|Hawaiian monk seal|
|Hawaiian monk seal range|
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 cleanup, 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. The Hawaiian monk seals are adopted to be Hawaii's state mammal.
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 family Phocidae, 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, on average, slightly larger, at 400 to 600 pounds (180 to 270 kg) and 8 feet (2.4 m) 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.
The monk seals are members of the Phocidae. In an influential 1977 paper, Repenning and Ray proposed, based on certain unspecialized features, that they were the most primitive living seals. However, this idea has since been entirely superseded.
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. The species may have evolved in the Pacific or Atlantic, but in either case, came to Hawaii long before the first Polynesians.
The majority of the Hawaiian monk seal population can be found around the Northwest Hawaiian Islands but a small and growing population lives around the main Hawaiian Islands. These seals spend two-thirds of their time at sea. Early studies (done at Midway Atoll) concluded that they frequently stayed inside the lagoons as opposed to the deep ocean, because of the larger abundance of fish found in their coral reefs. However, recent use of animal-born video imaging, temperature/depth recorders, and satellite telemetry has shown that monk seals actually spend much more time foraging in deeper water outside the reefs at subphotic depths of 300 metres (160 fathoms) or more. Hawaiian monk seals breed and haul-out on sand, corals, and volcanic rock; sandy beaches are more commonly used for pupping. Due to the immense distance separating the Hawaiian Islands from other land masses capable of supporting the Hawaiian monk seal, its habitat is limited to the Hawaiian Islands.
Hawaiian monk seals mainly prey on bony fish, but they also prey on cephalopods, and crustaceans. Both juveniles and sub-adults prey more on smaller octopus 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.
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 between March and June. Pups start around 16 kilograms (35 lb) and are about 1 metre (3 ft 3 in) long.
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 total population of Hawaiian monk seals is in decline - the larger population that inhabits the northwest islands is declining while the smaller population on the main Hawaiian Islands is increasing. In 2010, it was estimated that only 1100 individuals remained.
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. Community volunteers on Oʻahu have made many anecdotal blog reports of sightings around the island since 2008. In early June 2010, two seals hauled out on Oʻahu's popular Waikiki beach. Seals have hauled out at O'ahu's Turtle Bay, and again beached at Waikiki on March 4, 2011, by the Moana Hotel. Yet another adult came ashore for a rest next to the breakwater in Kapiolani Park Waikiki on the morning of 11 December 2012, after first being spotted traveling west along the reef break from the Aquarium side of the Park. 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. Since 2012 and possibly earlier, there have been many anecdotal reports of monk seals hauling out on O'ahu's Kaena Point.
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 the 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.
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 can be affected by 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). Throughout the 1980s, the National Marine Fisheries Service completed various versions of an Environmental Impact Statement that designated the Northwest Hawaiian Islands as a critical habitat for the Hawaiian monk seal. The designation prohibited lobster fishing in waters less than 10 fathoms in the Northwest Hawaiian Islands and within 20 nautical miles of Laysan Island. The National Marine Fisheries Service designated all beach areas, lagoon waters, and ocean waters out to a depth of 10 fathoms (later 20 fathoms) around the Northwestern Hawaiian Islands, except for one of the Midway group, Sand Island. In 2006, a Presidential Proclamation established the Papahanaumokuakea Marine National Monument, which incorporated the Northwestern Hawaiian Islands Coral Reef Ecosystem Reserve, the Midway Atoll National Wildlife Refuge, the Hawaiian Islands National Wildlife Refuge, and the Battle of Midway National Memorial, thus creating the largest marine protected area in the world and affording the Hawaiian monk seal further protection.
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.
From NOAA, several programs and networks were formed in order monk seal. Community programs such as PIRO have helped to improve community standards for the Hawaiian monk seal. The program also creates networks with the Native Hawaiians on the island to network more people in the fight for conservation of the seals. The Marine Mammal Response Network (MMRN) is partnered with NOAA and several other government agencies that deal with land and marine wildlife.
The Recovery Plan for the Hawaiian Monk Seal identifies public outreach and education as a key action for promoting the conservation of the Hawaiian monk seal and its habitat.
The task is to identify a manner of alleviation that is possible, cost-effective, and likely to maximize the organic return (in terms of growth potential) until much time has passed and natural conditions allow scientists to observe the effects. .
One 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.
It is also important to consider the mothers who nurse their (female and male) pups. Seal milk is very rich in nutrients which also allows pups to gain weight rapidly. With the rich milk from the mother the pup is more prone to quadruple their initial weight before weaning. The mother seal also loses a tremendous amount of weight while nursing.
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