The number of bison dead from anthrax in the N.W.T. is now at 429.

Tony Vermillion, the Department of Environment and Natural Resources’ manager of wildlife and environment for the South Slave region, said he doesn't think the latest bison carcasses are from a new outbreak — they're simply deaths they didn't find in earlier searches.

The N.W.T.'s Department of Environment and Natural Resources prepares the carcasses of bison dead from anthrax for incineration. (CBC)

"The way it worked out is we found such a large number right off the bat,” he said. “We had to start dealing with those and did more reconnaissance flights and flew more in the area with rotary helicopters coming up on more carcasses and dealing with those as we went along."

Last week the number of deaths was estimated at 340, making this the largest ever anthrax outbreak among bison in the territory.

The largest deposit of dead bison was initially found at Mills Lake near Fort Providence, where there were more than 150. Now, more than 100 are being incinerated between Mink Lake and the Horn plateau.

Bison carcasses have also been found along the western shore of Great Slave Lake and up Highway 3 to Frank’s Channel.

In 2000, the N.W.T. estimated the number of bison in the Mackenzie population at about 2,000.