|Spot the male|
Sea lions and "true" (or "earless") seals belong to different, if closely related, families, but their reproductive strategy is much the same. In both cases, they spend most of their lives at seal, but they can't give birth there without their pups drowning. The majority of species breed once every year, with the females coming ashore, first to give birth, and then, almost immediately after, to get pregnant again before returning to the sea.
The precise details vary from species to species, but the South American sea lion (Otaria flavescens *) is a typical example. In December each year (that is to say, in early summer, this being the Southern Hemisphere), males haul themselves out onto beaches and fight one another for the best spots. Naturally, the largest and most aggressive males win, with the smaller and younger individuals forced out, to either wait another year, or to make daring raids when the larger ones aren't looking.