Marine mammal

Marine mammal

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Marine mammals, which include seal
Pinniped
Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semiaquatic marine mammals comprising the families Odobenidae , Otariidae , and Phocidae .-Overview: Pinnipeds are typically sleek-bodied and barrel-shaped...

s, whale
Whale
Whale is the common name for various marine mammals of the order Cetacea. The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises, which belong to suborder Odontoceti . This suborder also includes the sperm whale, killer whale, pilot whale, and beluga...

s, dolphin
Dolphin
Dolphins are marine mammals that are closely related to whales and porpoises. There are almost forty species of dolphin in 17 genera. They vary in size from and , up to and . They are found worldwide, mostly in the shallower seas of the continental shelves, and are carnivores, mostly eating...

s, and walrus
Walrus
The walrus is a large flippered marine mammal with a discontinuous circumpolar distribution in the Arctic Ocean and sub-Arctic seas of the Northern Hemisphere. The walrus is the only living species in the Odobenidae family and Odobenus genus. It is subdivided into three subspecies: the Atlantic...

es, form a diverse group of 128 species that rely on the ocean for their existence. They do not represent a distinct biological grouping, but rather are unified by their reliance on the marine environment for feeding. The level of dependence on the marine environment for existence varies considerably with species. For example, dolphin
Dolphin
Dolphins are marine mammals that are closely related to whales and porpoises. There are almost forty species of dolphin in 17 genera. They vary in size from and , up to and . They are found worldwide, mostly in the shallower seas of the continental shelves, and are carnivores, mostly eating...

s and whale
Whale
Whale is the common name for various marine mammals of the order Cetacea. The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises, which belong to suborder Odontoceti . This suborder also includes the sperm whale, killer whale, pilot whale, and beluga...

s are completely dependent on the marine environment for all stages of their life, whereas seal
Pinniped
Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semiaquatic marine mammals comprising the families Odobenidae , Otariidae , and Phocidae .-Overview: Pinnipeds are typically sleek-bodied and barrel-shaped...

s feed in the ocean, but breed on land. Marine mammals can be subdivided into four recognised groups; cetaceans (whale
Whale
Whale is the common name for various marine mammals of the order Cetacea. The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises, which belong to suborder Odontoceti . This suborder also includes the sperm whale, killer whale, pilot whale, and beluga...

s, dolphin
Dolphin
Dolphins are marine mammals that are closely related to whales and porpoises. There are almost forty species of dolphin in 17 genera. They vary in size from and , up to and . They are found worldwide, mostly in the shallower seas of the continental shelves, and are carnivores, mostly eating...

s and porpoise
Porpoise
Porpoises are small cetaceans of the family Phocoenidae; they are related to whales and dolphins. They are distinct from dolphins, although the word "porpoise" has been used to refer to any small dolphin, especially by sailors and fishermen...

s), pinniped
Pinniped
Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semiaquatic marine mammals comprising the families Odobenidae , Otariidae , and Phocidae .-Overview: Pinnipeds are typically sleek-bodied and barrel-shaped...

s (seal
Pinniped
Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semiaquatic marine mammals comprising the families Odobenidae , Otariidae , and Phocidae .-Overview: Pinnipeds are typically sleek-bodied and barrel-shaped...

s, sea lion
Sea Lion
Sea lions are pinnipeds characterized by external ear-flaps, long fore-flippers, the ability to walk on all fours, and short thick hair. Together with the fur seal, they comprise the family Otariidae, or eared seals. There are six extant and one extinct species in five genera...

s and walrus
Walrus
The walrus is a large flippered marine mammal with a discontinuous circumpolar distribution in the Arctic Ocean and sub-Arctic seas of the Northern Hemisphere. The walrus is the only living species in the Odobenidae family and Odobenus genus. It is subdivided into three subspecies: the Atlantic...

es), sirenians (manatee
Manatee
Manatees are large, fully aquatic, mostly herbivorous marine mammals sometimes known as sea cows...

s and dugong
Dugong
The dugong is a large marine mammal which, together with the manatees, is one of four living species of the order Sirenia. It is the only living representative of the once-diverse family Dugongidae; its closest modern relative, Steller's sea cow , was hunted to extinction in the 18th century...

s), and fissipeds, which are the group of carnivores with separate digits (the polar bear
Polar Bear
The polar bear is a bear native largely within the Arctic Circle encompassing the Arctic Ocean, its surrounding seas and surrounding land masses. It is the world's largest land carnivore and also the largest bear, together with the omnivorous Kodiak Bear, which is approximately the same size...

, and two species of otter
Otter
The Otters are twelve species of semi-aquatic mammals which feed on fish and shellfish, and also other invertebrates, amphibians, birds and small mammals....

). Both cetaceans and sirenians are fully aquatic and therefore are obligate ocean dwellers. Pinniped
Pinniped
Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semiaquatic marine mammals comprising the families Odobenidae , Otariidae , and Phocidae .-Overview: Pinnipeds are typically sleek-bodied and barrel-shaped...

s are semi-aquatic; they spend the majority of their time in the water, but need to return to land for important activities such as mating
Mating
In biology, mating is the pairing of opposite-sex or hermaphroditic organisms for copulation. In social animals, it also includes the raising of their offspring. Copulation is the union of the sex organs of two sexually reproducing animals for insemination and subsequent internal fertilization...

, breeding
Breeding
Breeding is the reproduction, that is, producing of offspring, usually animals or plants:* Breeding in the wild, the natural process of reproduction in the animal kingdom* Animal husbandry, through selected specimens such as dogs, horses, and rabbits...

 and molting. In contrast, both otter
Otter
The Otters are twelve species of semi-aquatic mammals which feed on fish and shellfish, and also other invertebrates, amphibians, birds and small mammals....

s and the polar bear
Polar Bear
The polar bear is a bear native largely within the Arctic Circle encompassing the Arctic Ocean, its surrounding seas and surrounding land masses. It is the world's largest land carnivore and also the largest bear, together with the omnivorous Kodiak Bear, which is approximately the same size...

 are much less adapted to ocean living. While the number of marine mammals is small compared to those found on land, their total biomass
Biomass
Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....

 is large. They play important roles in maintaining marine ecosystem
Marine ecosystem
Marine ecosystems are among the largest of Earth's aquatic ecosystems. They include oceans, salt marsh and intertidal ecology, estuaries and lagoons, mangroves and coral reefs, the deep sea and the sea floor. They can be contrasted with freshwater ecosystems, which have a lower salt content. Marine...

s, especially through regulation of prey populations.These two factors make them an integral component of the marine environment. This is of particular concern considering 23% of marine mammal species are currently threatened.

Taxonomy


Mammals have returned to the water in at least nine separate evolutionary lineage
Lineage
Lineage may refer to:- Science :* Lineage or kinship, descent group that can demonstrate their common descent from an apical ancestor or a direct line of decent from an ancestor....

s (Cetacea
Cetacea
The order Cetacea includes the marine mammals commonly known as whales, dolphins, and porpoises. Cetus is Latin and is used in biological names to mean "whale"; its original meaning, "large sea animal", was more general. It comes from Ancient Greek , meaning "whale" or "any huge fish or sea...

, Sirenia
Sirenia
Sirenia is an order of fully aquatic, herbivorous mammals that inhabit swamps, rivers, estuaries, marine wetlands, and coastal marine waters. Four species are living, in two families and genera. These are the dugong and manatees...

, Desmostylia
Desmostylia
Desmostylia is an extinct order of marine mammals which existed from the Arikareean age of the late Oligocene epoch to the Tortonian age of the late Miocene epoch . Their dental and skeletal form suggests desmostylians were amphibious herbivores dependent on littoral habitats...

, Pinnipedia, Ursus maritimus (polar bear
Polar Bear
The polar bear is a bear native largely within the Arctic Circle encompassing the Arctic Ocean, its surrounding seas and surrounding land masses. It is the world's largest land carnivore and also the largest bear, together with the omnivorous Kodiak Bear, which is approximately the same size...

), Kolponomos
Kolponomos
Kolponomos is an extinct genus of marine bears which existed from the Hemingfordian age to the Aquitanian age of the Miocene epoch, about 20 million years ago. It was described in 1960 by Ruben A. Stirton, a paleontologist at the American Museum of Natural History, from a partial skull and jaw...

 (marine bear), Thalassocnus
Thalassocnus
Thalassocnus is an extinct genus of semi-aquatic or aquatic marine sloth from the Miocene and Pliocene of South America. Fossils found to date have been from the coast of Peru. They were apparently grazers of sea grass and seaweed. Over time, they apparently shifted from a preference for feeding...

 (aquatic sloth), Enhydra lutris (sea otter
Sea Otter
The sea otter is a marine mammal native to the coasts of the northern and eastern North Pacific Ocean. Adult sea otters typically weigh between 14 and 45 kg , making them the heaviest members of the weasel family, but among the smallest marine mammals...

) and Lontra feline (marine otter
Marine Otter
The marine otter, Lontra felina, is a rare and poorly-known South American mammal of the weasel family . The scientific name means "otter cat", and in Spanish the marine otter is also often referred to as : "marine cat"...

)). Three of these lineages are extinct (Desmostylia
Desmostylia
Desmostylia is an extinct order of marine mammals which existed from the Arikareean age of the late Oligocene epoch to the Tortonian age of the late Miocene epoch . Their dental and skeletal form suggests desmostylians were amphibious herbivores dependent on littoral habitats...

; Kolponomos
Kolponomos
Kolponomos is an extinct genus of marine bears which existed from the Hemingfordian age to the Aquitanian age of the Miocene epoch, about 20 million years ago. It was described in 1960 by Ruben A. Stirton, a paleontologist at the American Museum of Natural History, from a partial skull and jaw...

; Thalassocnus
Thalassocnus
Thalassocnus is an extinct genus of semi-aquatic or aquatic marine sloth from the Miocene and Pliocene of South America. Fossils found to date have been from the coast of Peru. They were apparently grazers of sea grass and seaweed. Over time, they apparently shifted from a preference for feeding...

). Despite the diversity in morphology seen between groups, improving foraging efficiency has been the main driver in the evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...

 in these lineages. Today, marine mammals belong to one of three orders; Cetacea
Cetacea
The order Cetacea includes the marine mammals commonly known as whales, dolphins, and porpoises. Cetus is Latin and is used in biological names to mean "whale"; its original meaning, "large sea animal", was more general. It comes from Ancient Greek , meaning "whale" or "any huge fish or sea...

, Sirenia
Sirenia
Sirenia is an order of fully aquatic, herbivorous mammals that inhabit swamps, rivers, estuaries, marine wetlands, and coastal marine waters. Four species are living, in two families and genera. These are the dugong and manatees...

, or Carnivora
Carnivora
The diverse order Carnivora |Latin]] carō "flesh", + vorāre "to devour") includes over 260 species of placental mammals. Its members are formally referred to as carnivorans, while the word "carnivore" can refer to any meat-eating animal...

. Within the Order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 Carnivora
Carnivora
The diverse order Carnivora |Latin]] carō "flesh", + vorāre "to devour") includes over 260 species of placental mammals. Its members are formally referred to as carnivorans, while the word "carnivore" can refer to any meat-eating animal...

 are the pinniped
Pinniped
Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semiaquatic marine mammals comprising the families Odobenidae , Otariidae , and Phocidae .-Overview: Pinnipeds are typically sleek-bodied and barrel-shaped...

s (sealions, walrus
Walrus
The walrus is a large flippered marine mammal with a discontinuous circumpolar distribution in the Arctic Ocean and sub-Arctic seas of the Northern Hemisphere. The walrus is the only living species in the Odobenidae family and Odobenus genus. It is subdivided into three subspecies: the Atlantic...

es and seal
Pinniped
Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semiaquatic marine mammals comprising the families Odobenidae , Otariidae , and Phocidae .-Overview: Pinnipeds are typically sleek-bodied and barrel-shaped...

s), the polar bear
Polar Bear
The polar bear is a bear native largely within the Arctic Circle encompassing the Arctic Ocean, its surrounding seas and surrounding land masses. It is the world's largest land carnivore and also the largest bear, together with the omnivorous Kodiak Bear, which is approximately the same size...

 (Ursus maritimus), and two otter
Otter
The Otters are twelve species of semi-aquatic mammals which feed on fish and shellfish, and also other invertebrates, amphibians, birds and small mammals....

s (Endydra lutris and Lontra feline.
  • Order Cetacea
    • Suborder Mysticeti (baleen wales)
      • Family Balaenidae
        Balaenidae
        Balaenidae is a family of mysticete whales that contains two living genera. Commonly called the right whales as it contains mainly right whale species...

         (right and bowhead whales) = 2 genera; four species
      • Family Neobalaenidae (pygmy right whale
        Pygmy Right Whale
        The pygmy right whale is a baleen whale, the sole member of the family Neobalaenidae. First described by John Edward Gray in 1846, it is the smallest of the baleen whales, ranging between and in length and 3,000 and 3,500 kg in mass...

        ) = one species
      • Family Balaenopteridae (rorqual
        Rorqual
        Rorquals are the largest group of baleen whales, with nine species in two genera. They include the largest animal that has ever lived, the Blue Whale, which can reach , and another that easily reaches ; even the smallest of the group, the Northern Minke Whale, reaches .-Characteristics:Rorquals...

        s) = 2 genera; 8 species
      • Family Eschrichtiidae
        Eschrichtiidae
        Eschrichtiidae is a family of baleen whales in the suborder Mysticeti.At least five genera are recognised, but only a single species from one genus is still alive, the gray whale, Eschrichtius robustus....

         (gray whale
        Gray Whale
        The gray whale, Eschrichtius robustus, is a baleen whale that migrates between feeding and breeding grounds yearly. It reaches a length of about , a weight of , and lives 50–70 years. The common name of the whale comes from the gray patches and white mottling on its dark skin. Gray whales were...

        ) = 1 species
    • Suborder Odontoceti (toothed whale
      Toothed whale
      The toothed whales form a suborder of the cetaceans, including sperm whales, beaked whales, dolphins, and others. As the name suggests, the suborder is characterized by the presence of teeth rather than the baleen of other whales.-Anatomy:Toothed whales have a single blowhole on the top of the head...

      s)
      • Family Physeteridae (sperm whale
        Sperm Whale
        The sperm whale, Physeter macrocephalus, is a marine mammal species, order Cetacea, a toothed whale having the largest brain of any animal. The name comes from the milky-white waxy substance, spermaceti, found in the animal's head. The sperm whale is the only living member of genus Physeter...

        ) = 1 species
      • Family Kogiidae (pygmy and dwarf sperm whales = 1 genera; 2 species
      • Family Monodontidae
        Monodontidae
        The cetacean family Monodontidae comprises two unusual whale species, the narwhal, in which the male has a long tusk, and the white beluga whale...

         (narwhal and beluga) = two genera; two species
      • Family Ziphiidae (beaked whale
        Beaked whale
        Beaked whales are 21 species of toothed whales, members of the family Ziphiidae, are notable for their elongated beaks. Beaked whales are one of the world's most extreme divers. They can dive for long periods—20 to 30 minutes is common, and 85 minute dives have been recorded—and to...

        s) = 6 genera; 21 species
      • Family Delphinidae (ocean whales) = 17 genera; 36 species
      • Family Phocoenidae (porpoise
        Porpoise
        Porpoises are small cetaceans of the family Phocoenidae; they are related to whales and dolphins. They are distinct from dolphins, although the word "porpoise" has been used to refer to any small dolphin, especially by sailors and fishermen...

        s) = 2 genera; 6 species
      • Family Platanistidae (South Asia river dolphin) = 1 species
      • Family Iniidae
        Iniidae
        Iniidae is a family of river dolphins containing one living and three extinct genera.-Taxonomy:The family was described by John Edward Gray in 1846.Current classifications include a single living genera, Inia, with one species and three subspecies...

         (boto) 1 species
      • Family Lipotidae (Baji) probably extinct
      • Family Pontoporiidae (franciscana) = 1 species
  • Order Sirenia
    Sirenia
    Sirenia is an order of fully aquatic, herbivorous mammals that inhabit swamps, rivers, estuaries, marine wetlands, and coastal marine waters. Four species are living, in two families and genera. These are the dugong and manatees...

     (sea cows)
      • Family Trichechidae (manatee
        Manatee
        Manatees are large, fully aquatic, mostly herbivorous marine mammals sometimes known as sea cows...

        s) = 1 genus; 3 species
      • Family Dugongidae
        Dugongidae
        Dugongidae is a family in the order of Sirenia.The family has one surviving species, the Dugong , one recently extinct species, the Steller's Sea Cow , and a number of extinct genera known from the fossil record....

         (dugong
        Dugong
        The dugong is a large marine mammal which, together with the manatees, is one of four living species of the order Sirenia. It is the only living representative of the once-diverse family Dugongidae; its closest modern relative, Steller's sea cow , was hunted to extinction in the 18th century...

        s) = 1 species
  • Order Carnivora
    Carnivora
    The diverse order Carnivora |Latin]] carō "flesh", + vorāre "to devour") includes over 260 species of placental mammals. Its members are formally referred to as carnivorans, while the word "carnivore" can refer to any meat-eating animal...

     (carnivore
    Carnivore
    A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...

    s):
      • Family Mustelidae
        Mustelidae
        Mustelidae , commonly referred to as the weasel family, are a family of carnivorous mammals. Mustelids are diverse and the largest family in the order Carnivora, at least partly because in the past it has been a catch-all category for many early or poorly differentiated taxa...

         (otter
        Otter
        The Otters are twelve species of semi-aquatic mammals which feed on fish and shellfish, and also other invertebrates, amphibians, birds and small mammals....

        s) Enhydra lutris (sea otter
        Sea Otter
        The sea otter is a marine mammal native to the coasts of the northern and eastern North Pacific Ocean. Adult sea otters typically weigh between 14 and 45 kg , making them the heaviest members of the weasel family, but among the smallest marine mammals...

        ) Lontra feline (marine otter
        Marine Otter
        The marine otter, Lontra felina, is a rare and poorly-known South American mammal of the weasel family . The scientific name means "otter cat", and in Spanish the marine otter is also often referred to as : "marine cat"...

        )
      • Family Ursidae (bear
        Bear
        Bears are mammals of the family Ursidae. Bears are classified as caniforms, or doglike carnivorans, with the pinnipeds being their closest living relatives. Although there are only eight living species of bear, they are widespread, appearing in a wide variety of habitats throughout the Northern...

        s) Ursus maritimus (polar bear
        Polar Bear
        The polar bear is a bear native largely within the Arctic Circle encompassing the Arctic Ocean, its surrounding seas and surrounding land masses. It is the world's largest land carnivore and also the largest bear, together with the omnivorous Kodiak Bear, which is approximately the same size...

        )
    • Suborder Pinniped
      Pinniped
      Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semiaquatic marine mammals comprising the families Odobenidae , Otariidae , and Phocidae .-Overview: Pinnipeds are typically sleek-bodied and barrel-shaped...

      ia (sealions, walruses, seals)
      • Family Otariidae
        Eared Seal
        The eared seals or otariids are marine mammals in the family Otariidae, one of three groupings of Pinnipeds. They comprise 16 species in seven genera commonly known either as sea lions or fur seals, distinct from true seals and the Walrus...

         (fur seal
        Fur seal
        Fur seals are any of nine species of pinnipeds in the Otariidae family. One species, the northern fur seal inhabits the North Pacific, while seven species in the Arctocephalus genus are found primarily in the Southern hemisphere...

        s and sea lion
        Sea Lion
        Sea lions are pinnipeds characterized by external ear-flaps, long fore-flippers, the ability to walk on all fours, and short thick hair. Together with the fur seal, they comprise the family Otariidae, or eared seals. There are six extant and one extinct species in five genera...

        s) = 7 genera; 16 species
      • Family Odobenidae
        Odobenidae
        Odobenidae is a family of Pinnipeds. The only living species is walrus.In the past, however, the group was much more diverse, and includes more than ten fossil genera.- Taxonomy :All genera, except Odobenus, are extinct.*Prototaria...

         (walrus
        Walrus
        The walrus is a large flippered marine mammal with a discontinuous circumpolar distribution in the Arctic Ocean and sub-Arctic seas of the Northern Hemisphere. The walrus is the only living species in the Odobenidae family and Odobenus genus. It is subdivided into three subspecies: the Atlantic...

        ) = 1 species
      • Family Phocidae
        Earless seal
        The true seals or earless seals are one of the three main groups of mammals within the seal superfamily, Pinnipedia. All true seals are members of the family Phocidae . They are sometimes called crawling seals to distinguish them from the fur seals and sea lions of the family Otariidae...

         (true seals) = 13 genera; 18 species

Diversity, distribution and habitat


Marine mammals are widely distributed throughout the globe, but their distribution is patchy and coincides with the productivity of the oceans. Species richness peaks at around 40°of latitude both north and south. This corresponds to the highest levels of primary production
Primary production
400px|thumb|Global oceanic and terrestrial photoautotroph abundance, from September [[1997]] to August 2000. As an estimate of autotroph biomass, it is only a rough indicator of primary production potential, and not an actual estimate of it...

 around North and South America
Americas
The Americas, or America , are lands in the Western hemisphere, also known as the New World. In English, the plural form the Americas is often used to refer to the landmasses of North America and South America with their associated islands and regions, while the singular form America is primarily...

, Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...

, Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...

 and Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

. Total species range is highly variable for marine mammal species. On average most marine mammals have ranges which are equivalent or smaller than one-fifth of the Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...

.The variation observed in range size is a result of the different ecological requirements of each species and their ability to cope with a broad range of environmental conditions. There is a high degree of overlap between marine mammal species richness and areas of human impact on the environment which is of concern.

Anatomy and physiology


Marine mammals have a number of physiological and anatomical features to overcome the unique challenges associated with aquatic living. Some of these features are very species specific. Marine mammals have developed a number of features for efficient locomotion
Locomotion
The term locomotion means movement or travel. It may refer to:* Motion * Animal locomotion** Terrestrial locomotion* TravelLocomotion may refer to specific types of motion:* Gait analysis* walking* running, including trotting...

 such as torpedo shaped bodies to reduce drag; modified limbs for propulsion and steering
Steering
Steering is the term applied to the collection of components, linkages, etc. which will allow a vessel or vehicle to follow the desired course...

; tail flukes and dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...

s for propulsion and balance. Marine mammals are adept at thermoregulation
Thermoregulation
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different...

 using dense fur
Fur
Fur is a synonym for hair, used more in reference to non-human animals, usually mammals; particularly those with extensives body hair coverage. The term is sometimes used to refer to the body hair of an animal as a complete coat, also known as the "pelage". Fur is also used to refer to animal...

 or blubber
Blubber
Blubber is a thick layer of vascularized adipose tissue found under the skin of all cetaceans, pinnipeds and sirenians.-Description:Lipid-rich, collagen fiber–laced blubber comprises the hypodermis and covers the whole body, except for parts of the appendages, strongly attached to the musculature...

 to reduce heat loss; as well as circulatory adjustments to conserve their body temperature (counter-current heat exchangers); torpedo shaped bodies, reduced appendages, and large size to prevent heat loss. Most marine mammals are hypoosmotic and as a result they are constantly losing water to the surrounding environment. They have evolved a number of mechanisms to overcome this, but most retain their water by using highly efficient kidney
Kidney
The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...

s, that can concentrate urine. Marine mammals are able to dive for long periods of time. Both pinniped
Pinniped
Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semiaquatic marine mammals comprising the families Odobenidae , Otariidae , and Phocidae .-Overview: Pinnipeds are typically sleek-bodied and barrel-shaped...

s and cetaceans have large and complex blood vessel
Blood vessel
The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...

 systems which serve to store oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 to support deep diving. Other important reservoirs include muscle
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...

s, blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....

, and the spleen
Spleen
The spleen is an organ found in virtually all vertebrate animals with important roles in regard to red blood cells and the immune system. In humans, it is located in the left upper quadrant of the abdomen. It removes old red blood cells and holds a reserve of blood in case of hemorrhagic shock...

 which all have the capacity to hold a high concentration of oxygen. Other features include bradycardia
Bradycardia
Bradycardia , in the context of adult medicine, is the resting heart rate of under 60 beats per minute, though it is seldom symptomatic until the rate drops below 50 beat/min. It may cause cardiac arrest in some patients, because those with bradycardia may not be pumping enough oxygen to their heart...

 (reduced heart rate), and vasoconstriction
Vasoconstriction
Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, particularly the large arteries, small arterioles and veins. The process is the opposite of vasodilation, the widening of blood vessels. The process is particularly important in...

 (shunts most of the oxygen to vital organs such as the brain and heart) also assist with extended diving and oxygen deprivation. Sound travels differently through water therefore marine mammals have developed a number of ways to ensure effective communication
Communication
Communication is the activity of conveying meaningful information. Communication requires a sender, a message, and an intended recipient, although the receiver need not be present or aware of the sender's intent to communicate at the time of communication; thus communication can occur across vast...

, prey capture, and predator detection. The most notable adaptation is the development of echolocation
Echolocation
Echolocation may refer to:* Acoustic location, the general use of sound to locate objects* Animal echolocation, non-human animals emitting sound waves and listening to the echo in order to locate objects or navigate...

 in whale
Whale
Whale is the common name for various marine mammals of the order Cetacea. The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises, which belong to suborder Odontoceti . This suborder also includes the sperm whale, killer whale, pilot whale, and beluga...

s and dolphin
Dolphin
Dolphins are marine mammals that are closely related to whales and porpoises. There are almost forty species of dolphin in 17 genera. They vary in size from and , up to and . They are found worldwide, mostly in the shallower seas of the continental shelves, and are carnivores, mostly eating...

s. Lastly, Marine mammals have evolved a number features for feeding, which are mainly seen in their dentition
Dentition
Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, the characteristic arrangement, kind, and number of teeth in a given species at a given age...

. For example, the cheek teeth of pinniped
Pinniped
Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semiaquatic marine mammals comprising the families Odobenidae , Otariidae , and Phocidae .-Overview: Pinnipeds are typically sleek-bodied and barrel-shaped...

 and odontocetes are designed specifically to capture fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

 and squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...

. In contrast, Mysticetes have evolved baleen plates to filter feed plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...

 and small fish from the water.

Exploitation


Marine mammals were hunted by coastal aboriginal humans historically for food and other resources. The effects of this were only localised as hunting efforts were on a relatively small scale. Later, commercial hunting
Hunting
Hunting is the practice of pursuing any living thing, usually wildlife, for food, recreation, or trade. In present-day use, the term refers to lawful hunting, as distinguished from poaching, which is the killing, trapping or capture of the hunted species contrary to applicable law...

 was developed and marine mammals were heavily exploited. This led to the extinction of the Steller's Sea Cow
Steller's Sea Cow
Steller's sea cow was a large herbivorous marine mammal. In historical times, it was the largest member of the order Sirenia, which includes its closest living relative, the dugong , and the manatees...

, the Caribbean monk seal
Caribbean Monk Seal
The Caribbean monk seal or West Indian monk seal is an extinct species of seal. It is the only seal ever known to be native to the Caribbean Sea and the Gulf of Mexico. The last verified recorded sighting occurred in 1952 at Serranilla Bank...

, and the Atlantic gray whale. Today, population
Population
A population is all the organisms that both belong to the same group or species and live in the same geographical area. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals...

s of species that were historically hunted, such as blue whale
Blue Whale
The blue whale is a marine mammal belonging to the suborder of baleen whales . At in length and or more in weight, it is the largest known animal to have ever existed....

s Balaenoptera musculus and B. m. brevicauda), and the humpback whale
Humpback Whale
The humpback whale is a species of baleen whale. One of the larger rorqual species, adults range in length from and weigh approximately . The humpback has a distinctive body shape, with unusually long pectoral fins and a knobbly head. It is an acrobatic animal, often breaching and slapping the...

 (Megaptera novaeangliae), are much lower compared to their pre-exploited levels. Because whales generally have slow growth rates, are slow to reach sexual maturity
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...

, and have a low reproductive output, population recovery has been very slow.
Despite the fact commercial whaling is generally a thing of the past since the passage of the International Whaling Commission
International Whaling Commission
The International Whaling Commission is an international body set up by the terms of the International Convention for the Regulation of Whaling , which was signed in Washington, D.C...

’s (IWC) moratorium on commercial whaling, a number of marine mammals are still subject to direct hunting. The only remaining commercial hunting of whales is by Norway
Norway
Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...

 where several hundred northeastern North Atlantic minke whales are harvested each year. Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

 also harvests several hundred Antarctic and North Pacific minke whales each year under the guise of scientific research. However, the illegal trade of whale and dolphin meat is a significant market in some countries. Seals and sealions are also still hunted in some areas such as Canada.

Entanglements


By-catch
By-catch
The term “bycatch” is usually used for fish caught unintentionally in a fishery while intending to catch other fish. It may however also indicate untargeted catch in other forms of animal harvesting or collecting...

 is the incidental capture of non-target species in fisheries. Fixed and drift gill nets cause the highest mortality
Mortality rate
Mortality rate is a measure of the number of deaths in a population, scaled to the size of that population, per unit time...

 levels for both cetaceans and pinniped
Pinniped
Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semiaquatic marine mammals comprising the families Odobenidae , Otariidae , and Phocidae .-Overview: Pinnipeds are typically sleek-bodied and barrel-shaped...

s, however, entanglements in both trap and pot lines are also common, long lines, and mid-water trawls. Tuna
Tuna
Tuna is a salt water fish from the family Scombridae, mostly in the genus Thunnus. Tuna are fast swimmers, and some species are capable of speeds of . Unlike most fish, which have white flesh, the muscle tissue of tuna ranges from pink to dark red. The red coloration derives from myoglobin, an...

 seines are particularly problematic for entanglement by dolphins. By-catch affects all cetaceans, both small and big, in all habitat types. However, smaller cetaceans and pinniped
Pinniped
Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semiaquatic marine mammals comprising the families Odobenidae , Otariidae , and Phocidae .-Overview: Pinnipeds are typically sleek-bodied and barrel-shaped...

s are most vulnerable as their size means that escape once they are entangled is highly unlikely and they frequently drown. While larger cetaceans are capable of dragging nets with them, the nets sometimes remain tightly attached to the individual and can impede the animal from feeding sometimes leading to starvation
Starvation
Starvation is a severe deficiency in caloric energy, nutrient and vitamin intake. It is the most extreme form of malnutrition. In humans, prolonged starvation can cause permanent organ damage and eventually, death...

. Abandoned or lost nets and lines cause mortality through ingestion
Ingestion
Ingestion is the consumption of a substance by an organism. In animals, it normally is accomplished by taking in the substance through the mouth into the gastrointestinal tract, such as through eating or drinking...

 or entanglement. Marine mammals also get entangled in aquaculture
Aquaculture
Aquaculture, also known as aquafarming, is the farming of aquatic organisms such as fish, crustaceans, molluscs and aquatic plants. Aquaculture involves cultivating freshwater and saltwater populations under controlled conditions, and can be contrasted with commercial fishing, which is the...

 nets, however, these are rare events and not prevalent enough to impact populations

Vessel Strikes and activity


Vessel strikes cause death for a number of marine mammals, especially whale
Whale
Whale is the common name for various marine mammals of the order Cetacea. The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises, which belong to suborder Odontoceti . This suborder also includes the sperm whale, killer whale, pilot whale, and beluga...

s. In particular, fast commercial vessels such as container ship
Container ship
Container ships are cargo ships that carry all of their load in truck-size intermodal containers, in a technique called containerization. They form a common means of commercial intermodal freight transport.-History:...

s can cause major injuries or death when they collide with marine mammals. Collisions occur both with large commercial vessels and recreational boats and cause injury to whales or smaller cetaceans. The critically endangered northern right whale
Northern Right Whale
There are two species of Northern Right Whale:*North Pacific Right Whale *North Atlantic Right Whale...

 is particularly affected by vessel strikes. Tourism
Tourism
Tourism is travel for recreational, leisure or business purposes. The World Tourism Organization defines tourists as people "traveling to and staying in places outside their usual environment for not more than one consecutive year for leisure, business and other purposes".Tourism has become a...

 boats designed for whale and dolphin watching can also negatively impact on marine mammals by interfering with their natural behavior

Habitat loss and degradation


Habitat degradation is caused by a number of human activities. Marine mammals that live in coastal environments are most likely to be affected by habitat degradation and loss. Developments such as sewage marine outfall
Marine outfall
A marine outfall is a pipeline or tunnel that discharges municipal or industrial wastewater, stormwater, combined sewer overflows, cooling water, or brine effluents from water desalination plants to the sea. Usually they discharge under the sea's surface...

s, moorings, dredging, blasting, dumping, port
Port
A port is a location on a coast or shore containing one or more harbors where ships can dock and transfer people or cargo to or from land....

 construction, hydroelectric projects, and aquaculture
Aquaculture
Aquaculture, also known as aquafarming, is the farming of aquatic organisms such as fish, crustaceans, molluscs and aquatic plants. Aquaculture involves cultivating freshwater and saltwater populations under controlled conditions, and can be contrasted with commercial fishing, which is the...

 both degrade the environment and take up valuable habitat. For example, extensive shellfish aquaculture takes up valuable space used by coastal marine mammals for important activities such as breeding, foraging and resting.

Competition/conflict with fisheries


The fishery industry not only threatens marine mammals through by-catch, but also through competition for food. Large scale fisheries have led to the depletion of fish stock
Fish stock
Fish stocks are subpopulations of a particular species of fish, for which intrinsic parameters are the only significant factors in determining population dynamics, while extrinsic factors are considered to be insignificant.-The stock concept:All species have geographic limits to their...

s that are important prey species for marine mammals. Pinniped
Pinniped
Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semiaquatic marine mammals comprising the families Odobenidae , Otariidae , and Phocidae .-Overview: Pinnipeds are typically sleek-bodied and barrel-shaped...

s have been especially affected by the direct loss of food supplies and in some cases the harvesting of fish has led to food shortages or dietary deficiencies, starvation of young, and reduced recruitment into the population. As the fish stocks have been depleted, the competition
Competition
Competition is a contest between individuals, groups, animals, etc. for territory, a niche, or a location of resources. It arises whenever two and only two strive for a goal which cannot be shared. Competition occurs naturally between living organisms which co-exist in the same environment. For...

 between marine mammals and fisheries has sometimes led to conflict. Large-scale culling of populations of marine mammals by commercial fishers has been initiated in a number of areas in order to protect fish stocks for human consumption.

Competition/Conflict with Aquaculture


Shellfish aquaculture takes up space so in effect creates competition for space. However, there is little direct competition for aquaculture shellfish harvest
Harvest
Harvest is the process of gathering mature crops from the fields. Reaping is the cutting of grain or pulse for harvest, typically using a scythe, sickle, or reaper...

. On the other hand, marine mammals regularly take finfish from farms, which creates significant problems for marine farmers. While there are usually legal mechanisms designed to deter marine mammals, such as anti-predator nets or harassment devices, individuals are often illegally shot.

Pollution


Contaminants that are discharged
Effluent
Effluent is an outflowing of water or gas from a natural body of water, or from a human-made structure.Effluent is defined by the United States Environmental Protection Agency as “wastewater - treated or untreated - that flows out of a treatment plant, sewer, or industrial outfall. Generally refers...

 into the marine environment accumulate in the bodies of marine mammals when they are stored unintentionally in their blubber
Blubber
Blubber is a thick layer of vascularized adipose tissue found under the skin of all cetaceans, pinnipeds and sirenians.-Description:Lipid-rich, collagen fiber–laced blubber comprises the hypodermis and covers the whole body, except for parts of the appendages, strongly attached to the musculature...

 along with energy. Contaminants that are found in the tissues of marine mammals include heavy metals
Heavy metals
A heavy metal is a member of a loosely-defined subset of elements that exhibit metallic properties. It mainly includes the transition metals, some metalloids, lanthanides, and actinides. Many different definitions have been proposed—some based on density, some on atomic number or atomic weight,...

 such as mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

 and lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...

; organochloride
Organochloride
An organochloride, organochlorine, chlorocarbon, chlorinated hydrocarbon, or chlorinated solvent is an organic compound containing at least one covalently bonded chlorine atom. Their wide structural variety and divergent chemical properties lead to a broad range of applications...

s; and polycyclic aromatic hydrocarbon
Polycyclic aromatic hydrocarbon
Polycyclic aromatic hydrocarbons , also known as poly-aromatic hydrocarbons or polynuclear aromatic hydrocarbons, are potent atmospheric pollutants that consist of fused aromatic rings and do not contain heteroatoms or carry substituents. Naphthalene is the simplest example of a PAH...

s. For example, These can cause disruptive effects on endocrine system
Endocrine system
In physiology, the endocrine system is a system of glands, each of which secretes a type of hormone directly into the bloodstream to regulate the body. The endocrine system is in contrast to the exocrine system, which secretes its chemicals using ducts. It derives from the Greek words "endo"...

s; impair the reproductive system, and lower the immune system of individuals, leading to a higher number of deaths. Other pollutants such as oil, plastic debris and sewage
Sewage
Sewage is water-carried waste, in solution or suspension, that is intended to be removed from a community. Also known as wastewater, it is more than 99% water and is characterized by volume or rate of flow, physical condition, chemical constituents and the bacteriological organisms that it contains...

 threaten the livelihood of marine mammals. Noise pollution
Noise pollution
Noise pollution is excessive, displeasing human, animal or machine-created environmental noise that disrupts the activity or balance of human or animal life...

 from anthropogenic activites is another major concern for marine mammals. This is a problem because underwater noise pollution interferes with the abilities of some marine mammals to communicate, and locate both predators and prey. Underwater explosion
Underwater explosion
An underwater explosion, also known as an UNDEX, is an explosion beneath the surface of water. The type of explosion may be chemical or nuclear...

s are used for a variety of purposes including military
Military
A military is an organization authorized by its greater society to use lethal force, usually including use of weapons, in defending its country by combating actual or perceived threats. The military may have additional functions of use to its greater society, such as advancing a political agenda e.g...

 activities, construction and oceanographic or geophysical research. They can cause injuries such as hemorrhaging of the lungs, and contusion and ulceration of the gastrointestinal tract
Gastrointestinal tract
The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....

. Underwater noise is generated from shipping
Shipping
Shipping has multiple meanings. It can be a physical process of transporting commodities and merchandise goods and cargo, by land, air, and sea. It also can describe the movement of objects by ship.Land or "ground" shipping can be by train or by truck...

, the oil and gas industry, research
Research
Research can be defined as the scientific search for knowledge, or as any systematic investigation, to establish novel facts, solve new or existing problems, prove new ideas, or develop new theories, usually using a scientific method...

, and military use of sonar
Sonar
Sonar is a technique that uses sound propagation to navigate, communicate with or detect other vessels...

 and oceanographic acoustic experimentation. Acoustic harassment devices and acoustic deterrent devices used by aquaculture
Aquaculture
Aquaculture, also known as aquafarming, is the farming of aquatic organisms such as fish, crustaceans, molluscs and aquatic plants. Aquaculture involves cultivating freshwater and saltwater populations under controlled conditions, and can be contrasted with commercial fishing, which is the...

 facilities to scare away marine mammals emit loud and noxious underwater sounds.

Global Climate Change


Two changes to the global atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...

 due to anthropogenic activity threaten marine mammals. The first is increases in ultraviolet radiation due to ozone depletion
Ozone depletion
Ozone depletion describes two distinct but related phenomena observed since the late 1970s: a steady decline of about 4% per decade in the total volume of ozone in Earth's stratosphere , and a much larger springtime decrease in stratospheric ozone over Earth's polar regions. The latter phenomenon...

, and this mainly affects the Antarctic
Antarctic
The Antarctic is the region around the Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica and the ice shelves, waters and island territories in the Southern Ocean situated south of the Antarctic Convergence...

 and other areas of the southern hemisphere
Southern Hemisphere
The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...

. An increase in ultraviolet radiation has the capacity to decrease phytoplankton
Phytoplankton
Phytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτόν , meaning "plant", and πλαγκτός , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...

 abundance, which forms the basis of the food chain
Food chain
A food web depicts feeding connections in an ecological community. Ecologists can broadly lump all life forms into one of two categories called trophic levels: 1) the autotrophs, and 2) the heterotrophs...

 in the ocean. The second effect of global climate change is global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...

 due to increased carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

levels in the atmosphere. Raised sea levels, sea temperature and changed currents are expected to affect marine mammals by altering the distribution of important prey species, and changing the suitability of breeding sites and migratory routes.

External links


"http://www.ucmp.berkeley.edu/mammal/mesaxonia/desmostylia.html"http://www.ucmp.berkeley.edu/mammal/mesaxonia/desmostylia.html