All pinnipeds have four flippers, a layer of blubber, and sensitive whiskers on their snouts. The Harbor seal has all of these and a lot more. Like many marine animals, Harbor seals have streamlined fusiform bodies, tapered at both ends. Harbor seals have spotty coats. The dorsal side has more spots then the ventral side. To move around, the Harbor seal depends on its flippers. The pectoral, or fore, flippers are short and webbed with five bony digits. The digits are about the same length and each has a blunt claw, around one to two inches long. In the water, the fore flippers are used for steering. The webbed hind flippers also have five bony digits. But the outside bones are longer and wider then the inside ones. Moving the hind flippers from side to side propels the Harbor seal through the water.
Harbor seals are very graceful swimmers, but because their hind flippers don’t rotate, they’re very clumsy on land. Tucked in between the hind flippers is a short tail. Harbor seals are covered in short, thick hair. Each year after breeding season, they shed their hair in patches. Molting lasts one to two months. All that hair doesn’t keep them warm, however. For that, they rely on their insulating blubber. Harbor seals are endothermic animals. They control their body temperatures by burning internal fuel, which in turn, keeps them warm.
Harbor seals have a mouth full of teeth, but they don’t use any of them for chewing. Their front teeth are sharp and pointed, and great for grasping and tearing. Back molars are used for crushing the shells of crustaceans and mollusks. Being a pinniped, the Harbor seal can open and close its nostrils. When the nose muscles are relaxed, the nostrils are closed and airtight. The lenses in their eyes are adapted for focusing on refracted light in the water. Their pupils are similar to cats’ pupils: opening wide in dim light and closing to slits when it’s bright. They also have a reflective membrane that makes their eyes glow when hit with light, just like cats eyes. Instead of ear flaps, Harbor seals have an external ear opening to the ear canal. It opens and closes when they dive. They have good hearing above and below the water, but respond to sound better in air. The whiskers are called vibrissae, and each vibrissa moves independently. The vibrissae are very sensitive to movement and can detect the smallest vibrations. These signals help with navigation and in finding food, especially in dark water and at night when vision is limited.
All of these parts working together make the harbor seals one amazing marine mammal.