Sometime in the 1940s, wolves crossed 20-some miles of Lake Superior ice to reach Isle Royale, a 45-mile long island that had been recently designated as a national park. The wolves found a huge herd of moose in the isolated wilderness, and over the years the predators flourished. In fact, the interaction spawned the Wolves and Moose of Isle Royale study begun in 1958 and continues to this day, the longest continuous study of any predator-prey system in the world.

But in April, the annual wolf census revealed what researchers had feared—the wolves were no longer sustainable. The Canis lupus population has boomed and gone bust over the decades but has stayed relatively stable, numbering in 20s. In the last decade, however, it crashed hard, mainly due to generations of inbreeding according to a press release. In 2009, there were 24 wolves counted on the island. In 2015 researchers counted three wolves. In early 2016 they believed only two, an 8-year-old father and his 6-year-old daughter—elderly by Isle Royale standards—remained on the island.

“Last year, there was every reason to believe wolves were destined for extinction and moose are destined to grow rapidly in the near future, likely to the point of damaging the forest,” John Vucetich, a professor of ecology at Michigan Tech who works on the long-range study, said in the press release. “This year, we did not observe anything to make us think that circumstance has changed.”

Now, the National Park Service has taken the unexpected step of proposing a wolf reintroduction on the island.

According to Christine Dell'Amore at National Geographic, the National Park Service took a firm stance in 2014, saying they had no immediate plans to replenish the wolf population on the island. Instead, the NPS said they would develop new management plans and environmental analysis. In a statement, they emphasized that no wolves existed on the island when it was established, and pointed out that there was still a chance new wolves could make it to the island over an ice bridge.

So it was a shock when the NPS released a proposal last week to introduce 20 to 30 new wolves to the island over the next three years, reports Christine Mlot at Science. “This catches me by surprise,” environmental ethicist Michael Paul Nelson of Oregon State University in Corvallis tells Mlot. “[This is] a really important step. We are facing a future where human intervention is going to be required to secure ecosystem health. … We can’t just do nothing.”

In a draft environmental impact statement, the Park Service lays out four options for introducing the wolves. According to John Flesher at the AP, the preferred strategy is to release the wolves in the park sometime in the next three years, with a release of additional wolves over the following two years if the new packs face any setbacks. Another option is to release six to 15 wolves immediately and add more to the park over time. Officials will make their decision after a 90-day public comment period, which will end March 15.

The apparent reversal on policy, reports Flesher, isn’t about the wolves' popularity, though they do draw many visitors to the remote island. Nancy Finley, natural resources director for the park service’s central region says it's more about ecosystem management. Without the apex predator controlling the moose population, the large ungulates boom, destroying young trees on the island and eventually starve. Currently, without major wolf predation, the moose population has grown to 1,200 animals.

“The focus really needs to be on ecosystems,” Isle Royale Park Superintendent Phyllis Green tells Mlot. If things go as planned, she says the new wolves will likely be released in the winter of 2018/2019.