Silting has further caused a demise of vascular plants and eliminated feeding ground. Cold water is also the enemy of manatee. At about 68 degrees, the manatees begin to show signs of cold-water shock. When water temperatures drop below 65 degrees, manatees begin to die. Feeding sessions last between 30 and 90 minutes.
Calves feed with shorter or less concentration but more frequently.
Nostrils open as soon as the manatee surface and close just before it submerges. Manatees take just one breath at the surface and can remain submerged for 15-20 minutes. In calves less than 2 meters long, the interval was about 4.5 minutes. These young animals have a smaller lung capacity. Respiration also increases when traveling or when water gets colder.