Nutrition, other factors cause decline in Jackson-area herds, scientist says
JEFF GEARINO | Posted: Tuesday, September 14, 2004 12:00 am
Southwest Wyoming bureau
GREEN RIVER - Malnutrition and starvation - not wolves - have drastically reduced moose numbers in northwest Wyoming, the author of a new decade-long study says.
"I know people don't want to believe this … but moose are not in the diets of wolves," Joel Berger, a senior scientist with the Wildlife Conservation Society, told Wyoming Game and Fish commissioners during a meeting last week in Casper.
The study is one part of the larger debate in recent years about the effects of wolf predation on the state's big game species - particularly on elk in western Wyoming herds.
Wyoming Game and Fish Department biologists say wolves continue to expand their range in western Wyoming. Wolves have now killed elk on 14 of the 22 state-operated feedgrounds and have displaced elk at several feedgrounds in the Gros Ventre and North Piney area. But there were little data about wolf impacts on moose populations.
Three moose herds in the Jackson area comprise the moose unit under study. The unit is well below the Game and Fish Department's desired population objective of 3,600 animals.
Some outfitters and others have complained that moose numbers have been harmed by the transplanting of Canadian wolves into Yellowstone National Park in the mid-'90s. But Berger said his study showed the decline in moose populations in the Jackson unit is more of a problem with nutrition and habitat than with predators.
"There's a lot of other things going on besides predators … habitat, changing weather, lags in vegetation response, poor willow growth, disease … and we're losing (moose) habitat not only in quantity, but in quality too," he said.
"Wolf predation overall has not been intense in the unit … and there's been little grizzly bear predation recently as well," Berger said.
The study showed about 14 to 18 percent of mortality in adult Jackson moose was due to grizzly bears and less than 2 percent due to wolf predation. Car collisions accounted for about 8 percent of total adult mortality, Berger noted.
"About 60 percent of adult female mortality is due to malnutrition… Less than 5 percent of adult females are lost due to predation," he said.
Berger said the 10-year study revealed that moose birth rates, and rates of twin births, are also down significantly.
"There's no secret that moose are disappearing," he said.
The Game and Fish Department averaged about 500 moose hunting licenses issued each year for the unit during the 1970s and 1980s. Now, the agency sells about 145 permits per year.
"To get back to the days of 500 permits … it may not happen, but it will depend mostly on vegetative quality," he said.
Commissioner Bill Williams said after the meeting it was important to get the word out about the study to the state's sportsmen and hunters.
"I was surprised… I think a lot of people have the misperception that wolves were responsible" for moose population declines, he said.
The study looked at, among other items, fecal steroids left by moose which allowed researchers to assess pregnancies, calving and birth rates, moose/calf relationships with predators, and twin birth rates.
Berger said the Jackson moose unit has been plagued by unusually low pregnancy rates in recent years.
"They're in the bottom percentage in the country… Their 10-15 percent pregnancy rate is the lowest in North America," he said.
The study also tried to determine how fast moose learn to deal with wolves and grizzly bears over time.
"The mothers seem to be learning… They exhibited a heightened vigilance, especially after a calf lost to wolves or bears," Berger said.
The Jackson moose unit population averaged 2,400 animals from 1998 to 2002, according to Game and Fish data. The population rose slightly in 2003 and was estimated at 2,736 animals. The agency has a statewide population objective of 14,630 moose.
Because the herd unit is well below the desired objective, the department has been eliminating hunting permits accordingly, wildlife biologists said.
For the first time since 1971, no anterless moose tags will be issued for the Jackson herd during the 2004 hunting season because of population declines. The 2004 hunting season is the seventh year in which a restriction against taking cow moose accompanied by a calf has been in effect.
Southwest Wyoming Bureau reporter Jeff Gearino can be reached at 307-875-5359 or at gearino@trib.com.