Are Wolves At Isle Royale National Park On Their Last Legs?
The nine wolves now roaming Isle Royale National Park represent the lowest total ever counted since annual observations of wolves and moose on the Lake Superior island began in 1958, raising concerns that the predators might soon be gone from the park.
In just the past year the wolf population on the heavily forested island has been cut nearly in half, as the 2010-11 census counted 16 of the predators. Indeed, the latest survey seems to indicate that the 25-mile-long island's wolf population is on the verge of total collapse, as inbreeding, gender disparities -- there might be just one female among those nine wolves -- and even climate change seem to be conspiring to doom the wolves.
But appearances can be deceiving when it comes to wolves, according to Dr. John Vucetich, who along with Dr. Peterson is co-director of the Wolves and Moose of Isle Royale project.
“The thing we know for sure is that it’s impossible to say," Dr. Vucetich said Sunday when asked how long the wolves might hang on. "Again, without hyperbole, no exaggeration, the females could be gone any day. And then the rest of the wolves, the males, would be dead without four or five years, something like that."
The population collapse has come relatively quickly, at least from a human's perspective. Multiple packs totaling 50 individuals roamed the island in 1980. By the end of 2009, though, that number had dwindled to 19, and 10 of those were females, according to the researchers.
While Isle Royale's wolf packs have largely ebbed and flowed along the island's moose population, it's hard to pin today's wolf population low on the moose. Despite a growing population of moose (the estimate is 750 individuals), the wolves have been struggling in recent years to maintain their niche on the island.
Disease has played a role in the low wolf numbers, and the increasingly infrequent formation of ice bridges to the mainland that could allow new wolves to arrive also have been involved in the decline, according to Dr. Vucetich. Another key problem that can't be overlooked is the inbreeding that has gone on for years among the island's wolves, he said.
"I think a lot of this is kind of superimposed on the background that the island is a small place, as far as wolves are concerned," he said. "So the average population size is about 24, and so any population will fluctuate, it will go up and down, but when your average population size is 24 and you get to low numbers, well, those low numbers are going to be pretty close to zero. If the island were five times its size, the inbreeding depression would be not quite such a potent force.”
Inbreeding is difficult to counter without human intervention. Newcomers to Isle Royale are hard to come by as ice bridges that allow wolves to cover the 15-20 miles across Lake Superior from Ontario to the island are few and fragile due to warming waters and somewhat milder winters.
During the winter of 2011-2012 warm temperatures and frequent high winds prevented the formation of any ice bridge to the mainland. With each passing decade, ice bridges have formed less frequently. In the 1960s an ice bridge formed two out of three winters, on average, while in the 2000s ice bridges formed about one year in ten. The declining frequency of ice bridge formation is probably a consequence of anthropogenic climate change, reflecting warmer winters but especially windier conditions. The decline in ice is significant because it reduces the possibility of a wolf immigrating from the mainland, which appears to be necessary for maintaining the genetic health of the Isle Royale wolf population.
How soon that inbreeding, or the loss of the remaining females, might deal Isle Royale's wolves a final, fatal, card is difficult to say.
“Like many ecological phenomena, this will reveal itself relatively slowly in terms of the ways in which we’d like to see things unfold," said Dr. Vucetich. "We’ve got to just wait one year at a time. In the next one or two years, it’s possible to lose all of the females. Not just possible, it’s plausible. And in the next two years it’s also plausible that there could be maybe the number of females would increase to two or three or four or something like that.
“If the number of females increases to something like that, well then it would still be a little bit precarious, reasonable precarious, but less so than it had been," he went on.
"Here’s the point: It could go down the tubes in a real hurry. But if it improves and kind of gets to say a more comfortable situation, that’s going to happen kinda slowly. Again, the sex ratio is the immediate problem. And the sex ratio can’t improve that quickly, one or two females a year at the most for the next couple of years.”
Genetic problems associated with inbreeding could quickly cripple the remaining wolves, or play out over a number of generations, the biologist said.
"They could go for two or three or four more decades. If that sex ratio were to even up a little bit," said Dr. Vucetich, though he said inbreeding problems are something of a wild card.
"Sometimes inbreeding depression advances very quickly, gets very, very bad in just a short period of time," he explained. "In other cases, inbreeding depression gets worse, but very, very slowly. The rate at which inbreeding advances is measured in generations, which for wolves is about four years."
At this point, the biologists and National Park Service officials at Isle Royale are discussing whether to respond to the decline, and if so, how.
"There are a couple of possibilities," said Dr. Vucetich. "One possibility, of course, is to do nothing. Another possibility is to wait until wolves go extinct (from the island) and then just basically restore them. And then the last, the third possibility, is to do something now. Or soon. And that will be for the purposes of kind of mitigating inbreeding depression."
Traveler footnote: For more insights into the wolves at Isle Royale, check out the Wolves and Moose of Isle Royale project's website. It contains a graph that shows the ebbs and flows of both the wolf and moose populations on the island since 1959, an overview of the two species' interlocked dynamics, and a dozen videos on wolf/moose research on the island.
You might also consider donating to the project, as a lack of funding currently is preventing the DNA analysis of wolf scat collected on the island, information that would help biologists determine not just how many females are alive but also the ages of the remaining wolves.