If you could not get any closer--I would either crop from the bottom to get rid of the sand as I don't think it adds to the image, or crop so that that the animals are in the lower left corner...
Oh wow! I didn't know they do it out of the water like that. Very interesting. As suggested filling the frame a little more will allow your viewer to focus more in your main subject.
Very interesting behavior. Lighting was not flatering.. Wish you could have had the subjects a bit tigher in the frame and that you could see the head of the other 2 manatees. They look like rocks in the surf. All you do is be patient and be ready to shoot when you see the right position of your subjects....
Although the light wasn't flattering I think you've captured some really interesting behavior. I've never seen photographs of this, so it might be worth to spend some more time with them during mating season. As Robert stated, just be patient, spend a lot of time with your subject and one day miracles will happen.