Our Wildlife Friends: The Manatee
By Donna M. Kazo
What a sensation it is, to be quietly paddling a canoe on almost any South Florida waterway, to suddenly hear the sound of something taking a breath directly behind you! And then, upon whirling around (carefully, you are in a canoe, remember) to see a pair of nostrils protruding from the surface! This is an experience shared by many of us in Wildlife Research Team: a curious manatee tagging along with our black canoes as if we are all part of the same herd.
This brief article can serve only as a warm introduction to this friendly marine mammal, distant cousin of the elephant, because the more one researches manatees, the more there is to know. The one thing I do know from my fifteen years of being a WRT guide: whenever people come out in our canoes, they really want to see manatees. The questions in this article are some of the most Frequently Asked Questions, which should serve as a way to get you started on your manatee studies. At the end of this article, I'll give you references so that you can explore more deeply. There are a lot of myths involving manatees, and only research and education can establish the facts.
Q: Are manatees native to Florida?
A: They've sure been here a lot longer than humans! Fossils of manatees found in our state have been dated back to the Pleistocene epoch, more than a million years ago. There is an "urban legend' that manatees were imported a few decades ago for aquatic weed control; not true!
Q: Are manatees related to walruses? They sure look like it.
A: I agree on the resemblance, and they are both marine mammals, but manatees and their cousins, the dugongs (who may sport walrus-like tusks, to add to the confusion) are vegetarians, classified in the Order Sirenia, while walruses are in the Order Carnivora— they eat meat. (Although manatees have been seen to nab a fish now and then, just to keep us all on our toes!) Walruses, although just as portly, have a different sort of blubber to keep their body temperatures stable; more on that in a moment.
The name "Sirenia" even is derived from folklore; sailors who obviously were at sea for a very long time, upon spotting manatees, mistook them for beautiful mermaids or sirens —who sang such a tempting song that the sailors lost their judgment and let the ship crash into the rocks— and the name has stuck through the centuries. The manatees we see in Florida are a subspecies of the West Indian manatee, Trichechus manatus latirostris.
Q: Why are manatees so huge, and shaped like giant sweet potatoes?
A: Remember how when you go for a swim, how cold you can get even in the summer? That's because water pulls the heat from your body 25 times faster than when you are dry. Marine mammals need all that bulk to keep their core at a constant body temperature. Whether you're a human, a peacock, a gerbil or a manatee, your body is designed to work best at certain temperatures. Each moment within us, countless chemical processes are taking place which can only work properly if at the right temperatures. Manatees are especially sensitive to cold; they have a very low metabolism, and it's hard for their insides to stay warm enough to keep them from getting sick from cold stress in the winter. Their type of blubber is made differently than that of seals and walruses, which thrive in subzero temperatures, and their thick, heavy skin does not provide as much cold protection as you'd think. It does help them to stay submerged, however. Scientists have discovered that our Florida manatees are bigger around than those further south, and it could be that it's a way for these tropical mammals to survive Florida's often surprisingly cold winters.
Q: Manatees are also called sea cows; does that mean they eat like cows, and chew their cud?
A: "Land" cows are classified as ruminants, as they have several stomachs with one called the rumen. They need several stomachs at the beginning of their digestive tract so as to fully break down that tough grass and hay they are fed. Grass contains a lot of cellulose, a fiber tough to digest without a lot of work, and several stomachs to digest and ferment the cellulose. What we call "cud" is a mouthful of regurgitated stomach contents that will be broken down further by the cow's chewing of it (yum!). All of this means that cows do a good job extracting the nutrients from their food. Sea cows are more like horses: they don't have rumens, have one stomach, and don't chew a cud, and their major area of digestion is further from the beginning of the digestive tract. Since they get less out of their food, they must eat more frequently; manatees may eat eight hours a day. There are two interesting side effects of the digestion of cellulose in the sea cow: it causes heat, so it's sort of a furnace inside the manatee, helping it to survive life in cool water; and it causes gas, which may help to keep the manatee buoyant! Some scientists even think that manatees are able to adjust the position of their diaphragms and control the gas pressure in their large intestine, influencing their buoyancy. Another, more distressing way that they are sea cows, is that they've been killed and butchered for food throughout human history. Although in Florida, we think of sea cows as friends, even cute friends, in other countries they are still hunted for food; think of it, that one full grown manatee, weighing a ton, could literally feed a village.
Q: So if manatees eat plants all the time, what happens to their teeth?
A: Some of the plants they eat not only are full of tough cellulose, but have gritty sand or other deposits on them, which wears down manatee teeth. So, they are continually being replaced, with new molars continually drifting from the back of the mouth forward. The roots of the teeth are absorbed and by the time the teeth have made it to the front of the jaw, are ready to fall out.
Q: How long do manatees live?
A: That's a surprisingly controversial question, despite being well studied by scientists. It's always hard to study the ages of animals living in the wild, and those in captivity may not be representative of the species due to the unique, unnatural conditions in which they are kept. Like the growth rings in a tree trunk, the ear bones of the manatee have rings which tell how old the animal was when it died. A longterm study of over 2,000 manatee carcasses by Meghan Pitchford of the Florida Fish and Wildlife Conservation Commission, reported that although some manatees live to be over 50, many don't make it past eight years old. What is most disturbing to scientists is that females are frequently not living long enough to: 1. become wise old mothers who can guide their calves to warm waters during cold spells, or rich supplies of food in a new area if familiar grazing grounds are destroyed by a natural or man-made event; and 2. that they are not living long enough to produce more than one calf. There are varying opinions as to how old a manatee cow must be to become pregnant, ranging from 3 to 5 years. This is actually fairly young for such a big mammal, and has provided some hope for manatee researchers, in that the manatee has the potential to reproduce itself fairly rapidly. A manatee gestates from 11-14 months, and there is a period between calves of about 2-1/2 years, so if she doesn't live past seven years, she may only have replaced herself in the population and not added to it. Sadly, even if a manatee lives a long life, if she's been wounded by accidents with boats, stressed by cold, sickened by ingesting poisons from red tide or human-caused accidents, or unable to find enough food, she still may not be able to reproduce.
Q: Now for the big questions: how many manatees are in Florida, and is the population growing or shrinking in number?
A: The range I usually see when I do my research is 2,000-3,000. Quite a difference in range! A lot of people care about manatees, and numerous attempts are made to count them each year. Aerial counts are one way, but murky water, choppy water or glare on the surface of calm water often frustrate airborne counters. As manatees are well-known to seek the warm waters of power plant discharges during the winter, Florida Power and Light has provided a valuable service by conducting aerial surveys every year since 1977. Both manatees and tourists also flock to the warm waters of natural springs. The town of Crystal Springs hosts over 10,000 manatee-loving visitors each year. Individual manatees are often named, recognized, sadly enough, by the propeller scars on their backs. (Sometimes people have carved their initials on the backs of these harmless giants. I hope our readers have the same reaction to that cruelty as we do in our Team.)
WRT assisted in a scientific study of the Broward manatee population a few years ago; manatees have always been curious about our canoes and certainly are safer when swimming near our type of vessel. One problem is that we don't know how many manatees there were before we began to study them so intensely. In the 1950s, there could have been 10,000 or 500. Some older Floridians claim they see manatees a lot more now: but it could also be that people are now all over Florida, and there are few areas that are not under observation. If more manatees are being hit by boats today than ever before, is it because there are more manatees or more boats?
Perhaps we see more manatees because they feel safer; if anyone harms one in Florida, the person will be punished by the authorities and vilified by the public. But in developing countries, as previously mentioned, manatees are not cute 'n' cuddly, but a source of lots of food and high quality oil. Scientists from the U.S. who travel to these countries to study them learn that manatees are much more elusive there. So, don't make the mistake of thinking that these giant tuber-shaped critters are as dumb as vegetables! The more we study them, the more intriguing they are. Biologically, they are quite improbable creatures.
I am personally frustrated by not having space in this article to answer even more common questions, such as how fast do they swim, what about their senses of taste, vision, smell, and hearing? Do they make sounds? (yes) How much do they eat each day? Studies have shown perhaps as much as 9% of their body weight, so a 1500-lb manatee could eat 135 pounds of plant material! Do they need fresh water to drink? They love a freshwater drink, but it seems as if they don't require a regular source of fresh water, and their kidneys are adapted to deal with salt water conditions. Do manatees eat marine debris such as fishing line, and plastic? Yes, examinations of manatee carcasses has found all kinds of harmful human-created materials in the digestive systems of manatees. Plus, manatees are often observed entangled in fishing line; which is one reason WRT canoes venture into the habitat every single month of the year for cleanups. Here's a last question to ponder: What will happen when power plants are phased out and their warm waters no longer can serve as refuges for manatees? Think about it!
It makes sense to look to manatees as guides, and indicators: if they are healthy, the waters of Florida we love and need are also healthy. The expression "canary in a coal mine" is a cliché precisely because of its truth, and although it may bring a smile to your lips to think of our big bulbous buddies covered with bright yellow feathers like Tweetiebird, they do serve well as indicators of healthy habitats, or ones which need our help.
I will leave you with the words of a respected sirenian authority, Dr. Daryl P. Domning. His essay, "Why Save the Manatee?" was first published in Manatees and Dugongs, by J.E. Reynolds, III, and D.K. Odell, in 1991. I found it in Mysterious Manatees, by J.E. Reynolds, III, published 2003, and it follows:
- Manatees are an interesting esthetic resource that people enjoy watching. For many people, Florida would be a less interesting place without manatees.
- Manatees consume exotic plants, thereby reducing weed growth. This provides an economic benefit and reduces the need for toxic herbicides.
- Manatees may represent an important entity in healthy ecosystems in Florida... manatee grazing may promote productivity in seagrasses and thereby affect overall ecosystem productivity (including productivity of commercially and recreationally important species).
- In this age of genetic engineering, manatees, with their hodge-podge of adaptations, may serve as an important genetic resource for human health or other benefits.
- Human mental health depends to some extent on healthy natural systems. Our natural affinity for living things has even developed its own name —biophilia— and it is manifest in our having pets, building birdhouses, visiting zoos, and other activities. Thus, manatee health and well-being go hand-in-hand with ecosystem health and well-being, which help maintain human health and well-being.
- Humans have awesome ability to destroy nature and other things— but this ability carries with it a responsibility not to do so. Our species should exercise good stewardship.
- What excuse could we possibly give our descendants if we did not save the Florida manatee?
Feel free to write us with your manatee questions: we are here to answer them!
Photo Credits— Surfacing manatee: Dr. Jaap Vos. Two manatees investigating a WRT canoe: Dr. Tom Kazo. Another surfacing manatee: Dr. Jaap Vos. Manatees in a refuge: Donna M. Kazo.
- Reynolds, John. E. III, Karen Glaser. Mysterious Manatees. 2003. University Press of Florida. Gainesville, Florida.
- Powell, James. Manatees: Natural History and Conservation. 2002. Voyageur Press, Stillwater, Minnesota.
- Runge, Michael C. A Model for Assessing Incidental Take of Manatees Due to Watercraft-related Activities. USGS Patuxent Wildlife Research Center, Laurel Maryland.
- www.savethemanatee.org Official website of Save the Manatee Club