Hawaiian Monk Seals 101: Protecting a Hawaiian Endangered Species            

By Jamie Thomton

A monk seal and its pup are seen here on the shore. Photo by NOAA Fisheries

The Hawaiian monk seal is one of the most endangered seal species in the world. The population overall has been declining for more than 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, and nowhere 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. NOAA Fisheries is the lead federal agency responsible for monk seal conservation.

Status

Approximately three-to-five seal pups are born on Kaua‘i each year, including RL52 pictured here. Photo by NOAA Fisheries

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. Kaua‘i has a population of 40-to-50 seals.

A prolonged decline of the Hawaiian monk seal population in the NWHI occurred from the late 1950s until very recently. 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:

• Recolonization and significant growth of the Main Hawaiian Islands monk seal subpopulation from low numbers to approximately 300
• Overall species population growth average of 2 percent each year between 2013 and 2019
• Promising advances in juvenile seal survival enhancement research

Appearance

Applied bleach marks and flipper tags help staff and volunteers within the Marine Animal Response Network to identify individual seals. Photo by NOAA Fisheries

Each year, approximately three to five monk seal pups are born on Kaua‘i. 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 on their fur, such as scars or natural bleach marks (white spots), which help identify them. We also apply bleach marks to their hair for easy identification. NOAA Fisheries staff and partners also apply identifying tags to their rear flippers. Tracking tags are applied to select seals and those instruments usually go between the seal’s shoulders. 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 to see 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 fish, squid, octopus, eels, and crustaceans (crabs, shrimps and lobsters). Diet studies indicate 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 (juvenile ulua) and ‘ō‘io (bonefish).

Hawaiian monk seals can hold their breath for up to 20 minutes and dive more than 1,800 feet below the surface. 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, but they do not defend territories.

Lifespan and Reproduction

Monk seals can live for more than 30 years, but few live that long.

Monk seals mate in the water. The youngest documented female to give birth was four years old, but typically females begin reproducing at age five or six in the Main Hawaiian Islands and age seven to 10 in the Northwestern Hawaiian Islands.

Threats

This hook was removed from a Hawaiian monk seal. Report seal sightings and injuries to the NOAA Marine Wildlife Hotline to support these endangered animals. Photo by NOAA Fisheries

The major threats faced by monk seals in the Main Hawaiian Islands differ from the threats in the NWHI. The NWHI primary threats are food limitation, shark predation, entanglement in marine debris, male seal aggression and habitat loss. Threats to monk seals in the Main Hawaiian Islands include:

• Fishery Interactions

Between 1976 and 2016, interactions in nearshore recreational and subsistence fisheries have occurred in the Main Hawaiian Islands. This includes 155 documented hookings and entanglements in gill nets, which resulted in 12 monk seal deaths. Expert fishermen have worked with state and federal wildlife managers to develop best practice guidance. The guidance is 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 toxoplasmosis and distemper viruses (morbillivirus). There is also the threat of emergent diseases that have yet to make it to Hawai‘i, such as West Nile virus. The lack of antibodies to morbillivirus led NOAA to develop the first of its kind population-wide vaccination program, and it is now being implemented to help prevent an outbreak that could devastate the species. Since 2001, there have been a minimum of 13 monk seal deaths from toxoplasmosis in the Hawaiian Islands, with at least eight 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 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. Human-seal interactions pose both a threat to human and seal safety.

• Intentional Killing

Intentional killing of seals is an extreme example of negative human impacts in the Main Hawaiian Islands. As of 2018, 13 seals have died of suspected intentional killings.

How Can You Help?

Hawaiian monk seals are part of the identity of our islands and hold a special place in our hearts and minds. While viewing monk seals, you should ensure that your actions do not disturb them. Since an animal’s reaction will vary, carefully observe all animals and leave the vicinity if you see possible signs of disturbance. Remember:

• It is natural for monk seals to come ashore or haul out on the beach for long periods of time. Maintain a distance of at least 50 feet.
• Signed off areas on the beach are for your safety and their protection — please do not enter.
• Pets, especially dogs, can pose a significant risk to monk seals. Please keep them on a leash when in the presence of monk seals to avoid injury or disease transmission.
• Help eliminate the threat of toxoplasmosis by keeping your cats indoors and not feeding feral cats.
• If approached by a seal, move away to avoid interaction. If in the ocean, cautiously exit the water.
• In the ocean, monk seals may exhibit inquisitive behavior. Approaching or attempting to play or swim with them may alter their behavior and their ability to fend for themselves in the wild. Further, monk seals are large wild animals and can pose a risk to human safety if they are protecting a pup or feel threatened by your actions.
• You can help us to track and monitor monk seals by reporting all sightings to the NOAA Fisheries statewide marine wildlife hotline at (888) 256-9840.

• Jamie Thomton is the Kaua‘i Marine Mammal Response Coordinator at Protected Resources Division, Pacific Islands Regional Office, NOAA Fisheries