Seals are semi-aquatic marine mammals adapted to thrive in both aquatic and terrestrial environments. Part of the Pinniped order, seals regularly transition between ocean and land, a behavior known as “hauling out.” This dual existence raises questions about how long they can comfortably remain on land and why. Their time ashore is crucial for their biology and life cycle.
Why Seals Come Ashore
Seals use land for essential activities not possible in water. Resting and conserving energy are primary reasons, as land offers a stable platform away from currents and aquatic disturbances. They also come ashore for thermoregulation, basking to warm or seeking shade to cool when temperatures are high. Annually, seals molt, shedding old fur for a new coat, typically on land. Land is also indispensable for reproduction, as most species give birth and nurse young on solid ground or ice.
Physiological Adaptations for Land
Seals have biological characteristics enabling terrestrial stays. A thick blubber layer, up to 50% of body weight, insulates against temperature extremes and serves as an energy reserve during land fasting. Their circulatory system includes adaptations like counter-current heat exchange in flippers, minimizing heat loss by transferring warmth from arterial to venous blood. Efficient kidney systems also conserve water and manage salt intake, aiding hydration during extended periods away from the marine environment.
Factors Influencing Land Duration
Land duration for seals varies, influenced by several factors. Species vary; harbor seals typically haul out 7-12 hours daily for thermoregulation and rest. Elephant seals, in contrast, can stay on land for up to a month during molting, shedding fur and skin without eating. Purpose significantly impacts duration; short rests last hours, while pupping, nursing, and molting extend for weeks.
Environmental conditions play a role; seals return to water to cool in hot weather, especially without shade. Predators or human disturbance can shorten terrestrial stays, as seals may flee into water if threatened. Health and age are also relevant; sick or injured seals may haul out longer to conserve energy, and young pups often spend weeks on land before fully venturing into water. Grey seal pups, for instance, remain on land for approximately three weeks while nursing, then another three weeks as they molt their white fur and develop a waterproof coat, living off blubber reserves.
Risks and Limitations of Prolonged Land Stay
While essential for certain life stages, extended land stays present challenges for seals. Dehydration is a concern, particularly in warm conditions, as seals primarily obtain water from food and lack fresh water sources on shore. Overheating is another risk; thick blubber, beneficial in cold water, can cause them to become too warm in direct sunlight for prolonged periods. Seals are also more susceptible to predation from land carnivores when ashore, especially pups.
Human disturbance poses a threat, as human presence can stress seals, interrupt rest, and cause stampedes into water, potentially separating mothers from pups. Such disturbances waste energy and increase vulnerability. Additionally, seals on land are more prone to injuries or illnesses, including entanglement in fishing gear or plastic waste. Despite adaptations, land is not their primary habitat, and stays beyond natural cycles can lead to detrimental effects on health and survival.