Prey decloaks hovering over the whaling  ship in the Bering Sea. Close enough that they are hit with a  harpoon, so that suggests they were only a few feet above sea level,  which means they were operating in Earths gravity. Obviously the  ship was built to stay airborne in a planets atmosphere. However,  when Scotty beamed up the whales and the water, the total mass of  the ship instantaneously increased by 400 tonnes (according to  Scotty).