Elephant seal pups are born with a solid black coat, unlike the brown coat with a light belly and dark back they will acquire. They molt that dark wavy coat after they are weaned. That's the condition of this fat weaner enjoying the sun today on the beach.
The black coat is technically considered lanugo, a preliminary coat. Even humans have a lanugo stage during fetal development. Elephant seals keep theirs after they are born.
The black skin peels off, revealing a silvery coat. Marianne Riedman in her book on The Pinnipeds reports that males molt later than females, so perhaps this one is a female. It's hard to tell with youngsters. Females also get teeth sooner than their brothers.