Killer Whales in Aquatic Biology Term Paper

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The following is a brief overview of the biological classification, diet, distribution and social behavior of the mammalian orcinus orca. The research also outlines the factors that are responsible for the decline in orcinus orca population around the world today. Special emphasis has been given to resident orcinus orca to demystify the concept that orcas are lethal to the fishermen and hence should be targeted for hunting.

Orcinus orca, commonly known as the killer whale, is a top predator marine mammal. Orcas are very social animals and live in pods. During the past 30 years extensive research has been conducted for the species regarding behavioral ecology, genetics, population monitoring, behavioral studies and acoustic research. Much of that research has been dedicated to the study of resident orcas. In recent years there has been a sharp decline in the numbers of resident orcas. In the following study the author outlines the various issues relating to the cause of the decline have been suggested, some of them are declining fish populations, vessel traffic, toxic exposure and underwater noise. The researcher will also prove the misconception that killer whales are harmless to humans.

DISCUSSION

Classification

Kingdom: Animalia

Phylum: Chordata

Subphylum: Vertebrata

Class: Mammalia

Order: Cetacean (all whales, dolphins and porpoises)

Suborder: Odontoceti (all toothed whales)

Family: Delphinidae (all ocean dolphins)

Genus: Orcinus

Species: orca ("British Columbia Killer Whale Adoption Program" 2004)

Distribution

After humans, killer whales are the most widely distributed mammals on earth. Although they are found in all oceans, they prefer colder areas especially the polar areas and are most abundant in Antarctica, Northern Japan, Iceland, Norway, Alaska and the Pacific Coast of North America. The largest population is estimated to be 160000 in Antarctica. A lot of researches on orcas have been conducted in the British Columbia and Southeastern Alaska. Two types of orcas are found in these regions the resident and transient. These two vary in terms of morphology, habitat, diet and vocal patterns. The resident orcas are further divided into Northern and Southern clans.

Transients and residents have been located along the western coast of North America from Southeast Alaska to California. Off shore orcas have been encountered far from the coast line from the West Coast of Vancouver Island to Los Angeles.

Structural Details

The killer whale or the 'wolf of the sea' is the largest member of the dolphin family Delphinidae. The orcas can be distinguished by their distinct black skin and white patterns and their large dorsal fins. The adult male grows up to 9m (10,000 kg), the female 7m (7,500 kg) while the calf or juvenile is 2.5m (200 kg). The average life expectancy of females is longer than that of the male; 50 to 90 years for females compared to 30 to 60 years for males.("British Columbia Killer Whale Adoption Program" 2004) The principal difference between the male orca and female orca is the difference in length, weight and structure of the dorsal fin. The dorsal fin of the male is longer and more up right than that of the female which slightly bends backwards. The male dorsal fin can grow up to 2m and the female 1m. It is difficult to determine the sex of the juvenile since the dorsal fin of the calf is very similar to the dorsal fin of the female (Lacey, Hughes and Miller 2000)

The killer whale has a stocky body with lateral tail fins, a rounded head, large flappers or pectoral fins and a sickle shaped triangular dorsal fin. The dorsal fin is more pointed and centrally positioned in a transient killer whale. The vertical movement of the symmetrical tail fins and the pectoral fins can propel a killer whale to a maximum speed of 45 km/hr. The average traveling speed of the killer whale is 6 to 8 km / hr. The high and short burst of speed is very effective during the act of catching prey.

The killer whale has very acute senses of sight and hearing and they respond well to touch. A distinctive white patch is located over the eyes and ears of a killer whale. The large teeth of the killer whale are conical, enameled and interlocking. A maximum of 26 pairs or 52 teeth are present in an adult. To facilitate hunting the teeth are bent inwards and backwards. The blow hole is located near the top of the head. The orcas breathe air at the surface of the water through this nostril and emit a low misty column of water.

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Killer whales usually stay on the surface of water since they have to breathe air but when they do dive, the blow hole is locked by nasal plugs which are operated with fast acting muscles. The killer whale can dive down up to 100 meters and transient orcas can stay underwater for 5 to 15 minutes whereas the residents can stay below for only 4 minutes.("The (Orca) Killer Whale" 2004)

For hunting purposes it is necessary for the killer whale to be as camouflaged as possible. Their black upper skin and white lower skin help them to remain inconspicuous. Viewed from above, the black skin blends with water and viewed from below and underwater, the white skin remains indistinguishable from the light surface water.

Diet few decades ago there was a misconception about killer whales, and fishermen used to kill them on sight. The killer whale has never been known to attack humans. It is true that the killer whale is at the top of the food chain in the marine world and its meals include fishes, seals, squids and whales. Resident killer whales mostly feed on fishes like salmon and squids, it has not yet been established that birds are one of their diet items. It is believed that the transient killer whales are more opportunistic hunters feeding on any mammal they can find. ("British Columbia Killer Whale Adoption Program" 2004)Transient killer whales are also more silent and do not involve themselves into much playful activities which actually helps them in hunting and taking the prey by surprise. Transient killer whales usually hunt mammals which have ears. Off shore killer whales feed on schools of fish. ("British Columbia Killer Whale Adoption Program" 2004)These orcas have more nicks and scaring on their fins suggesting that sharks may be included in their diet.

Residents hunt in larger groups or pods whereas the transient killer whales hunt in smaller groups. All the members of the group may cooperate and hunt together. Typically the resident killer whale would emit noises to locate prey, the sound would bounce back from objects or prey and hence the killer whale would be able to locate its prey. This process is known as echolocation. Transient killer whales sometimes play with the pray by slapping it and tossing it in the air. Often the bounty is shared by all members of the group.

Social Behavior

Whales do not have marked territories and belong at any place where they are. The pod is the primary social structure of the killer whale and each orca belongs to a pod for life. These pods develop distinct dialects and vocal noises. This distinct pattern of vocalization helps them determine a member from non-member.

The structure of the pod is matriarchal. A pod is made up of many matrilines in which the females move around with their offspring. The infant calf is nurtured by the mother till the calf reaches adolescence which is usually 15 years. The bond is not broken when the mother dies.

Transient killer whales display a more variable social structure in which the male may leave a pod upon maturity and join another clan or he may hunt as a loner. Transient pods are also smaller (1 to 7) than resident pods (5 to 25) and sometimes two or more resident pods may combine to form super pods of 150 whales. ("The (Orca) Killer Whale" 2004)Killer whales do not migrate seasonally but they do travel long distances with their respective pods in search for food.

Killer Whales exhibit numerous social and playful activities like diving, breaching, spy hopping and tail slaps. They are also kept in large aquariums for circus show and entertainment purposes.

Genetics

It has been proven that the transient and resident killer whales have no direct lineages and there is also no apparent interbreeding between the two. Similar results are found in the case of northern and southern killer whales. Killer whales do not interbreed within their own pods and matrilines. Mating does occur outside pods. ("British Columbia Killer Whale Adoption Program" 2004)

Issues Affecting the Recent Decline in Orca Numbers

Decline in fish populations

Over fishing and degradation of the fish habitat has decreased the fish populations in oceans. Resident killer whales have been shown to feed mostly on salmon (90%) and now salmon fish are very scarce. ("Issues Affecting the Southern Resident Orcas" 2004)This might compel resident orcas to.....

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