Key findings about rare ocean animals:
- The rarest marine animal is the vaquita (Spanish for “little cow”), a tiny porpoise found only in the Gulf of Mexico. It is also the world's most endangered marine animal, with only 10 individuals left in the wild.
- Some of the ocean's rarest animals may live in the uncharted depths of the ocean, including areas such as the “midnight zone” where light from the surface cannot penetrate.
- The most mysterious sea animal can be of several species, including the ghostly octopus Casper.
Despite everything we have learned about planet Earth, the ocean remains as vast and mysterious as ever. It covers approximately 70 percent of the globe but is still largely unexplored, and scientists believe that more 90 percent marine species not yet classified.
Of those we know, many are so elusive or endangered that encountering them in the wild is astronomically unlikely.
When biologists talk about rarity, “we're really talking about a couple of different things,” says Craig McClain, who studies deep-sea life at the University of Lafayette. “Not all rare species are rare for the same reasons.”
Some have small but widespread populations, while others are abundant within a limited geographic range or ecological niche. Some have likely always existed in small numbers, but McClain notes that many are rare “because humans made them that way through overfishing, habitat loss, or climate change.”
Here are seven of the ocean's rarest inhabitants—creatures that remind us how much of the world remains beyond our reach and how fragile its wonders are.
Read more: 5 Endangered Animals You Should Meet
What is the rarest animal in the ocean?
The vaquita, Spanish for “little cow,” is a tiny porpoise found only in the Gulf of California in Mexico. It is also the most endangered marine animal. only 10 people remained in the wild. Less than five feet long, with dark markings around its eyes and mouth, the vaquita was only discovered in 1958. It is now listed as critically endangered by the International Union for Conservation of Nature (IUCN), just one step away from extinction.
Rare marine animal vaquita.
(Image credit: AbdulSalam453/Shutterstock)
Experts say the main reason for the population decline is bycatch: creatures caught in gill nets set to catch totoaba, a species of fish prized for its swim bladder and a Chinese delicacy. Despite international bans, illegal fishing persists, and conservationists are now rushing to save the vaquita.
Read more: The pygmy right whale was a family oddity and never went extinct
1. Rare North Atlantic right whale
At the other end of the size spectrum is another cetacean: the North Atlantic right whale. Commercial whalers hunting for blubber and oil had already seen their numbers sharply decline by the late 1800s. Today, about 360 individuals leftincluding 70 reproductively active females.
A rare sea animal is the North Atlantic right whale.
(Image credit: lego 19861111/Shutterstock)
As they migrate along the east coast of the United States, these whales remain at risk from ship strikes and entanglement in fishing gear. They sometimes surface near busy ports, where collisions can be fatal. Scientists are tracking the species by unique patterns of rough skin on its head, called calluses, and the results are grim: North Atlantic right whales have been experiencing an ongoing “unusual mortality event” since 2017, with more than 150 individuals killed, seriously injured or in poor health.
2. Kemp's Ridley: The Most Endangered Sea Turtle
The smallest and most endangered sea turtle, Kemp's ridley, nests along the Gulf Coast and Texas. Its synchronized mass nesting events, called arribadas, which means “arrival” in Spanish, once attracted thousands of females to the shore. By the 1980s, however, only a few hundred had arrived. Today they are classified as endangered.
A rare sea animal is the Kemp's Ridley sea turtle.
(Image credit: Mahmoud Hidayat/Shutterstock)
After a record low of 702 nests in 1985, fishing regulations and protection of nesting beaches helped the population recover by about 15 percent annually during the 1990s and 2000s. However, oil spills and warming seas continue to pose serious threats to Kemp's ridley.
Read more: Brain coral looks like a brain and can live up to 900 years
3. The Endangered Chagos Brain Coral
Corals may seem less charismatic than marine mammals, but Chagos Brain Coral is a fascinating piece of polyps. With labyrinthine folds snaking across its domed surface, it bears an eerie resemblance to its namesake. Moreover, it can live for centuries.
Found only in the remote Chagos Archipelago in the Indian Ocean, this remarkable coral is also endangered. The main culprit is climate change: repeated marine heatwaves have bleached much of the coral, leaving survivors susceptible to disease. On the plus side, as of 2010, its habitat is part of the Chagos Marine Protected Area, which includes the world's largest coral atoll.
4. Goblin Shark: A Rare Living Fossil
All animals so far have been driven to the brink of extinction by human activity in one way or another. But some ocean creatures become vulnerable naturally. In fact, McClain says, in the deep sea, “rare is the norm.” Thousands of feet below the earth's surface, a lack of food and suitable habitat ensure that most populations remain small and dispersed.
goblin shark falls into this category. With pink translucent skin, a ridiculously long pointed snout and retractable jaw which in the blink of an eye rushes forward to grab its prey, the goblin shark looks like some kind of scary movie monster. Because it is the only species remaining in the ancient family Mitsukurinidae, it is often called a “living fossil”. These sharks patrol the continental slopes at depths of more than 4,000 feet, hunting not by sight but by sound, smell and the electrical fields created by other animals.
Read more: These 12 Deep Sea Creatures Are More Comical Than Creepy
5. Giant Ghost Jellyfish: A Rare Ocean Phenomenon
Measuring over 30 feet in length, giant ghost jellyfish – one of the largest invertebrates in the ocean. However, despite its size, it is also one of the rarest. Since biologists first described this jellyfish in 1910, it has only been seen alive about a hundred times.
With a billowing, domed bell over 3 feet in diameter and ribbon-like arms trailing down the depths behind it, the ghost jellyfish truly deserves its ghostly name. It is usually found in the “midnight” zone, down to 22,000 feet, where light never penetrates.
6. The most mysterious sea animal
That title could go to any number of deep-sea species whose behavior and lifestyles are virtually unknown to science—giant squid, anglerfish with their bioluminescent lures, and tube siphonophores, colonial creatures that can grow longer than blue whales.
But as deep-sea expeditions become more common, scientists are still discovering entirely new species. One of them, first spotted in 2016, is the Casper octopus, a pale, ghostly creature found on the seabed near the Hawaiian Islands, more than two miles deep. Its dull skin surprised experts because octopuses are usually brightly colored – even those that live in the dark.
“They're probably quite common,” Janet Voight, assistant curator of invertebrate zoology at the Field Museum of Natural History in Chicago, told the BBC. “It's just an indication of how little we know about what's down there.”
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