quite a few manatees get injered/killed every week from boaters that are not paying attention that they are in manatee waters. sometimes it is polution that kills them or every once in a while they die from natural causes. manatees float near the surface and so it is easy for them to get injured, and they are very slow so when they realize that it is a boat it is already to late. manatees comunicate through high squeeks and boats make a low rumbling noise.