The Amy H Remley Foundation  

Manatee Life


Manatee feeding on seagrass

The several hundred manatees comprising the Crystal River population prefer to eat the sea grasses offshore in the Gulf of Mexico as opposed to the fresh water variants in the river system. However, the sea temperatures are too low for manatees during the winter months which encourages them to occupy the warmer waters served by the forty springs discharging into Kings Bay. The manatee's preferred food choice of the river system's submerged aquatic vegetation (Valisineria or eel grass) has become depleted over the years forcing the manatees to eat less favored varieties. The hydrilla, and leafier plants like water hyacinth and water lettuce have also greatly reduced due to storm surges of saltier water from the Gulf, chemical treatments or harvesting to improve recreational water quality. Lengthy drought conditions and rates of domestic and agricultural pumping have reduced aquifer head levels prompting more saltier water to issue from the springs causing a trend toward more salt tolerant plants and exotic species able to compete and displace traditional species. A case in point is the earlier more vigorous bloom of marine algal species of chaetomorpha which reduces incidence of the fresh water algal species of Lyngbia by over shading. Harvesting of the more dense and more easily harvested chaetomorpha also removes fodder plants along with the algae. Grasses eaten during winter recover in summer time with the fewer manatees remaining in Crystal River and Kings Bay during summer months.

The result of these factors and increasing numbers of manatees in the local population has recently caused some stress, weight loss and behavioral changes in the population forcing the seeking of food sources in less environmentally favorable locations.

A one thousand pound manatee needs to eat and digest between 100 and 150 pounds of choice submersed aquatic vegetation a day. This equates roughly to all the packets of fresh greens packed on shelves in a typical supermarket, requiring most of the available waking hours to chomp through the food. When we interrupt their routine of traveling, eating or nursing we cause them to suffer stress. Do we have any right to accost them like that? The law says we may not harass them.

Teeth of a manatee are all molars for grinding up the submersed aquatic vegetation that they eat. Saliva from oversized glands employed in the process provides the first stage of digestion. The teeth eventually drop out as they are ground down by sand and shale taken in with the food. Manatees constantly replace their teeth by growing rows of teeth that move forward replacing the worn out teeth - an adaptation called "marching molars". Other mammals including us, have teeth replaced from above or below.

Manatees will sometimes chew on ropes, crab pot lines or anchor lines almost as if they are flossing their teeth. Unfortunately, some of these ropes get entangled around flippers and can cause injuries if circulation is cut off.

"Flossing" upside down   "Flossing" on a mooring rope
Manatee Manatee


Manatee "footprints" moving away from boat.
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Despite the absence of external ear lobes, as we have, and the small size of the auditory openings, manatees hear very well. A phD thesis recorded manatee behavioral response to different sounds. The sounds made by depth sounders and fish finders within their hearing range were generally not heeded (perhaps they may have become inured to so many of the sounds in real life). Recordings of boats under power did produce responses - slow cruising noise was noticed by pausing other activity, noise of boats on plane prompted speedier swimming (as if to be ready to evade on-coming boats), while noise from personal water craft (PWC) appeared to terrorize them into vacating the area even when foraging or having to leave their young. Perhaps the PWC were recognized as more threatening by their speed and fast changes in direction assessed by the manatee from doppler effects to the sound.


Calf swimming with Mother
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Manatees make sounds to communicate with other manatees. Described variously as squeaks, chirps, screams or grunts the sounds are used to convey circumstances and even emotions. Young separated from their mother call repeatedly until the mother answers enabling the young to move in the direction of the answering sound until alongside the mother again. A mother and calf will engage in a sounds duet or a nursing calf will call repeatedly begging to be fed. Other sounds indicate, for example, simply, "I am here", socialized greetings, fear, anger, or danger.

Manatees also emit non-vocal sounds which may be heard by others nearby, for example, when rising to exhale and take in a breath of air, the sound of swirling water when making a vigorous movement, chewing on vegetation, and when releasing flatulence (" breaking wind"), followed by gas bubble sounds.


Manatee mother nursing calf
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Manatees rarely go into waters below 63 degrees Fahrenheit and cannot survive cold water for long periods of time. In winter manatees seek out the warmer water issuing from springs to keep warm and often congregate closely together (either to mutually preserve body temperatures, or possibly the many manatees seeking warmth must necessarily crowd into a restricted area of relative warmth.) Manatees suffering injuries from boat collisions or propeller cuts will sometimes seek a warm spring flow in which to rest and recover.

Mother and calf - Crystal River
Two Manatee

Some manatees acclimatize to human attention and, like us, submit to a gentle stroking and touch, but may easily become scared with aggressive movements. Imagine yourself resting quietly or eating lunch being approached by an animal with a large eye blowing bubbles and waving feelers at you. How would you feel? Worse still, what would you do if this thing did not see that your child was nearby or you were nursing and it wanted to come up and touch you? There is a lot to be said about watching wildlife from a distance or encouraging them to come to you. Put yourself in their place and mind your manners so that manatees do not have to change their behavior.

Manatees rest from 2 to 12 hours a day either suspended near the surface or lying on the bottom in shallow areas. When resting, manatees may surface to breathe every 15-20 minutes. When active or feeding, manatees surface to breathe at 3-5 minute intervals.

As waters warm up in the Gulf of Mexico, manatees leave their winter warm waters to forage among the sea grass meadows. Some travel long distances to rivers, springs and bays in other Gulf states as far west as Texas.

Manatee kiss
Two Manatee
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A manatee calf separated from its mother calls repeatedly until receiving an answer and swims off in the direction of the answering call until united once more.

Three Sisters Springs

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This video will play for about twelve minutes. Take time to enjoy it, please.

The U. S. Geological Survey, Sirenia Project
The manatee sound recordings on these pages are property of the United States Government Fish and Wildlife Service and may not be reproduced or analyzed without permission of the Denver Wildlife Research Center.

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