Seals are marine mammals, known for their aquatic presence. These animals belong to a group called pinnipeds, a term translating to “fin-footed,” which also includes sea lions and walruses. While seals are well-known for their aquatic prowess, their lives are intrinsically linked to both water and land. Their existence revolves around the ocean, where they spend the majority of their time, but they also regularly utilize terrestrial habitats.
Masters of the Aquatic Realm
Seals exhibit remarkable adaptations that allow them to flourish in marine environments. Their bodies are streamlined and torpedo-shaped, minimizing drag as they glide through the water with exceptional speed. Seals propel themselves using their strong hind flippers, moving them back and forth like a fish’s tail, while their front flippers serve mainly for steering. To navigate and hunt in murky or dark waters, seals possess large eyes adapted for low-light conditions and highly sensitive whiskers, known as vibrissae. These whiskers can detect subtle water movements and pressure changes, allowing seals to track the hydrodynamic trails left by swimming fish even in zero visibility.
Seals are also exceptional divers, capable of holding their breath for extended periods. This ability is supported by physiological adaptations such as a higher blood volume and a greater concentration of myoglobin in their muscles, which store oxygen. When diving, their heart rate slows dramatically, and blood flow is redirected to essential organs like the brain and heart, conserving oxygen for longer underwater excursions.
Why Seals Come Ashore
Despite their profound aquatic adaptations, seals regularly come ashore, a behavior known as “hauling out,” for several essential reasons. One primary purpose is breeding and giving birth, as most seal species deliver their pups on land or ice. Pups are born on land and rely on their mothers for milk, allowing them to grow rapidly. Seals also haul out to molt, a process where they shed their old fur and sometimes even skin, replacing it with a new coat. This period requires them to spend significant time on land because increased blood flow to the skin is needed for hair growth, and being in cold water would lead to excessive heat loss during this vulnerable time.
Resting is another frequent reason seals come ashore, allowing them to conserve energy and recover from foraging trips. During these rest periods, they can often be seen in a “banana” position, arching their backs with their heads and tails elevated. Thermoregulation also plays a role; seals may bask in the sun to warm their bodies or, conversely, use behaviors like flipping cool sand onto themselves or increasing blood flow to their flippers to dissipate excess heat when on land. Occasionally, seals come ashore to escape aquatic predators like sharks and orcas, finding temporary refuge from threats in the water. These periods on land, while temporary, are fundamental to their life cycle and well-being.
Remarkable Adaptations for Both Worlds
Seals possess physical and physiological adaptations that enable them to navigate both their aquatic and terrestrial worlds effectively. Their thick blubber serves multiple purposes; it acts as an insulating blanket in cold water, provides buoyancy for efficient swimming, and functions as a crucial energy reserve during fasting periods, such as breeding or molting. This blubber can account for a significant portion of their body weight, providing sustenance when food is scarce.
Specialized nostrils automatically close underwater, preventing water from entering their respiratory system during dives. While their powerful flippers are optimized for aquatic propulsion, seals can also use them for movement on land, albeit often clumsily, by dragging their bodies in a caterpillar-like motion. Furthermore, their circulatory system allows for remarkable control over blood flow and heart rate, which not only facilitates deep and prolonged dives but also assists in regulating body temperature when they are out of the water.