Quick Facts

Weight 400 to 600 pounds

Length 6 to 7 feet

Lifespan Maximum age over 30 years

Threats Food limitation, Shark predation, Entanglement, Male aggression, Habitat loss, Disease, Human impacts.

Region Pacific Islands

HAWAIIAN MONK SEAL

About the Species

The Hawaiian monk seal is one of the most endangered seal species in the world and is one of NOAA Fisheries' Species in the Spotlight. Its population had been declining for approximately six decades. Today, the population is increasing, but it is still only about a third of its historic size. A key reason for this upward trend is NOAA Fisheries' recovery efforts.

Hawaiian monk seals are endemic to the Hawaiian archipelago—occurring nowhere else in the world. Their range includes the main Hawaiian Islands and Papahānaumokuākea Marine National Monument (Northwestern Hawaiian Islands). Rarely, they’re found at Johnston Atoll, which lies nearly 1,000 miles southwest of Hawaiʻi, in the Pacific Islands Heritage Marine National Monument.

Hawaiian monk seals are protected under the Endangered Species Act, the Marine Mammal Protection Act, and State of Hawaiʻi law.

Population Status

We estimate the population to be around 1,600 seals—nearly 1,200 seals in Papahānaumokuākea, and 400 seals in the main Hawaiian Islands.

Seal hunting expeditions during the mid-19th century reduced the Hawaiian monk seal population to near extinction across the Hawaiian Islands. The population rebounded by the late 1950s, but then subsequently began a prolonged decline.

In Papahānaumokuākea, low juvenile survival—likely related to limited food availability—led to further decline from the late 1990s through the early 2010s.

The Hawaiian monk seal population began to increase gradually in 2013 in both Papahānaumokuākea and main Hawaiian Islands thanks to monitoring and recovery efforts. It continues to grow at a slow, steady rate.

Encouraging recovery developments include:

Overall population growth (surpassing 1,500 seals in 2021 for the first time in more than two decades)
Visible recolonization and significant growth of the main Hawaiian Islands population
Advances in juvenile seal survival enhancement research, such as evaluating how translocation affects survival and continued efforts to improve medical treatments

Appearance

Newborn monk seal pups have black fur. Weaned pups and older seals have dark gray to brown fur on their back, and light gray to yellowish brown fur on their belly.

Monk seals undergo a "catastrophic molt" about once per year. At that time, they shed the top layer of their skin and fur (similar to elephant seals). Seals that spend a long time at sea foraging can grow algae on their fur. Those that look green haven't molted recently and may be getting ready to shed into a new silvery coat.

Most Hawaiian monk seals have unique natural markings, such as scars or natural bleach marks (white spots), on their fur which help identify them. Personnel authorized by NOAA Fisheries often apply identification tags to their rear flippers. Tagging and tracking, in combination with identification of unique markings, enable long-term monitoring of individuals.

Male and female monk seals are similar in size. The only way to confirm whether a seal is female or male is by looking at its belly.

Behavior and Diet

Hawaiian monk seals are "generalist" feeders. They eat a wide variety of foods depending on what is available. They eat many types of common fishes, squids, octopuses, eels, and crustaceans (crabs, shrimps, and lobsters). Diet studies indicate that they forage at or near the seafloor, and they prefer prey that hides in the sand or under rocks. They do not target most of the locally popular Hawaiʻi gamefish species, such as ulua (giant trevally), pāpio (young ulua), and ‘ō‘io (bonefish).

Hawaiian monk seals can hold their breath for up to 20 minutes and dive more than 1,800 feet. However, they usually dive an average of 6 minutes to depths of less than 200 feet to forage at the seafloor.

Hawaiian monk seals are mostly solitary. They don't live in colonies like sea lions or other seals. They do sometimes lie near each other—usually not close enough to make physical contact—in small groups. Usually monk seals sleep on beaches, sometimes for days at a time. They also occasionally sleep in small underwater caves.

Monk seals do not migrate seasonally, but some seals have traveled hundreds of miles in the open ocean. Individual seals often frequent the same beaches over and over, but they do not defend territories.

Where They Live

Hawaiian monk seals are found throughout the entire Hawaiian archipelago, a distance of 1,500 miles from Kure Atoll (Hōlanikū) in the northwest to Hawaiʻi Island in the southeast. The majority of Hawaiian monk seals (about 1,200 individuals) live in Papahānaumokuākea, and a much smaller number (about 400) live in the main Hawaiian Islands. There have also been rare sightings of Hawaiian monk seals, as well as a single birth, at Johnston Atoll, the closest atoll southwest of the Hawaiian Islands.

Monk seals live in warm, subtropical waters and spend two-thirds of their time at sea. They use the waters surrounding atolls and islands, and areas farther offshore on reefs and submerged banks. They also use deepwater coral beds to look for food. On land, monk seals haul out to rest, molt, give birth, and nurse. They use a variety of shoreline types, including sand, coral rubble, and volcanic rock. They generally prefer sandy, protected beaches surrounded by shallow waters for pupping.

Lifespan & Reproduction

Monk seals can live to more than 30 years of age, but few live that long. Monk seals mate in the water. The youngest documented female to give birth was 4 years old. Typically females begin reproducing at ages 5 to 6 in the main Hawaiian Islands and ages 7 to 10 in Papahānaumokuākea.

Threats

Food Limitation

Limited food intake (starvation) by juvenile seals was a major factor driving the population decline in Papahānaumokuākea for many years. However, improved survival of young seals in recent years seems to be driving the positive abundance trends. In Papahānaumokuākea, seals must compete for food with large populations of other apex predators, such as sharks and large jacks (like ulua). Shifts in ecosystem productivity, caused by global climate change and/or cyclical changes, may also contribute to food limitation.

Shark Predation

From the late 1990s until recently, predation by Galapagos sharks on pre-weaned and recently weaned seal pups was a chronic and significant cause of injury and mortality specific to Lalo (French Frigate Shoals) in Papahānaumokuākea. This unique threat appears to result from atypical behavior of a limited number of Galapagos sharks that prey on pups in nearshore waters, often in just a few feet of water.

Entanglement

Hawaiian monk seals have one of the highest documented entanglement rates of any pinniped species. Pups and juveniles are the most often entangled. Marine debris and derelict fishing gear are chronic forms of pollution affecting monk seal habitat, particularly in Papahānaumokuākea Marine National Monument. From 1974 to 2022, NOAA Fisheries has documented 437 entanglements there. NOAA, the U.S. Coast Guard, and other partners removed 945 metric tons of marine debris at Papahānaumokuākea between 1996 and 2022. However, accumulation rates of marine debris appear to remain constant. Large-scale removal of marine debris in Papahānaumokuākea substantially reduces seal entanglements.

Male Seal Aggression

Aggressive male seals, particularly at Kamole (Laysan) and Kapou (Lisianski) islands in Papahānaumokuākea, were a leading threat to female and juvenile monk seals in the 1980s and early 1990s. In other instances, single males have aggressively attacked and lethally injured recently weaned pups at Lalo and Hōlanikū (Kure Atoll). NOAA Fisheries found that removal of specific aggressive males appears to be an effective method to address this threat. Other interventions include: hazing of the aggressor; translocating young seals away from areas with the aggressive males; and treating injured seals. Male aggression is less of a threat today. It tends to be episodic, geographically limited, and largely manageable, provided necessary resources are available.

Habitat Loss

The loss of terrestrial habitat is a significant issue in Papahānaumokuākea. The mostly low-lying atolls—many of which are less than 6.5 feet above sea level—are subject to beach loss from storm erosion and sea level rise. Some significant habitat loss has already occurred at primary pupping sites at Lalo. This includes the disappearance of Whale-Skate and Trig Islands, and the reduced size of East Island after Hurricane Walaka in 2019. Sea level rise over the longer term may threaten a large portion of the resting and pupping habitat in Papahānaumokuākea.

Fishery Interactions

Interactions in nearshore recreational and subsistence fisheries occur frequently with Hawaiian monk seals in the main Hawaiian Islands. Between 1976 and 2024, NOAA Fisheries documented 317 hookings, 13 net entanglements, and 14 mortalities associated with these fisheries. We’ve reduced the risk and total number of mortalities by responding to injured and stranded seals through the Marine Mammal Response Network. Expert fishermen, together with state and federal wildlife managers, also developed best practice guidance for fishermen who engage in spearfishing, shorecasting, and gillnet fishing.

Disease and Contaminants

One of the primary diseases of concern to Hawaiian monk seals is toxoplasmosis. Toxoplasmosis is a leading cause of seal deaths in the main Hawaiian Islands. The first case of toxoplasmosis in a Hawaiian monk seal was identified in 2004. There have been at least 15 known deaths of Hawaiian monk seals caused directly by this parasite, including two clusters of cases in 2018 and 2020. Seals with toxoplasmosis are usually found dead. However, not all carcasses are found, so it is likely that more seals have been affected than are reported. There are more documented cases of toxoplasmosis in females than males. Because of this, the disease has direct impacts on the species' reproductive potential and population growth.

NOAA Fisheries also focuses on early detection and prevention of other diseases, including West Nile virus, morbillivirus, and bird flu (Highly Pathogenic Avian Influenza or HPAI). While none of these viruses has been detected in wild Hawaiian monk seals to date, they are known to be lethal in seals, and some have caused mass mortality to seal populations. Since 2016, NOAA Fisheries has routinely vaccinated seals against morbillivirus. Other infections detected in Hawaiian monk seals include Brucella, herpesvirus, and, rarely, Leptospira. Their significance varies, but they’re generally not thought to have population-level impacts. Persistent organic pollutants and other contaminants in Hawaiian monk seals are below the levels that have been identified as causing health effects in other marine mammal species.

Human-Seal Interactions

Intentional feeding, disturbance of sleeping or resting seals (including dog attacks), boat or vehicle strikes, and other direct human interactions, such as swimming with juvenile seals, are threats to the main Hawaiian Islands population. Beaches that are popular for human recreation are increasingly used by monk seals for "hauling out" (resting) and molting, and some female monk seals are also pupping on popular recreational beaches. During these pupping events, mother-pup pairs remain on the beach to nurse for up to 7 weeks, making them particularly vulnerable to human disturbance and dog attacks. Mother seals’ protective and aggressive nature is also a human safety concern. Seals “conditioned” to human interactions in the wild have occasionally required relocation to remote locations to prevent human injury or harm.

Intentional Killing

Intentional killing of seals is an extreme example of negative human impacts in the main Hawaiian Islands. As of 2024, at least six seals died from apparent gunshots (including one pregnant female) and twelve from blunt force trauma. These events are a serious concern and are investigated by law enforcement.

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