The 55-year saga of wolves on Isle Royale may be coming to a close.

The latest survey shows only two wolves left — a male-female pair that are so old and closely inbred that they are unlikely to successfully reproduce.

That, however, has increased the urgency of a major question hanging over the National Park Service: Will their story continue with a precedent-setting decision to artificially bring new wolves to the island?

In their annual report, released Monday, researchers from Michigan Technological University said that in the last year the number of wolves has dropped from three to two — and is now the lowest number on the island ever since a few of them first crossed an ice bridge from Canada in the 1940s.

Researchers have been studying the interaction between wolves, moose and other species on the island since the 1960s, the longest-known study ever conducted on predator and prey and their interaction in a largely closed ecosystem.

The wolf numbers peaked at about 50, but in recent years, inbreeding and freak accidents have suppressed their numbers sharply. With warmer winters, ice bridges have become increasingly rare, greatly reducing the chance that badly needed new blood for the wolves could wander over.

And without enough predators to keep them in check, moose numbers are rising by about 20 percent per year, putting pressure on vegetation. Their numbers have more than doubled since 2005, to 1,300 or more this year. That raises the specter that the moose population is starting a repeating cycle of explosive growth, followed by starvation and a crash in numbers.

Last month, after scientists found that the only pup born to the wolf pair had likely died, the Park Service decided to change an ongoing environmental review from a comprehensive management plan that included the impact of climate change to a narrower one that focuses just on the controversial question of whether to introduce new wolves.

Setting a precedent?

In addition to being a National Park, Isle Royale is a wilderness area, meaning that only nature is supposed to prevail. Taking the step of artificially introducing a predator to the island would be a precedent-setting decision for Park Service officials that could ripple through the management of publicly owned lands across the country.

The issue has drawn the attention of wildlife researchers and conservation groups from around the world. So far, the Park Service has received thousands of comments from the public.

And while biologists say it’s impossible to predict what will happen, now even those who a few years ago were optimistic about the wolves’ survival say it appears increasingly unlikely.

“If they didn’t reproduce last year, I’m pessimistic about whether they will reproduce this year,” said David Mech, a wolf researcher with the U.S. Geological Service. “There’s always that chance, but I’d have to say it’s looking more and more likely that they won’t.”

Nonetheless, even with the narrower scope, a decision is not likely until the end of 2017.

Rolf Peterson, a wolf researcher at Michigan Tech who leads the Isle Royale study, said now the only option for keeping the species going is to bring an entire new pack to the island. The two surviving wolves are already a pair, and would be highly unlikely to breed if only one or two new wolves arrived. And they are unlikely to reproduce themselves because they are past their peak reproductive years. The male, who is father to the female, is eight. She is six years old.

They were both born to the same mother — a stark indication of how inbred the population had become.

Their pup, born in 2014, has disappeared. Peterson said it most likely died because researchers did not find its DNA near a moose kill this winter. “That’s surprising, because it had been there two weeks earlier,” Peterson said.

But the young wolf was badly deformed, so much so that researchers could see his deformed back and stubby tail from the airplane.

Peterson said he always knew he might outlive his research subjects. The wolf population almost disappeared after parvovirus, a disease carried by dogs, swept through the packs, driving numbers down to a dozen and intensifying inbreeding. But in the late 1990s they were saved by a solitary male wolf who crossed an ice bridge, rejuvenating the genetics for generations.

“I used to think, well, if they were heading down hill, it would be good to see what a wolf-free island would look like,” he said. In recent years, “we’ve had what is essentially a wolf-free island, and I’m satisfied with the answer — that wolves are really important.”