Pinnipeds, which arose from land mammals, have evolved slick, torpedo-shaped bodies ideal for gliding through water. Males fight to establish territories on the beach, then maintain the boundaries with displays of barking, head-shaking, and ritualized fighting.
Females come ashore shortly after the males to give birth to pups conceived the previous season.
Each bull then mates with as many females in his territory as possible. Drinking milk that is 60 percent fat, each pup consumes about 65,000 calories a day, gaining 60 pounds and doubling its birth weight before weaning.