Isle Royale wolves dwindling; moose holding on
Wolves on Isle Royale declined 21 percent over the past year due in part to "toxic" inbreeding and battles between packs, while moose on the island continue to feel the effects of a warming climate.
That's according to a report released Wednesday from the 52nd annual study of the predator-prey relationship between wolves and moose on the big Lake Superior island.
Wolves dropped from 24 in 2009 to 19 this year, and two of the island's four wolf packs have disappeared.
Researchers Rolf Peterson and John Vucetich, Michigan Technological University biologists, said the extinction of two packs follows a winter with fewer moose as well as the "toxic effects of inbreeding" and attacks by rival wolves.
"East pack's extinction is the end of a dynasty. There has been a wolf pack centered on the east end of the island since 1972," Peterson said.
Researchers last year confirmed that inbreeding is causing wolf deformities such as weak vertebrae. A spinal deformity has been found in 100 percent of wolf skeletons tested.
Wolves crossed ice and first came to the island in about 1950, and it's not clear if any new wolves have arrived since then to bolster the gene pool. Wolf numbers have ranged from a low 11 in 1993 to a high of 50 in 1980.
Peterson added, however, that wolves on the island don't necessarily face demise.
"The moose have been on the ropes for a few years, now it's the wolves' turn," Peterson said. "There may not be many of them [wolves], but they are in good shape."
Moose numbers on the island are down to about half of the historic average over the past half-century, hitting an estimated 510 animals this winter. That's about the same as last year and down from 650 two years ago.
Researchers say moose appear to have bottomed-out at 385 in 2007 and now have stabilized and that the big animals may now be more threatened by global warming than by wolves. Moose have been hit hard by winter ticks and other stressing factors made worse by warmer summers and winters. Last summer was cooler and wetter and better-suited for moose, however, and tick numbers were down.
Researchers saw more calves on the island than usual, a sign moose are rebounding, and saw the first set of twin calves since 2005.
"We seem to have moved from a predator-controlled system to a climate-controlled system," Vucetich said in the new report.
Moose came to the island about the year 1900, peaking at 2,445 in 1995.
Scientists were on the island from January to March, counting and studying wolves and moose. It's considered the world's longest-running study of a simple predator-prey relationship with almost no human intrusion on the ecosystem.
Isle Royale, a U.S. National Park, sits about 15 miles from Grand Portage off Minnesota's North Shore and is primarily a wilderness area.
Moose breath, pollution drops and eating until full
More findings from the Isle Royale wolf-moose study:
- Wolves generally don't kill more than they can eat. Researchers determined that wolves on average consume between 91 and 95 percent of edible portions of a moose carcass. Wolves tend to eat more of each moose when they face more difficult hunting conditions and less of each moose when more moose are available.
- Analysis of teeth from dead moose collected for the past 52 years shows that levels of toxic lead and mercury, which reach the island in the air and drop in rain and snow, have declined in recent decades since pollution regulations went into effect. Mercury dropped suddenly in the 1980s and has remained constant. Lead levels dropped after it was ordered out of gasoline in 1975 and are now 80 percent lower than pre-1980 levels.
- Eleven of the 16 moose killed by wolves while researchers were on the island had severe periodontitis, gum disease, to the point the moose were weakened by the problem. Scientists say the odor from the bacteria infection likely is strong enough for wolves to know which moose are infected.