Moose populations continue to decline in both northeastern and northwestern Minnesota, according to results of aerial surveys released today by the Minnesota Department of Natural Resources.

In the northeast, wildlife researchers estimate there are 6,500 moose, down 23 percent from last year's count of 8,400. The northwest moose population numbered just 84 animals, down from the 2003 survey, which estimated 253 animals.

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"It's still too soon to predict the long-term trend for the northeast moose population," said Mark Lenarz, a DNR wildlife researcher. "We continue to work with scientists from around the world to determine what might be causing mortality in these moose. In the northwest, results of a recent study suggest climate change, in combination with pathogens and malnutrition caused the decline of the moose population."

Moose in Minnesota are at the southern limits of their North American range.

While scientists still consider Minnesota's northwest and northeast moose populations distinct, Lenarz said the difference is becoming less apparent with so few animals in left the northwest. The northwest population, which numbered about 4,000 animals in the mid-1980s, is now concentrated in a narrow strip from Thief River Falls to the Canadian border.

With so few animals in the northwest population, Lenarz said it's difficult to get an accurate population estimate. Moreover, in recent years of there hasn't been enough snow on the ground to conduct a survey. Insufficient snow makes spotting moose during aerial surveys difficult. "You need at least eight inches of snow on the ground to effectively see moose from the air," Lenarz said. "Deeper snow also makes moose tracks more visible, which, in turn makes them easier to spot from the air."

Warmer weather is also partly to blame for the northwest moose population's decline, according to a recent study published in Wildlife Monographs, a peer reviewed publication of The Wildlife Society.

The study, which began in 1995, documented temperature increases and a longer growing season in northwest Minnesota. It was a cooperative effort between the DNR, the U.S. Fish and Wildlife Service and the universities of Massachusetts and Idaho.

Increasing temperatures could contribute to a declining moose population, Lenarz said, as the animals must expend additional energy to stay cool. "Moose expend energy to regulate their temperature in the warmer months by panting," he said. "If they're panting, they can't eat as much and that saps their energy reserves, making them more susceptible to disease and malnutrition."

Northeast Moose

The decline in this year's survey estimate from northeastern Minnesota was not unexpected. A study of radio-collared moose has identified nonhunting moose mortality that ranged from 9 to 34 percent in the past five years.

This year's nonhunting mortality rate in northeastern Minnesota was 34 percent, Lenarz said. The nonhunting mortality rate for moose is generally between 8 and 12 percent elsewhere in North America.

During the past five years of the study, 80 of the 116 moose that were radio-collared have died. A few have been killed by hunters, wolves, or in collisions with motor vehicles, but the majority appears to have been killed by some unknown diseases or parasites.

"We've tested for all of the diseases and parasites known to kill moose yet the cause of death in most cases, remains unclear," Lenarz said.

Aerial surveys have been conducted each year since 1960 in the northeast and are based on flying transects in 36 to 40 randomly selected plots spread across the Arrowhead.

The addition of a helicopter and new survey techniques in 2004 improved the survey's accuracy. The Fond du Lac band and 1854 Treaty Authority contributed funding and provided personnel for the annual survey.

A copy of the aerial survey report is available online at: http://www.dnr.state.mn.us/hunting/moose/index.html.