Abstract

The Florida manatee, Trichechus manatus, is considered endangered, and is on the brink of extinction. This paper presents a discussion of captive manatee husbandry, including housing requirements, fresh water needs, nutritional requirements, etc. Blood data is presented taken from two captive manatees at Epcot's Living Seas Exhibit. Data includes hormonal assays to determine reproductive status in the female, along with physical measurements and behavioral observations.

History

The Manatee is a herbivorous aquatic mammal in the order Sirenia. At present there are four species living today in the order Sirenia; Trichechus manatus, or the West Indian Manatee, Trichechus senegalensis, or West African Manatee, Trichechus inunguis, the Amazonian Manatee of South America and the Dugong, Dugong dugong, found in Indonesia. All species are considered highly endangered and are threatened with extinction. The manatee's future, ironically, lies in the hands of its only true predator, man. Although hunting of manatees for food and their hide still persist in South American and Africa, the most single important threat to their future existence is the rapid disappearance of their natural environment, by man's uncontrolled development and pollution.

Although the study of the West Indian Manatee has increased considerably in recent times, very little is known of their natural biology. Because of its dense bone structure, voracious appetite, unique tooth formation, hind gut digestion, and blood cell morphology, the manatee is thought to have evolved from a line similar to that of the elephant.

This paper will deal with captive West Indian Manatees, or Florida Manatees, (Trichechus manatus latirostris). This subspecies is found mainly in the coastal waterways, rivers and estuaries of Florida. This manatee can be found as far North Carolina, on the East Coast, in warm seasons, and in the Gulf of Mexico's coastal waters, as far South as Mexico on occasion. The exact number of West Indian Manatees is unknown, in that there has never been a population count. There have been various estimates, based on aerial surveys conducted during winter months when the animals aggregate for the warmth of the spring fed, fresh water rivers on both coasts of Florida, as well as the warm water effluent of nuclear power plants.

Historically, the animal was first reported by the explorer Columbus, in his ship's log, in 1493. He wrote of the sighting of a group of sea animals that must "be mermaids, although they were not as pretty as they had been painted".

Food Requirements

The manatee is a voracious feeder, and spends one-quarter to one-third of its time feeding. They are regarded as indiscriminate and opportunistic in the aquatic plants they consume, eating approximately 7 to 9 per cent of their body weight per day. (1,2,3). They have a highly prehensile upper lip, and utilize their fore limbs to gather foodstuffs to the mouth. Their dentation is somewhat similar to the elephant, in that they have hard palates instead of incisor, and have 5 to 6 molar teeth on each jaw. These molars are constantly being reproduced from teeth buds in the posterior jaw that migrate cranially as worn. The older, most anterior teeth fall out when replaced. Captive manatees have been fed a wide variety of wild, harvested plants, as well as a range of vegetables produced by man, including lettuce cabbage, carrots and celery. (4) Nutritional research by the writer (White) in the early '70s indicated that manatees maintained on a diet of lettuce and cabbage in captivity had a definite calcium/phosphorus imbalance and required mineral supplements for successful reproduction. In the wild this need for minerals is more-than likely supplied by the ingesting of larval vertebrates and invertebrates inhabiting the vegetation they are feeding upon. (4,5) Hydroponically grown oat sprouts were introduced as the major food of the captive manatee's diet in 1980, for several benefits. The mass-produced oat sprouts provides a more reliable protein source, as well as to eliminate the danger of toxicity from pesticides and insecticides usually used in manproduced vegetables. The minor supplementation of lettuce and carrots, from a reliable source, is still recommended. Vitamin and mineral supplements are administered via bananas and/or the occasional small fish. Purina's High-protein Monkey Chow is also recommended to be fed at a rate of 1-2 lbs. per animal, per day, for additional protein and minerals. These small, bite-size biscuits are readily taken, and are especially useful in behavioral training for clinical procedures. (4)

Digestion and Fresh Water Requirements

The exact freshwater needs for the manatee are unknown. Freeranging animals have been observed drinking from a variety of fresh water sources. (1,6,7) Limited clinical studies have supported assumptions that manatees, in marine environments, have the capability to physiologically excrete more concentrated levels of sodium and chloride ions than animals in fresh water, and other terrestrial mammals. (8) The manatee is a unique aquatic mammal in that it regularly moves from a fresh water habitat to a marine or brackish water environment. They can remain in each for extended periods, with no obvious harmful signs, which suggest unique osmoregulatory capabilities. (1,8) In the absence of specific data establishing the animal's fresh water requirements, it is strongly recommended that a source of fresh drinking water be supplied to captive manatees maintained in salt water.

The bulk of cellulose digestion occurs in the cecum and colon in the manatee, and passage of foodstuffs through the upper digestive system is relatively rapid. The highly efficient microbial fermentation, and nutrient absorption, that occurs in the lower digestive tract has been compared to the hind-gut digestion in the horse, and allows for a relatively slow transit time, estimated at 146 hours. (9)

Housing

Housing requirements for sirenians are defined in the Animal Welfare Act (10) and are similar to standards established for small (Group I) cetaceans. Regulations specify space requirements in terms of minimum horizontal dimension (MHD), depth, surface area, and volume of pool.

Manatees have been successfully maintained in both fresh and salt water facilities since the early 1900's. When maintained in man-made tanks, the holding waters should be cleaned through rapid sand and gravel filters, with a complete turn-over rate of four hours. If maintained in a natural, fenced-in facility, it should be down-stream to a natural warm-water spring.

Algae growth can be an aesthetic problem for manatees housed in outdoor facilities. The algae tends to accumulate on the dorsal surface of animals, as well as on the walls and floor of the tank. (11) Algae can provide habitat for protozoans, nematodes, isopods, and other invertebrates, however, it should be pointed out that these have not been implicated in disease problems in the manatee. (12,5) Biological control of algae can be achieved on both manatees and wall surfaces by placing mullet (Mugil cephalus) in the manatee tank. Chemical control of algae can be achieved by adding copper sulfate to the water system at a level of 0.05 mg/1. It should be pointed out that copper sulfate can be potentially toxic to marine mammals, and should be used at the above levels.

Sex Differentiation

There is vague, somewhat argumentive, sexual dimorphism in the manatee; therefore, visualization of the ventral surface is necessary to sex the animal. In the female, the urogenital slit is in close proximity to the anus (7-10cm). The penial slit in the male, however, is situated some 40-90cm anterior to the anus. The mammary glands are locate in the axillary area, like the elephant.

Captive Breeding

The first manatee to be both conceived and born in captivity was in the facilities of the Miami Seaquarium on May 3, 1975. (White, pers comm.) This birth was the first of nine (9) manatees born in these facilities through 1985, to a group of rescued, rehabilitated manatees. The female born in 1975 was subsequently transferred to Epcot's Living Seas exhibit, and is considered in this report. The male, under consideration, was a rescued orphan brought into the Seaquarium, at approximately 2 weeks of age, in August, 1980. Both animals were transferred to Living Seas in 1988.

Early signs of estrus, slight swelling of the genital pore, was noticed in August, 1989. Mating was first noted on September -. Blood results, including hormone assay is presented, along with physical measurements. Blood sampling were continued through April, 1990. No other samples were taken, to avoid any possible complications of pregnancy, due to stranding stress.