They are solitary animals, like some monks. The Hawaiian monk seal is one of two remaining monk seal species; the other is the Mediterranean monk seal. A third species, the Caribbean monk seal, is extinct.
The Hawaiian monk seal is the only seal native to Hawaii.
These monk seals are a conservation reliant endangered species. The small population of about 1,100 individuals is threatened by human encroachment, very low levels of genetic variation, entanglement in fishing nets, marine debris, disease, and past commercial hunting for skins. There are many methods of conservation biology when it comes to endangered species; translocation, captive care, habitat clean up, and educating the public about the Hawaiian monk seal are some of the methods that can be employed.
Known to native Hawaiians as ʻIlio-holo-i-ka-uaua, or "dog that runs in rough water", its scientific name is from Hugo Hermann Schauinsland, a German scientist who discovered a skull on Laysan Island in 1899. Its common name comes from short hairs on its head, said to resemble a monk.
Its grey coat, white belly, and slender physique distinguish them from their cousin, the harbor seal (Phoca vitulina). The monk seal’s physique is ideal for hunting its prey: fish, lobster, octopus and squid in deep water coral beds. When it is not hunting and eating, it generally basks on the sandy beaches and volcanic rock of the Northwest Hawaiian Islands.
The Hawaiian monk seal is part of the Phocidae family, being named so for its characteristic lack of external ears and inability to rotate its hind flippers under the body. The Hawaiian monk seal has a relatively small, flat head with large black eyes, eight pairs of teeth, and short snouts with the nostril on top of the snout and vibrissae on each side. The nostrils are small vertical slits which close when the seal dives underwater. Additionally, their slender, torpedo-shaped body and hind flippers allow them to be very agile swimmers.
Adult males are 300 to 400 pounds (140 to 180 kg) in weight and 7 feet (2.1 m) in length while adult females tend to be slightly larger, at400 to 600 pounds (180 to 270 kg) pounds and 8 feet (2.4 m) feet in length. When monk seal pups are born, they average 30 to 40 pounds (14 to 18 kg) and 40 inches (1.0 m) in length. As they nurse for approximately six weeks, the grow considerably, eventually weighing between 150 to 200 pounds (68 to 91 kg) by the time they are weaned, while the mother loses up to 300 pounds (140 kg).
Monk seals, like elephant seals, shed their hair and the outer layer of their skin in an annual catastrophic molt. During the most active period of the molt, about 10 days for the Hawaiian monk seal, the seal remains on the beach. The hair, generally dark gray on the dorsal side and lighter silver ventrally, gradually changes color through the year with exposure to atmospheric conditions. Sunlight and seawater cause the dark gray to become brown and the light silver to become yellow-brown, while long periods of time spent in the water can also promote algae growth, giving many seals a green tinge. The juvenile coat of the monk seal, manifest in a molt by the time a pup is weaned is silver-gray; pups are born with black pelage. Many Hawaiian monk seals sport scars from shark attacks or entanglements with fishing gear. Maximum life expectancy is 25 to 30 years.
Evolution and migration
Based on its prehistoric and unspecialized skeletal and vascular anatomy, the Hawaiian monk seal is considered the most primitive of living seals and that descends from the Caribbean species, M. tropicalis; all three species originated in the North Atlantic separated from its congeners as early as 15 million years ago.
In an effort to inform the public and conserve the seals, the National Oceanic Atmospheric Administration (NOAA) Fisheries Service developed a historical timeline to demonstrate that the Hawaiian islands has been home to the seals for millions of years and that the seals belong there. Evidence points to monk seals migrating to Hawaii between 4-11 million years ago (mya) through an open water passage between North and South America called the Central American Seaway. The Isthmus of Panama closed the Seaway approximately 3 million years ago.
Berta and Sumich ask how this species came to the Hawaiian Islands when its closest relatives are on the other side of the world in the North Atlantic and Mediterranean Sea. No one knows whether the Hawaiian is the oldest or the youngest seal in the Monachus genus. The species may have evolved in the Pacific or Atlantic, but in either case, came to Hawaii long before the first Polynesians.
Hawaiian monk seals mainly prey on teleosts (bony fish), but they also prey on cephalopods, and crustaceans. Both juveniles and sub-adults prey more on smaller octopi species, such as Octopus leteus and O. hawaiiensis, nocturnal octopi species, and eels than the adult Hawaiian monk seals. While, adult seals feed mostly on larger octopi species such as O. cyanea. Hawaiian monk seals have a broad and diverse diet due to foraging plasticity which allows them to be opportunistic predators that feed on a wide variety of available prey.
Tiger sharks and Galapagos sharks are both predators.
Hawaiian monk seals mate in the water during their breeding season, which occurs between December and August. Females reach maturity at age four and bear one pup a year. The fetus takes nine months to develop, with birth occurring in March and June. Pups start around 16 kilograms (35 lb) and are about 1 metre (3 ft 3 in) long. Pups are born with a black coat which they shed at about six weeks and replace it with a gray coat on the back and white on the belly.
The pups are born on beaches and nursed for about six weeks. The mother does not eat or leave the pup while nursing. After that time, the mother deserts the pup, leaving it on its own, and returns to the sea to forage for the first time since the pup’s arrival.
The Hawaiian monk seal is critically endangered, although its cousin species the Mediterranean monk seal (M. monachus) is even rarer, and the Caribbean monk seal (M. tropicalis), last sighted in the 1950s, was officially declared extinct in June 2008. The population of Hawaiian monk seals is in decline. In 2010, it was estimated that only 1100 individuals remained. The larger population that inhabits the northwest islands is declining.
Seals nearly disappeared from the main Hawaiian Islands, but the population has begun to recover. The growing population there was approximately 150 as of 2004. Individuals have been sighted in surf breaks and on beaches in Kauaʻi, Niʻihau and Maui. In early June 2010, 2 seals hauled out on Oʻahu's popular Waikiki beach. Seals hauled out at O'ahu's Turtle Bay, and again beached at Waikiki on March 4, 2011, by the Moana Hotel. In 2006, twelve pups were born in the main Hawaiian Islands, rising to thirteen in 2007, and eighteen in 2008. As of 2008 43 pups had been counted in the main Hawaiian islands.
The Hawaiian monk seal was officially designated as an endangered species on November 23, 1976, and is now protected by the Endangered Species Act and the Marine Mammal Protection Act. It is illegal to kill, capture or harass a Hawaiian monk seal. Even with these protections, human activity along Hawaii's fragile coastlines (and in the world at large) still provides many stressors.
Natural factors threatening the Hawaiian monk seal include low juvenile survival rates, reduction of habitat/prey associated with environmental changes, increased male aggression, and subsequent skewed gender ratios. Anthropogenic or human impacts include hunting (during 1800s and 1900s) and the resulting small gene pool, continuing human disturbance, entanglement in marine debris, and fishery interactions..
Low juvenile survival rates continue to threaten the species. High juvenile mortality is due to starvation and marine debris entanglement. Another contributor to the low juvenile survival rates is the predation from sharks, including tiger sharks. Most mature monk seals bear scars from shark encounters—many such attacks have been observed.
Reduced prey abundance can lead to starvation. A reduction in habitat associated with environmental changes is one cause. Habitat is shrinking due to erosion in the Northwest Hawaiian Islands, reducing the islands/beaches. Lobsters, the seals' preferred food other than fish, have been overfished. Competition from other apex predators such as sharks, jacks, and barracudas, leaves little for developing pups. The creation of Papahānaumokuākea Marine National Monument which encloses these islands may expand food supplies.
Mobbing is a practice among the seals that involves multiple males attacking one female in mating attempts. Mobbing is responsible for many deaths especially to females.
Mobbing leaves the targeted individual with wounds that increase vulnerability to septicemia, killing the victim via infection. Smaller populations were more likely to experience mobbing as a result of the higher male/female ratio and male aggression. Unbalanced sex-ratios were more likely to occur in slow-growing populations.
One infectious pathogen found in Hawaiian waters is ciguatera. Further, postmortem examinations of some seal carcasses revealed gastric ulcerations caused by parasites.
In the nineteenth century, large numbers of seals were killed by whalers and sealers for meat, oil and skin. U.S. military forces hunted them during World War II, while occupying Laysan Island and Midway.The Hawaiian monk seal has the lowest level of genetic variability among the 18 pinniped species. This low genetic variability was allegedly due to a population bottleneck caused by intense hunting in the 19th century. This limited genetic variability reduces the species ability to adapt to environmental pressures and limits natural selection thus increasing their risk of extinction. Given the monk seal's small population, the effects of disease could be disastrous.
Monk seals are dying from the toxoplasmosis pathogen in cat feces that enters the ocean in polluted runoff and wastewater, a new phenomenon. Over the past ten years, toxoplasmosis killed at least four seals. Other human-introduced pathogens, including leptospirosis, have infected monk seals.
Human disturbances have had immense effects on the populations of the Hawaiian monk seal. Monk seals tend to avoid beaches where they are disturbed; after continual disturbance the seal may completely abandon the beach, thus reducing its habitat size, subsequently limiting population growth. For instance, large beach crowds and beach structures limit the seal’s habitat. Although the WWII military bases in the northwestern islands were closed, minimal human activities can be enough to disturb the species.
Marine fisheries can potentially interact with monk seals via direct and indirect relationships. Directly the seal can become snared by fishing equipment, entangled in discarded debris, and even feed on fish refuse.
Entanglement can result in mortality because the seals get trapped in marine debris such as fishing nets and cannot maneuver or even reach the surface to breathe. International law prohibits the intentional discarding of debris from ships at sea. Monk seals have one of the highest documented rates of entanglement of any pinniped species.
Reversing the population decline hinges on a comprehensive, scientifically sound characterization and mitigation of relevant natural and anthropogenic factors along with better understanding of the species' particular vulnerabilities.
Genetic data analysis is needed because identifying individuals genetically along with confirming maternity and paternity can provide information about male and female reproductive rates which are crucial to wildlife managers.
In 1909, President Theodore Roosevelt created the Hawaiian Islands Reservation that included the Northwest Hawaiian islands. The Reservation later became the Hawaiian Islands National Wildlife Refuge (HINWR) and moved under the jurisdiction of the U.S. Fish and Wildlife Service (USFWS). This marine sanctuary greatly benefited the seals.
To raise awareness of the species' plight, the Hawaiian monk seal was declared Hawaii's official State Mammal on June 11, 2008.
Public outreach and education remain the most powerful tools for promoting the conservation of the Hawaiian monk seal and its habitat.
NOAA cultivated a network of volunteers to protect the seals while they bask or bear and nurse their young. NOAA is funding considerable research on seal population dynamics and health in conjunction with the Marine Mammal Center.
Protecting female pupsOne key natural factor affecting the seal populations is the male-biased sex-ratio, which results in increased aggressive behaviors such as mobbing. These aggressive behaviors decrease the number of females in the population. Two programs effectively aid female survival rates.
Project “Headstart” began in 1981, collected and tagged female pups after weaning, and placed them in a large, enclosed water and beach area with food and lacking disturbances. The female pups remain during the summer months, leaving at roughly age three to seven months.
Another project began in 1984 at French Frigate Shoals. It collected severely underweight female pups, placed them in protective care and fed them. The pups were released as yearlings and relocated to the Kure Atoll.
Some habitats are better suited to increase survival probability making relocation a popular and promising method. Although no direct links between infectious diseases and seal mortality rates have been found, unidentified infectious diseases could prove detrimental to relocation strategies. Identification and mitigation of these and other possible factors (e.g., disease) limiting population growth represent ongoing challenges and are the primary objectives of the Hawaiian monk seal conservation and recovery effort.
Draft environment impact statement
In 2011, the National Marine Fisheries Service issued a controversial draft programmatic environmental impact statement intended to improve protections for the monk seal. The plan includes:
- Expanded surveys using technology such as remote cameras and unmanned, remotely operated aircraft.
- Vaccination studies and vaccination programs.
- De-worming program to improve juvenile survival.
- Relocation to the Northwestern Hawaiian Islands.
- Diet supplements at feeding stations in the Northwestern Hawaiian Islands.
- Tools to modify undesirable contact with people and fishing gear in the main Hawaiian Islands.
- Chemical alteration of aggressive monk seal behavior.