WASHINGTON - Manatees were taken off the US Interior Department's list of endangered species on Thursday and reclassified as threatened, a move condemned by conservationists who say it weakens protections for the giant marine mammal, also known as a sea cow.The relisting recognizes a population rebound by the West Indian manatee, a native of the Florida coastline whose range extends from the southeastern United States through the Caribbean basin. Its numbers have soared to more than 6,600 in Florida alone from a few hundred in the 1970s, the Interior Department said.The recovery resulted from more than 30 years of conservation efforts by states, the US government, Caribbean countries and environmentalists. Among the measures that have benefited the species were a redesign of locks and levees, setting up manatee sanctuaries and speed limits on boats to avoid collisions, the department said in a statement."We consider this a success story," Phil Kloer, a spokesman for the department's Fish and Wildlife Service, said by telephone. "It has been doing very well, it has been coming back."Despite the new classification, federal protections for the species will remain in place, the department said.But Frank Jackalone, director of the Florida chapter of the Sierra Club, criticized the decision, saying that local and state authorities likely will ease boating rules designed to protect manatees."Florida boaters are going to take this as a signal that they can increase their speed in manatee" zones, he said by telephone. Florida state numbers show 520 manatees deaths last year, 104 of them from watercraft.