Grand Teton National Park mountain goats’ time is ticking. To help with habitat competition and keep the spread of disease away from “one of the most unique bighorn sheep herds in the West,” park biologists have decided to kill or remove over 100 of the non-native species over the next five years, the Casper Star Tribune reports.

Park biologist Sarah Dewey said that “the decision to eliminate a charismatic creature wasn’t easy, but it was pretty clear.”

The non-native mountain goats infiltrated the park (and Wyoming) from neighboring Idaho, where they’d been introduced in the 1960s and 1970s. In contrast, the “fragile and shrinking” bighorn sheep herd that roams the park has been there “genetically unchanged” for “tens of thousands of years,” according to the Casper Star Tribune.

“The sheep are struggling, and this is kind of one more straw, and is it the straw that will break the camel’s back and send the herd into an irreversible decline? The trouble is, if that happens, we don’t get the sheep back,” said Dewey.

The mountain goats have also recently tested positive for pneumonia pathogens. To keep the bighorn sheep from completely dying off, something had to be done—even if it was a difficult decision to make.

“And so we feel like we need to try this, as well as a lot of other things, to shore up the fate of the sheep herd,” said Dewey. “And so yes, it is hard, it’s one of the more challenging kinds of resource problems that I’ve ever encountered.”

The park plans to use sharp shooters and relocation methods to remove the mountain goats from the area.

Stay tuned to GOHUNT for further updates.