Named for the trunklike noses of adult males, elephant seals (Mirounga angustirostris) are among the largest of all pinnipeds, or fin-footed marine mammals. When inflated, the nose amplifies battle cries meant to ward off other males vying for breeding rights. But some foes still fight, fiercely biting at each other's necks, which are shielded by thick, coarse skin and blubber.

Elephant seals are awkward on land, but they are long-distance swimmers and expert divers. Twice a year—between molting and breeding—they journey between the California coast and Alaskan waters. They spend about 90 percent of the trip underwater, diving for food along the way.

© Marilyn Kazmers / Dembinsky Photo Associates

CONSERVATION: On the Rebound
From the mid-1800s to the early 1900s, elephant seals were heavily hunted for blubber, from which valuable oil was extracted. By 1890 perhaps as few as 100 seals remained; they were thought to be extinct by 1896. But a small group survived on Mexico's remote Guadalupe Island, as depicted in this diorama. The species bounced back after receiving protection by the Mexican government in 1922.

Today, all northern elephant seals apparently share the same male ancestor. Such inbreeding can limit the genetic variation of the species-but it also offers a rare opportunity to study how genes diversify in a population.

Supporting the next generation
Female elephant seals endure a stressful time at the beach each year when they return to their rookeries to breed.

Each January and February, elephant seal cows give birth—each to a single pup—on isolated beaches and islands off the Californian and Mexican coasts. Pups weigh 45 kilograms (100 pounds) at birth, but they gain 150 kilograms (300 pounds) in just one month of nursing on their mothers' rich milk—more than 50 percent fat. Meanwhile, the cow fasts and loses 40 percent of her own body weight.

Weak and exhausted, the female then mates with the dominant male before weaning her pup and heading out to sea for nearly three months in search of food. During this time, the fertilized egg implants in her uterus, restarting the annual cycle. Such delayed implantation is common among seals and sea lions.

Secrets of Diving Success
Northern elephant seals dive longer and deeper than most other marine mammals.

Researchers use satellite tags to track the migration habits of elephant seals, including distance traveled and diving depths. Glued to the seal's fur, these lightweight devices fall off when the animal returns to the rookery to molt. © Daniel Costa, University of California at Santa Cruz

Elephant seals can stay submerged for up to two hours and survive the crushing pressure at ocean depths of 1500 meters (nearly one mile). As they dive, they exhale to collapse their lungs. Their heart rate slows dramatically, and the bloodstream carries oxygen only to vital organs. At the surface, elephant seals rest for a mere two to three minutes before diving again.

Plunging into the blackness of the deep sea, elephant seals feast on the bounty of squid lurking there. At such depth, few other marine mammals compete for food, and predators such as white sharks and killer whales are not active so far below the surface.