It’s fairly easy to tell the difference between male and female fur seals: Males are much larger than females. A bull can weigh almost 600 pounds and has a very thick neck and mane. In breeding season, adult males won’t eat and can lose up to 20% of their body weight.

Breeding season gets very competitive. Most of the breeding activity is centralized—almost 75% of the world’s population of fur seals breed on the Pribilof Islands. Male fur seals will arrive at the breeding site about a month before the females and start fighting for territory. These fights can be brutal, and they use their sharp teeth and strong necks to slash at opponents. Only the biggest and most powerful males can land the coveted title of “beachmaster,” while the smaller males are relegated to the edge of the breeding zone. When the females arrive, they are attracted to the male’s territory and then choose a mate and become part of his “harem.”