Return to the Sea: The Life and Evolutionary Times of Marine Mammals

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The rest of the whales, as well as all dolphins and porpoises, are grouped together as odontocetes because they have teeth.


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Sperm whales, the largest odontocetes at up to 18 meters 60 feet long, dive to as deep as 1. Most females of both sperm and pilot whales stay with their mothers their entire lives; but the males more often leave and form all-male groups. In sperm whales, they even live alone as "bachelors," only meeting up with other whales for breeding. The manatee left , a member of the herbivorous order Sirenia, is found in warm coastal waters, including the southern United States. The elephant seal right belongs to the pinniped suborder of the order Carnivora, and is found as separate species in the northern Pacific, and in the southern Atlantic and Antarctic islands.

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Although called a whale because of its size, the killer whale Orcinus orca is actually the largest member of the dolphin Dephinidae family. Killer whales, also often called orcas, have been studied most extensively in the Puget Sound off Washington state and British Columbia, where they are divided into two types: residents and transients. Resident orcas eat fish and spend their lives in specific regions.

Male and female offspring stay with their mothers their entire lives. Transient orcas eat primarily marine mammals, but even birds, turtles, or sharks are eaten on occasion. Transient orcas move between areas much more frequently; consequently, their family units are not as stable as the residents' units. The smaller dolphins feed on a wide variety of organisms. Some, such as the pan-tropical spotted dolphin or the common dolphin, feed in the deep waters of the open ocean and are not seen by humans as often as the many species that come close to shore. Spinner dolphins have different forms: some live only in the deep ocean like those mentioned above, whereas others feed in deep water at night but rest in shallow bays during the daytime.

Several dolphins, called river dolphins, live only in fresh water.

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Dusky dolphins of the southern hemisphere cooperate to herd schooling fish, to feed on them more successfully. Bottlenose dolphins are very common in the wild and can be found close to shore almost anywhere except in Arctic and Antarctic waters. These dolphins feed on a wide variety of prey, mostly fishes, and many have adapted to living in areas close to humans. Flipper was a trained bottlenose dolphin that starred in a movie and a television show in the s. Porpoises are similar to dolphins, but tend to occur more often in colder waters.


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They also have different teeth, dorsal fin shape, and skull structure from those of true dolphins. The vaquita, or Gulf of California harbor porpoise, is endangered due to many individuals being killed in gill nets.

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Manatees and dugongs are included in the order Sirenia. They are the only herbivores among marine mammals, feeding on sea grasses in tropical waters. They are slow-moving coastal animals, which is unfortunate for many manatees that often are struck by boats, being killed or severely injured. Because of their slow movements and inshore habitats, manatees often are kept successfully in large commercial aquaria. The order Carnivora, of which cats and dogs are members, includes the pinnipeds seals, sea lions, and walruses ; sea and marine otters; and polar bears.

All pinnipeds spend part of their time on land or ice but feed in the sea. Most mate on land or ice, and all need to be out of the water to give birth. The newborn pups are nursed anywhere from 3 days to 3 years, depending on species, and are mostly independent afterwards. True seals, such as harbor seals, harp seals, or elephant seals, have thick blubber layers for insulation and have a strange way of getting around on land.

They have to wiggle forward like an inchworm because their front flippers do not reach the ground. Despite their clumsiness on land, they are excellent swimmers. True seals have shorter infant care than the other pinnipeds. Fur seals and sea lions have thinner blubber layers, and rely more on hair for insulation.

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They can walk on all four flippers, but generally do not dive as deep as the true seals. California sea lions are commonly trained to clap and play with balls in aquaria. Walrus, known for their long ivory tusks, occur only in the Arctic Ocean. They are also common entertainers in aquaria. Sea otters and marine otters, both of the Pacific coast of the Americas, have the thickest fur of all marine mammals, and spend much of their time keeping it clean.

Sea otters use their paws to gather shellfish to eat, and may even use rocks to crack open the shells. Marine otters cannot use their paws the way that sea otters do, and instead just grab prey with their mouths. Although they do not spend as much time in the water as other marine mammals, polar bears are well adapted to life in the water. They swim with large paddle-shaped fore and hind feet, and feed on fishes in the water and seals on land or ice.

Occasionally, they will even eat white whales and have been known to attack humans when threatened or approached too closely.

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Marine mammals still serve as a primary food source for many aboriginal societies living near coasts worldwide. This seal meat is drying outside a residence in Savoonga, a small community on St. Lawrence Island in the Bering Sea, Alaska. Marine mammals are prominent residents and entertainers at aquaria and entertainment complexes throughout the world.

This bottlenose dolphin "smiles" for the camera with its celebrity visitors, track and field athletes Calvin and Alvin Harrison. Humans have had a long history of interaction with marine mammals, primarily with humans as hunters and marine mammals as prey.

Whales Returned to the Sea | Smithsonian Ocean

By the middle of the twentieth century, large-scale, unregulated whaling led to severe depletion of some populations. Within the last half century, recognition of this fact, combined with insights into the intelligence of marine mammals, has led to the emergence of protection and appreciation as the primary interactions between humans and marine mammals. Aboriginal hunters of many coastal groups have long exploited whales, seals, sea lions, and other marine mammals for subsistence survival and, in the case of seals, fur. The effect of Native hunters on population levels was almost always small, unlike for some terrestrial mammals, because hunting large mammals on the open ocean is hard and dangerous, and an enormous amount of meat can be harvested from a single kill.

Shore-dwelling seals are more susceptible to local extirpation, but even that was rare in the absence of commercial rather than subsistence hunting. Unregulated commercial hunting, however, can and has led to widespread decline in marine mammal populations. For example, fur seals were driven close to extinction in the s by overhunting.

In colonial times, oil rendered from whale fat blubber was the main product that drove commercial whaling. Before the development of petroleumbased fuels, whale oil was widely used in lamps. Commercial whaling in the American colonies and elsewhere depleted coastal whale populations early on. Larger whaling ships and longer voyages further out to sea were the pattern in the s, until exploitation of fossil fuels largely ended commercial whaling for oil.

Whaling for meat continued to be a commercially profitable enterprise, however, and the development of sea-based "factory ships" for processing whales led to continued decline in the numbers of whales. Recognizing the serious depletion of whale populations, the International Whaling Commission IWC was founded by international agreement in to regulate the whaling industry. Volume 29 , Issue 1 January Pages Related Information.

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