Creature Feature: Hawaiian Monk Seal

Nestled smack dab in the middle of the Pacific, the Hawaiian Islands are the most isolated land mass in the world.1 Thanks to this geographic isolation, the Hawaiian archipelago boasts many endemic species, i.e. species native to Hawaii and not found anywhere else in the world. Arguably one of the most charismatic of these endemic species is the State’s official mammal, the Hawaiian monk seal (Neomonachus schauinslandi). However, many of these endemic species, including the Hawaiian monk seal, face the threat of extinction due to massive anthropogenic (human-caused) environmental change.

The Hawaiian monk seal, as its name suggests, is endemic to the Hawaiian archipelago. [Source]
Of all Phocidae family species, monk seals (paraphyletic group including Neomonachus and Monachus) are considered the most primitive, as many anatomical features are also present in fossil specimens from 14-16 million years ago; this was supported by subsequent genetic analysis.2 Once prevalent throughout the archipelago, the Hawaiian monk seal population faced near extinction after British explorers arrived in the Hawaiian islands in the late 18th century (oh, the classic “explorer pillages new environment” scenario) and were rarely sighted during the 19th century.3 While the Hawaiian monk seal population began to bounce back in the 1970s–after The Marine Mammal Protection Act of 1972 and The Endangered Species Act of 1973 were passed– their population is still critically endangered, with approximately 1,100 seals in the Northwestern Hawaiian Islands (NWHI) and 300 in the Main Hawaiian Islands (MHI).4

National Marine Fisheries Service (NMFS) map of Hawaiian Islands. [Source]
Millions of visitors flock to Hawaii each year to spend their days napping on sunny beaches, swimming in warm, tropical seas, and eating fresh seafood. While Hawaiian monk seals get to do that every day, their natural history doesn’t permit a seemingly permanent, island vacation life. As benthic feeders–meaning that they forage on the ocean floor–they spend 2/3 of their time in the water diving to depths between 18-90 meters (60-300 feet) deep to hunt for fish, cephalopods (e.g. octopus, squid), and crustaceans (e.g. lobster) that hide in coral reefs and sandy beds.2,5 They have developed a specialized strategy of rock-flipping and blowing bubbles of air to flush out prey from their hiding places.They also have been found diving deeper than 300m (984 ft!) in coral heads containing eels.6 However, hunting can be quite competitive, especially for juvenile Hawaiian monk seals. Reef sharks and pelagic fish will wait for the seal to do the hard work of flushing out prey, and if the Hawaiian monk seal isn’t quick enough, the free-loaders will grab whatever tasty reef snack comes out from the coral head. This competition is exacerbated by food limitation, leading to starvation for juveniles and sub-adults who haven’t perfected their hunting strategies.2,5

A Hawaiian monk seal ilioholokauaua (Neomonachus schauinslandi) swimming above a healthy coral bed. [Photo by: Andrew Gray/NOAA, 2017, Source]
Their name in native Hawaiian language is īlio-holo-i-ka-uaua, which means ‘dog that runs in rough water’ and it’s not hard to see why; round faces, big eyes, “bald” heads, and a curious, puppy-like demeanor make them seem like a familiar four-legged friend. Like our best terrestrial pals, Hawaiian monk seals are often curious about their environment. Unfortunately, this curiosity can be detrimental when living in the middle of the Pacific Garbage Patch. Hawaiian monk seals have the highest documented entanglement rates of any pinniped species, and this is one of the main causes of mortality, which is in part attributed to the replacement of natural fibers to durable plastic materials for netting material within the maritime industry.2 However, the blame cannot solely be placed on the fishing industry; Hawaiian monk seals have also been seen entangled in non-maritime related debris such as bicycle tires, rubber hoses, diving fins, and buckets. Most recently, a newly weaned Hawaiian monk seal pup was seen interacting with a kitchen knife in her mouth on the Big Island of Hawaii! While net entanglements are a great concern for marine life, these interactions with man-made trash highlight the importance of ocean stewardship among the general population (so remember, when outdoors, think aʻole ʻōpala – no trash, and always follow the “leave no trace” mantra).

As a result circulating ocean currents and the resulting Pacific Garbage Patch, abandoned fishing gear from all over the Pacific is brought to the Hawaiian archipelago where marine mammals such as these monk seals often get entangled. [Source]
The Hawaiian monk seal population has struggled for the past 100 years and with the environmental challenges highlighted here, their recovery plan is an uphill battle. However, with the help of governmental agencies (e.g. National Marine Fisheries Service and the National Oceanic and Atmospheric Administration), local non-profits (e.g. Ke Kai Ola, Waikiki Aquarium), and citizen science (i.e. volunteers and beachgoers who report Hawaiian monk seal sightings throughout the MHI), Hawaiian monk seals still have a fighting chance at recovery. In fact, it seems that the number of seals in the NWHI is stabilizing, and perhaps even increasing in the MHI.7

Female RA20 and her pup Manuʻiwa, born February 8, 2018 on the island of Hawaii.
[Photo by: Sheila Latta/Ke Kai Ola, Source]
Population increases seem especially hopeful when a female comes to the beach to give birth to a single pup. At birth, pups weigh between 14-17 kg (30-37 lb), and after approximately 39 days of nursing, pups can weigh up to 100 kg (220 lb), nearly quadrupling their body size.2 Since female monk seals fast during nursing, much of their time during those 39 days is spent resting on the beach, or splashing in the shore break. By the end of nursing, moms are hungry, and pups are ready to explore the ocean on their own. It is then our kuleana (responsibility), whether it be researchers who track development, volunteers who educate the public, or visitors who respect the animal by keeping a safe distance, to ensure the survival of the pup, and long-term survival of the Hawaiian monk seal species.

Female, RH58 (aka Rocky) and her pup Kaimana, born on a beach (her namesake) near Waikiki in ʻOahu. [Photo by: Anthony Quintano, Source]

[By: Karli Chudeau]



2National Oceanic and Atmospheric Administration. 2007. Recovery Plan for the Hawaiian Monk Seal (Monachus schauinslandi). Second Revision. National Marine Fisheries Service, Silver Spring, MD. 165pp.



5Wilson, K., Littnan, C., Halpin, P., & Read, A. (2017). Integrating multiple technologies to understand the foraging behaviour of Hawaiian monk seals. 

6Parrish, Frank, A., Abernathy, K., Marshall, G. J., & Buhleier, Birgit, M. (2002). Hawaiian Monk Seals (Monachus schauinslandi) Foraging in Deep-Water Coral Beds. Marine Mammal Science, 18(1), 244–258. 


Additional references:

Pacific Garbage Patch link:

Kitchen knife link:…playing-with-knife/1127836602

The Marine Mammal Protection Act link:

The Endangered Species Act link:

Leave no trace link:

Ke Kai Ola link:

Hawaiian language words were double-checked using:

Main feature image [Source]

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