RIVERTON, Wyoming — A 31-year-old Utah man has died in a bear attack in the Bridger-Teton National Forest in central Wyoming.

Officials aren't certain yet what type of bear killed Adam Thomas Stewart of Virgin, Utah.

"I'm assuming grizzly, but we don't have the bear so I can't say for certain," Fremont County Coroner Ed McAuslan said Monday. "At this particular time we're still putting stuff together."

Fremont County Undersheriff Ryan Lee says Stewart was in a remote area checking on a research plot during earlier this month. He failed to return, prompting a search that began on Sept. 8. His body was found last Friday between his campsite and the research plot.

Lee declined to release details as to why authorities believe it was a bear attack.

Jason Hunter, a regional supervisor with the Wyoming Game and Fish Department, said investigators saw signs of both grizzly and black bears in the area where Stewart's body was found.

"There's high densities of grizzlies and black bears up there," Hunter said.

Investigators likely will have to use DNA to help determine whether a grizzly or black bear was involved in Stewart's death, he said.

Mark Gocke, spokesman for the Wyoming Game and Fish Department, said most bear attacks on human are by grizzly bears, which are protected by federal law.

Each year there are hundreds of conflicts - mostly involving domestic livestock - between grizzly bears and humans in the Greater Yellowstone Ecosystem, which includes areas of Wyoming, Montana and Idaho. But bear attacks on people are rare.

For example, in 2013, there were five instances where a grizzly bear showed aggression toward a human, but only one person was injured.

Hunter said Wyoming sees an average of about two people injured a year by bears with most injuries being minor.

The last deadly bear attack in Wyoming was in 2010, when a grizzly bear killed a man near Yellowstone.

The most recent fatal bear attack in North America was in May, when a 36-year-old woman was killed by a black bear in Alberta, Canada.

Additional reporting by Mashable