Natural predators of seals include large sharks, especially the great white shark, the orca, or killer whale, and other seals such as the leopard seal. Polar bears kill seals on land and ice in the Arctic. There are even reports of eagle attacks on baby Caspian seals.

Perhaps the greatest menace to seals are humans, who have long hunted seals for food and seal skins, used for clothing and even housing and small boats. Commercial sealing developed into a profitable business in Europe and colonial America by the 1700s. Like whales, seals were hunted for their blubber, which was converted to oil for fuel, lubrication, and tanning. Fur seals were especially valued for their luxuriant pelts. Today seals are still killed for their skins in some countries, such as Canada and Russia.

After only fifty years of commercial hunting in the 1800s, the northern elephant seal became nearly extinct. Hawaiian and Mediterranean monk seals live along warm shores and are easily approachable, making them particularly vulnerable to human hunters. Both monk seal species are currently endangered. A third monk seal, once abundant throughout the Caribbean Sea, became extinct by about 1950.

One of the first formal attempts to protect seal populations occurred in 1911, when the United States, Canada, Russia, and Japan agreed to ban open-sea hunting of seals. After Mexico banned seal hunting in 1922, the northern elephant seal population began to grow. In 1910, only 100 seals were found on Isla de Guadalupe; today this species numbers around 150,000 and has recolonized much of its former range from northern Mexico to southern Alaska. However, another species, the Guadalupe fur seal, hunted during the same period, has not recovered its former abundance along the California and Mexican coasts.

Some countries have enacted laws to protect seals and other marine mammals. Sadly, these laws came too late to save the Caribbean monk seal. Even though the hunting of seals is now much less intense than in the past, threats from pollution, especially oil spills, and the accumulation of marine debris such as lost or discarded fishing line and nets still cause many deaths among seals.

Scientific classification: Seals are classified in the suborder Pinnipedia of the large mammalian order, Carnivora. The true seals make up the family Phocidae, and the harbor seal is classified as Phoca vitulina; the northern elephant seal is classified as Mirounga angustirostris; and the Hawaiian monk seal is classified as Monachus schauinslandi. The eared seals make up the family Otariidae and include the northern fur seal, classified as Callorhinus ursinus; and the California sea lion, classified as Zalophus californianus. The walrus is the only member of the walrus family, Odobenidae, and is classified as Odobenus rosmarus.