The manatee is an aquatic mammal closely related to elephants, and there are only 3 species in the world, namely the American manatee, the Amazon manatee and the African manatee, and they are listed on the Red List of Endangered Species, which shows its rarity and vulnerability, of which the American manatee is listed as endangered. According to the U.S. Biological Conservation Agency, in the first two months of this year, the number of American manatees living mainly in Florida waters has risen to more than 430, more than three times the level of the region in the same period last year. So, what causes them to die in large numbers?
<h1 class="pgc-h-arrow-right" > first look at the basic situation of manatees</h1>
Manatees are larger, reaching 3-4 meters in adult individuals and weighing between 0.5-0.8 tons. From a distance, the manatee's body resembles a small whale, with a smoother body and gray-black skin. The forelimbs have become fin-like, and the hind feet have degenerated and disappeared, and a wide and fat tail fin grows at the tail to facilitate their free movement in the water.
Through research, scientists believe that manatees were mammalian tetrapods living on land 60 million years ago, and have a common ancestor with elephants today. Later, due to the great changes in the natural environment of the land, coupled with their large size and insufficient defense capabilities, perhaps in order to escape the capture of predators and obtain a more abundant food source, they slowly shifted their living areas from land to water.
Through a long period of adaptation, the current habitat pattern was finally formed, and the body structure was transformed into a feature that was more conducive to moving and foraging in the water, but their eating habits did not change, or maintained the habit of "grazing", but changed from terrestrial plants to various aquatic plants and other aquatic plants in the water.
<h1 class="pgc-h-arrow-right" > several key features of manatees</h1>
From the physiological habits and behavior habits of manatees, they have the following characteristics: First, they can survive in fresh water and seawater, so they can cope with them in rivers, estuaries or offshore waters.
The second is to like warm waters, manatees do not have a large subcutaneous fat content as imagined, so the body's insulation ability is not strong, so it can not live in cold waters, usually the minimum temperature of the water must be above 16 degrees Celsius, if the temperature is lower than this value, then they will migrate to waters with higher water temperatures. Therefore, the Amazon basin on the east and west sides of the Atlantic Ocean, the coast of West Africa, the Caribbean Sea, the florida sea and the Gulf of Mexico are the most ideal places for them to live and breed.
Third, the amount of food is amazing, due to the huge size of the manatee, activities in the water, regular ventilation on the surface of the water and other behaviors, all need to consume a lot of energy, and the energy density of aquatic plants is very low, so you must eat a lot of food every day to ensure the needs of the body. According to monitoring, the amount of aquatic plants that adult manatees eat every day should reach 6%-10% of their body weight, otherwise the physical strength of manatees will be significantly reduced, and they are also prone to diseases.
Fourth, the auditory degradation, manatee ears can only hear higher frequency sound waves, such as high-frequency sounds such as birds calling will attract their attention, and like ship engines, whistles such as more dull low-frequency sounds, manatees are difficult to hear clearly, more can not distinguish the direction and distance of the sound, this situation sometimes causes some manatees and ships to collide accidents.
Fifth, the number is sparse and the reproductive ability is low, the number of rarity can be concluded from their list of endangered species, from the perspective of reproductive ability, whether female or male, the estrus period is short and the interval is long, the gestation period after pregnancy of the female is as long as 11-13 months, the growth rate of the bred offspring is also very slow, and the female and male cubs take 5 years and 9 years to sexually mature, respectively.
< h1 class = "pgc-h-arrow-right" > why American manatees die in large numbers</h1>
According to the main living habits of the above-mentioned manatees, some scientists have conducted an in-depth analysis of the causes of the mass death of American manatees this year, mainly believing that there are the following factors:
One is low temperature. This year, due to the impact of the high intensity of arctic cold air going south, there have been rare snowstorms in the central and eastern parts of the United States, the temperature has continued to rise, and manatees living in low- and middle-latitude waters have experienced "cold stress" reactions. Because there is no thick enough fat protection, the manatee's thermal insulation function is severely challenged, at the same time as the metabolic rate becomes low, a lot of heat is taken away from the body, and the decline in mobility makes no more food to supplement, so many manatees are trapped in place, the tail fin of the body and other parts of the body appear obvious signs of "frostbite", some organs have also atrophied, and finally died due to long-term cold and hunger.
The second is pollution. Affected by industrial enterprises and agricultural non-point source pollution, the content of nitrogen, phosphorus and other substances in the waters where manatees live in the United States has always been at a high level, and these substances are an excellent source of nutrition for algae in the water. The large growth of algae, on the one hand, blocks the sunlight and makes the temperature of the bottom of the water become lower; on the other hand, it consumes a large amount of dissolved oxygen in the water, so that the presence area of aquatic grass gradually shrinks, especially the seagrass at the bottom of the water is becoming less and less due to the loss of abundant oxygen, and a large number of fish and shrimp also die due to the lack of oxygen and food, and the water ecosystem is destroyed. The main food source of manatees is water weeds, which cannot be eaten underwater, so many manatees are starved to death.
The third is other factors. For example, the waves, this year's east coast of the United States is affected by bad weather, often set off huge waves, because the body of the manatee is relatively large, the degree of flexibility is not good, the ability to adapt to the impact of huge currents is insufficient, so some manatees died under the attack of huge winds and waves. There is also the impact of the ship, because the manatee's sensory system is not developed, so in the area where the manatee lives, there will be a certain chance that the manatee will collide with it, if the relative speed is very large, the manatee body will be seriously damaged or even directly cause death, which has always been the cause of the death of some manatees.
Under the combined influence of the above factors, the survival of the American manatee has been greatly challenged this year, the suitable living area has shrunk a lot, and those manatees with strong mobility can only migrate to the water near the drainage of the power plant near the Atlantic coast in Florida, because there is hot water discharged from the power plant, although the water quality is not good, but it is still OK to barely overwinter.
Local officials and volunteers have taken many measures to clean up the excessive breeding of algae in the waters, and try to treat those injured or trapped manatees, but whether it is cleaning work or treatment, can not achieve full coverage, will not be fully effective in the short term, especially the restoration of regional ecological and environmental systems, it takes a long time to buffer and improve, the survival prospects of American manatees are still not very optimistic.