Last Updated Jan 11, 2014 11:40 PM EST The group raised $350,000 Saturday by auctioning off the right to shoot and kill a black rhinoceros in the African nation of Namibia. Safari Club spokesman Steve Wagner confirmed the sale of the permit at the closed-door event. He declined to name the buyer. The auction has drawn howls from critics, including wildlife and animal rights groups, and the FBI earlier this week said it was investigating death threats against members of the club. The auction took Saturday night in downtown Dallas under tight security and behind closed doors. About 40 protesters gathered early Saturday evening outside the convention center where the auction and a pre-auction dinner took place. They held signs and chanted. Jim and Lauren Ries traveled with their children from Atlanta to protest the auction of the rare black rhino hunting permit in Dallas. Jim Ries said it was his son Carter, 12, and daughter Olivia, 11, who pushed for them to go and participate. "We heard what the Dallas Safari Club was doing and we thought it was just wrong that they were auctioning off to kill a black rhino and we really got upset that they were thinking this," Carter Ries said. Jim Ries said his children are passionate about animal conservation and were working to help adopt cheetahs in Africa. The family started a nonprofit called One More Generation, dedicated to saving endangered species. "There's less than 5,000 black rhinos left on the planet," the father said, "and if our kids ever want to see a rhino left in the wild, we can't be pulling the trigger on every one we say is too old to breed."