Monachus schauinslandi
Hawaiian monk seal

These seals occur on small, uninhabited northwestern Hawaiian islands. Principle sites are on Nihoa and Necker islands, French Frigate Shoals, Pearl and Hermes Reef, Kure Atoll, and Laysan, Lisianski, and Midway islands.

Hawaiian monk seals frequent reefs (for feeding), beaches (for basking and delivering their young), and coves. They spend a great deal of time wallowing in damp sand at the water's edge, presumably to avoid overheating.

Hawaiian monk seals do not migrate, although certain individuals may disperse over long distances. These animals are mostly solitary, although females will sometimes foster another female's youngster. Approaches by large dominant males elicit submissive behavior from other seals. Females with pups are extremely sensitive to disturbances; they will threaten, or if necessary, attack invaders. These aggressive interactions among females often lead to pups switching mothers. Females fast for 2-3 months after weaning their young.

These monk seals are primarily nocturnal, resting during daytime heat and diving for food at night.

Monk seals feed mainly on benthic and reef-dwelling fishes and invertebrates, including flatfish, scorpenids, eels, octopuses, and spiny lobsters. They forage in depths from 10m-40m along the slopes of coral reefs.

These seals were an important part of the economy in the nineteenth century, when they were actively hunted for their meat and fur. Today they are no longer of great economic importance, because of their dwindling numbers and because the demand for seal meat and seal by-products has diminished. Hawaiian monk seals are held in captivity in the San Diego Zoo, Waikiki Aquarium, and Sea Life Park. Here, they draw the attention of tourists from all over the world.

Monk seals are "genetically tame" and therefore easy to find and kill. This makes them vulnerable to rapid depletion. In 1824, the last monk seal in the Pacific was thought to have been killed. They obviously survived, probably on beaches difficult to access from the sea. The species has continued to decline due to disturbance by humans, shark predation and disease. They were declared endangered in 1976. Downward counts in the population seemed to be reversed in the 1980's, and the count is now approximately 1200 individuals. The greatest threats are the disturbance of the mother during her breeding season (which causes her to find a new, less preferred site to give birth and nurse), ciguatera poisoning from reef fishes, and shark attacks. All but two of the Leeward Islands are protected from exploitation under the Hawaiian Islands national Wildlife Refuge. Of the protected islands, three are inhabited by humans: Green Island in Kure Atoll, Sand Island in Midway Atoll, and Tern Island in French Frigates Shoal.

Hawaiian monk seals are unique because they are a completely tropical phocid, but they have no obvious anatomical adaptations for a warm habitat. Their blubber content is equivalent to that of polar seals. They appear to have adapted to warm climates by staying inactive during the day. Another unique aspect of the biology of these seals is that their ear structure is very primitive. They also have unfused bases of the tibia and fibula.