The Hawaiian monk seal, known in Hawaiian as 'ilio-holo-i-ka-uaua ("dog that runs in rough water"), is one of just two surviving monk seal species and the only seal native to the Hawaiian archipelago [NOAA 2024a]. Once driven to low numbers by hunting and disturbance, the species has slowly rebuilt its population through decades of intensive recovery work, though it remains among the most imperiled marine mammals in the United States [Robinson & Barbieri 2024]. Today it survives only across the remote atolls and inhabited shores of a single island chain [NOAA 2024a].
Biology and Identification
Adult Hawaiian monk seals measure roughly 6 to 7 feet (about 2.1 meters) in length and weigh between 400 and 600 pounds (about 180–270 kg), with females generally larger than males [NOAA 2024a]. They have slender, torpedo-shaped bodies, short snouts, and silvery-gray coats that fade to brown with age and frequently host green algae, giving older animals a mottled appearance [NOAA 2024a]. Maximum recorded lifespan exceeds 30 years, though few individuals reach that age [NOAA 2024a].
These seals are generalist foragers that hunt at or near the seafloor, taking a varied diet of fishes, octopuses, squids, eels, and crustaceans [NOAA 2024a]. They are capable divers, typically descending for about six minutes to depths under 200 feet but documented to reach beyond 1,800 feet [NOAA 2024a]. Outside of foraging, they spend much of their time hauled out on beaches to rest, molt, and nurse pups [NOAA 2024b].
Habitat and Range
The Hawaiian monk seal is endemic to the Hawaiian Islands, ranging across roughly 1,500 miles of the archipelago from Kure Atoll and the Northwestern Hawaiian Islands in the northwest to Hawai'i Island in the southeast, with rare sightings as far as Johnston Atoll [NOAA 2024a]. The species depends on sandy beaches, atolls, and shallow reefs for hauling out and pupping, and on surrounding reef and slope habitats for foraging [Robinson & Barbieri 2024].
Approximately three-quarters of the population lives in the remote, largely uninhabited Northwestern Hawaiian Islands within the Papahānaumokuākea Marine National Monument, while the remaining quarter inhabits the populated main Hawaiian Islands, where seals increasingly share beaches with people [NOAA 2024a].
Conservation Status
The Hawaiian monk seal is listed as Vulnerable on the IUCN Red List, assessed in 2024 [Robinson & Barbieri 2024]. This represents a reclassification from its previous Endangered listing and reflects sustained population growth. NOAA Fisheries estimates the total population at around 1,600 individuals — roughly 1,200 in the Northwestern Hawaiian Islands and about 400 in the main Hawaiian Islands — and after decades of decline the population has grown gradually since 2013, surpassing 1,500 animals in 2021 for the first time in more than two decades [NOAA 2024a; NOAA 2024c]. Despite this improvement, the species remains protected under the U.S. Endangered Species Act, under which it has been listed since 1976, and it is also protected under the Marine Mammal Protection Act and listed on Appendix I of CITES [USFWS 2024; NOAA 2024a]. Its small absolute population and restricted single-archipelago range keep it highly susceptible to setbacks.
Threats
Recovery is constrained by several documented threats. Food limitation, especially affecting juvenile survival in the Northwestern Hawaiian Islands, has historically been a leading driver of population decline [NOAA 2024a]. Entanglement in derelict fishing gear and marine debris, which accumulates heavily in the Northwestern Hawaiian Islands, injures and kills seals across age and sex classes, with adult females shown to face particularly high entanglement risk [Baker 2026; Baker et al. 2024; NOAA 2024a]. Shark predation on pups, aggression among males, and disease pose additional risks, with toxoplasmosis — caused by a parasite spread through cat feces carried in runoff — identified as a leading cause of death in the main Hawaiian Islands [NOAA 2024a]. In the main islands, human interactions including intentional killing, fisheries interactions, and disturbance remain concerns, while sea-level rise threatens to erode the low-lying beaches the seals need for pupping [NOAA 2024a].
What Is Being Done
NOAA Fisheries leads a coordinated recovery program that includes annual population monitoring and life-saving interventions such as disentangling seals from debris, reuniting separated pups, and translocating weaned pups away from areas of high shark-predation risk [NOAA 2024a; NOAA 2024b]. Large-scale removal of abandoned fishing gear from the Northwestern Hawaiian Islands has measurably reduced entanglement harm over four decades of monitoring [Baker et al. 2024]. NOAA has also conducted the first vaccination program of its kind for a wild marine mammal population, immunizing hundreds of seals against morbillivirus, and veterinary partners operate dedicated rehabilitation facilities for malnourished and injured animals [NOAA 2024b]. The State of Hawai'i Division of Aquatic Resources supports stranding response alongside federal partners, while the protected waters of Papahānaumokuākea Marine National Monument safeguard the species' core breeding range [DLNR 2024; NOAA 2024a]. Community volunteer networks help monitor seals hauled out on busy beaches and educate the public to reduce harmful interactions [NOAA 2024a].
How You Can Help
Members of the public can support the species' recovery in factual, low-impact ways. Keeping a respectful distance from hauled-out seals — following posted guidance and never approaching, feeding, or disturbing them — reduces stress and harmful interactions [NOAA 2024a]. Reporting sightings and injured, entangled, or stranded animals to the NOAA Marine Wildlife Hotline contributes valuable monitoring data [NOAA 2024a]. Keeping pet cats indoors helps limit the spread of Toxoplasma gondii into coastal waters, and reducing and properly disposing of plastic and fishing-related waste lessens entanglement risk [NOAA 2024a; Baker et al. 2024]. Supporting established, science-based conservation and research organizations, and informed advocacy for marine protected areas, further aids long-term recovery.
References
[Baker 2026] Baker, J.D., et al. (2026). Hawaiian Monk Seal (Neomonachus schauinslandi) Marine Debris Entanglement Risk Varies With Size Class and Sex. Marine Mammal Science, 42, e70081. https://onlinelibrary.wiley.com/doi/10.1111/mms.70081
[Baker et al. 2024] Baker, J.D., Johanos, T.C., Ronco, H., Becker, B.L., Morioka, J., O'Brien, K., & Donohue, M.J. (2024). Four decades of Hawaiian monk seal entanglement data reveal the benefits of plastic debris removal. Science, 385(6716), 1491–1495. https://doi.org/10.1126/science.ado2834
[DLNR 2024] Hawai'i Department of Land and Natural Resources, Division of Aquatic Resources. (2024). Hawaiian Monk Seal. https://dlnr.hawaii.gov/dar/hawaiian-monk-seal/
[NOAA 2024a] NOAA Fisheries. (2024). Hawaiian Monk Seal. National Oceanic and Atmospheric Administration. https://www.fisheries.noaa.gov/species/hawaiian-monk-seal
[NOAA 2024b] NOAA Fisheries. (2024). Hawaiian Monk Seal: Conservation Management. National Oceanic and Atmospheric Administration. https://www.fisheries.noaa.gov/species/hawaiian-monk-seal/conservation-management
[NOAA 2024c] NOAA Fisheries. (2024). Hawaiian Monk Seal Population Status and Recovery Activities. NOAA Institutional Repository. https://repository.library.noaa.gov/view/noaa/67229
[Robinson & Barbieri 2024] Robinson, S. & Barbieri, M. (2024). Neomonachus schauinslandi. The IUCN Red List of Threatened Species 2024. https://www.iucnredlist.org/species/13654/4307371
[USFWS 2024] U.S. Fish & Wildlife Service. (2024). Hawaiian Monk Seal (Neomonachus schauinslandi). https://www.fws.gov/species/hawaiian-monk-seal-neomonachus-schauinslandi