Degree of Threat: B : Moderately threatened throughout its range, communities provide natural resources that when exploited alter the composition and structure of the community over the long-term, but are apparently recoverable
Comments: OVERVIEW: Threats include habitat loss and degradation, and mortality from boat collisions, hunting, fishing, red tide poisoning, entrapment in water control structures, entanglement in fishing gear, and exposure to cold temperatures. Manatees are vulnerable to catastrophic mortality when gathered in large numbers at winter aggregation sites in Florida. In Florida, primary human-related threats include mortality and injury from collisions with watercraft, entrapment and/or crushing in water control structures, and entanglement in fishing gear (USFWS 2007). Natural threats include exposure to cold (loss of warm-water winter refuges) and red tide (brevitoxicosis) (USFWS 2007). The most significant threats to Florida manatees are collisions with boats and potential loss of warm water habitat throughout the state (USFWS 2007). In Belize, watercraft-related mortality was reported as the major threat, followed by illegal hunting and entanglement in fishing gear, whereas in northeastern Brazil the stranding of live-orphaned calves was identified as the main recent threat (Parente et al. 2004, cited by Deutsch et al. 2008).
In many areas this species is threatened by high mortality often associated with human activity (especially collisions with boats in Florida), in conjunction with low reproductive rate and habitat loss. In Florida, mortality from boat collisions is increasing (69-95 deaths per year during 2000-2007; data from Florida Wildlife Research Institute). Mortality from collisions with boats is believed to be the primary threat to the small manatee population in Puerto Rico (USFWS 2007).
A significant threat to manatee habitat is the potential loss of natural and man-made warm-water refugia (USFWS 2007). Natural springs are vulnerable to reductions in water quality and flow(resulting in part from human consumption of groundwater) and are threatened by factors that affect manatee access and use of the springs, whereas power plants are not permanent reliable sources of warm water, and many power plants upon which manatees now depend are expected to terminate operations within the next couple of decades (USFWS 2007).
In Florida, habitat loss caused by residential and commercial development of coastal land remains a problem.
In Florida in 1996, about 160 died apparently as a result of the toxic effects of the "red tide" alga Gymnodinium breve (Turner 1996).
Fisheries result in low numbers of deaths and nonlethal injuries in Florida but may be significant elsewhere in the range.
Hunting is responsible for the decline throughout much of the range. Illegal hunting is still a problem in much of the range in Mexico, the West Indies, and Central and South America. Opportunistic taking by fishermen is a major source of mortality in the Greater Antilles.
Manatees have low tolerance of human disturbance in calving areas, but are moderately tolerant of swimmers in wintering sites. There are no data at this time to indicate that harassment is limiting the recovery of the Florida manatee (USFWS 2007).