A federal judge in Boston on Friday cleared the way for rescuers to use a sedative to free a whale tangled in fishing line while fighting for its life off the coast of Cape Cod, Mass. District Judge George O'Toole rejected a motion by an environmental activist who said a sedative would kill the 50-ton North Atlantic right whale -- one of an estimated 100 to 500 of the endangered species remaining. The Center for Coastal Studies, a rescue group from Provincetown, Mass., plans to sedate the whale on Saturday and remove green fishing line deeply embedded in the whale's upper jaw. The whale suffers from a massive infection and has been uncooperative with rescuers. Environmental activist Richard Max Strahan argued the sedative, untested on right whales, would kill the animal.