From earthquakes to fires and trumpeter swans to pronghorn, natural clues are helping scientists and resource managers gauge the health of the Greater Yellowstone Ecosystem.

The Yellowstone Center for Resources recently released a report that looks at how the area’s natural resources are changing based on more than two dozen so-called “vital signs.”

“We do believe Yellowstone is in a healthy state,” Dave Hallac, chief of the Yellowstone Center for Resources, said Monday. “But the purpose is not really to give (Yellowstone) a ‘B’ or a ‘C’ or an ‘A’ grade. It’s to provide raw, unedited information …that can be used in many management arenas.”

According to the report, there were more than 3,000 earthquakes in the park last year, including a swarm of 2,400 that occurred northwest of Old Faithful — the largest concentration since 1985. The two largest quakes were magnitude 3.7 and 3.8.

Grizzly bear populations reached 602 in the Greater Yellowstone Ecosystem in 2010, the largest number since the recovery program began in 1975.

The wolf population, at 97, was at its lowest in the park since 1999. Wolf numbers throughout the ecosystem, however, have increased.

Those are just a few highlights. The report looks at diverse vital signs categorized by environmental quality, native species, ecosystem drivers such as climate and fire, and stressors such as nonnative species and park visitation.

One of Yellowstone’s management goals is to minimize human interference with its ecological processes, according to the report. But determining whether changes are due to ecology or human influence requires careful monitoring of the vital signs.

For example, there were 11 known wildfires in the park in 2010. Two were considered human-caused.

Last year, 41 grizzly bears died in the Greater Yellowstone Ecosystem, including six in the park. Three of the deaths were natural, and three were undetermined. Humans caused the other 35 deaths, which were either hunting-related, road accidents or the result of bears killing livestock or people. A half dozen live bears were also removed from the area.

The report also provides insight into how the ecosystem is affected naturally.

For example, a 1982 pinkeye epidemic reduced the population of bighorn sheep by more than half. Since the winter of 1996, though, the herd numbers have generally grown.

This year, the Northern Yellowstone Cooperative Wildlife Working Group counted 363 sheep, with 38 lambs per 100 ewes. The report noted that the population has increased since the 1995 wolf reintroduction began.

Pronghorn have been affected throughout the last century both by people and by the environment. Fluctuations in their population — which has ranged from about 100 to about 800 — have shown the “effects of management interventions as well as natural shifts in forage availability, competition with elk, and predation,” the report said.

They’ve been fenced, fed, and removed from the park because of “perceived sagebrush degradation.”

Currently, pronghorn fawn survival is low due to coyote predation. Development of private land north of the park has reduced their available winter range.

Trumpeter swans, which had a peak population of 69 in 1961, now winter in some greater Yellowstone waters, but few stay to build nests.

The report was released for the first time in 2008, and since then has helped inform various management decisions. Hallac said data from the report helped formulate the park’s native fish conservation plan. The report will be released periodically, though Hallac said officials are still deciding on how often.

“It’s the best place you can go to get a good, succinct summary of scientific data on the status of indicators in the park and the Greater Yellowstone Ecosystem,” he said. “Our superintendent, or a manager of a national forest next to the park, can pick this up and in a very short period of time get an idea of what’s happening.”

Carly Flandro may be reached at 582-2638 or cflandro@dailychronicle.com.