Isle Royale wolf population collapses

The wolf pack on Isle Royale National Park, Michigan is part of the world’s longest running predator-prey study, of wolves and moose. However, due to the lack of genetic diversity leading to inbreeding, the once thriving pack is now down to its last three wolves.

The latest annual Winter Study reported that the lone group, likely to be a mating pair and their pup, are a sharp decline from the nine wolves observed last year, the 24 wolves observed in 2009 and the 50 that were once present. Scientists estimate that there are 1,250 moose on the island, illustrating the growing gap between the predator and prey populations that has been tracked over the past four years.


This winter, for only the third time in 16 years, ice formed a bridge between the island and the mainland allowing the wolves to cross between the two. This has meant that any wolves from the pack that have not died, may have migrated to the mainland. Radio collars have allowed scientists to identify wolves from the pack that may have migrated in search for new mates as well as allowing them to see if wolves from other packs have been visiting the island, possibly in search of prey.

The observed decline has been due to the lack of genetic diversity in the group, leading to inbreeding and causing related physiological difficulties. The remaining pup does not appear to be healthy, showing signs of a constricted waistline, hunched posture and a deformed tail. Researchers predict that it is unlikely to survive the next year. Even with a healthy pup, and a mating pair, it is unlikely that the population will recover. The only likely hope of rescue would be to introduce new genetic material into the pack by introducing new wolves, however it is unlikely that the pair would be interested in new potential mates.


Another possible action would be to do nothing and see what happens naturally. However Rolf Peterson, a professor at Michigan Tech, points out that it is important to use the word ‘naturally’ carefully with “the human imprint written all over the dynamics of this wolf population in recent decades”. For example, the decline in the frequency of ice bridges in winter, due to climate change, has meant that there has been a reduction in the number of wolves with new genetic material visiting the island.

Associate professor of wildlife ecology, John Vucetich, who co-leads the study with Peterson, expressed that “It’s not the presence of wolves that matters so much, it’s whether wolves are performing their ecological function”. The correlated increase in the number of moose over the last few years has had a considerable impact on the forest vegetation. It is believed that the continued increase in moose abundance, no longer being controlled by the wolves, will lead to long-tern damage of the islands vegetation community.

However, it isn’t all bad news. Nearby, in Canada, researchers have found that three mainland wolves have crossed the ice to a smaller island with different prey, resulting in a very similar experiment. It will be interesting to see how it compares.


For more information on the wolves on Isle Royale visit:

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Abi Gardner

I'm a Ecosystem Services (MSc) student at The University of Edinburgh, with a background in Environmental Geography. I'm passionate about ecology, biogeography, environmental management, sustainability and climate change.

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