The Hawaiian monk seal (Neomonachus schauinslandi) is an endangered species of earless seal native to the Hawaiian Islands. It is one of two extant monk seal species; the other is the Mediterranean monk seal. A third species, the Caribbean monk seal, is extinct. The Hawaiian monk seal is the only seal native to Hawaii.
The grey coat, white belly, and slender physique distinguish this species from its cousin, the Harbor seal (Phoca vitulina). The Hawaiian monk seal lacks external ears and inability to rotate its hind flippers under the body. It has a relatively small, flat head with large black eyes, eight pairs of teeth, and short snouts with the nostril on top of the snout and vibrissae on each side. The nostrils are small vertical slits which close when the seal dives underwater. Additionally, their slender, torpedo-shaped body and hind flippers allow them to be very agile swimmers. Monk seals shed their hair and the outer layer of their skin in an annual catastrophic molt. During the most active period of the molt, about 10 days for the Hawaiian monk seal, the seal remains on the beach. The hair, generally dark gray on the dorsal side and lighter silver ventrally, gradually changes color through the year with exposure to atmospheric conditions. Sunlight and seawater cause the dark gray to become brown and the light silver to become yellow-brown, while long periods of time spent in the water can also promote algae growth, giving many seals a green tinge. The juvenile coat of the monk seal, manifest in a molt by the time a pup is weaned is silver-gray; pups are born with black pelage. Many Hawaiian monk seals sport scars from shark attacks or entanglements with fishing gear.
The majority of the Hawaiian monk seal population can be found around the Northwest Hawaiian Islands but a small and growing population lives around the main Hawaiian Islands. These seals live in warm waters and spend most of their time at sea. When on land they breed and haul out on the sand, corals, and volcanic rock and prefer sandy beaches with shallow waters for pupping.
Hawaiian monk seals are generally solitary and prefer to spend their time singly. However, they may sometimes bask or sleep in small groups lying not too close to each other. These seals are active during the night spending much of their time foraging in deeper water outside of shallow lagoon reefs at depths of 300 meters (160 fathoms) or more. When they are not hunting and eating, they generally bask on the sandy beaches and volcanic rocks. Hawaiian monk seals do not migrate seasonally and some individuals may only travel hundreds of miles in the open ocean.
Hawaiian monk seals are carnivorous (piscivorous) and opportunistic predators that feed on a wide variety of available prey. They mainly feed on reef-dwelling bony fish, but they also prey on cephalopods and crustaceans.
Hawaiian monk seals are polygynous meaning that males mate with multiple females. Their mating season occurs between June and August. Females give birth to a single pup after the gestation period that lasts 9 months; births usually occur between March and June. The pups are born on beaches and nursed for about 6 weeks. The mother does not eat or leave the pup while nursing. After that time, the mother deserts the pup, leaving it on its own, and returns to the sea to forage for the first time since the pup's arrival. Both the males and the females reach reproductive maturity between 4 and 10 years of age.
The main threats to the Hawaiian monk seal include human encroachment, very low levels of genetic variation, entanglement in fishing nets, marine debris, disease, and past commercial hunting for skins. Low juvenile survival rates continue to threaten the species; high juvenile mortality is due to starvation, marine debris entanglement, and predation from sharks. Reduced prey abundance is another cause of the population decline and can lead to starvation. Lobsters, the seals' preferred food other than fish, have been overfished and competition from other apex predators such as sharks, jacks, and barracudas leaves little for developing pups. Hawaiian monk seals also suffer from increased male aggression (mobbing) that involves multiple males attacking one female in mating attempts. Mobbing is responsible for many deaths, especially in females.
According to the IUCN Red List, the total population size of Hawaiian monk seals is 1,209 individuals. Currently, this species is classified as Endangered (EN) on the IUCN Red List, and its numbers today are decreasing.
Due to their diet habits, Hawaiian monk seals have an influence on the fish and other marine animals' population. They are also an important food source for sharks, their main predators.
