Is the story of sailors spotting mermaids just a myth? Are there any animals that could account to be the origins of these sightings. I've heard manatees as one explanation but I don't they can survive in open salt water. What do you think?

The Manatee is a coastal creature. Most of the sightings were made when ships were coming onto land, therefore they were in the coastal area of the ocean. The very few sightings that occured in the middle of the ocean were probably all sorts of things like hallucinations from the blaring sun and sea sickness, mixed with the intense heat and tedious labor. Or there are large fish that can jump out of the water, also dolphins and whales jump, and Great Whites can even catch some massive air.

How about dolphins? cruising in front of ships, leading the way, until they smash on rocks? ;-P

I think thats better than the manatee... Dolphins are beautiful creatures too ;-P

Other than that, then no. Mermaids are just a fishermens tale of guys who go out to see and want a lovely babe so much that they just create stories in thier heads and give an analytical view of what women are to them in the real world. They are beautiful and they can lead you to follow them in love and tease you with their punani, then they get you in between a rock and a hard palce, reality comes crashing down and your married with children, drink beer coz your depressed witht he baby crying and all, then ya get a beer gut, health woes occur and bam your drowning your sorow away.

hahah

Better explanation?

When female manatees and dugongs are pregnant and lactating they grow two large breasts on the chest area similar to those of human females. Manatees and dungongs also like to play in the water, and one of their favourite tricks is to swim upside down, almost like doing backstroke. So you can imagine what the old pirates/explorers/fishermen must have thought when they saw a pair of breasts and then a tail coming out of the water!!
In the old days mermaids were not seen as wearing shells on their chests either, that is simply something disney made up to edit nudie bits for "The Little Mermaid". As for the singing and leading them into rocks... maybe the pirates/explorers/fishermen were just embarrassed that they ran their ship onto the rocks trying to perve on this "woman" so they made up the story of her luring them in with song.

I think it's mostly a myth, just as the Ripley's bealieve it or not mermaids. I've seen many a manatee when living in Florida, they hardly resemble what a mermaid is said to be! Possible that the mermaid was just a human female, but seen in the dark swimming the sea, thus not seeing flippers but assuming they exist.