It's that time of year when manatees, the slow-moving aquatic mammals of the southeast coast of North America, start to migrate south into warmer waters—and often run into trouble.

In Florida, many of the languid giants—also called sea cows—are killed each year in boating collisions. (See also: "Record 829 Manatee Deaths in 2013 Puzzle Scientists.")

That's why November is also Manatee Awareness Month, which just this year became official in the state of Florida. Governor Rick Scott issued a proclamation to protect the state's official mammal as a "distinctive, valuable, and beloved natural resource."

The International Union for Conservation of Nature lists the American manatee—also known as the West Indian manatee—as vulnerable, with less than 10,000 individuals of that species left in the wild, according to its website. The population in Florida is estimated at 4,831, according to Save the Manatee. The manatee is a sirenian—an order of aquatic mammals that includes three species of manatees and their Pacific cousin, the dugong.

The ocean's largest herbivore, sirenians are also notable as the creatures that have long fueled mermaid myths and legend across cultures. Below we take a look at some of the most fascinating fables.

"Their Faces Had Some Masculine Traits"

Christopher Columbus, in his first journey to the Americas, caught a glimpse of three "mermaids" off the prow of his ship, writing in his journal:

"On the previous day [8 Jan 1493], when the Admiral went to the Rio del Oro [Haiti], he said he quite distinctly saw three mermaids, which rose well out of the sea; but they are not so beautiful as they are said to be, for their faces had some masculine traits." (Voyages of Columbus 218)."

NG Live!: The Mermaid Myth Photographer Brian Skerry reveals the creatures once believed to be mermaids.

Indeed, manatees and dugongs are both known to rise out of the sea like the alluring sirens of Greek myth, occasionally performing "tail stands" in shallow water. (See "Severe Scurvy Struck Christopher Columbus's Crew.")

With forelimbs containing five sets of fingerlike bones, and neck vertebrae that allow them to turn their heads, it's possible that manatees could be mistaken for humans from afar.

Following Columbus's expedition to the Americas, sideshows in Europe advertised "recently discovered" mermaids from the new world, often a deceased sirenian.

"A short time back, the skeleton of a mermaid, as it was called, was brought to Portsmouth, which had been shot in the vicinity of the island of Mombass. This was allowed to be submitted to the members of the Philosophical Society, when it proved to be the Dugong … It was, if I recollect right, about six feet long: the lower dorsal vertebrae, with the broad caudal extremity, suggested the idea of a powerful fish-like termination; whilst the fore legs, from the scapula to the extremities of the phalanges, presented to the unskillful eye an exact resemblance to the bones of a small female arm." —Description of a mermaid in England's Magazine of Natural History.

Lady of the Sea

Thousands of miles from the seas Columbus sailed, the dugong—found in the Pacific Ocean—had been living in legend for centuries.

In 1959, 3,000-year-old cave drawings depicting dugongs—the word translates to "lady of the sea" in the Malay language—inside Malaysia's Tambun Cave were discovered. (Watch video: "Arabian Sea Cows Going Hungry?")

In Palau, a Pacific nation that extends across 340 islands, the dugong plays a central role in traditional ceremony and lore. Stories of young women transformed into these gentle grazers endure, and wooden storyboard carvings illustrate dugongs aiding fishermen lost at sea.

Olympia E. Morei, director of the Belau National Museum, says that "Palauans respected their environment and all the living things in that environment—trees, plants, all the animals and birds. We believed that dugong was once a human, according to the legend."

The International Union for Conservation of Nature also lists the dugong as vulnerable to extinction.

The animal's population across its range remains unknown, but up to 15 animals are likely killed in Palau each year for food, according to the Etpison Museum's Dugong Awareness Project.

"If the dugong were to be extinct [in Palau], we would, as a people, lose our connection to our environment and to our tradition," Morei said.

Without stronger conservation efforts, the gentle creatures that once inspired fantastic mermaid myths will themselves be consigned to mere legend.