1. What a Dugong Is Really Like: A Three-Meter Plant Eater
A dugong is a marine mammal that lives in warm, shallow coastal waters from East Africa across the Indian Ocean to the western Pacific. An adult is about 3 meters (10 feet) long and can weigh up to about 500 kilograms (1,100 pounds) [1]. It has a thick grey-brown body, two paddle-shaped front flippers, and a tail with two lobes like a dolphin's. Its snout points downward, which suits an animal that eats seagrass from the sea floor. An adult eats roughly 30 kilograms (66 pounds) of it a day [1].
Dugongs belong to a small group of animals called sirenians, which also includes the manatees. Both are distantly related to elephants, not to other marine mammals such as whales or seals [1]. In Japan, the dugong is often suggested as one animal that may have inspired mermaid stories, and the Japanese word for mermaid is ningyo, which literally means “human-fish.” So the question is: if you really saw one, would you see a person?
2. Does the Popular “Mother Holding Her Baby” Story Match the Animal?
The most common version of the story says a mother dugong held her calf upright against her chest to nurse it, so she looked like a human mother. What do animal references say? Females have milk glands under the front flippers, and the calf suckles there [2]. A mother nurses her calf for one to two years, and a female has a calf only every three to seven years [1].
The sources we could read describe where the calf feeds, but none of them describe a mother cradling her baby in her flippers like a person. So the “human mother” image may be a lovely story rather than an observed behavior. That does not prove nobody was ever fooled. It only means this popular detail is not a solid foundation for the whole legend.
3. Japan's Oldest Mermaid Record Mentions Neither Dugongs Nor Mermaids
The oldest Japanese record usually linked to mermaids is in the Nihon Shoki (“Chronicle of Japan”), a history written in the eighth century. It describes events in the 27th year of Empress Suiko's reign, roughly 619. A fisherman in Settsu Province (today part of Osaka and Hyōgo) caught something that was “neither human nor fish.” In the same year, something “resembling a human” appeared in a river in Ōmi Province (today Shiga Prefecture) [3].
The record does not use the word ningyo, and it says nothing about dugongs. That word appears in a Japanese dictionary from the year 937, which describes a creature with a fish's body and a human face [3]. In the Meiji era (1868–1912), the scholar Minakata Kumagusu suggested the 619 creatures might have been salamanders [3]. So the same old lines have been tied to different animals by different readers. The oldest record cannot be used as proof for the dugong idea.
4. Did the Mermaid Always Look Like a Woman With a Fish Tail?
If mermaids were based on one real animal, you would expect them to look alike across time. In Japan they do not. A 1687 story collection by the writer Ihara Saikaku describes a merfolk creature with the face of a beautiful woman and a chicken's comb on its head. A medieval record from the year 1247 describes “a large fish like a human corpse” found in the sea off Tsugaru [3]. Only in the illustrated encyclopedia Wakan Sansai Zue (1713) do we find a drawing of a woman's upper body on a fish's lower body, close to today's standard image [3].
When the “mermaid” keeps changing, asking whether the dugong looks like the mermaid has no single answer. It depends on which picture you hold up.
5. Mermaid Stories Also Exist in Seas Where No Dugongs Live
NOAA, the United States ocean agency, notes that half-human, half-fish sea beings appear in the stories of many seafaring cultures, from ancient Greece (Homer's Odyssey) to Australia's Aboriginal peoples, and that no evidence of real human-like sea beings has ever been found [4]. Dugongs live only in the warm Indian and western Pacific waters, so they cannot be behind a story from a cold or far-off sea.
A famous case is Christopher Columbus. In his ship's journal, on January 9, 1493, he wrote that on the previous day, off what is now the Dominican Republic, he saw three “mermaids.” He added that they were “not half as beautiful as they are painted.” Today they are usually thought to have been manatees [5]. The original journal is lost and translations differ slightly, so this is best read as a summary of what he reported.
There was also a giant relative of the dugong, Steller's sea cow. In 1741, a Russian expedition that had been shipwrecked near the Bering Sea encountered it. It was slow, tame, and good to eat, and it was gone by 1768 [6]. Mistaking some sea cows for mermaids is very plausible. But it is only one of many ingredients in the story.
6. In Dugong Waters, Mermaid Stories and Dugongs Do Sometimes Meet
None of this means the dugong idea is wrong everywhere. In Japan's best-known mermaid tale, a girl eats mermaid flesh and lives for 800 years as “Yao Bikuni,” the eight-hundred-year nun. It is told in many versions, mainly around Wakasa (today's Fukui Prefecture) [3]. Some modern writers link such “mermaid meat” to dugong meat, but we did not find an older record that makes that link, so treat it as a later guess.
The dugong also matters in its own right. The Queensland government lists it as a vulnerable species. A long life of up to about 70 years and slow breeding make dugongs hard to replace once they are lost. Threats include damaged seagrass beds, boat strikes, and fishing nets [1]. Mermaid stories can also make people curious about the real animal.
7. How to Test the Dugong Idea Yourself
Here is a short plan for finding out for yourself. First, find three mermaid pictures from picture books or encyclopedias. Write down what each shows in the head, the upper body, and the tail. Next, look up a dugong photo and a manatee photo and compare them with your pictures: which parts match, and which do not? Then divide a dugong's weight (up to about 500 kilograms, or roughly 1,100 pounds, for a large adult) by your weight. The answer tells you how many people your size would weigh about as much as one dugong.
If you visit an aquarium that keeps dugongs or manatees, watch how they swim and eat, then decide for yourself whether you would ever take one for a person. Finally, remember what the sources do and do not say: the dugong can explain some stories, but not the oldest Japanese one, and not the stories from seas without dugongs.