Peter Nygard, the Canadian fashion executive, has been charged with sex trafficking, racketeering conspiracy and other crimes that involved dozens of women and teenage girls as victims in the United States, the Bahamas and Canada, federal prosecutors in Manhattan said on Tuesday. Mr. Nygard, 79, used his company’s influence, its money and its employees to recruit adult and “minor-aged female victims” over a 25-year period for the sexual gratification of him and his associates, according to a nine-count federal indictment. Mr. Nygard sexually assaulted some, it said, while his associates assaulted or drugged others “to ensure their compliance with Nygard’s sexual demands.” 