Hawaiian Monk Seal
Hawaiian Monk Seal
|Listed||November 23, 1976|
|Family||Phocidae (Earless Seals)|
|Description||Large earless seal with an offwhite belly and a brown back tinged with gray.|
|Habitat||Submerged reefs, beaches in protected coves.|
|Food||Octopuses, squid, spiny lobsters, ocean fishes.|
|Reproduction||One pup per season.|
The Hawaiian monk seal is a moderately large seal, brown in color and tinged with gray on the back. The flanks gradually lighten to yellowish white beneath. Mature males reach about 7 ft (2.1 m) in length and weigh up to 375 lbs (169 kg). The larger female reaches 7.5 ft (2.25 m) and an average weight of about 450 lbs (203 kg).
The genus Monachus was composed of three geographically separated species of monk seals: the Hawaiian, the Mediterranean (M. monachus ), and the Caribbean (M. tropicalis ). The Caribbean monk seal became extinct in the 1950s.
The monk seal feeds on octopi, squids, spiny lobsters, and various ocean fishes and may dive for food as many as 50 times per day. Between dives the seal hauls itself out of the water to rest and bask. Breeding season is from December to early July, with most births occurring from March to late May. Pups weigh about 40 lbs (18 kg) at birth and are strong swimmers after only a few days in the water.
The rich marine life associated with submerged reefs and atolls provides the most productive feeding habitats for the monk seal. For pupping and nursing, monk seals prefer sandy beaches in shallow, protected coves, where the pups can develop and learn to feed in comparative safety. Rocky ledges or gravel beaches are sometimes used for basking.
The Hawaiian monk seal is distributed among the islands and atolls of the northwestern Hawaiian archipelago, extending from Nihoa Island to tiny Kure Atoll, nearly 1,355 mi (2,180 km) northwest of Honolulu. Once numbering many thousands, the seal population has declined steadily since the eighteenth century, mostly due to human actions.
The monk seal is still found in declining numbers throughout the historic range. Primary islands used by the seal for breeding are Nihoa Island, Necker Island, French Frigate Shoals, Laysan Island (the largest land area), Lisianski Island, Pearl and Hermes Reef, the Midway Islands, and Kure Atoll. Only three islands—Green Island at Kure Atoll, Sand Island in the Midways, and Tern Island in the French Frigate Shoals—are inhabited by humans.
Between 1989 and 1990, total births at the major pupping beaches declined by 40% from the 1988 level. Declines were reported at all five major breeding sites in 1990. In 1991 the number of births recovered to previous levels at three sites but continued to decline at the largest colony. In 1991, a total of 165 births were recorded, 30% below the 1988 level. At the French Frigate Shoals, the average beach counts of juvenile and adult seals declined 30% from 1989 to 1991. Possibly 150-200 animals were lost from that colony.
Habitat disturbance and shark predation seem to be the primary culprits in the current precarious situation of the monk seal, although research is still rudimentary. Sharks take large numbers of seal pups and may be responsible for a low survival rate among immature seals.
Other factors contributing to the decline are over-fishing which decreases the amount of available prey and entrapment in a decaying seawall on Tern Island. In addition, death and injury of adult females and younger animals of both sexes occurs by overly aggressive males attempting to mate.
Conservation and Recovery
Many of the seal's islands and atolls were incorporated into the Hawaiian Islands National Wildlife Refuge in 1940 and were further declared a Research Natural Area in 1967. These actions have limited unauthorized landings on uninhabited islands and decreased human disturbance of seal beaches.
Since the 1960s, over a thousand seals have been tagged and monitored in capture-recapture studies. Pups especially are being closely monitored to document survival rates into maturity. Some pups have been kept in shark-proof enclosures until large enough to feed confidently and then released to determine if they are better able to avoid predators.
U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N.E. 11th Ave.
Portland, Oregon 97232-4181
Marine Mammal Commission. 1991. "Annual Report to Congress."
U. S. Department of Commerce. 1983. "Recovery Plan for the Hawaiian Monk Seal." U. S. Department of Commerce (NOAA), Southwest Region.
U. S. Fish and Wildlife Service. 1986. "Endangered Species Technical Bulletin" 11(1): 4.
U. S. Fish and Wildlife Service. 1979. "Endangered Species Technical Bulletin."
Wirtz, W. O. 1968. "Reproduction, Growth and Development, and Juvenile Mortality in the Hawaiian Monk Seal." Journal of Mammalogy