About The Species
The Hawaiian monk seal is one of the most endangered seal species in the world. The population overall has been declining for over six decades and current numbers are only about one-third of historic population levels. Importantly, however, the prolonged decline has slowed over the last 10 years, thanks in many ways to recovery efforts.
Hawaiian monk seals are found in the Hawaiian archipelago which includes both the main and Northwestern Hawaiian Islands and rarely at Johnston Atoll which lies nearly 1,000 miles southwest of Hawai'i. These monk seals are endemic to these islands, occurring no where else in the world. Hawaiian monk seals are protected under the Endangered Species Act, the Marine Mammal Protection Act, and State of Hawai'i law.
The Hawaiian monk seal is one of NOAA Fisheries' Species in the Spotlight.
Rocky, the Famous Hawaiian Monk Seal
Rocky became famous in 2017 when she had a pup on a busy beach in Waikiki. She returned to Kauai on July 14, 2018, and on July 16, 2018, she was observed with a new pup.
Get monk seal updates and "pupdates"
Status
The population is estimated to be around 1,400 seals—about 1,100 seals in the Northwestern Hawaiian Islands and 300 seals in the main Hawaiian Islands.
A prolonged decline of the Hawaiian monk seal population in the NWHI occurred after the late 1950s, lasting until very recently. While individual subpopulations increased or decreased during that time, the total number of seals in the NWHI declined. Although this decline means that a full recovery of the species is a long way off, there have been some relatively recent, encouraging developments, including:
- Apparent recolonization and significant growth of the main Hawaiian Islands monk seal subpopulation from low numbers to approximately 300 over the past two or more decades.
- Overall species population growth of 3 percent each year between 2014 and 2016.
- Promising advances in juvenile seal survival enhancement research.
The decline that occurred in the NWHI has been attributed to a number of factors at various regions and time periods. However, low juvenile survival, likely related to inadequate prey availability, has been the primary driver of the decline during the past 25 years.
Protected Status
Appearance
Newborn monk seal pups are born black, while weaned pups and older seals are dark gray to brown on their back and light gray to yellowish brown on their belly.
Monk seals undergo a "catastrophic molt" about once per year, where 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 tracking tags to their rear flippers. Tagging and tracking used 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, which means they eat a wide variety of foods depending on what's 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 prefer prey that hide in the sand or under rocks. They do not target most of the locally popular gamefish species such as ulua (giant trevally), pāpio (baby 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 and don't live in colonies like sea lions or other seals. But they do sometimes lie near each other—usually not close enough to make physical contact—in small groups. They usually 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 1,549 miles from Kure Atoll in the northwest to Hawaiʻi Island in the southeast. The majority of Hawaiian monk seals (about 1,100 individuals) live in the Northwestern Hawaiian Islands, and a much smaller population (about 300) lives 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 as foraging habitat. When on land, monk seals breed and haul-out to rest, give birth, and molt on sand, corals, and volcanic rock shorelines. They prefer sandy, protected beaches surrounded by shallow waters for pupping.
World map providing approximate representation of the Hawaiian monk seal's range.
Lifespan & Reproduction
Monk seals can live to over 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, but typically females begin reproducing at age 5 to 6 in the main Hawaiian Islands and age 7 to 10 in the Northwestern Hawaiian Islands.
Threats
Food Limitation
Limited food intake by juvenile seals was the dominant factor driving the population decline in the Northwestern Hawaiian Islands for many years, and it remains a limiting factor for juvenile survival despite recent, positive signs that the population is stabilizing. In the NWHI, seals must compete for food with large populations of other apex predators, such as large jacks (carangids) and sharks. Shifts in ecosystem productivity, caused by global climate change and/or cyclical changes, may also contribute to food limitation.
Shark Predation
Predation by Galapagos sharks on pre-weaned or recently weaned seal pups has become a major cause of injury and mortality specific to French Frigate Shoals in the Northwestern Hawaiian Islands. This is a unique and relatively recent type of seal mortality that appears to result from atypical behavior of a limited number of Galapagos sharks that prey on pups in near shore waters, often in just a few feet of water. Learn more about our monk seal pup protection efforts at French Frigate Shoals.
Entanglement
Hawaiian monk seals have one of the highest documented entanglement rates of any pinniped species, and 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 the Northwestern Hawaiian Islands. The number of monk seals found entangled each year has generally remained unchanged. Undertaken by various agencies within NOAA, the U.S. Coast Guard, and other partners, marine debris removal efforts have extracted over 800 metric tons of debris in the NWHI since 1996, but accumulation rates of marine debris appear to remain constant.
Male Seal Aggression
A significant cause of female and juvenile monk seal mortality—and overall population decline—during the 1980s and early 1990s was by aggression from multiple male seals (especially at Laysan and Lisianski Islands). In other instances, single males have aggressively attacked and lethally injured recently weaned pups at French Frigate Shoals and 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 as appropriate. Male aggression continues to be a concern, even though 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 the Northwestern Hawaiian Islands, which has mostly low-lying atolls (many islands less than 6.5 feet above sea level) subject to beach loss from storm erosion and sea level rise. Some significant habitat loss—such as the disappearance of Whale-Skate Island at French Frigate Shoals which was previously a primary pupping site—has already occurred, and sea level rise over the longer term may threaten a large portion of the resting and pupping habitat in the NWHI.
Fishery Interactions
Since 1990, fishery management measures have eliminated interactions with monk seals in U.S.-managed commercial fisheries in the Northwestern Hawaiian Islands. But interactions in nearshore recreational and subsistence fisheries have occurred in the main Hawaiian Islands. Between 1976 and 2016, there have been 155 documented hookings and entanglements in gill nets, which resulted in 12 monk seal deaths. Expert fishermen, together with state and federal wildlife managers, have developed best practice guidance for fishermen that participate in the three main Hawaiian Islands nearshore fisheries that may interact with monk seals: spearfishing, shorecasting, and gillnet fishing.
Disease
The primary diseases of concern to monk seals include distemper viruses (morbillivirus), West Nile virus, leptospirosis, and toxoplasmosis. There is also the threat of emergent diseases that have yet to make it to Hawai'i. The lack of antibodies in monk seals to these diseases makes them extremely vulnerable to potential infection. Since 2001, there have been a minimum of eight monk seal deaths from toxoplasmosis in the Hawaiian Islands, with at least three deaths occurring since 2014. This number is likely a significant underestimate of the true numbers of cases of this disease and its impact on the population.
Human-Seal Interactions
Intentional feeding, disturbance of sleeping or resting seals, and/or other direct human interactions, such as swimming with juvenile seals, has become a serious concern for 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, at which time they're particularly vulnerable to human disturbance. This also presents a serious human safety concern, as mother seals are protective and aggressive. Human-seal interactions pose both a threat to human and seal safety and have necessitated the relocation of "conditioned" seals to remote locations in some cases.
Intentional Killing
Intentional killing of seals is an extreme example of negative human impacts in the main Hawaiian Islands. As of June 2017, at least four seals have died from apparent gunshots (including one pregnant female) and five from blunt force trauma. Foul play could not be ruled out as the cause of death for at least one other seal.
Scientific Classification
Animalia |
Chordata |
Mammalia |
Carnivora |
Phocidae |
Neomonachus |
schauinslandi |