Unusually cold winters can kill manatees. The minimum water temperature that manatees can tolerate ranges from 62 to 64 degrees Fahrenheit. As the water temperature drops below this range, manatees become sluggish and may stop eating. Young are especially susceptible to the effects of cold water. Periodic outbreaks of red tide can cause some manatee deaths.
Red tide is a result of a bloom of small microorganisms.
Sea squirts, a filter-feeding animal associated with sea grasses, accumulate toxins from the red tide organisms. Manatees accidentally ingest these organisms while feeding on sea grasses. Biologists count manatees from airplanes. It is difficult to obtain an exact population figure because poor weather or murky water conditions make it difficult to see manatees clearly. In 1994, aerial surveys counted a minimum of 1,822 manatees.