There is a very negative impact from humans on manatees. Most manatee mortality is caused by the manatees having collisions with motors on the boats, and being trapped in confined areas. Some manatees have been killed by being trapped in canals and being crushed. ingestion of fish hooks, litter, and entanglement in crab trap lines. The loss of their habitat is the most serious threat facing manatees in the U.S. There is a minimum population count of 4,831 manatees as of January 2014.