And Then There Were Three: Park Wolf Numbers Decimated

By Joshua Rapp Learn

Wolves Only three wolves appear to remain at Isle Royale National Park. The population has declined due to inbreeding and warmer winters that don’t allow for ice bridges connecting the island with the mainland on Lake Superior’s north shore in Canada.
Image Credit: Rolf Peterson

Three isn’t always company — especially when the number applies to the entire remaining wolf population on Isle Royale due to warming winters and weakening genes.

A researcher that helped to compile a new annual report on gray wolves (Canis lupus) in the Isle Royale National Park on the island near the north shore of Lake Superior says the only wolves that appear to be left consist of an adult male and female and one “unfit” pup of unknown sex with some evident tail deformities.

“This follows a meltdown we’ve seen since 2008,” said Rolf Peterson, the coauthor of the report posted recently on the national park’s website and a research professor at the Michigan Technological University. Peterson said four wolf packs have disappeared since 2008, when the numbers of the canines sat between 20 and 30.

“Wolves are expected to go extinct if there isn’t some gene flow real fast. It’s probably too late to engineer that, or to intervene on behalf of the wolves.”

One of the main problems with the wolves is the island’s isolation. The roughly 200 square-mile island sits around 20 miles south of the Canadian city of Thunder Bay, meaning population movements on and off the island can only occur when enough of the lake freezes over to create a bridge to the mainland.

Peterson said this used to occur relatively frequently — four out of five years saw ice bridges as recently as the 1960s — but with warming winters, the probability has gone down to one in every 10 years. Ice bridges and population exchanges have occurred only a handful of times in recent years, and each time has seen a net loss of Isle Royale wolves rather than an increase in populations. Several radio-collared wolves left the island for good in 2008 and another escaped on an ice bridge formed in 2013.

In February of this year, a couple of wolves made the trip to the island, but didn’t stay long. The isolation of the island and consequent lack of gene flow has resulted in a high degree of inbreeding among the wolves on the island. And while the animals have continued to breed over the past couple decades, the decreasing genetic diversity has led to a low survival rate among pups.

“They’re the most inbred wolves ever documented. Zoos go to great lengths to avoid this situation,” Peterson said.

The new visitors this year could have sensed this upon their arrival to Isle Royale, Peterson said.

“Wolf geneticists tell us that wolves can detect genetic fitness in other wolves.” Whatever their reasons, the two individuals turned around and left. “The last three ice bridges didn’t lead to a fix of this problem.”

No Wolves, More Moose, Less Forests

If these last few wolves die off without leaving successors, Peterson said said there is likely to be larger ecological consequences. Wolves help control the moose population on the island, that otherwise would increase unchecked with a negative impact on the forest ecology of the island.

But this will no longer be the case if wolves disappear. Moose populations have gone through big boosts in the past when wolves have been relatively absent or small in numbers. While there was no record of moose or wolves in the area before the 20th century, moose ran rampant on the island by 1934. Near the end of the 1900s, wolves on the island were affected by a disease that wiped out a lot of the wild canines and moose populations increased again.

“Everyone that has known this national park that’s still alive has something in mind when they think of Isle Royal,” Peterson said. “Wolves have essentially managed that island for the past 60 years in a biological sense.”

Joshua LearnJoshua Rapp Learn is a science writer at The Wildlife Society.

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