Seals, with their sleek and hydrodynamic forms, are often mistakenly thought to have smooth, hairless skin. Like most mammals, seals are covered in hair, which serves various crucial functions for their survival in diverse aquatic environments. Their unique hair structure, though different from terrestrial animals, is a defining characteristic of their adaptation to a life largely spent in water.
Understanding Seal Fur
Seal fur is remarkably adapted to their aquatic lifestyle, differing significantly from the coats of land mammals. This fur is exceptionally dense, with some species like the Northern fur seal possessing up to 300,000 hairs per square inch, or approximately 60,000 hairs per square centimeter. The individual hairs are typically short, about half an inch in length, and are designed to lie flat against the body when wet, contributing to their streamlined appearance in water.
The coat generally comprises two distinct layers: an outer layer of stiff guard hairs and a thicker, softer underfur beneath. In some “true seal” species, such as the harp seal, the coat consists primarily of long, shiny guard hairs with minimal or no underfur. Conversely, harbor seals feature coarse guard hairs along with finer, denser underhairs, where each guard hair can be associated with three to six underhair fibers. Seals also undergo an annual molting process, shedding their old fur to grow a fresh coat.
The Purpose of Seal Fur
The primary function of a seal’s fur is insulation, which is fundamental for maintaining their body temperature in cold water. Their dense fur traps a layer of air close to the skin, creating an insulating barrier that minimizes heat loss to the surrounding frigid water. This trapped air is warmed by the seal’s body heat, forming a thermal buffer. While this fur insulation is highly effective in air and at the water’s surface, its insulating capacity can diminish significantly during deep dives as the immense water pressure can compress the fur and expel the trapped air.
Beyond insulation, seal fur plays a significant role in waterproofing. The guard hairs are naturally oily, which enables water to wick off and prevents it from soaking into the skin. When submerged, these guard hairs press together, forming a compact barrier that further enhances water repellency. The fur also provides a protective layer for the skin, offering a degree of cushioning against abrasions and minor injuries.
Additionally, the varied coloration and spotted patterns of some seal species can serve as effective camouflage, helping them blend into their environment and evade predators. Some seal species, particularly “fur seals,” rely heavily on this dense fur for thermoregulation, distinguishing them from “true seals” that depend more on a thick layer of blubber for insulation.