The ancient Hawaiian name was "llio holo I ka uaua" meaning "dog that runs in rough water." The Hawaiian monk seal is one of the most endangered marine mammals in the world, and the rarest seal or sea lion in US waters. Weighing between 375-450 pounds (170-205 kg) and 7-7.5 feet (2.1-2.3 m) in length, females are slightly larger than males. Pups are 35 pounds (16 kg) at birth and 3 feet (1 m) long. Silvery-grey colored backs with lighter creamy coloration on their underside; newborns are black. Additional light patches and red and green tinged coloration from attached algae are common. The back of the animals may become darker with age, especially in males. Monk seals are known to live between 25-30 years.
The Hawaiian monk seal's entire range is within U.S. waters. The majority of monk seals live in six main breeding subpopulations in the Northwestern Hawaiian Islands (NWHI) at:
- Kure Atoll
- Midway Islands
- Pearl and Hermes Reef
- Lisianski Island
- Laysan Island
- French Frigate Shoals
Monk seals live in warm subtropical waters and spend two-thirds of their time at sea. They use waters surrounding atolls, islands, and areas farther offshore on reefs and submerged banks. Monk seals are also found using deepwater coral beds as foraging habitat. When on land, monk seals breed and haul-out on sand, corals, and volcanic rock. Sandy, protected beaches surrounded by shallow waters are preferred when pupping. Monk seals are often seen resting on beaches during the day.
Smaller breeding sub-populations also occur on Necker Island and Nihoa Island, and monk seals have been observed at Gardner Pinnacles and Maro Reef. Most of the population is within the Papahānaumokuākea Marine National Monument, designated in 2006. Monk seals are now also found on the main Hawaiian Islands (MHI) where births have occurred on many of the major islands.
Females generally mature at age 5-6 and it is unknown when males mature. Monk seals are promiscuous and mate underwater. Given male-dominated sex ratios at some breeding colonies, group mobbing of "estrus" females is known to occur, sometimes causing serious injury or even death to the female. The gestation period is 10-11 months. Birthing rates vary with a range of 30-70% of adult females birthing in a given year. While most births occur in late March and early April, birthing has been recorded year round. Newborns are black, and then molt near the end of their nursing period. Nursing occurs for about 39 days, during which time the mother fasts and remains on land. After this period, the mother abandons her pup and returns to sea. Although they are generally solitary animals, females have been observed fostering others' offspring.
Monk seals are primarily benthic foragers, feeding on a variety of prey including fish, cephalopods, and crustaceans. Their diet varies by location, sex, and age. Adults are generally nocturnal hunters while juveniles spend more time hunting species that hide in the sand or under rocks during the day. Monk seals generally hunt for food outside of the immediate shoreline areas in waters 60-300 feet (18-90 m) deep. Monk seals are also known to forage deeper than 1,000 feet (330 m), where they prey on eels and other benthic organisms. Tiger sharks and Galapagos sharks prey on monk seals.
Hunted to the brink of extinction in the late 19th century, Hawaiian monk seals have been declining since modern surveying. The monk seal population is currently declining at 4% annually and is estimated at fewer than 1,200 individuals. Biologists predict this number will dip below 1,000 in the next 3-4 years, placing this species among the world's most endangered. While the larger NWHI population is shrinking, the MHI population is growing, with a population estimated at over 100 animals.
At The Marine Mammal Center
While outside of The Marine Mammal Center’s 600 mile rescue range, we still help provide care for Hawaiian monk seals through a partnership with NOAA and the National Marine Fisheries Service due to their endangered population and need for help. In the Fall of 2012, The Marine Mammal Center will break ground on a new state-of-the-art hospital and visitor center for Hawaiian monk seals on Kona Island, which will provide a facility to allow for the rescue, rehabilitation and release of sick and hurt monk seals on the islands.
|Pup||< 1 month||< 1 month|
|Weaner||1-12 months||1-12 months|
|Yearling||1-2 years||1-2 years|
|Juvenile||n/a (classified as subadults)||n/a (classified as subadults)|
|Subadult||2-3 years||2-3 years|
|Adult||3+ years||3+ years|
Learn more about the Hawaiian Monk Seal and the efforts The Marine Mammal Center is taking to build a rescue hospital for this endangered species.