by the veins. This means that instead of losing heat from blood travelling through the arteries into the environment, the heat is transferred to the venous blood (fig. 8). This is called countercurrent heat exchange. Furthermore, as the killer whale dives, circulation at the skin thins out, which brings blood within the insulated body core.

On the other hand, during prolonged physical activities or swimming in warm water, killer whales may have to dissipate the body heat. They do this by increasing circulation near flippers, flukes and dorsal fin, and the excess heat is transferred to the environment.


 * How it helped the animal survive ** : Regulating body heat prevents the body systems of the killer whale from shutting down, as often venture into colder regions.


 * Environmental pressure ** : Since all mammals are warm-blooded, killer whales’ core temperature is at about 36.4 to 38 degrees Celsius – close to that of a human’s. However, as killer whales live in the sea, it poses a threat to its ability to survive, because water conducts about 27 times faster than normal air. As a result, killer whales have learnt to adapt to these colder environments by through thermoregulation, one of the ways being adjustment of the circulatory system.

**Bibliography**


 * Animal Planet. (2008). //Untamed and Uncut: Orcas Attack Seal// [video]. Retrieved 26 June 2011, from []
 * Beyineé, M. (no date). //Orca – A Giant Dolphin//. Madrid, Spain: Bayard Presse S.A.
 * Dolphins World. (2009). //Killer Whale Anatomy//. Retrieved 19 June 2011, from []
 * National Geographic. (no date). //Killer Whale (Orca)//. Retrieved 16 June 2011, from []
 * Robins Island. (no date). //Evolution of Cetaceans Dolphins and Whales//. Retrieved 20 June 2011, from []
 * Seaworld. (no date). //Killer Whales Adaptations for an Aquatic Environment//. Retrieved 20 June 2011, from []
 * Seaworld. (no date). //Killer Whales Habitat and Distribution//. Retrieved 18 June 2011, from []
 * Seaworld. (no date). //Killer Whales Physical Characteristics//. Retrieved 19 June 2011, from []
 * Think Quest. (no date). //The Respiratory System//. Retrieved 25 June 2011, from []
 * Whale Images. (no date). //Killer Whale Information Facts Pictures//. Retrieved 19 June 2011, from []
 * Wikipedia. (no date). //Blowhole (anatomy)//. Retrieved 19 June 2011, from []
 * Wikipedia. (2011). //Killer Whale//. Retrieved 16 June 2011, from []
 * Wikipedia. (2011). //Evolution of Cetaceans//. Retrieved 20 June, 2011, from []
 * Wikipedia. (2011). //Evolutionary History of Cephalopods//. Retrieved 20 June, 2011, from []


 * Image Sources **


 * Fig.1: Killer whale range (in blue). Source: []
 * Fig. 2: Killer whale about to attack a group of seals. Source: []
 * Fig. 3: Labelled diagram of a killer whale. Source: []
 * Fig. 4: Killer whales have a set of strong, sharp teeth. Source: []
 * Fig. 5: Exhalation process of killer whales. Source: []
 * Fig. 6: A killer whale matriline. Source: []
 * Fig. 7: Animation of how echolocation works. Source: []
 * Fig. 8: Diagram of countercurrent heat exchange. Source: []

//By Joyce Ng 10A//