The Narwhal: Physical Characteristics and Deep-Sea Adaptations

Key Insight

Adult male narwhals are impressive, measuring 16 feet long and weighing upwards of 3300 pounds, about a quarter larger than adult females. They are distinguished by an ivory tusk, which pierces the upper lip on the left side and can extend up to 10 feet; rarely, females can have a tusk, or individuals may have two. The narwhal's head is small and blunt, dominated by a high, rounded forehead filled with bioacoustical lipids that enable sound communication and navigation in its three-dimensional world. Its short front flippers serve mainly as diving planes, and its cone-shaped body tapers from an 8-foot girth behind the flippers to a vertical ellipse at the tail, featuring a low dorsal ridge about five feet long instead of a dorsal fin, and unique heart-shaped, ginkgo-leaf-like tail flukes.

Narwhal calves are uniformly gray, developing spreading white patches and streaks on the belly and marbling on the flanks as young adults. Adults feature dark gray on top of the head and back, with lighter grays on flippers and flukes, and whites or light yellow-whites underneath. The back and flanks are marbled with blackish-grays; older males can become almost entirely white. The marbled skin, described as feeling like smooth, oiled stone, exhibits curvilinear streaks of dark gray overlapping whitish-gray tones, particularly on the flukes. Spots are prevalent elsewhere, being darkest and most crowded on the back (up to 2 inches in diameter) and fainter on the sides and belly. The skin itself is a half-inch thick, and in water, narwhals can display hues ranging from deep sea green to intense lake blue.

Narwhals possess extraordinary adaptations for their deep-sea, acoustical environment. Their oxygen storage is optimized for 15-minute dives, with only 9 percent in lungs, 41 percent in blood, 41 percent in muscles, and 9 percent in other tissues. Circulatory system modifications, including 'wonder nets' of blood vessels (rete mirabile) and enlarged hepatic veins, allow them to endure high pressures without getting 'the bends.' Their senses are profoundly rearranged: taste and smell are mostly absent, but their tactile sense and sensitivity to pressure are acute, enabling them to detect depth and the subtle turbulence of prey. Sight is atrophied due to low light and is adapted to high pressure and salt, resulting in fixed, astigmatic vision. Consequently, narwhals predominantly inhabit and 'know' a three-dimensional acoustical space, where they receive waterborne sound independently on each side of their head to determine direction, a crucial adaptation for survival.