Saturday, December 4, 2010

Gentle Giants and Graceful Grazers; A Look at the Florida Manatee

The Florida manatee, Trichechus manatus latirostris, is known for its gentle nature and lumbersome ways. Its nickname, the sea cow, comes with good reason. This mammal spends nearly 8 hours out of its day doing nothing but eating, yes nothing but eating. During these 8 hours of munching, the manatee can consume about 7.5% its own body weight in food per day. Their diet consists of over 60 different types of aquatic plants including turtle grass, mangrove leaves, and types of algae. That is a lot of food considering adult manatees can reach nearly 10 feet long weighing in at around 1,500 lbs. That is a big cow! A unique aspect of the manatee is that it is the only herbivorous mammal that is specifically designed to live the entirety of its live in the water.

The Florida manatee is found in the southeastern part of the U.S. mainly in Florida. Its main habitat consists of coastal wetlands and the warm waters of shallow rivers, bays, and estuaries. They can be found in several different parts of Florida including the North and Southwestern Florida, the Atlantic coast, and St. Johns River along with the Gulf. In these areas, not all of the water is salt water and the sea cows can survive in saltwater as long as there is freshwater nearby and available. They are also found in brackish areas. During the winter months, they will travel further into the gulf and gather in the rivers and the natural springs located there. The internal temperature of a sea cow is 97.5 degrees Fahrenheit and if the temperature of the water that they are in reaches below 65 degrees Fahrenheit, they can get "cold stress syndrome" and can possibly die.

While in the water, manatees have been clocked at swimming nearly 20 miles an hour, however they typically only swim at around 3-6 miles per hour, doing somersaults and barrel rolls and can be seen gliding through the water upside-down. To swim, the manatee uses its forearms that are reduced to simple paddles that are used for steering and also are flexible enough to help bring food towards its mouth and to scratch their eyes and face. These paddles each have 4 nails at the tip of each and the rear paddle, or tail, is where the manatee gets its power while swimming. Although the manatee is designed to live in the water for its entire life, it does take breaks from eating and sleeping to come to the surface and take a breath. In fact, the manatee takes a breath every 3 to 4 minutes during activity but can hold its breath for up to 20 minutes during rest. The reason that a manatee can hold its breath for so long is because the lungs in an adult can reach nearly 3 feet in length and when it takes a breath, it can replace up to 90% of the air versus humans who only replace 10%. This air also aids in buoyancy.

Another really cool aspect of the manatee is that its bones are solid and do not contain any marrow or hollow cavities and this is too help the manatee be able to sink to eat the aquatic plants off of the river bed. The bones help to indicate age as well with the growth layers. In the wild, a manatee can live upwards of 50-60 years and in captivity just short of around 65 years. Their lifespan is so long because the manatee has not natural predators and its only threat are people and the cold weather. Boat propellers and jet skis are a huge threat to the manatees along with habitat destruction. The numbers of manatees is declining in the wild because of those previously mentioned and also because they have a very slow reproduction rate. They only have one calf every 5-7 years with a 12 month gestation period. Females also do not typically breed until the age of 6-10 years.

Sea cows are gray to brown in color with small, widest set eyes and they have ears that lack external lobes. Since they eat so many plants, they are hind-gut fermenters with a very long digestive tract. Because they are constantly eating, they need to have great teeth to withstand the grinding. With this wear and tear on the teeth, they continuously replace their back molars. The molars erupt from the back of each jaw and pushes forward, forcing out old teeth at the front .

I looked at a study done at the University of Florida on the material properties that make up the rib in manatees. This is so interesting because the ribs in manatees are completely solid to help with the density to sink the bottom to graze without using mush energy. However, even though they sink to eat, they still get hit by boats and other water craft. This is analyzing what kind of impact these bones can withstand to be able to better mark speeds that boats can travel in manatee areas. The results show that manatee bone is not as strong and tough as other mammalian bone. Their bones cannot absorb much in the way of energy or impact leading to more fatalities of these creatures when hit by boats. This decrease in energy absorption is because of the density and mineral content of the bone. This was tested by examining the strength, modulus, work of fracture and fracture toughness.