In this undated photo provided by the Wildlife Conservation Research Unit, Cecil the lion rests in Hwange National Park, in Hwange, Zimbabwe. (Andy Loveridge/Wildlife Conservation Research via Associated Press)

Six months after Cecil the lion was hunted and killed by a Minnesota dentist, it is about to become far more difficult for hunters to import legally any more lion trophies into the United States.

The U.S. Fish and Wildlife Service is set to declare Monday that two lion subspecies located in India and western and central Africa have been added to the endangered species list, according to officials from the International Fund for Animal Welfare and the Humane Society International, two of the petitioners who requested the designation nearly five years ago.

“This is going to be a very exciting announcement for those who want to see greater protection for lions,” said Jeff Flocken, the North American regional director of the animal welfare fund.

And although the decision is not the direct result of Cecil’s death, but rather new data, he said, “it would be impossible to ignore the public outcry” and its effect on worldwide opinion.

Under the rules of the Endangered Species Act, the hunting of lions will not be prevented, but U.S. hunters will be required to obtain an import permit from the Fish and Wildlife Service to bring back trophies. To acquire a permit, a hunter will have “to demonstrate that the hunting and the trophy enhance survival of the species,” said Teresa Telecky, the director of wildlife at the Humane Society International.

“This is a very high bar,” she said.

Lion populations in northern, western and central Africa will be listed as endangered, while the eastern and southern populations, which are slightly more plentiful, will be listed as threatened.

“Regardless of endangered or threatened, anywhere [lions] exist, after tomorrow, the hunter will have to get an import permit from U.S. Fish and Wildlife,” Telecky said.

Officials at U.S. Fish and Wildlife did not immediately return calls for comment, but Telecky and Flocken, who said they have spoken directly with the agency, said they think the decision is based chiefly on a study released this summer by the International Union for the Conservation of Nature, which indicated that fewer than 30,000 lions in Africa were still in existence and perhaps as few as 20,000. In the past 21 years, according to the report, the lion population has declined 60 percent, and the animals now exist in only 8 percent of their historic range.

“Habitat and loss of prey are top [reasons for the decline], but poorly regulated trophy hunting was one of the biggest threats mentioned in their assessment,” Telecky said. “Another huge and emerging threat: the trade in lion bones to Asia, where they’re used in traditional Asian medicine.”

The lion is now the last big cat to join tigers, leopards, cheetahs, jaguars and cougars on the endangered species list.

The new regulation will not prevent the hunting of lions, if the host country permits it, but trophies such as skins and heads cannot be imported into the United States without the required permit.

Lions remain one of the most coveted animals of big game trophy hunters, and Americans represent the largest number of trophy takers. In the past 10 years, Telecky said, parts of 5,647 lions were imported into the United States.

The petition of the Humane Society and others took on renewed significance in July after Cecil, a 13-year-old black-maned big cat, was lured from his Zimbabwe sanctuary and legally killed by Walter Palmer of Minnesota. Although the dentist acknowledged that he was the hunter, he said he did not know that the lion he had killed had a name and was a beloved tourist attraction. What followed his identification, however, was weeks of worldwide vitriol that forced Palmer to temporarily close his practice and move with his family into hiding.