Hawaiian Monk Seal
(Monachus schauinslandi)

This page is currently (August 2011) being updated


Distribution and Numbers
The second most endangered pinniped species in the world, there are an estimated 1,300 to 1,400 Hawaiian monk seals still in existence, mostly inhabiting the Northwestern Hawaiian Islands (NWHI). The species' main reproductive populations are at French Frigate Shoals (the largest population), Laysan Island, Lisianski Island, Pearl and Hermes Reef. They occurred also at Midway Atoll and Kure Atoll at the extreme NW of the Hawaiian chain, but these sites were virtually abandoned by the late 1960s (Kenyon, 1981; King, 1983). Towards the SE of the Hawaiian chain there are small numbers at Necker Island and Nihoa Island, while a small number of seals are also found in the main Hawaiian Islands (MHI) (Monachus Guardian).

The Hawaiian monk seal population was hunted to near extinction during commercial sealing expeditions in the mid-19th century, and other opportunistic hunters further depeleted the surviving population during the late 1800s and the early 1900s, and the mnk seal was thought to be extinct by the early 20th century (Kenyon and Rice, 1959). However, expeditipns in the mid-20th century reported increasing numbers of seals in the Leeward chain (Kenyon and Rice, 1959). Beach counts, an index of monk seal population abundance, have recorded populatio trends since the mid-20th century. Kenyon (1981) reported an overall decline from 1350 seals in 1958 to fewer than 700 in 1978. The decline was not evenly distributed, with the greatest decline in the NW Kure and Midway Atolls, Pearl and Hermes reefs and Lisianski and Laysan islands (Johnson et al., 1982). The decline at Kure Atoll was due partly to disturbance caused by recreational beach actvities of the US Coastguard personnel stationed on Green Island since 1960, but this decline was reversed from the late 1980s due to a decrease in human disturbance (Gerroddette and Gilmartin, 1990). Conversely, the colony on Tern Island in French Frigate Shoals showed a sharp increase in numbers after the US Coastguard vacated the station there in 1979 (Gerrodette and Gilmartin, 1990).The impact of military and coastguard presence on monk seals has now been recognised, and steps taken to avoid repetition of this problem.

Since 2001 the total abundance at the six main NWHI sites has been declining at an average annual rate of about 4.5%. The primary cause of the continuing decline appears to be low juvenile survival, with only 20% of pups surviving to reproductive age (NOAA Fisheries Service). However, sightings in the main Hawaiian islands (MHI) have increased from almost none to 77 in 2005 and 153 in 2010, with 25 births reported in 2010 (NOAA Fisheries Service). The current best estimate of the total population is 1,100–1,200 (NOAA population fact sheet).

Monachus schauinslandi - Image 1

Photo: Mitch Craig,

NMFS Honolulu Laboratory

Although the Hawaiian monk seals are one coniguous species occurring all along the Hawaiian chain, the NWHI and MHI populations face different threats. In the NWHI the primary threats include food limtation for juveniles, shark predation on juveniles, entanglement in marine debris, adult male seal attacks on females and juveniles and shoreline habitat loss. Threats in the MHI include disease and human impacts inclding reacreatinal disturbance, fisheries interactions, habituation to humans and, even recently, intentional killings.

A lack of food resources in the area has probably been a major cause of the continuing decline of seals in the NWHI, particularly at French Frigate Shoals where evidence of limited prey availability has included small and emaciated pups, nursing females who were smaller and thinner than at other colonies and a later age of reproduction to 11–12 years in some females (U.S. Marine Mammal Commission, 2000). Of particular concern have been the effects of the commercial lobster fishery which has taken place in the Northwestern Hawaiian Islands since the early 1980s. A long-running dispute took place between the US Marine Mammal Commission and the National Marine Fisheries Sevice (U.S.  Marine Mammal Commission, 2000). The MMC provided evidence that lobsters were an important prey item for juvenile and female seals in the NWHI, and repeatedly requested that The NMFS should disallow a lobster fishery in these areas so as not to erode the seals' food base and also to avoid the bycatch of octopus, crabs and small reef fish, which are all part of the seals' diet. The NMFS repeatedly responded that the evidence for a major lobster proportion to juvenile seal diet was not sufficiently strong, and therefore the fishery continued to be permitted, and to be extended to the French Frigate Shoals (U.S. Marine Mammal Commission, 2000).
However, in June 2000 the NMFS banned any further commercial lobster fishing in Hawaiian waters for the rest of the year. A coalition of environmental groups was also involved in an ongoing law suit seeking longer-term protection for the monk seal from the impacts of commercial fishing in the Northwestern Hawaiian Islands. As a result, the U.S. Federal District Court issued an injunction in November 2000 closing down the lobster fishery in order to protect the monk seals in the Northwestern Hawaiian Islands. The injunction was to remain in force until the NMFS could complete an Environmental Impact Statement as well as an analysis of the fishery's impacts under the Endangered Species Act.
The entanglement of Hawaiian monk seals in marine debris may also be a major cause of death, particularly of young seals which are far more prone to entanglement. During field visits to the majority of major monk seal breeding sites in 1999, 25 entangled seals were observed. A survey which took place at French Frigate Shoals during the winter of 1996-1997 estimated that the area contained more than 29,000 net fragments in waters less than 10m deep, mostly trawl webbing transported to the area from outside the Hawaiian islands by ocean currents. NOAA agencies and the US coastguard frequently remove dangerous marine debris from beaches and disentangle seals. Concerted efforts have also begun to remove debris from reefs within the seals' habitat, a cooperative federal-state-private clean-up operation in November 1998 amassing 7.5 tonnes of discarded fishing nets from 1.5 square kilometres of coral reef near major pupping beaches at French Frigate Shoals. A similar clean-up at Lisianski Island and Pearl and Hermes Reef in 1999 amassed almost 23 tonnes of discarded fishing nets. 700 tons of debris are estimated to have been removed since 1996, yet debris accumulation does not seem to lessen (NOAA fisheries service).

The interactions of monk seals and active fisheries gear was highlighted in 1990 when a rapidly expanding pelagic swordfish longline fishery began operating near major monk seal breeding sites and several seals were found with longline hooks embedded in their mouths and skin (Nitta and Henderson, 1993). A protected species management zone was subsequently created around the Northwestern Hawaiian Islands banning pelagic longline fishing within 50 nautical miles of the islands. No seals have been found with embedded longline hooks since the creation of the zone. A demersal shark longline fishery that was recently opened in the islands has now closed down and the Western Pacific Regional Fishery Management Council is moving to ban demersal longlining permanently in the zone and in certain areas around the main Hawaiian Islands. This move is due to concerns regarding the impact of the fishery on both coastal sharks and on protected species such as monk seals. The Marine Mammal Commission has recommended that all future fisheries within the protected species management zone be subject to assessment of their likely impact on monk seals before they are allowed to take place.

Monachus schauinslandi - Image 2

Photo: Mitch Craig,

NMFS Honolulu Laboratory
Other problems that may affect the ability of the species to recover include "mobbing" by adult males (see "Life history" below). Since 1982 a significant number of juveniles and females have been injured, often fatally, after being mobbed. Two adult males that had been particularly aggressive towards pups at French Frigate Shoals were captured and relocated in 1998. In recent years an increase in the occurrence of shark predation on monk seals has also been observed, mostly by Galapagos sharks. Pups that have not yet learned to avoid sharks are particularly vulnerable and it is thought that as many as 27% of the pups born at French Frigate Shoals in 1999 may have died due to shark predation. The lack of genetic diversity caused by the decline in population numbers may also compromise the future survival of the species. A study showed very low genetic diversity within sub-populations on individual islands, with the suggestion made that there may be high individual site fidelity and low exchange of between the different island groups (Kretzmann et al., 1997). However, further genetic study has shown that although genetic variability is low, the seals do move freely between the islands of the Hawaiian chain, resulting in free gene flow hroughut the population (Schultz et al., 2011). The low genetic diversity was thought to have been due to intensive hunting in the 19th century severely deleting the population, but computer simulation has shown that in fact the low genetic diversity predated human influence (Schultz et al., 2009).
There have been problems caused by fishing vessels running aground on reefs near monk seal habitat. In April 1999 a 29 metre longliner grounded off the coast of Kauai releasing 4,200 litres of diesel fuel, around 1,000 hooked monofilament fishing lines and various debris into the ocean. There were also worries that sharks might be attracted into the area by the boat's cargo of fish which had been released. In June 2000 a 26 metre longliner ran aground on a coral reef in the Northwestern Hawaiian Islands carrying over 20,000 litres of diesel fuel, kilometres of monofilament main line and thousands of branch lines containing hooks. Other potential problem areas that need to be monitored for effects on monk seals include recent interest in the harvest of coral in monk seal foraging habitat, entrapment hazards caused by the degrading sea wall at Tern Island (French Frigate Shoals), potentially toxic discards from fisheries, ecotourism activities at Midway Atoll, and recreational fisheries around the islands.

The seals' breeding areas in the Northwest Hawaiian Islands are covered by either the Hawaiian Islands National Wildlife Refuge, the Midway Atoll National Wildlife Refuge or the State of Hawai'i Seabird Sanctuary at Kure Atoll.  The conservation, assessment and recovery of the Hawaiian monk seal is the responsibility of the U.S. National Marine Fisheries Service (NMFS)'s Honolulu Laboratory.In January 2001 a new reserve was finalised, the Northwest Hawaiian Islands Coral Reef Ecosystem Reserve, covering 339,260 square kilometres (34 million hectares) along a 1,930km chain of Hawaiian islands. Under the terms of the reserve, oil, gas and mineral production and exploration is banned, commercial and recreational fishing is capped at pre-reserve levels, the removal of coral is banned, and dumping is prohibited. In addition, stricter regulations apply in 15 special areas within the reserve. Access to all of these protected areas requires permits. In June 2011 the NOAA Fisheries Service proposed an expansion fo the critical (protected) habitat around the NW islands and adding new areas around the main Hawaiian islands. However the latter proposal has met with opposition from local fishermen from the main islands, who regard the seals as a nuisance.

The Hawaiian monk seal was listed as Endangered under the U.S. Endangered Species Act when the beach counts published in 1982 revealed a 50% decline (Atkinson et al., 1993; Johnson et al., 1982) and as Depleted under the U.S. Marine Mammal Protection Act. The species is also listed as Critically Endangered on the IUCN Red List (Lowry et al., 2008) and as an Appendix I species under CITES. In 2010 a new law in Hawaii made it a felony to harm a monk seal with a fine of up to $50,000 for commtting a crime against monk seals.

Life history
Females appear to prefer relatively short lengths of beach, with very shallow water next to the shoreline, for pupping and nursing their pups. This is possibly to protect against rough waves and shark predation. They haul out several days before giving birth, pups mostly being born from February to July, though mostly between March and May (King, 1983). Observations suggest that labour begins during the night or early morning Mother and pup exchange frequent nosing contacts and vocalisations (Eliason et al., 1990). Newborn pups have a black coat which they moult by the time that they have weaned and which will eventually be replaced by the adult coat of grey-brown on top, a lighter cream colour underneath. Mothers nurse their pups for 5-6 weeks after birth, remaining near to the birth site. They do not feed during this period and lose up to an estimated 90kg in weight. Females quite often foster temporarily, or fully adopt a pup, sometimes after their own pup has died, and nursing pups are sometimes exchanged between mothers. This is most likely to occur where the density of females is high, and hence separated females and pups will encounter another potential partner before reuniting (Boness et al., 1990). This predisposition of females to foster an unfamiliar pup has facilitated human assisted fostering of pups who have lost their moher (Gerrodette et al., 1992). After the pup is weaned and mother leaves, the pup fasts for a few weeks, living off its reserves. The pup then gradually learns to feed and begins making longer trips away from its birth location.

The mating of Hawaiian monk seals usually occurs at sea and is rarely seen. However, injuries related to mating (mainly sperficial bite wounds and scratches on the back of the females neck) are an indicator of mating activity, and male testosterone levels rise during the mating season (Atkinson and Gilmartin, 1992). Some adult male Hawaiian monk seals exhibit an aggressive behaviour called "mobbing" where they gang together and attempt to mate with, and by doing so injure and often kill, adult females and immature seals of both sexes, although the majority of attacks are on females in oestrous (Atkinson et al., 1994). This behaviour seems to occur to a far greater extent in those populations where there are more males than females, and would appear to be a pathological for of the normal mating pattern, possibly related to the low population levels and sexual imbalance in the small populations. Since the pupping season is protracted, this means that while males have high testosterone levels there may be very few females in oestrous in the small population at any one time, and hence the mobbing behaviour. This unfortunately occurs sufficiently often to be a significant threat to breeding female and juvenile survival in some small populations.

Monk seals appear to be 'genetically tame', in that they seem to show almost no flight response to humans, nor to pay attention to human presence nearby - so long as they are not being threatened, approached or interfered with (see video links below). Their lack of flight response to humans was doubtless the reason for their falling easy prey to the 19th century hunters.

Hawaiian monk seals feed primarily on bottom fishes (including eels and flatfish), crustaceans (lobster, crab, shrimp) and molluscs (octopus) diet is known to include octopus, lobster and fish, including eels and flatfish. Their prey is typically found on the seabed in shallow water. The coral reefs of the Hawaiian Atoll lagoons and bordering sand areas are the prime foraging habitat (Kenyon and Rice, 1959).  
Monachus schauinslandi - Image 3

Photo: Mitch Craig,

NMFS Honolulu Laboratory
Pro-active measures to promote population recovery

In 1981 The U.S. authorities began an innovative programme at Kure Atoll in order to enhance the probability of the pups' survival and to rebuild the colony. This programme was called 'head-start'. Female pups were collected at weaning, hind-flipper tagged, and kept in a large (40x60m) beach enclosure stocked with live fish, and released in September each year when the pups were 3–7 months old. Survival rates to one year were high, at 14/15 pups (Gerrodette and Gilmartin, 1990; Bergmann, 1991).

The Captive Care project is currently continuing, based at Midway Atoll. In 2006 rare twin pups were found to have been weaned at only 70lb instead of the normal 120lb and were taken to the Kewalo research facility at Honolulu, where they were successfully rehabilitated and returned to Midway Atoll. Six pups in all were rehabilitated in 2006.

A second programme to boost the Kure Atoll colony began in 1984. Severely underweight female pups were collected after weaning at the larger French Frigate Shoals colony, rehabilitated at a centre in Honolulu and released as yearlings the following spring. 6 of 8 females thus translocated in 1987 were foud to be alive at Kure Atoll in 1988, one had emigrated to the Medway islands, and the last was not seen (Gerrodette & Gilmartin, 1990). However similar translocations to Midway Atoll in 1992-1993 resulted in most of the translocated pups disappearing or being found dead. After a change of procedures a total of 12 pups was captured in 1995 for transfer to Midway Atoll but these developed eye problems, resulting in the blindness of most of the pups and these seals are now being held in permanent captivity (MarineBio.org). Further translocations were postponed in 1998 when studies revealed the possible presence of antibodies to morbillivirus in seals tested at French Frigate Shoals. The virus has since been shown not to be present in the colony's monk seals but translocation was suspended due to improved first-year survival rates for seals born there.

A recent translocation was reported in July 2011, when a pup was removed from Gin Island in the French Frigate Shoals, where a number of pups have recently been killed by shark attacks. The pup 'Kaloko' has been translocated to Kure Atoll, and has already made one safe return trip to Trig Island, 3 miles away. However, a new translocaction programme has now been proposed to try to stop the population continuing to decline at its present alarmng 4% per annum. The idea is to translocate female weaned pups from the remote Atolls to the main Hawaiian islands, monitor them closely and then return them to their natal site.

A suggestion was made to treat aggressive adult male seals with a substance to suppress testosterone levels and thus control attacks. Experimental treatment of captive male seals showed that testicular androgen could indeed be controlled by a single dose of the testosterone agonist  (Atkinson et al., 1993). However, it is not known if this has been attempted in the field. The problem of male atacks continues to the present. One young male born at Kure Atoll was tagged at birth in 2003 and has been monitored ever since. His behaviour changed in 2011 (when he will have reached sexual maturity) and he started to show 'very focussed hyper-aggressive behaviour' towards pups, and was believed to have killed three pups in the 2011 season. NOAA made a decision to euthanise him, but he disappeared before they could catch him, at the end of the breeding season. Scientists hope that if his behaviour resumes next season that he may be taken into an aquarium. Possibly a testosterone agonist treatment might help in the management of this seal as an aletnative to euthenasia.

The first comprehensive Recovery Plan for the Hawaiian monk seal (Gilmartin, 1983) was a major step forward in the concerted efforts at a national level to save the species from extinction. However, more than 20 years later the species was still in dangerous decline, and the Recovery Plan was revised in 2007 (NMFS, 2007). The recovery strategy details measures, including research, maintaining a field presence and active intervention, to improve the survivorship of females, especially juveniles, in the NWHI. Active intervention includes the continual removal of marine debris, rescuing entangled seals and the captive care programme.The natural growth of the seal population in the MHI will be fostered by reducing threats including fisheries interactons, disturbance and exposure to diseases, and developing a culture of co-existence between humans and seals. The programme will also seek to reduce the probability of introduction of infectious diseases into the population.

There is currently a plan, in association with the Marine Mammal Centre in California, to build a dedicated monk seal rehabilitation centre at Kona.

Adult Hawaiian monk seals weigh 180-270kg and the females are thought to be slightly larger than the males. Pups are born weighing about 15–20kg and measuring about 95cm to 1m in length. Four pups weighed and measured from birth to post-weaning were born at about 18kg, weaned at body masses of 36, 50, and 64kg (two pups), and each lost about 9kg  during the first three weeks postweaning. The mean weight of 3 other pups was 60kg. One pup weighing 64kg measured 123 cm. After weaning the pups reportedly do not start to feed immediately. The mean weight of six yearlings was 45kg and mean length was 130cm (Kenyon and Rice, 1959).

Hawaiian monk seals have been known to dive to depths of 500m or more. Females give birth for the first time at 5-10 years of age. The maximum age for the species is 25-30 years, but few seals live that long.

Internet links

Pacific Islands Fisheries Science Center (NOAA Marine Fisheries Service)

NOAA Fisheries Service Protected Resources Division Pacific Islands Regional Office

The Monachus Guardian

Video of two juvenile seals and an adult female interacting playfully while moving in and out of the water beside people at a public beach resort (Poipu beach). The seals appear oblivious to the proximity of humans. The people nearby did not interfere with the seals at all.

Video of a large monk seal pup hauling out to its mother on Kauai beach, interacting with her, then returning to the water followed by its mother. Again, this is a public beach, with people watching the seals from nearby, but not approaching them. Again, the seals paid no apparent attention to the human presence.

Video of two monk seals swimming together and interacting underwater near Oahu

Video of a monk seal swmming among coral at 500m depth


Atkinson, S. and Gilmartin, W.G. (1992).  Seasonal testosterone pattern in Hawaiian monk seals (Monachus schauinslandi). J. Reprod. Fert. 96: 35–39.

Atknson, S., Gilmartin, W.G. and Lasley, B.L. (1993).  Testosterone response to a gonadotrophinreleasing hormone agonist in Hawaiian monk seals (Monachus schauinslandi). J. Reprod. Fert. 97: 35–38.

Atkinson, S., Becker, B.L., Johanos, T.C., Pietrazek, J.R. and Kuhn, B.C.S. (1994).  Reproductive morphlogy and status of female Hawaiian monk seals (Monachus schauinsandi) fatally injured by adult male seals.  J. Reprod. Fert. 100: 225–230.

Bergmann, C. (1991). Rescuing Hawaii's 'brine children' with a Head Start.  Smithsonian, December 1991: 86–98.

Boness, D.J., Craig, M.P., Honigman, L. and Austin S. (1990). Fostering behavior and the effect of female density in Hawaiian monk seals, Monachus schauinslandi. J. Mammal. 79(3): 1060–1069.

Eliason J.J., Johanos, T.C. and Webber, M.A. (1990). Parturition in the Hawaiian monk seal (Monachus schauinslandi). Mar. Mamm. Sci. 6(2): 146–151.

Gerrodette, T. and Gilmartin, W.G. (1990).  Demographic consequences of changed pupping and hauling sites of the Hawaiian monk seal.  Conserv. Biol. 4(4): 423–430.

Gerrodette, T. Craig, M.P. and Johanos, T.C. (1992).  Human-assisted fostering of Hawaiian monk seal pups.  Elepaio 52(7): 43–46.

Gilmartin, W.G. (1983). Recovery plan for the Hawaiian monk seal, Monachus schauinslandi.  U.S Dept. Commerce, NOAA, NMFS, SW region.

.Johnson, A.M., Delong, R.L., Fiscus, C.H. and Kenyon, K.W. (1982).  Population status of the Hawaiian monk seal (Monachus schauinslandi), 1978.  J. Mammal. 63(3): 415–421.

Kenyon, K.W. (1981).  Monk seals Monachus Fleming, 1822.  In Handbook of marine mammals, eds. Ridgway, S.H. and Harrison, F.R.S.  Vol. 2: Seals.  Ch. 8, pp 195–220. Academic Press, London & NY.  359pp.

Kenyon, K.W. and Rice, D. (1959). Life history of the Hawaiian monk seal. Pacific Science 13(3): 215–252.

Kretzmann, M.B., Gilmartin, W.G., Meyer, A., Zegers, G.P., Fain, S.R., Taylor, B.F. and Costa, D.P. (1997).  Low genetic variability in the Hawaiian monk seal.  Conserv. Biol. 11(2): 482–490.

Lowry, L. & Aguilar, A. 2008. Monachus schauinslandi. In: IUCN 2011. IUCN Red List of Threatened Species. Version 2011.1. <www.iucnredlist.org>.

Marine Mammal Commission. 2000. Hawaiian monk seal (Monachus schauinslandi). Pages 44-55 in Chapter III, Species of Special Concern, Annual Report to Congress, 1999. Marine Mammal Commission, Bethesda, Maryland.

Nitta, E.T. and Henderson, J.R. (1993).  A review of interactions between Hawaii's fisheries and protected species.  Mar. Fish. Review 55(2): 83–92.

National Marine Fisheries Service. 2007. Recovery Plan for the Hawaiian Monk Seal (Monachus schauinslandi). Second Revision. National Marine Fisheries Service, Silver Spring, MD. 165 pp.

Schultz, J.K., Baker, J.D., Toonen, R.J. and Bowen, B.W. (2009).  Extremely low genetic diversity in the endangered Hawaiian monk seal (Monachus schauinslandi). J Hered. 100(1): 25-33. Epub 2008 Sep 23.

Schultz, J.K., Baker, J.D., Toonen, R.J., Harting, A.L. and Bowen, B.W. (2011). Range-wide genetic connectivity of the Hawaiian monk seal and implications for translocation. Conserv. Biol.  25(1): 124-32. doi: 10.1111/j.1523-1739.2010.01615.x. Epub 2010 Dec 16.