As is often the case in species where males compete to mate with as many females as possible, northern elephant seal males are much larger than females (1,800 kg versus 650 kg on average). Competitions can be battles, but more often involve mock threats and loud vocalizations. The dominant (alpha) male gets to mate with the most females, maximizing the number of offspring he produces. Fasting is part of their life cycle: males stay on the beach and fast for up to three months during the breeding season, while they are guarding a harem. Females stay on shore with their pups and fast for about a month while they are nursing. Afterward, males and females spend 8-10 mostly solitary months at sea. Males often migrate along a northern route and the females remain farther south. They may travel as far as Japan and log more than 20,000 km annually, spending much of their time underwater foraging for squid and fish. Dives can be as deep as 1,500 m and last as long as two hours, but the seals typically stay submerged for about 18-25 minutes and forage at depths of 350-650 m.

Links:
Mammal Species of the World
Click here for The American Society of Mammalogists species account