Someone will become very rich when they invent a manatee warning
device. Why not you?

There are plenty of studies that say a high reving propeller is a good manatee
warning device. It is the slow ones they have trouble hearing. (low frequency
hearing weakness)
You also don't see many propeller scars with a skeg mark!
Local environmental conditions (cold water, viruses and red tide) still kill a
lot more of them than boats.
You just don't hear that much from SMC.
In 2002 there were 58 dead manatee in Lee County, 13 were killed by boats
according to Fish and Wildlife.
http://www.floridamarine.org/manatee...ch_summary.asp