The Hawaiian monk seal (Neomonachus schauinslandi) is a type of earless seal in the family Phocidae. It is found only in the Hawaiian Islands and is at risk of becoming extinct.

This seal is one of two surviving monk seal species. The other is the Mediterranean monk seal. A third species, the Caribbean monk seal, no longer exists. The Hawaiian monk seal is the only living animal in the genus Neomonachus.

The Hawaiian monk seal is the only seal that lives naturally in Hawaii. Along with the Hawaiian hoary bat, it is one of only two mammals that are found only in the Hawaiian Islands.

Neomonachus schauinslandi is a species that depends on human efforts to survive. Its population, which includes about 1,400 individuals, is in danger because of human activity, very low genetic diversity, fishing nets that trap the seals, trash in the ocean, illness, and past hunting for their skins. To help protect this species, scientists use methods such as moving seals to safer areas, caring for them in protected places, cleaning up their habitats, and teaching people about the importance of saving the Hawaiian monk seal.

Etymology

Known to native Hawaiians as ʻīlio-holo-i-ka-uaua, or "dog that runs in rough water," its scientific name comes from Hugo Schauinsland, a German scientist who found a skull on Laysan Island in 1899. Its common name and the first part of its scientific name are based on short hairs on its head, which look like a monk's hair. It is the official state mammal of Hawaii.

Description

The Hawaiian monk seal has a gray coat, white belly, and thin body shape that make it look different from the harbor seal (Phoca vitulina). Its body is well-suited for hunting fish, lobster, octopus, and squid in deep underwater coral areas. When it is not hunting, it usually rests on sandy beaches and volcanic rock in the Northwest Hawaiian Islands.

The Hawaiian monk seal belongs to the family Phocidae, named for its lack of external ears and inability to move its hind flippers under its body. It has a small, flat head with large black eyes, eight pairs of teeth, and a short nose with a nostril on top. The nostrils are small vertical slits that close when the seal dives underwater. Its thin, torpedo-shaped body and hind flippers help it swim quickly.

Adult males weigh between 300 to 400 pounds and are about 7 feet long. Adult females are usually slightly larger, weighing 400 to 600 pounds and measuring about 8 feet long. When monk seal pups are born, they average 30 to 40 pounds and are about 40 inches long. After nursing for about six weeks, they grow significantly, reaching 150 to 200 pounds by the time they are weaned. During this time, the mother can lose up to 300 pounds.

Like elephant seals, monk seals shed their hair and outer skin layer during an annual molt. During the most active part of the molt, which lasts about 10 days, the seal stays on the beach. The hair is usually dark gray on the back and lighter silver on the belly. Over time, sunlight and seawater change the colors, turning dark gray to brown and light silver to yellow-brown. Spending long periods in water can also cause algae to grow, giving some seals a green tint. The juvenile coat, which appears during the molt after a pup is weaned, is silver-gray. Pups are born with black fur. Many Hawaiian monk seals have scars from shark attacks or fishing gear. The maximum life expectancy of these seals is 25 to 30 years.

Evolution and migration

Monk seals are part of the family Phocidae. In a 1977 study, Repenning and Ray suggested that monk seals were the most basic living seals based on some simple traits. However, this idea is no longer accepted.

To help people understand and protect monk seals, the National Oceanic and Atmospheric Administration (NOAA) Fisheries Service created a timeline showing that monk seals have lived in the Hawaiian Islands for millions of years and that they naturally belong there. Evidence suggests that monk seals moved to Hawaii between 4 and 11 million years ago through a water passage between North and South America called the Central American Seaway. This passage was blocked by the formation of the Isthmus of Panama about 3 million years ago.

Berta and Sumich question how monk seals arrived in the Hawaiian Islands when their closest relatives live on the other side of the world in the North Atlantic and Mediterranean Sea. The species may have developed in the Pacific or Atlantic Ocean, but in either case, they reached Hawaii long before the first Polynesians arrived.

Ecology

The Hawaiian monk seal population is mostly found around the Northwest Hawaiian Islands, but a small and growing group lives near the main Hawaiian Islands. These seals spend about two-thirds of their time in the ocean. They search for food in deep waters beyond shallow reef areas, often diving to depths of 300 meters (160 fathoms) or more. Hawaiian monk seals breed and rest on sand, coral, and volcanic rock. Sandy beaches are most often used for giving birth. Because the Hawaiian Islands are far from other land areas that can support these seals, their habitat is limited to the Hawaiian Islands.

Hawaiian monk seals mainly eat fish that live near coral reefs, but they also eat octopuses and crustaceans. They prefer fish from the families Muraenidae, Labridae, Holocentridae, Balistidae, and Polymixiidae. Juvenile and young adult seals eat more small octopuses, like Octopus leteus and O. hawaiiensis, as well as nocturnal octopuses and eels, compared to adult seals. Adult seals mostly eat larger octopus species, such as O. cyanea. Hawaiian monk seals have a wide range of prey because they can adapt their hunting habits to find different types of food.

Hawaiian monk seals can hold their breath for up to 20 minutes and dive more than 550 meters (1,800 feet). However, they usually dive for about 6 minutes to depths less than 60 meters (200 feet) to search for food on the ocean floor.

The main predators of the Hawaiian monk seal are tiger sharks, great white sharks, and Galapagos sharks.

Behavior

Hawaiian monk seals mate in the water during their breeding season, which happens from June to August. Female seals reach maturity at age four and give birth to one pup each year. The fetus develops for nine months, and the baby is born between March and June. Pups are born weighing about 16 kg (35 lb) and are approximately 1 m (3 ft 3 in) long.

The pups are born on beaches and are nursed for about six weeks. The mother does not eat or leave the pup during this time. After this time, the mother leaves the pup alone and returns to the sea to search for food for the first time since the pup was born.

Status

Most seals live in the Northwestern Hawaiian Islands. The Hawaiian monk seal is endangered. Its cousin, the Mediterranean monk seal (M. monachus), is even rarer. The Caribbean monk seal (N. tropicalis), which is closely related, was last seen in the 1950s and was declared extinct in June 2008. In 2010, about 1,100 Hawaiian monk seals remained. A 2016 study, which included more detailed surveys, estimated the population to be around 1,400 individuals.

Seals nearly disappeared from the main Hawaiian islands, but their numbers have started to increase. In 2004, about 150 seals lived there, and by 2016, the number had grown to about 300. Seals have been seen in places like Kauaʻi, Niʻihau, and Maui. People on Oʻahu have reported seeing seals on beaches and in surf areas since 2008. In June 2010, two seals were spotted on Waikīkī beach. Other sightings have occurred at Turtle Bay on Oʻahu and at Waikīkī near the Moana Hotel. In July 2023, a seal was seen at Punaluʻu Black Sands Beach. In December 2012, an adult seal rested near Kapiʻolani Park in Waikīkī. In June 2017, a seal named "Rocky" gave birth to a pup on Kaimana Beach.

In 2006, 12 pups were born on the main islands. This number increased to 13 in 2007 and 18 in 2008. By 2008, 43 pups had been counted there. The Hawaiian monk seal was listed as endangered on November 23, 1976, and is now protected by the Endangered Species Act and the Marine Mammal Protection Act. It is illegal to harm, capture, or disturb a Hawaiian monk seal. Even with these protections, human activities near Hawaii’s coasts and globally still harm the species.

In 2024, the IUCN changed the Hawaiian monk seal’s status from Endangered to Vulnerable because its population has grown. Natural threats include low survival rates for young seals, loss of habitat and prey due to environmental changes, increased aggression among male seals, and unbalanced gender ratios. Human-related threats include hunting in the 1800s and 1900s, which reduced genetic diversity, ongoing human disturbances, entanglement in marine debris, and interactions with fisheries.

Low survival rates for young seals are a major threat. Many young seals die from starvation or entanglement in debris. Shark attacks also kill many young seals. Most adult seals have scars from shark encounters.

Habitat loss and reduced prey availability, such as overfishing of lobsters, can lead to starvation. Other predators, like sharks and fish, compete for food, leaving little for young seals. The Papahānaumokuākea Marine National Monument, which protects the Northwestern Hawaiian Islands, may help increase food supplies.

A behavior called "mobbing" occurs when multiple male seals attack a female during mating attempts. This behavior often leads to injury or death, especially for females. Wounds from mobbing can cause infections, which may kill the seals. Smaller populations are more likely to experience mobbing because of higher male-to-female ratios and aggressive behavior.

Postmortem exams of seal carcasses found ulcers caused by parasites. Diseases like distemper viruses, West Nile Virus, Leptospira spp., and Toxoplasma gondii also threaten the seals. Toxoplasmosis, caused by cat feces in polluted water, has killed at least 11 seals since 2001.

In the 19th century, whalers and sealers hunted seals for meat, oil, and skin. U.S. military forces also hunted seals during World War II on Laysan Island and Midway.

The Hawaiian monk seal has the lowest genetic diversity among 18 phocid species. This is believed to result from a population bottleneck caused by hunting in the 19th century. Limited genetic diversity makes it harder for the species to adapt to environmental changes and increases the risk of extinction.

Toxoplasmosis, caused by cat feces in polluted runoff, is a new threat to seals. Other human-related diseases, like leptospirosis, have also infected seals.

Human activities, such as beach crowds and structures, can force seals to abandon beaches, reducing their habitat and slowing population growth. Even small human disturbances can harm seals.

Fisheries may harm seals through entanglement in fishing gear or by consuming fish waste. Although laws prohibit dumping debris at sea, seals still get trapped in nets and other debris, which can be deadly. Monk seals have the highest recorded entanglement rate among pinniped species.

In 1909, President Theodore Roosevelt created the Hawaiian Islands Reservation, which later became the Hawaiian Islands National Wildlife Refuge. In the 1980s, the National Marine Fisheries Service designated the Northwestern Hawaiian Islands as a critical habitat for the Hawaiian monk seal. This protection banned lobster fishing in certain areas. In 2006, the Papahānaumokuākea Marine National Monument was established, combining several protected areas to create the world’s largest marine protected area and provide additional protection for the seals.