Seals are marine mammals belonging to the group pinnipeds, a Latin term meaning “fin-footed,” which includes true seals, sea lions, and walruses. Classified as semi-aquatic, they divide their lives between the ocean and land. While they spend significant time ashore, their survival is fundamentally tied to the marine environment for primary life functions. Seals cannot survive permanently on land, but they are adapted to spend hours, days, or even weeks out of the water when necessary.
Hauling Out: The Purpose of Being Ashore
The act of temporarily leaving the water to rest on land or ice is known as “hauling out.” This behavior is essential, fulfilling physiological and reproductive needs that cannot be met in the ocean. A primary reason is simple rest, allowing seals to recover energy between intensive foraging trips at sea.
Hauling out is also essential for thermoregulation, since water conducts heat away from the body much faster than air. Resting on land allows seals to warm up and conserve energy they would otherwise expend maintaining body temperature in cold water. Seals must also come ashore annually to undergo molting, the process of shedding their old coat of fur and skin. This process can last several weeks, and increased blood flow to the skin makes it difficult to maintain body heat in the water.
Reproduction is another major factor necessitating time on land, as all pinnipeds must give birth and nurse their young ashore. Females gather in rookeries to deliver and care for their pups, sometimes leaving them unattended while foraging. Depending on the species, a seal may remain hauled out for a few hours of rest or for an extended period up to a week during weaning or molting. Hauling out also provides a temporary refuge from marine predators, such as large sharks and orcas.
Locomotion: Differences Between Seal Families
A seal’s mobility and how long it can remain on land depends entirely on its family classification and terrestrial locomotion capabilities. The two main groups, true seals (Phocidae) and eared seals (Otariidae, including sea lions and fur seals), have distinct anatomical differences affecting their movement. True seals (phocids) have small fore-flippers and hind-flippers that cannot rotate forward underneath the pelvis.
When true seals move on land, they use a cumbersome, caterpillar-like motion, contracting their abdominal muscles and pushing off with their fore-flippers. This movement, known as galumphing, is inefficient and exhausting, limiting their ability to travel far inland or escape quickly. Their rear flippers trail behind them, functioning primarily as a rudder for steering and propulsion in the water.
Eared seals, in contrast, can rotate their large hind-flippers forward and position them beneath their body. This feature allows them to support their weight on all four limbs, resulting in a quadrupedal, walking gait. Otariids can move with agility, running across rocky terrain or climbing steep slopes. Their larger, muscular fore-flippers are their main source of propulsion in the water.
Terrestrial Constraints and Risks
Despite the need to come ashore, seals face constraints that prevent them from adopting a fully terrestrial lifestyle. The primary challenge is thermoregulation, especially in warmer conditions. The thick layer of blubber that insulates them in cold water can lead to overheating on land. To manage this, seals utilize their flippers, which contain vascular networks that dissipate excess heat.
Seals cannot drink freshwater, and ingesting seawater is detrimental; they must rely on metabolic water produced from their diet. This lack of a mechanism for sustained hydration necessitates a return to the ocean or ice, where they can find food and maintain their water balance. If air temperatures exceed approximately 30°C, many seals will enter the water simply to cool down.
The terrestrial environment also exposes seals to increased vulnerability, particularly for true seals whose slow, awkward movement makes escape difficult. On land, they are susceptible to terrestrial predators, including coyotes, bears, and human disturbance. The strongest constraint is the necessity of hunting, as seals are carnivores whose diet consists of fish, squid, and other marine life. They must return to the ocean to forage, linking their energy supply and long-term survival to their marine habitat.