(Matschie, 1905) - Hawaiian monk seal
Distinctive Characteristics
In Hawaiian monk seals, females grow slightly longer, and often heavier, than males. The long, fusiform body is robust, with short flippers. The relatively small head is wide and somewhat flat, with the eyes spaced fairly widely apart. The muzzle is wide and compressed from top to bottom. The mystacial pads are large and fleshy, extending beyond the nostrils. The nostrils are situated on the top of the muzzle, unlike any other North Pacific phocid species. The vibrissae are smooth, not beaded as in most phocids. They vary from short to moderately long, and are black at the base, often with lighter yellowish white tips. There can be a scattering of all light vibrissae throughout. There are 4 retractable mammary teats.
Just following the moult, most females and subadults are silvery to slate grey above, fading to cream or light silver-grey below. Over the years, the coat usually becomes brownish above and yellowish below. Males and some females become completely brownish to blackish as they age. There can be a variable amount of light highlighting on the mystacial area and on both the upper and lower lips. Adults and juveniles can have a greenish or reddish cast from algal growth. Also, Hawaiian monk seals can have irregular light blotches or patches anywhere on the body and flippers, associated nails may also be pale instead of blackish. Pups are born in a black woolly coat, which is moulted completely by about the sixth week. The first moult is a shedding of individual hairs, but each successive annual moult is a more dramatic epidermal moult of hair and skin, which detaches in patches. Most older animals of both sexes, but especially males, have some to many scars on their back, sides, and head.
The dental formula is I 2/2, C 1/1, PC 5/5.
Can be confused with
No other pinnipeds regularly occur within the tropical habitat of this seal. However, in recent years northern elephant seals have been recorded at Midway Island. Northern elephant seals are much larger and the size and shape of the head, muzzle, and orientation of the nostrils are diagnostic. Also, female northern elephant seals have only 2 teats.
Size
Adult male Hawaiian monk seals reach lengths of about 2.1 m, females 2.4 m. Males weigh an average of 200 kg, females up to 272 kg. Pups are about 1 m and 16 to 18 kg at birth.
Geographical Distribution
Hawaiian monk seals are distributed throughout the northwestern chain of Hawaiian Leeward Islands and are occasionally seen around the main Hawaiian Islands and at Johnston Atoll. Their habitat and movements at sea are not known; they have been seen up to 140 km from the nearest land. On land they haul-out and breed on beaches of sand and coral rubble, and on rocky terraces. They sometimes leave the beach if vegetation is available for shade.
Biology and Behaviour
Hawaiian monk seals are considered nonmigratory. The long breeding season lasts from late December to mid-August, although most pups are born between March and June. Males in this polygynous species patrol the water adjacent to the rookeries, or haul-out beside non-nursing females. There have been up to 3 times more breeding-age males than females at some colonies; this contributes to mobbing of estrus females, which are often injured and occasionally killed.
When approached by another seal or human on land, Hawaiian monk seals often roll to present the underside to the intruder, arch the back, raise a flipper in the air, and open the mouth. They are generally solitary, both on land and at sea. Even when seals gather together on land, they are not generally gregarious, and only mothers and pups regularly make physical contact.
Hawaiian monk seals feed on reef fishes, eels, cephalopods, and lobsters.
Exploitation
Hawaiian monk seals were seriously overexploited by sealers and other people in the Hawaiian leeward islands in the early 19th Century. Human disturbance has been nearly continuous since then with guano and bird collectors, lighthouse keepers, military bases and the second world war creating havoc and mortality to varying degrees at the different islands inhabited by these seals. These factors, in combination with shark predation and dinoflagellate toxins passed along to the seals through their fish prey species are suspected to have led to the massive decline in numbers. In recent years entanglement of Hawaiian monk seals in lost and discarded fishing gear and packing bands has also contributed to their decline. With hard work and luck the future for this species may be promising. Estimates of the total population increased in the 1980s to approximately 1500 animals. This has come about through aggressive protection measures including: placing nearly all of this seal's island habitat under protection of the U. S. Fish and Wildlife Service as a wildlife refuge, and initiating a research and recovery program by the National Marine Fisheries Service.
IUCN Status
Endangered.