Guwahati, Sept. 10 -- Checkmate Government Relations, a lobbying firm founded by a hunting friend of Donald Trump Jr., recently represented Vantara, a controversial private Indian zoo that has been in the spotlight over the questionable origins of some of its more than 150,000 animals, which include protected and endangered species.

Tristan Breijer, the head of the U.S.-based lobby firm Checkmate's London office, sent an unsolicited email "representing the Vantara initiative in the United Kingdom," sometime before July, according to a source who asked not to be named. Breijer is a lobbyist and has a history of representing pro-hunting groups in Europe.

Vantara is a massive private zoo that sprawls over 3,000 acres (1,200 hectares): It's...