Mammals of Alabama

Dugongs, Manatees, and Sea Cows

Dugongs, Manatees, and Sea Cows Order Sirenia Sirenia is derived from the word siren, the sea nymph of mythology, and dugongs and manatees may have been the basis of myths regarding mermaids. Geographic range of the order includes coastal regions of the western Pacific and Indian oceans from eastern Africa to southern Japan and Australia. Now extinct, Steller’s sea cows (Hydrodamalis gigas) once occurred in the Bering Sea. Sirenians also occur along coastal regions of the western and eastern Atlantic Ocean from about 30ºN to about 20ºS latitude. The order contains 2 families, 3 genera, and 5 species. These are the only completely aquatic mammals that are herbivores. Forelimbs are paddle-like flippers, there are no hind limbs, and the large, horizontally flattened tail forms a broad paddle. Sirenians are closely related to elephants . One family (Trichechidae) occurs in Alabama. Manatees Family Trichechidae Trichechidae contains 1 genus and 3 species. In addition to our West Indian manatee, the West African manatee (Trichechus senegalensis) also occupies freshwater and saltwater habitats (coastal ocean, bays, estuaries, and other shallow-water habitats) along the western coast of Africa, and the Amazonian manatee (T. inunguis) occupies only freshwater habitats throughout the Amazon and Orinoco drainages of South America. The distal end of the tail of manatees is rounded (spatulate) compared to the concave tail of dugongs. One species (West Indian manatee) occurs in Alabama . 24 SPECIES ACCOUNTS West Indian Manatee Trichechus manatus Identification A large, streamlined aquatic mammal with flippers instead of front legs (nails are present), no hind legs, and a flattened, spatulate tail. Color is grayish, there may be dark or pinkish splotches dorsally and ventrally, and algae, barnacles, and other incrustations may be on the skin. Appears hairless, but there are scattered 30–45-mm hairs on the body and stiff, thick bristles on the upper lip. Dental Formula In adults, no incisors or canines are present. At any time, manatees have 5–7 teeth on each side of the upper and lower jaws. These cheek teeth are replaced consecutively from the rear of the jaw as anterior teeth are worn down and lost. Up to 30 teeth may move through each quadrant of the jaw during the lifetime of a West Indian manatee. This adaptation is in response to the constant abrasion and wear of teeth caused by the coarse aquatic vegetation that is on sandy and muddy substrates . Size and Weight Range in body length is 2.5 m (8.3 feet) to more than 4.5 m (14.9 feet), with corresponding weights of 200 kg (440 pounds) to MANATEES 25 more than 1,600 kg (3,520 pounds). Average length is 3–4 m (9.9–13.2 feet) and average weight is less than 500 kg (1,100 pounds). Distribution Mobile Bay and adjacent waterways in southern Alabama northward to Claiborne Lock and Dam on the Alabama River. The West Indian manatee occurs southward from Florida and the Gulf of Mexico through the Caribbean Sea to northeastern Brazil, but it has been reported as far north as New Jersey and as far inland along the Mississippi River as Memphis, Tennessee. Ecology Present from May to November in Mobile Bay, the MobileTensaw Delta, and adjacent waterways of Alabama. West Indian manatees have no known predators, but sharks could potentially prey on them. Scars from boat propellers and keels are evidence that humans may have a significant impact on populations. Although they have been reported to consume fish, West Indian manatees are nearly completely herbivorous. They usually forage on vegetation in shallow, coastal freshwater and saltwater habitats, but they may move inland up to 800 km along river chanSubmerged with nostrils closed near a warmwater spring, this captive West Indian manatee is consuming lettuce provided by her caretakers. 26 SPECIES ACCOUNTS nels. About 6–8 hours/day are spent foraging at depths of 1–3 m. Foraging is divided into 1–2-hour bouts followed by 2–4 hours of resting. In captivity, West Indian manatees consume 30–50 kg of food/day. They are well adapted to diving and may dive as deep as 10 m. Heart rate gradually decreases from 50–60 beats/minute to about 30 beats/minute during an 8-minute dive. Causes of death associated with humans include collisions with boats; drowning in fishing nets; ingestion of fishing hooks, fishing lines, and wire; and entrapment in locks, dams, and...