The Hawaiian Islands are a globally significant hotspot for biodiversity, with a spectacular array of plants and animals calling the wide range of ecosystems—from high volcanic mountaintops to extensive coral reefs—their home. One major reason for Hawaii’s remarkable biodiversity is the archipelago’s astonishing isolation as the most remote populated island group in the world. Organisms here have evolved from intrepid, far-traveling, or storm-routed ancestors into unique forms found nowhere else on Earth.
One of these special endemic organisms is the Hawaiian monk seal, among the most endangered pinnipeds (the group of marine mammals that includes seals, sea lions, and walruses) on the planet. Called by Native Hawaiians Ilio-holo-i-ka-uaua, “dog running in rough seas,” the Hawaiian monk seal is a biological treasure that the luckiest visitors to the islands may nab a glimpse of—though viewing these sea mammals definitely demands caution, awareness, and respect on the part of the observer.
Introducing the Hawaiian Monk Seal
Hawaiian monk seals are one of three species of monk seals, only two of which still swim their limited ranges today. They are closely related to the extinct Caribbean monk seal, which vanished due to overhunting (primarily) by the mid-20th century, and more distantly related to the Mediterranean monk seal, a pinniped that’s even more rare than the Ilio-holo-i-ka-uaua.
Hawaiian monk seals are the only pinnipeds native to Hawaii, and the only endemic marine mammals in the archipelago. (That is, Hawaii’s other marine mammals, from spinner dolphins to humpback whales, are all found in other parts of the world; only the Hawaiian monk seal lives here and here only.)
Adults grow to six or seven feet long and may weigh up to about 600 pounds. Monk seals feed on a variety of sealife, especially bony fishes such as wrasses, soldierfish, triggerfish, and eels as well as octopuses, squid, and occasional crustaceans. While they’re capable of diving to depths close to 2,000 feet, they mainly forage in much shallower waters, hunting along the seafloor for reef critters on dives that average about six minutes long.
More solitary than many pinnipeds, Hawaiian monk seals spend roughly two-thirds of their lives at sea, coming ashore to rest, give birth, nurse pups, and molt. (Molting describes the annual shedding of the monk seal’s outer fur and skin, a process that helps get rid of the algal growth that builds up on these seagoing creatures over time.)
They may live up to 30 years, though many seals don’t make it that long. Important mortality factors include prey scarcity—which scientists suspect is a prime cause of high juvenile seal mortality over the past quarter-century or so—and predation by tiger and Galapagos sharks.
Where Are Monk Seals Found in Hawaii & How Many Are There?
Biologists estimate there are roughly 1,570 Hawaiian monk seals in the archipelago, with the majority of those animals inhabiting the Northwestern Hawaiian Islands: the remote collection of low rocky and sandy isles and atolls defining the northwestern reaches of the Hawaiian Islands.
The main seal hotspots within this huge area lie within Papahanaumokuakea Marine National Monument and include Necker, Nihoa, Laysan, and Lisianski islands, French Frigate Shoals, and Midway, Kure, Pearl, and Hermes atolls.
A smaller but increasing number of Hawaiian monk seals, perhaps 300 or 400 animals, also inhabit their once-widespread range in the main Hawaiian Islands. All things considered, the monk seal’s current range in Hawaii stretches from far-flung Kure Atoll southeastward all the way to the Big Island.
Monk seals occasionally also show up at Johnston Atoll, an isolated atoll nearly 1,000 miles southwest of the Hawaiian chain.
The Conservation Status of the Hawaiian Monk Seal
Today’s stock of Hawaiian monk seals is reckoned at perhaps one-third of historical numbers. Seals suffered at the hands of humankind, from early overhunting to habitat loss and disturbance on resting and pupping beaches, entanglement in fishing gear, and a reduced prey base due at least in part to human activity.
Rigorously protected not only by the Endangered Species Act and the Marine Mammal Protection Act but also Hawaiian state law, Hawaiian monk seals have, fortunately, begun to rebound from a catastrophic population decline beginning in the 1950s. According to the National Oceanic & Atmospheric Administration, the monk-seal population rose by about two percent each year between 2013 and 2021.
Viewing Hawaiian Monk Seals
The region where Hawaiian monk seals are most common—the Northwestern Hawaiian Islands—is remote and comparatively rarely visited (not least due to sheer logistics and restricted public access). But visitors to the main islands of Hawaii do have the chance to spot a monk seal just about anywhere and at any time of year. It’s most common to spot them hauled out on beaches and shoreline rocks, but snorkelers, divers, and keen-eyed watchers from coastal overlooks sometimes spy swimming seals as well.
It’s a thrill and a privilege to see this rare and endangered marine mammal in the wild. But you also need to be a respectful observer, as monk seals are very vulnerable to human disturbance that can tax their energy reserves and threaten the survival of young pups.
Obey any posted signs keeping people out of areas where monk seals regularly give birth, nurse, and bask. Even if there isn’t any such signage, you should stay at least 50 feet away from any monk seal you see, whether ashore or in the water, and at least 150 feet away from mothers and pups.
It may sound tricky to know whether you’re at least 50 feet away from a beached monk seal, but the “rule of thumb” (a pun!) is here to help. Make a thumbs-up with your arm held out straight in front of you toward the seal; then turn your thumb parallel to the ground and see whether it completely covers the animal, in which case you’re roughly at least 50 feet away. Again, though, you need to stay even farther back from a female seal and her pup.
Here’s hoping you luck out with a glimpse of a Hawaiian monk seal on your next getaway to the Hawaiian Islands—just remember, if you do, to give it plenty of elbow room!
