Sea lions are highly social marine mammals, classified as pinnipeds, that frequently gather in large numbers both on land and in the water. Their gregarious nature leads to the formation of aggregations that can sometimes number in the thousands. Because these groups form for different reasons and in varied locations, the specific name used depends heavily on the sea lions’ activity and environment.
Specific Names for Sea Lion Groups
The term used for a group of sea lions changes depending on their location and activity. When a mass of sea lions is observed resting on a beach or other landmass, the group is most commonly referred to as a colony. This term generally describes any large, non-breeding aggregation found on land.
When sea lions are floating together on the surface of the water, they form a raft, which is a small, closely packed group. During the reproductive season, the gathering transforms into a rookery, which specifically indicates a breeding ground. Within that breeding site, a dominant male’s group of females is called a harem.
Hauling Out and Grouping Behavior
The physical act of sea lions leaving the water to rest on a terrestrial site is known as “hauling out.” This behavior is necessary for their survival and is the primary reason for the formation of non-breeding colonies. Hauling out allows sea lions to rest and conserve energy after extended periods of foraging activity in the ocean.
One of the main functions of hauling out is thermoregulation. Sea lions can warm up by basking in the sun or cool down by flipping sand onto themselves or raising a flipper to release heat. Grouping together on land also provides safety by reducing the risk of predation from aquatic threats like great white sharks or orcas. Haul-out sites are often chosen for their suitability, such as having access to water at low tide and being sheltered, and they can be segregated by age and sex outside of the breeding season.
Social Structure and Breeding Colonies
During the breeding season, the sea lion colony becomes a rookery, characterized by a more complex and aggressive social structure. This is the period when adult males, often called bulls, establish and fiercely defend breeding territories, typically along the coast. A male’s success in defending his territory directly correlates with his ability to form a harem, which can consist of up to 30 females.
The social hierarchy is maintained through a variety of agonistic behaviors, which are displays of aggression and dominance. These disputes involve loud vocalizations, such as incessant barking, as well as physical actions like chest-to-chest pushing and grappling. Once established, the females in the harem give birth to their pups and later mate again, often forming strong bonds among themselves for collective care and protection of the young.