MINNEAPOLIS (AP) — Minnesota's moose population appears to have dropped again, and a lead researcher for the state Department of Natural Resources says the state may eventually have none.

Minnesota is one of the few strongholds for moose in the Lower 48 states, but an annual survey of the population found a 14 percent decline, the Department of Natural Resources reported Thursday. The reasons aren't clear, but scientists have speculated that disease, parasites and a warming climate are affecting the animals.

"We've basically lost half the moose population in northeastern Minnesota and unless we see a change in the mortality rates or improvements in reproduction, this population is going to continue down that path," Mark Lenarz, leader of the DNR's forest wildlife and populations research group, said in an interview with The Associated Press. "We're probably not going to have moose in Minnesota that much longer."

Lenarz led the aerial survey, which estimated Minnesota has 4,230 moose, down from an estimated 4,900 a year ago. Minnesota had nearly 9,000 moose — an iconic symbol of the state's north woods — just six years ago.

The agency said the continuing decline will affect an upcoming decision on whether to allow a moose hunt this fall.

The survey showed a couple of positive trends: improved calf survival and a higher bull-to-cow ratio, indicating more bulls available for breeding. Still, the cow-to-calf ratio of 36 calves per 100 cows is well below estimates from the 1990s.

In the U.S., only Alaska and parts of New England and the Rocky Mountains have large, stable populations. They're also common in Canada.

The state agency cautioned that its aerial estimates have a high margin of error, but say the long-term trend is clearly downward. Its estimates are based on data collected by helicopters flying over 49 randomly selected plots across northeastern Minnesota.

The agency said it will evaluate the new data and consult with tribal biologists before making a decision on a hunting season in coming weeks.

Margaret Levin, state director of the Sierra Club, said the state should consider not having a hunt.

But the agency, including Lenarz, insists hunting is not driving the decline. The agency allowed a bulls-only season in the fall and cut the number of permits in half, to 105. Hunters killed only 53 bulls, some of which would have died anyway, Lenarz said.

"Even if we stopped hunting moose it would not turn the population around in any way. We would continue to see this decline," he said.

Under the state's management plan, one trigger for closing the season is if the bull-to-cow ratio drops below 67 bulls per 100 cows for three straight years. It was below that last year, but rose this year to 108 bulls per 100 calves.

The agency said it doesn't believe a growing wolf population is responsible for the moose's decline. The department plans to begin a two-year, $600,000 study next year to try to identify diseases and parasites that might be responsible.

Lenarz said Minnesota's non-hunting mortality rates have been averaging about 20 percent, compared with about 8 percent elsewhere in North America. Changing that would require lower death rates among adult moose and increased survival of calves, he said. That leaves him pessimistic for the future of the majestic animals.

"In my opinion there is nothing that can be done to turn the population around," he said.

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Online:

DNR moose hunting page with links to annual reports: http://www.dnr.state.mn.us/hunting/moose/index.html

DNR moose management page: http://www.dnr.state.mn.us/moose/index.html

Copyright 2012 The Associated Press.