What you will often find when you further observe these large groups is that there are quite a few subgroups within it. The seals form a social hierarchy that takes place within those subgroups. This is how order is maintained and how they determine their place in the group. Males often have the most power and those that are the strongest are dominate. This is very true during mating but also holds true the rest of the time. This is why they are often challenged by younger males.