Omaha, Neb. ? An African elephant brought to Omaha’s Henry Doorly Zoo last year as part of a controversial relocation has died.

The zoo says in a news release that the male elephant named Warren died Thursday morning after being anesthetized to treat a cracked tusk.

The release says that during the procedure, Warren’s breathing slowed, then stopped. Emergency efforts failed to revive the elephant — estimated to be 8 or 9 years old.

The zoo says a necropsy will be performed.

Warren was one of 17 elephants flown from Swaziland to the U.S. in early 2016 and placed in the Omaha zoo and those in Wichita, Kansas, and Dallas.

Animal rights group Friends of Animals, which opposes elephants being kept in zoos, unsuccessfully sued to stop the importation of the elephants.