Northeastern Minnesota’s troubled moose herd continues to dwindle, according to the annual aerial survey headed by the Minnesota Department of Natural Resources.

While numbers vary from year to year based on survey conditions, such as the amount of snow on the ground, surveys continue to show that moose numbers are in trouble, the DNR reported Tuesday.

This year’s survey spurred a region-wide estimate of about 3,450 moose. That’s down from 4,350 last year but up from an estimated 2,760 in 2013.

It’s not likely that the population actually varied that much each year, but the recent numbers are less than half of the 8,840 moose estimated in 2006 and it’s the long, downward trend — not the annual numbers — that most worry wildlife managers.

“All wildlife population surveys have inherent degrees of uncertainty,” said Lou Cornicelli, DNR wildlife research manager, in a statement. “Long-term trend and population estimates are more informative and significant than annual point estimates.”

Researchers are finding that wolves are taking an increasingly large share of moose, especially calves. But the big animals also face other problems, from parasitic brainworms and winter ticks to declining habitat in some areas and generally warmer weather. Minnesota moose, at the southern edge of their range, don’t do well in warm temperatures.

The DNR, with the cooperation of other wildlife agencies, has conducted aerial moose population surveys in Northeastern Minnesota since 1960. A spotter counts moose as a pilot flies a helicopter across 52 randomly selected plots of 13 square miles each. Researchers plug those numbers into a model to reach a region-wide population estimate.

“It’s hard to say why we get numbers that go up and down like that. But over the years you can sort through the noise and see the real trend, and that still isn’t good,” said Mike Schrage, wildlife biologist for the Fond du lac Band of Chippewa, who helps count Minnesota moose each winter.

Schrage said there were some glimmers of hope, however. In areas where major forest fires occurred in the past decade, such as near Cavity and Ham lakes near the Gunflint Trail, “there were moose everywhere. They are really using those areas,” Schrage said, noting moose like to eat the young growth that occurs after a fire. “But then we had areas with very few moose, too.”

The DNR is heading a broad study of why moose are dying faster than they can rebuild the population. So far this year, fewer adult moose are dying.

“This year, 11 percent of collared adult moose died, as compared to 21 percent last year. Although adult mortality was slightly lower, which is good, the number of calves that survive to their first year has also been low,” Cornicelli said. “This indicates the population will likely continue to decline in the foreseeable future.”

The studies of both adult and calf moose are now in their third years. Researchers will radio collar an additional 36 adult moose in the next couple of weeks. Another 50 newborn calves will be collared this spring.

The crash in northeastern Minnesota moose follows the near disappearance of moose in northwestern Minnesota a decade ago.

Minnesota ended its moose hunting season in 2013.