Sea lions, like all mammals, possess hair, which is the direct answer to the common question prompted by their sleek, wet appearance. This hair, known as pelage, is structured differently from the thick coats of land mammals, serving a distinct purpose in their aquatic environment. The misconception that sea lions lack hair stems from their hydrodynamic look, which is a necessary adaptation for their life in the ocean.
Understanding Sea Lion Pelage
The pelage of a sea lion consists of short, coarse, and relatively sparse hair that lies flat against the skin. This coat is composed of tough guard hairs, typically accompanied by several shorter, finer underhairs. The density of this hair is significantly lower than that of their relatives, the fur seals, which possess a much thicker, insulating undercoat.
Glands beneath the skin secrete a thin film of oil, which waterproofs the coat and contributes to its shiny, slick appearance when wet. This oil also assists in drag reduction as the animal moves through the water. Sea lions undergo an annual process called molting, where they gradually shed and replace most of their hair, usually after the breeding season.
Unlike the dense fur of some other pinnipeds, the sea lion’s short pelage provides very little thermal insulation against the cold water. Instead, its main function is to streamline the body and offer some physical protection to the skin. The short hair avoids trapping a thick layer of air, which would increase drag and make them less efficient swimmers. Sea lions must rely on other biological systems to maintain their core body temperature.
How Sea Lions Manage Temperature
The primary mechanism sea lions use to stay warm is an insulating layer of fat known as blubber. This subcutaneous fat layer is thicker in sea lions than in fur seals, reflecting their greater reliance on blubber for thermal protection. Blubber not only provides thermal insulation but also serves as a crucial energy reserve during fasting periods, such as the male breeding season.
For temperature regulation, sea lions employ a specialized circulatory system known as regional heterothermy, which allows them to manage heat loss in certain body parts. Their flippers, which are poorly insulated and lack blubber, act as thermal windows for both heat conservation and dissipation. In cold water, a countercurrent heat exchange system operates, where warm arterial blood flowing to the flippers passes heat directly to the cool venous blood returning to the core. This mechanism prevents excessive heat loss from the extremities, keeping the core temperature stable.
When a sea lion needs to shed excess heat, it can increase blood flow to the surface of its flippers. By holding their flippers in the air, they allow the circulating blood to cool down rapidly before it returns to the body core. This behavior is a deliberate strategy to regulate their body temperature.