Texas millionaire Corey Knowlton paid hundreds of thousands of dollars to kill an African black rhino in the name of conservation. Creative Commons

A Texas millionaire has bagged his rhino trophy, but at the price of his popularity. Twitter users were outraged Wednesday to hear that oil heir Corey Knowlton, whose father owns the private energy firm BASA, followed through with a plan to kill an endangered African black rhino in Namibia. He paid $350,000 through an auction and won the chance to hunt the rhino -- money that the event’s organizer, the Dallas Safari Club, said would go toward anti-poaching efforts.

Knowlton won the auction in January 2014 and completed the hunt Monday, according to NPR. Social media users weren’t buying the kill-a-rhino-to-save-the-rhinos argument and were quick to lambaste Knowlton for the hunt.

Mia Farrow, the American actress and former fashion model, was among those who took to Twitter to criticize the hunt.

A Facebook group called “Stop Corey Knowlton From Killing Black Rhino” took to the social media site Tuesday to comment on the hunt. “We are so sorry we couldn't stop ‘CK,’ ” the group said in a post. “We certainly put out enough messages that the public would not look kindly on this. Now, the life of a black rhino is extinguished and the karma of a Texas millionaire begins.”

Fewer than 5,000 black rhinos exist in the world today, according to conservationists. Their numbers plummeted dramatically from 65,000 beginning in the 1970s because of illegal poaching. The rhinos’ horns are popular in traditional Chinese medicine and are extremely valuable on the black market.

The Namibian government issues five hunting permits a year to weed out older male rhinos -- ones that no longer breed but whose aggression can keep younger rhinos from procreating with females.

Knowlton responded to controversy in an interview with CNN. "I think people have a problem just with the fact that I like to hunt," Knowlton told CNN. "I want to see the black rhino as abundant as it can be. I believe in the survival of the species."