The terms “sea cow” and “manatee” are often used interchangeably. While all manatees are considered sea cows, “sea cow” is a broader designation. It encompasses a larger group of animals, with manatees being a specific member of this diverse order.
Understanding “Sea Cow”
“Sea cow” is the common name for any member of the order Sirenia, a group of fully aquatic, herbivorous mammals. This order includes living manatees and dugongs, plus the now-extinct Steller’s sea cow. Sirenians have robust, streamlined bodies, thick skin with sparse hair, and a horizontally flattened tail for propulsion. They evolved from four-legged land mammals over 50 million years ago, adapting completely to aquatic life. Their dense bones aid in buoyancy regulation, allowing them to remain submerged while feeding.
Manatees: The Gentle Giants
Manatees are large, slow-moving aquatic mammals, typically 3 to 3.7 meters (10-12 feet) long and weighing 360 to 540 kilograms (800-1,200 pounds). They have a distinctive broad, rounded, paddle-shaped tail and two forelimb flippers, often with three to four nails. Their wrinkled snouts are covered with sensitive whiskers, called vibrissae, which help them navigate and manipulate food.
These herbivores spend much of their day grazing on aquatic vegetation, consuming 4% to 9% of their body weight daily. Manatees are primarily found in warm coastal waters, slow-moving rivers, and estuaries. Three recognized species exist: the West Indian manatee (including Florida and Antillean subspecies), the Amazonian manatee, and the West African manatee, each in distinct geographic regions.
The Dugong Distinction
Dugongs are the other extant species within the Sirenia order. A primary distinction is their tail shape; dugongs have a fluke-like tail, similar to a whale or dolphin, which is distinctly notched and forked. This contrasts with the manatee’s rounded, paddle-shaped tail. Another difference is their snout, which is sharply downturned and broad, allowing them to efficiently graze on seagrass roots from the ocean floor.
Manatees, conversely, have a shorter, less pronounced snout, enabling them to feed on a wider variety of aquatic plants, including those near the water’s surface. Dugongs are exclusively marine, inhabiting warm coastal waters of the Indo-Pacific region where seagrass meadows are abundant. Unlike manatees, which inhabit freshwater, brackish, and saltwater, dugongs do not venture into freshwater. Adult male dugongs may also develop small tusks, overgrown incisors not present in manatees.
The Extinct Relative: Steller’s Sea Cow
The Steller’s sea cow (Hydrodamalis gigas) was another species classified as a “sea cow,” now extinct. This immense sirenian was the largest known, reaching 10 meters (33 feet) and weighing up to 10 metric tons (22,000 pounds). Its habitat was unique among sirenians, thriving in the cold, subarctic waters of the Bering Sea around the Commander Islands.
Discovered in 1741 by naturalist Georg Steller, the Steller’s sea cow primarily fed on kelp and seaweed, keeping it in shallow coastal waters. Its slow-moving nature, large size, and tendency to remain near the surface made it an easy target for hunters. Within just 27 years of its discovery, the species was hunted to extinction by 1768, primarily for its meat, fat, and hide.