The basis of nearly all life is the production of complex organic molecules by green plants that use sunlight as an energy source to fuel the process (photosynthesis). In addition to carbon dioxide and sunlight, plants need some other chemical elements to form enzymes and structural molecules. These elements include nitrogen, phosphate, potassium, calcium, silica, collectively called "nutrient salts," plus other things, such as certain vitamins. If any of these necessary elements were in short supply, all the sunlight in the world would not help biological production. In terms of the major nutrients, the Southern Ocean is one of the richest in the world. South of the Antarctic Convergence, the surface waters contain levels of these nutrient salts that equal or exceed the maximum concentrations found in other oceans. And during the long austral summer, there is a near-constant supply of sunlight to be used as energy. Under these favorable conditions the Southern ocean teems with vast amounts of microscopic and minute life forms.

"Krill" is a general term used to describe about 85 species of open-ocean crustaceans known as "euphausids." They are the dominant form of zooplankton in the Antarctic. As the keystone species in the Antarctic energy flow, their importance to the ecosystem is immense. The most important species in Southern Ocean waters is Euphausia superba; the Antarctic krill, which grows to lengths of 60 mm (2.5 in) upon which many species of creatures depend directly or indirectly.

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Compared to other oceans of the world, the Southern Ocean harbors a meager fish community. In the Arctic Ocean, for example, abundant schools of pelagic fish feed on zooplankton and are a major link in the northern food chains. Not so in the Antarctic where schools of fish are absent. One factor responsible for this scarcity is the probably related to the great depth at which the relatively narrow Antarctic continental shelf lies. Without the continental shelf, fish lack the shallower waters necessary for spawning.

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There’s a popular myth that says the Southern Ocean teems with bird life, yet only 43 species breed within the limits of the Antarctic Convergence and 19 on Antarctica proper. Relative abundance is distorted because birds cluster in dense breeding colonies on space. Antarctic birds cling to the periphery of the continent. And for these birds the sea is the fundamental source of food; even the terrestrial predatory birds are but one step removed from an ocean diet.
Many of the seabirds live on fish and squid as their main food sources. Smaller seabirds and penguins feed on fish and squid, too, but rely heavily on krill as the staple of their diet. This fact is a considerable advantage to an ocean living bird since krill is found near the base of the food chain and is thus abundant. Still, with the richness found in the water, many species of seabirds often fly endless miles in their search for food. Prey is widespread over a vast ocean.

The Peninsula is one area where the Arctic tern is absent, but the Antarctic tern (Sterna vittata) is present. It closely resembles the Arctic species, but is more robust. Antarctic terns live on the Peninsula all year, nesting and raising their chicks during the summer, feasting on tiny silverfish and krill. During the winter, the Antarctic terns may generate some heat by exercising - they shiver.

An unusual member of the Charadriiformes is the Snowy Sheathbill (Chionis alba). White and plump, these pigeon-sized birds with pink leathery skin near their bills, are gregarious and pugnacious birds, avid scavengers that haunt seal and penguin colonies to seize afterbirths, eggs, weak young, carcasses, and anything else they can find to consume. Sheathbills also pluck invertebrates from seaweed but are masters at stealing a meal by attacking and distracting penguins when the larger birds are feeding their own chicks. When the adult penguin is interrupted, it regurgitates its catch, which the sheathbill steals. Although they fly well and will make long journeys, even over sea, they spend most of their time on the ground. They swim well although they are the only birds in the Antarctic without webbed feet. Sheathbills nest in isolated pairs in a crevice or among rocks.

The second order of birds found in the Antarctic, on the Peninsula, is the Pelecaniformes, represented by the single species, the Imperial (formerly Blue-Eyed) Shag (Phalacrocorax atriceps). These elegant black and white cormorants nest in colonies close to sheltered waters. They build nests, often on cliffs, out of seaweed, lichens and feathers and glue it all together with wet guano. During the breeding season, the shag has a cobalt-blue eye ring and brilliant orange caruncles (fleshy structures in front of their eyes, above the bill). Imperial shags stay in Antarctica as long as there is open water available where they dive deep for fish and migrate north when the seas freeze over.

The third order of birds found in the Antarctic is the Procellariiformes, a group that is quite diverse with many species in it. A variety of these tube-nosed birds are observed when crossing the sea to Antarctica, and many breed on sub-Antarctic islands, but few breed south of the Convergence. The largest of these birds are the albatross with long tapering wings and elegant soaring flights. The Wandering Albatross (Diomedea exulans) is the largest of all followed closely by the Royal Albatross (Diomedea epomophora). With a wingspan of nearly 12 feet and a weight of 21 pounds, these large albatrosses glide effortlessly over the seas, wingtips appearing to caress the waves as the bird skims down into a wave trough and rises into the wind. Both Wandering and Royal Albatross spend much of their early lives at sea, coming to land once they begin to mature. These birds can live up to 80+ years but many are killed each year by the hooks of long-line fisheries.

Black-browed Albatross (Diomedea melanophris) and Grey-headed Albatross (Diomedea chrysostoma) are often seen on the Southern Ocean. These birds have wingspans of roughly 7 to 8 feet and nest on sub-Antarctic islands. The smaller Light-Mantled Sooty Albatross (Phoebetria palpebrata) is an exquisite bird of contrasting gray with a white ring setting off its dark eye. It, too, nests on islands north of the Convergence. Another large bird commonly seen on the Southern Ocean is the Southern Giant Petrel (Macronectes giganteus) and the very similar Northern Giant Petrel (M. halli). The Southern Giant Petrel, which has a greenish bill rather than one tinged red, is the more common one in the Antarctic region. Adults are quite large, with nearly 7-foot wingspans, but their bodies are chunkier than those of the albatrosses. Adults are either dark brown or white with brown flecks. Giant Petrels nest in scattered places on the Peninsula and have earned the nickname, stink-bird for their habit of spewing forth a noxious regurgitate of oil and food when bothered by an intruder.

The lovely brown and white Antarctic Petrel (Thalassoica antarctica) breeds in huge colonies on a few islands near Antarctica and along the Antarctic coasts in colonies that may number over a million birds. The slightly smaller Cape Petrel (Daption capense) is also brown and white, but wears its colors in a checkerboard pattern. It has similar nesting locations as the Antarctic Petrel, including on the Peninsula. The small, all-white Snow Petrel (Pagodroma nivea) is a characteristic bird of the pack ice and adjacent seas. Nesting on the Antarctic continent, often on rocky mountain slopes, and on the Peninsula, the Snow Petrel is sometimes seen resting on ice floes or icebergs.

The silvery Antarctic Fulmar (Fulmarus glacialoides) looks similar to a gull, but with tubenoses. Ocean scavengers and
Numerous other petrels, prions, shearwaters and storm-petrels roam the Southern Ocean, the most abundant of which is the tiny dark brown Wilson’s Storm Petrel (Oceanites oceanicus). Weighing but a couple of ounces, Wilson’s Storm Petrels flutter over the water, dangling their dark legs webbed with yellow highlights into the sea, pecking little organisms off the surface. Their nests are hidden in burrows and rock piles (in such places as on Elephant Island) to avoid the predatory skuas and gulls. During the winter, these little birds range as far north as New York.

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Penguins are the birds that people most often associate with the Antarctic. Worldwide, 18 species are recognized and confined to the Southern Hemisphere, but only 5 are truly Antarctic in the sense that they breed on the continent and adjacent islands, or fast ice attached to the continent.

Penguin feathers are extremely fine. At 70 feathers per square inch, the densest coverage of any bird, it almost seems as if the penguins are furred. Underneath this layer, a felt of woolly down overlays a thick layer of fat. A layer of bubbles trapped in the feathers provides further insulation. To keep their feathers in good shape, penguins preen a lot. They maintain their feathers with oil secreted by the uropygial gland (oil gland) found at the base of their tail. The bird dips its beak into the gland, spreads the oil over its feathers, and thus waterproofs its body, keeping the cold ocean away from its skin.

Penguins are so well insulated that they actually have trouble staying cool and can easily overheat on a hot summer day! It is not uncommon when the sun shines in a summer-blue sky to see penguins panting with mouths wide open, flippers held stretched out to let air carry away body heat, and feathers ruffled to let trapped warm air to escape.

During mating, the male acts like a perfect gentleman, often bowing to his mate, who returns the gesture as they reinforce their pair bond. Gentoos don’t fast before egg-laying as both parents forage during the day and return to the nest later on. Until the eggs hatch, both parents share incubation duties. After 3 weeks, the chicks form crèches and go to sea on their own at about 8 weeks of age but they come back to shore every evening to be fed by an incoming parent.

In areas where the breeding ranged of the three species of brush-tailed penguins overlap, they are ecologically segregated in order to divvy up the resources. The segregation during the summer breeding season results from differences in breeding chronology, foraging behavior, and life history tactics. For example, Chinstrap penguins feed up to 20 miles offshore, and dive to depths of 200 feet for their prey. In January, Chinstrap chicks are just entering crèches. Adélie penguins travel 30 miles on feeding forays, and dive to 250 feet. Their chicks are already fledging in January. Gentoo penguins may only go out 15 miles, but dive to depths over 400 feet for fish and squid.

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The great historical exploitation of the Southern Ocean, with the slaughter of whales, changed the face of the ocean dramatically. Since an Argentinean company established the first Antarctic whaling station at Grytviken on South Georgia in 1904, more than 1.5 million whales have been slaughtered in the Southern Ocean alone. Eight out of 10 species are now severely endangered, and some have lost over 90% of their numbers. Nonetheless, whales still frequent the Antarctic waters, providing a thrill to those travelers who cross the ocean to visit the continent.

Whales belong to the order "Cetacea" and are divided into two main groups: baleen whales, or Mysticeti ("mustache cetaceans"); and toothed whales, the Odontoceti ("toothed cetaceans"). The odontocetes for the largest group of cetaceans, and include porpoises and dolphins, some species of which are only 6 feet long, as well as the giant sperm whale, which may reach 50 feet in length. The teeth of these animals are generally conical, efficient for catching fish and squid. Atop their head, odontocetes sport a single blowhole. A major adaptation of toothed cetaceans is their ability to echolocate, or use high frequency clicks and whistles to navigate, and examine their environment. Other sounds made by the toothed whales allow the animals to communicate with one another.

Five species of Toothed Whales exist in the Southern Ocean. There is one predominant Dolphin species observed south of the Antarctic convergence.

Orca (Orcinus orca)

Although called "killer whale," the animal is no more a killer than any other predator and is actually the largest member of the dolphin family. Worldwide in distribution, orca seem to live in specialized subpopulations, each adapted to living off the resources in its home range.

With an extremely robust body marked in contrasting black and white areas, the orca is a striking animal. Its back and sides are black, as are the upper surfaces of flukes and flippers, while the undersides are white. White patches behind the eye, on the flank, and behind the dorsal fin characterize the species. The most prominent feature is the dorsal fin on their back. The fin is highly variable in shape but on adult males, it may reach a height of 1.8 meters (6 ft). On females and younger males, the dorsal fin is much smaller, perhaps only 3 feet tall.

At birth, an orca calf is about 2.5 meters (~ 8 ft) long and weighs roughly 160 kg (~ 350 lbs). An adult male may grow to lengths of 9 meters (30 ft) and weigh 5600 kg (6 tons). Males may live 50-60 years. Females reach lengths of 7.9 meters (26 ft) and weights of 3800 kg (4.2 tons) and live 80-90 years.

Orcas position themselves near the ice edge and in channels among the pack ice where they can prey on seals, penguins, and baleen whales. Orcas are often observed working together to catch a seal: the orcas locate a seal lying on an ice floe, then dive. As the surface, the orcas land on the ice, causing one side to tip towards them, dumping the seal into the water, and possibly into the waiting jaws of the hunters. It is estimated that about 80,000 orcas live in the Antarctic during the summer, and little is known about their migration away from the area during the winter. Some may even stay in Antarctic waters year-round.

The largest of the toothed cetaceans, the sperm whale is found in all oceans from the Arctic to the Antarctic. It gets its name from the spermaceti, a semiliquid waxy oil that fills the spermaceti organ, or "case" that in the whale’s head. While the function of this organ is uncertain, the spermaceti was commercially valuable in the 18th and 19th centuries for its use in making candles and later, as a base for cosmetics.

Stable, long-term groups of females form the core unit of sperm whale societies. Females give birth, once they reach sexual maturity, only once every 4 to 6 years, with a gestation period up to 18 months. With slow maturation of the calf and long-term care invested by the mother, sperm whale populations grow very slowly. Males leave the group when they are about 6 years old to join bachelor herds, and older males swim the world’s oceans, solitary in their prime and old age.

Sperm whales are among the deepest of divers. An extremely large and boxy head dominates the squarish body of the sperm whale; the name "macrocephalus" means "big head." The single blowhole angles to the left, giving the sperm whale a distinctive spout. Their dark, grayish brown body is wrinkled and the dorsal fin is small and rounded. The lower jaw of the sperm whale is very narrow and studded with 20 to 26 pairs of conical teeth that fit into sockets in the upper jaw, which lacks teeth.

Males are roughly 1/3 longer than females. They reach lengths of 18.3 meters (60 ft) while females only attain lengths of 11 meters (36 ft). Males may weigh 57,000 kg (28.5 tons) and females around 24,000 kg (12 tons). Sperm whales can live at least 60-70 years.

Solitary sperm whales are sometimes seen at sea, but most are observed (on a voyage to the Antarctic Peninsula) near Cape Horn, often in groups of 10-15. Only adult males are found closer to Antarctica where they move to feed. Their main food items are squid for which the whales dive to great depths. Sperm whales are capable of diving a mile or deeper for more than two hours.

Beaked whales, and the related bottlenose whales, are very rare to observe and several species of these unusual creatures have never been seen alive; they are known only from dead specimens or skeletons! Beaked whales have an elongated rostrum extending forward from a somewhat bulbous forehead (called a "melon"). Most species have only a single pair of teeth, which develop and erupt from the gums in adult males. These teeth are often exposed outside the closed mouth, like tusks. Females do not have these teeth. Beaked whales are deep divers that feed mainly on squid and fish. Because they spend so little time near the surface, it is always a surprise to see a beaked, or bottlenose, whale while crossing the Drake Passage en route to Antarctica.

Arnoux’s Beaked Whale is found throughout the Southern Ocean down to the ice edge around 78º S. Sometimes they become trapped by ice and are forced to overwinter in Antarctica. Many scars often mark their tubular gray body, which is about 30 feet in length. Generally shy they are also difficult to identify at sea. Very little is known about this species.

This 7-meter (25 foot) whale looks similar to Arnoux’s beaked whale with which it may easily be confused since their ranges overlap throughout the Southern Ocean. When compared to Arnoux’s beaked whale, the Southern Bottlenose Whale tends to be pale grayish brown or tan in color with a more prominent melon above a shorter rostrum. Adult males may appear almost white. Circumpolar in distribution, this cetacean has been observed as far south as 73º S, in the Ross Sea and tends to be found, during summer, within 60 nautical miles of the ice edge. Under the right conditions, the bushy blow of this whale is readily visible. An estimated 500,000 Southern Bottlenose Whales live south of the Antarctic Convergence during the austral summer.

This cetacean gets its name from the unique dentition of adult males. The two external teeth in the lower jaw extend upwards, growing to cross over the top of the beak and pressing tightly against it. This strange feature results in males being barely able to open their jaws; they must suck their prey, small squid, into their mouths! Rather than erupting from the tip of the lower jaw as in Arnoux’s species, the Strap-tooth teeth appear well behind the tip of the jaw.

Overall, the Strap-toothed Whale looks similar to Arnoux’s beaked whale in body shape, but its coloring is quite distinctive. Most of the animal’s head is white, with a dark mask covering the eye and melon region. The body shades to dark towards the rear. Very little is known about this species, but they are sometimes observed while crossing the Drake Passage between South America and the Antarctic Peninsula.

While many dolphin species are observed near South America, the primary dolphin that is seen south of the Antarctic Convergence is this striking black and white cetacean. A small dolphin barely 2 meters (~6 ft) in length, it likes to ride the bow waves of ships. Its name refers to the somewhat hourglass pattern of white on its flanks, but early American whalers called this animal the "sea skunk," in recognition of the black and white stripes on its sides. The Hourglass Dolphin has a very compact body with a short beak but large dorsal fin that is sometimes strongly hooked. It is often associated with the cool waters around Antarctica in the West Wind Drift.

Six species of baleen whales exist in the Southern Ocean.

Southern Right Whale (Eubalaena australis)

The Southern Right Whale is a large, black, rotund animal lacking a dorsal fin on its broad back. Its massive head has a strongly arched mouthline and numerous callosities (raised thickened and roughened patches of skin tissue usually infested with whale lice) that look like barnacles growing on the whale’s head. Very narrow and long (2.7 meters, or 9 ft) baleen plates hang from the Southern Right Whale’s upper jaw. They skim feed, moving through patches of zooplankton to filter prey through the fine fringe. These large animals reach about 17 meters (56 ft) in length and weigh around 90,000 kg (100 tons). About 60,000 were killed during the 19th century, being hunted to near extinction prior to the advent of modern 20th century whaling. These whales are sometimes seen off South America and may be observed during the austral summer when they feed in waters around Antarctica.

Sei Whale (Balaenoptera borealis)

Sei (pronounced "sigh") whales, when sighted, are typical alone. With a sleek, dark gray body the Sei whale is one of the fastest of the large whales. This animal grows to about 19.5 meters (64 ft) and may weigh around 45,000 kg (50 tons). It feeds on a variety of prey including small fish, squid, krill, and smaller zooplankton such as copepods. It is the only mysticete that both gulps and skims to filter food. Gulping is used to catch fish, and skimming to capture copepods. An estimated 200,000 Sei whales were killed in Southern Ocean waters during the 20th century whaling era and their populations remain severely depleted in the region. Northern populations seem to be reasonably abundant.

Antarctic Minke Whale (Balaenoptera bonaerensis)

Only recently assigned as a species separate from the common Minke Whale (Balaenoptera acutorostrata), the Antarctic Minke is a fairly small baleen whale, attaining lengths of 10.7 meters (35 ft) and weights of 9100 kg (10 tons). Like the Minke, this species is sleek with a sharply pointed head and a falcate dorsal fin. Unique to this species is the asymmetrical coloration of the baleen plates. Dark gray above and light below, the Antarctic Minke appears to be circumpolar around the continent. They summer around Antarctica, feeding mainly on krill, and are often observed around the Peninsula. Antarctic minkes often appear curious, approaching tour ships and the smaller zodiac inflatable boats.
More than 100,000 Minke whales were killed in the Southern hemisphere during the 20th century and Japan continues to kill several hundred a year, for questionable "scientific" purposes, although much of the meat ends up in the markets.

Fin Whale (Balaenoptera physalus)

The second-largest whale in the world, the Fin is a sleek giant. Growing to nearly 27 meters (90 ft) this giant weighs in at 120,000 kg (130 tons) and may live to be 80 years old. Dark gray above and whitish below, the Fin Whale sports an unusual pigmentation on its lower jaw: the left side is black, the right side white. This coloration has never satisfactorily been explained. Seen from above, the Fin has a chevron pattern of swirls on its head, markings that identify individual animals. The Fin is found in waters throughout the world, tending to concentrate in coastal and shelf waters. Fin whales feed on krill and small schooling fish, where those are to be found, and catch their prey by plunging, mouth agape, into prey schools. Pleats on the underside of their throat expand like an accordion to allow huge gulps of water and prey to be taken in at once.

Until the explosive harpoon and steam power to drive faster boats were invented, whalers were unable to catch the speedy Fin Whales. With the coming of the newer technology, Fins fell quickly, and in greater numbers than any other species, to the harpoon. Some 725,000 Fin Whales in the Southern hemisphere alone were killed. There is no reliable estimate on the remaining population in the Southern Ocean, but the Fins may be making a slow recovery off Antarctica.

Blue Whale (Balaenoptera musculus)

The largest animals ever to grace the planet, Blue Whales are giants of the sea. Prior to World War I, the largest Blue Whale killed by whalers measured more than 30 meters (100 ft) long and weighed nearly 180,000 kg (~200 tons)! Today, their numbers dramatically depleted, such huge individuals are rare.

The mottled blue-gray coloration of this species is unique. The large flat head has a prominent splashguard in front of the blowholes and the spout of this creature rises 30 feet when the Blue surfaces. Blue whales feed almost exclusively on krill by lunging into schools of the tiny crustaceans. The abundant Euphausia superba swarms around Antarctica provide a bountiful feast for them. A large Blue may eat 5500 kg (6 tons) of krill every day!

During the 20th century, 360,000 Blue Whales were killed in the Southern Hemisphere. Almost all populations were substantially reduced, some by as much as 99% of their original numbers. In Antarctica, the once vast populations of Blues are gone. Only a few hundred individuals are scattered through the Southern Ocean around the continent.

Humpback Whale (Megaptera novaeangliae)

The Humpback whale is probably the best known, and most easily recognized, of all the whales. Preferring waters close to shore allows people to frequently observe the Humpbacks, and a substantial tourism industry exists in many places around the world where people can go to watch these whales. The migrations of the humpback whales take them thousands of miles from summer feeding to winter breeding grounds and the Antarctic is no exception.

During the austral summer, many humpback whales feast in waters around the Antarctic Peninsula, consuming 2 tons of krill a day. The long pectoral flippers that are so characteristic of this species (their scientific name means - big wing of New England) allow the whale to maneuver to catch its prey. Humpbacks often slap the water with their flippers or leap clear of the water in a spectacular display called "breaching." No one knows for certain just why they perform such behaviors: it may be to communicate with other whales, to play, or to scratch an itch.

About 200,000 Humpbacks were killed in the Southern Hemisphere between 1904 and 1983. Prior to whaling, an estimated 100,000 Humpbacks were thought to visit Antarctic waters every year! Now, there may be 3,000 whales that visit the area, but their populations are recovering and an estimated 17,000 Humpbacks live in the Southern hemisphere. It is not unusual, during the latter part of an austral summer expedition, to see dozens and even a hundred whales.

Conclusions

With the decimation of so many of the great whales, an incredible abundance of krill filled the Southern Ocean. Just the loss of about 97,000 humpbacks per year represents about 23,280,000 tons of krill not being consumed. Add to that figure the amount of krill no longer consumed by the giant Blue Whales, and all the other species, and the amount of "surplus" krill is staggering.

Ripples reverberate throughout the Southern Ocean through the food chain: with the demise of hundreds of thousands of great whales, enormous stocks of krill now fill the seas around Antarctica. Other animals - birds, especially penguins, and seals - now have lots of krill to eat, and the populations of these species may reflect this change in the food chain.

All of the great whales are currently protected in Antarctic waters (with the aforementioned exception of the minke whale that is hunted by the Japanese), which have been designated a sanctuary. However, there is increasing pressure from certain nations to open these waters to more whaling, even though species like the Fin and Blue are protected worldwide as endangered.

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Three families of marine mammals are included in the group called "pinnepeds." Pinnipeds means ‘fin-footed’ and refers to the modified limbs that have a fin-like appearance in these animals. Each limb has 5 broadly webbed, oar-like digits, which form the flipper. Pinnipeds are carnivores that are historically related to bears or otters. Walrus (family Odobenidae) only live in the Arctic, and will not be considered here. Six species of true seals (family Phocidae) are found in the Antarctic and one species of eared seals, or sea lions, (family Otariidae) lives here, too. In fact, seals are the only truly indigenous terrestrial mammals in Antarctica.

Pinniped limbs are much shorter than those of most mammals. The "armpit" and "crotch" are actually the wrist and ankle, respectively. The bones of the hands and feet are greatly elongated. Bound together in a web of skin and tissue, these long bones form oars that propel the animal through the water.

Seals hear quite well above water, but they hear even better underwater. Some seals are even able to use sonar to navigate, locate prey, and avoid obstacles. If a seal’s ears provide sonar, its whiskers, or vibrissae, provide the radar. Whiskers are highly sensitive antennae, which allow the seal to feel underwater vibrations of their prey. Seals also use their whiskers as tactile organs, feeling out their environment or investigating a neighbor.

Like the eyes of a cat, seal eyes are designed for low-light hunting. On land, the pupils are little more than vertical slits, but underwater they dilate into huge rounds. The tapetum lucidum, a silvery layer being the retina, amplifies all available light, somewhat like the reflector on a flashlight. Seal vision is particularly sensitive to the greens of seawater. Upper and lower eyelids protect the eyes, together with a third eyelid called the nictitating membrane, which works like a windshield wiper to remove sand and other small particles.

True seals, or phocids, lack external earflaps and are thus often called "earless seals," somewhat of a misnomer because they do have ears! The ear opening is simply a small hole that closes underwater.
The earliest true seals fossils date back some 11 million years and indicate that a member of the mustelid, or weasel family that shared features similar to marine otters, were the ancestors of the Phocidae. Modern phocids became established about 4 million years ago, around the beginning of the Pleistocene Ice Ages.

Phocids propel themselves through the water by using their broad hindflippers. Their power comes from strong back muscles, so this part of their anatomy is well developed. The vertebrae at the tail end, where the propulsion muscles attach, are strongly built. Seals swim by stroking with their hind flippers; the front flippers stay tucked against the body. These modifications for life in the water have come at the cost of mobility on land.
With weak shoulder girdles and small forelimbs, phocids cannot lift themselves up to move across the ground. Instead, they drag themselves over the earth, lumbering like giant caterpillars. Sharp claws on the foreflippers help them to pull their bodies onto the ice and are useful in scratching an itch.

This seal is the largest phocid in the world and spend most of their lives out at sea. Remarkable divers, elephant seals can dive as deep as 1500 meters (5000 ft) and stay underwater for up to two hours! Adult males are massive - males are up to five times larger than females, weighing up to 5000 kg (5.5 tons) and reaching 5 meters (16 ft) in length. When sexually mature, males develop an elongated snout with an inflatable proboscis. This structure is inflated during aggressive encounters with other males, an impressive display as the males roar like lions, rear up high on their bellies, show their sharp teeth, and slam their necks into one another. Females are sleek, lack the large nose, and weigh in at 900 kg (~ 1 ton). Males live 15 years, females 23 years.

An unusual feature of the Southern Elephant Seal is that it undergoes a catastrophic molt every year. Not only is the hair shed, but also the upper layer of the skin sheds in large patches, leaving bare skin visible as the new hair emerges. While in this molt stage, elephant seals remain ashore, fasting for nearly a month. They often crowd tightly together.
Southern Elephant Seals migrate over vast areas of the Southern Ocean, breeding on many subantarctic islands, especially South Georgia. A number of them haul out in places along the Antarctic Peninsula.

Contrary to its name, the Crabeater seal feeds primarily on krill, typically foraging in the dusk, dawn, and nighttime hours when krill rise to the surface. To efficiently catch their prey, Crabeater seals are equipped with a unique dentition: the cheek teeth have highly modified lobes that interlock to form a sieve. In a way, these teeth function like baleen, straining the water out and leaving the krill in the mouth. A bony knob behind the last molar even closes off any escape route.

The long slender body (2.6 meters, or 8 ft) is silvery gray when the fur is dry, and dark when wet. Scars, from Leopard Seals that prey upon young Crabeaters, often mark the fur. They favor pack ice habitat and are observed, frequently in groups, hauled out on ice floes, sleeping after a night of diving for krill.

Crabeater seals are the most numerous seal on the planet. Estimates of their population, all of which is found in Antarctica, go as high as 30 million animals! Their numbers are even increasing, perhaps due to the surplus of krill now available with so few of the great whales to feed on the euphasids. In addition to the increasing population, females now reach maturity at a much younger age than ever before; since whaling has stopped, maturity has dropped from 4 to 2.5 years.
One of the strangest things about Crabeater Seals is that some of them wander far up into the Dry Valleys on the Antarctic continent where their mummified carcasses have been discovered at elevations of 1100 meters (3600 ft).

A long sinuous body, large heavy head with wide mouth, the Leopard Seal gives the impression of being a sinister animal and is often described as looking "reptilian." When hauled out on ice, this seal is dark above, silvery below, and quite spotted. Adults are about 3.5 meters (11.5 ft) long and weigh between 450 - 590kg (990 - 1300 lbs), with females being slightly larger than the males. Long foreflippers help power and steer the Leopard Seal gracefully through the water.

Leopard seals are the top predators in the Antarctic, ferociously preying on most everything in the food chain including krill, squid, fish, penguins, and other true seals and fur seals. Their dentition reflects the wide range of their diet. Large canine and postcanine teeth are used for eating seabirds and seals, while multilobed cheek teeth are similar to those found in Crabeater Seals and allow the Leopard Seal to eat krill. An estimated 200,000 or more Leopard Seals live throughout Antarctica

Because Weddell Seals are very approachable, they make easy research subjects and much is known about them. Scientists have outfitted Weddell Seals with all sorts of tags and instruments to study their physiology, diving capabilities, population dynamics, and feeding behaviors.

Weddell Seals mate and give birth in nearshore fast-ice habitats around Antarctica, a situation that gives rise to heightened competition among males who defend fast-ice territories during the austral summer. Males rarely haul out during this season and virtually all mating occurs under the ice. The single pup, born in early to mid summer, stays with the mother for 7 or 8 weeks, then is abruptly weaned and abandoned.

Because they spend their solitary lives in ice, Weddell Seals need a way to keep breathing holes open. They have very large, protruding canine and incisor teeth that they use as chisels to keep breathing holes in winter ice open. Though they lack predators in their fast-ice habitat, the eventual wearing down of these teeth may be one factor that limits their age. If the seal’s teeth are worn down to the extent they cannot open the ice, they drown, and Weddell Seals rarely attain the age of 20.

Weddell Seals eat a variety of prey, depending upon where they are. In some places, the seals eat mostly nototheniid fish, while in other locations krill is a favorite food. Deep divers, Weddell Seals go down 600 meters or more, perhaps to forage on the seafloor. Chinstrap penguins are sometimes killed and eaten by these seals.

Also called the "singing seal," the Ross Seal makes siren-like underwater vocalizations. When approached, it raises its head, opens its mouth, and growls and gurgles in a vocal threat display. Described by Captain James Ross in the early 1840’s, this seal is fairly small, with a broad head and large dark eyes. It reaches lengths of 2.4 meters (~8 ft) and weighs only 200 kg (440 lbs). Long streaks on its dark fur that run from the mouth down to its chest identify this seal that is rarely encountered.

With a widely dispersed but circumpolar distribution around the Antarctic continent, the solitary Ross Seal favors heavy, consolidated pack ice. Little is known about this seal, but data indicate that they prey primarily on deepwater squid and fish.

The eared seals date back to a time roughly 23 million years ago, when a bear-like land ancestor returned to the water and, over time, adapted to life in this new medium, giving rise to a new group of animals. Unlike the phocids, the otariids have a strong shoulder girdle to which their powerful propulsive muscles attach. The hindflippers have elongated digits with the "big toe" and "pinky toe" bones even longer than the other three. The middle digits have claws on them, which the eared seal uses for grooming. Eared seals can walk on land using both their hind and foreflippers. It is the foreflipper, a long fin-like structure that moves the eared seal through the water. Their massive necks attest to the strong muscles used to power the front limbs. The only eared seal found in the Antarctic is the Antarctic Fur Seal (Arctocephalus gazella). A short, dense layer of hair close to the skin traps air and provides waterproof insulation. An outer layer of longer, less dense hair is typically dark brown or charcoal. Males are much larger than females and have a thick neck and chest upon which grows a dark mane of fur. A large male may be 2 meters (6.7 ft) long and weigh 200 kg (440 lbs). Females lack the thick neck and are only 1.35 meters (4.5 ft) long and weigh 40 kg (88 lbs). Most pups are dark black when born, but a few are a lovely creamy color.

Breeding colonies of fur seals are scattered around Antarctica, with most occurring near the Peninsula and on islands around the Convergence. During the 18th and 19th centuries, Antarctic fur seals were virtually exterminated by commercial sealers who prized the fine pelts. Shortly after large-scale killing ended, a small colony near South Georgia Island increased to 2 million fur seals and this colony may have been the source of new animals for many other colonies.

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