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Marine Life of Midway Atoll

Hawaiian Monk Seal / Monachus schauinslandi

Description Adults are dark gray to brown above, light gray to yellow below. Adult body length: approximately 6 ft (2m). Weight: approximately 440 lbs (200 kg). Adult females generally larger than males. Pups jet black and weigh 25-30 lbs (11-14 kg) at birth. Five to six week nursing period. Seals undergo a complete molt each year, typically between April and December. The seals shed all of their hair and a layer of skin within approximately 7-10 days and usually remain on shore the majority of the time.

Hawaiian monk seal Photo credit: Robert Shallenberger

Distribution

Endemic to the Hawaiian archipelago and found mostly in the Northwestern Hawaiian Islands. Increasing sightings reported from main Hawaiian Islands. Approximately 1,300 seals are scattered throughout the entire archipelago. About 60 individuals reside at Midway Atoll. Most seals remain at their birth atoll for life, but there is some inter-atoll movement. Seals visit Midway intermittently from Pearl and Hermes and Kure Atolls. Monk seal population currently being monitored by National Marine Fisheries Service researchers.

Feeding

Hawaiian monk seals appear to be primarily benthic foragers, using diverse habitats including shallow reefs, atoll slopes, sand fields, banks, and sea mounts throughout the Northwestern Hawaiian Islands. Their diet includes reef fish, squid, octopus, and crustaceans.

Breeding

Females typically mature between 5-9 years of age. Males bite the back of females while mating and can rip skin and blubber. Mating takes place in the water. Females tend not to give birth on beaches where there is much human activity. Births can occur during any month, but most pups are born between March and August. Fourteen and twelve pups were born on Midway in 2000 and 2001, respectively.

Females nurse their pups for 5-6 weeks. Seal milk is very rich which allows pups to gain weight rapidly with pups more than quadrupling their initial weight before weaning. The mother seal loses a tremendous amount of weight while nursing.

From 2000-2008, the number of seals born at Midway ranged from 10 to 17. The average interval between consecutive births is 381 days, such that individuals tend to give birth later in the year as they age.

Mortality

Primary natural factors affecting monk seal recovery include predation by sharks, aggression by adult male monk seals, reduction of habitat and prey associated with environmental change. Entanglement in marine debris such as fishing nets and lines, and plastic rings are other sources of mortality.

Conservation

Monk seals haul out to rest or sleep, pup, and molt and should not be disturbed. If you see a seal on the beach, do not approach closer than 150 ft (50 m). Increase distance if seal is aware of you. Decreasing human activity on beaches will will aid in the recovery of Hawaiian monk seals at Midway Atoll.