HOUSTON -- Big-game hunters in Texas stirred controversy over the weekend by auctioning off a rare African permit to hunt the endangered black rhino in the name of conservation.

Dallas Safari Club officials have said they faced threats leading up to  Saturday's private auction and had contacted the FBI.

Protesters gathered outside the city's convention center, where the auction was held during the club’s annual meeting. Opposition to the move was vented online by celebrities including Mia Farrow, William Shatner and former "Price Is Right" host Bob Barker.

Barker released an online letter to the club via the animal rights group People for the Ethical Treatment of Animals that likened hunting an aged rhino to taking out a senior citizen.

"The rhino that your organization reportedly has in its cross hairs is an older 'non-breeding' male who has apparently been deemed expendable. As an older male myself, I must say that this seems like a rather harsh way of dealing with senior citizens,” wrote Barker, 90.

"I think that separating the animal to allow new life and old life to continue is a better move. I'm no expert on this; but I feel it's wrong," Shatner tweeted.

The southern African nation of Namibia has held six such rhino permit auctions, but Saturday’s was the first held overseas. Organizers said they were approached by Namibian officials in October and hoped to break the previous high bid of $223,000.

According to a statement on the club’s Facebook page, Namibian wildlife officials will accompany the hunter in Mangetti National Park “to ensure the correct type of animal is taken,” and “if the hunt is successful, meat from the animal will feed a nearby community.”

Club officials wrote that all of the auction proceeds “go into a special fund used by the Namibian Ministry of Environment and Tourism for anti-poaching patrols, habitat protection, research and other measures crucial for protecting populations of endangered black rhinos.”

After the auction, club officials announced that the permit, one of several issued annually, had sold for $350,000. They declined to name the winning bidder, but rumors soon began to circulate online.

Speculation zeroed in on the Facebook page of a 35-year-old from Texas who works for a company that organizes big-game hunts and posted the following on Monday:

“Thank you all for your comments about conservation and the current situation regarding the Black Rhino. I am considering all sides and concerns involved in this unique situation. Please don't rush to judgment with emotionally driven criticism towards individuals on either sides of this issue. I deeply care about all of the inhabitants of this planet and I am looking forward to more educated discussion regarding the ongoing conservation effort for the Black Rhino.”

Conservationists in South Africa wrote back, urging the hunter to shoot the rhino with a dart to subdue and transport it to a sanctuary rather than kill it. Hunters wrote too, urging him to follow through on a big-game dream hunt.

“The antis will never understand so just get the hunt done. They all need to realize that they don't get to control our life choices because they disagree with it. Stick to what you believe in and don't change what you love to do,” wrote Gus Brookshier of Ontario, Ore.

Elizabeth Winton of Reading, England, pleaded with the hunter to change his plans, noting that she and her children have been raising money for the organization Save the Rhino.

“I would ask that you reconsider, for the sake of the rhinos and everyone who works tirelessly to help protect these beautiful animals. Gun v animal is no sport. Please do not do this,” she wrote.

Brandon Huntsman of Midvale, Utah, wrote that the man was in a “lose/lose situation.”

“If you kill the rhino then the antis will harass and threaten you no matter how much good it does for the rhino population, if you choose to let it live and cave to the antis then you lose some integrity from a majority of hunters who can be a little more ignorant and aggressive to the antis,” Huntsman wrote. “Only you and your immediate family and closest friends should have any say at all in the matter. I won't hold any negativity towards you, as any smart educated hunter wouldn't either in whatever your choice is. Good luck man!

The man did not respond to messages or phone calls. Neither did his employer.

For most of the 20th century the black rhino was the most numerous of all rhino species. It became endangered largely because of poaching and loss of its African habitat due to regional wars. Fewer than 5,000 survived in Africa, fewer than 2,000 in Namibia, down from 70,000 worldwide in the 1960s.