into captivity after being found stranded to facilitate their recovery, and there are many instances of manatees being successfully rehabilitated and released into the wild. As all extant sirenian species are rated as Vulnerable, these rehabilitation programs present a useful means to support these species. However, the vulnerability of these animals also means that the taking of manatees from the wild for commercial purposes is a conservation issue. Diet in captivity Manatees tend to do well in a captive environment and have been known to thrive. However, it can be difficult to replicate the conditions of their natural environment to the extent necessary to maintain a manatee at its healthiest; the typical diet fed to captive manatee populations may contain insufficient quantities of the nutrients they need. Manatee captive-fed diets vary greatly from the manatee's diet in the wild. In captivity manatees are fed 70–80% leafy green vegetables, 10–20% dried forage, and 5% vegetables and fruits. Dried forage is foods such as hay and timothy grass, which are often used as horse and cattle feed. The vegetables and fruits that are fed to manatees include romaine lettuce, carrots, and apples. In their natural habitat approximately half of the manatee's diet is marine or estuarine plants. When compared to the captive diet, aquatic plants have more dry matter and soluble neutral detergent fiber, and less digestible nutrients. Although more easily digestible nutrients may seem to represent a better diet, a manatee's gastrointestinal tract is adapted to the wild diet through microbial processes of fermentation. Threats and conservation The three extant manatee species (family Trichechidae) and the dugong (family Dugongidae) are rated as Vulnerable on the IUCN Red List of Threatened Species. All four are vulnerable to extinction from habitat loss and other negative impacts related to human population growth and coastal development. Steller's sea cow, extinct since 1768, was hunted to extinction by humans. The meat, oil, bones, and skin of manatees have commercial value. In some countries, such as Nigeria and Cameroon, African manatees are sold to zoos, aquariums, and online as pets, sometimes being shipped internationally. Though hunting of them is illegal, lack of law enforcement in these areas allows poaching. Some residents of West African countries, such as Mali and Chad, believe that the oil of the African manatee can cure ailments such as ear infections, rheumatism, and skin conditions. Hunting is the largest source of mortality in