Aggression

The most dominant male, the beachmaster, gets breeding priority, but in these early days before the females come into estrus,  less dominant males are causing uproar among the mothers. Some are attempting to breed with the new mothers, even though they have not come into estrus yet. Their pups are small, and easily overlooked as the males attempt to bully a female into mating.

Kathleen Curtis made this video of a male harassing a mother.

Dominance reduces aggression on the beach, by sending aggressive but less dominant males packing. the females come into estrus at the end of lactation, and become willing to breed. None of the females has finished nursing yet, so none are yet in estrus.

Patrick Robinson, director of the Ano Nuevo Island Reserve, said as the females come into estrus, the dominant beachmasters should become more vigilant.

Pups can be killed, in the rough and tumble as the male tries to mate and the female tries to escape. The male may kill the pup by biting its head. The pup may be separated from its mother, which is the most common cause of pup death. Struggling with a bigger male uses the mother's limited store of energy (blubber), which she needs to feed her pup.

It's a tough life down there on the beach. Despite all that, over 90 percent of the pups at Piedras Blancas survive to be weaned.