Females land on the beach heavily pregnant from the previous breeding season and eager to find a strong male to protect them. They give birth almost immediately to a black-coated pup weighing about 75 pounds. The far larger alpha males, on the other hand, spend the breeding season fighting to guard their females. As I stand watching the action on the beach, a small male sneaks into the closest harem and climbs on top of a squealing female. He jiggles away as soon as the alpha male begins to lumber over.
The move isn't unusual: dominant males are constantly tested. Older males' chests are covered in thick carpets of scar tissue from countless tussles. Only one in 20 males are big and aggressive enough to have their own harem.
To head off the rest, the alphas must be on constant watch. Breeding season is a brutal endurance contest—the males spend up to four months straight on the beach, not eating or drinking. Full-size males can be 16 feet long, with the biggest weighing in at 4,500 pounds, roughly the size of a Chevy Blazer SUV; they'll lose a third of that before heading out to sea again.
The most successful males will mate with 50 females during the winter months. "Imagine not eating for four months and fighting off competitors and breeding with females," says Samantha Simmons, a marine biologist at the University of California at Santa Cruz and an expert on elephant seals. "It's hard."
Researchers have been visiting Año Nuevo for decades to watch the seals and learn about their life cycle. But for decades, the rest of the elephant seals's story remained a mystery. What did they do in the eight long months they spent at sea? Where did they go, and what did they feed on to pack on all those pounds?
The answers began to come in the 1980s, when University of California at Santa Cruz biologists began gluing satellite tracking tags to the seals' fur with marine epoxy. What their data revealed was stunning: elephant seals can spend up to two hours underwater, longer than sperm whales, and dive to depths of almost a mile looking for food. While at sea, they spend just a few minutes at a time on the surface. "They're the consummate divers," says Simmons. "We should almost call them surfacers rather than divers—the vast majority of their life is spent under the surface of the ocean at depths we just don't understand."
Andrew Curry is a writer based in Berlin, Germany.