An emergency ban on caribou hunting along the Dempster Highway has been imposed because of the presence of the Fortymile caribou herd.

It's the first time in decades that the Fortymile has moved so far east and north of the Yukon River in large numbers.

Hunting the Fortymile barren-land caribou is prohibited in the Yukon, as the herd is subject to a joint Yukon-Alaska recovery effort.

Environment Yukon spokeswoman Nancy Campbell said this morning the herd – estimated at 52,000 caribou – is scattered throughout the Dawson area and north along the Dempster all the way to the Ogilvie River Bridge at kilometre 195.

"I was talking to the regional biologist up there and he said if they are not all in the Yukon, a good 90 per cent of them are.

"They have moved beyond where we would normally see them and up along the Dempster into their historical range.”

The hunting ban along the Dempster begins at the Dempster Highway cutoff, kilometre 0, and goes up to the Ogilvie River.

The Fortymile herd was once thought to be one of the largest barren-land caribou herds in North America, if the not the largest at more than 500,000 animals, ranging from Fairbanks to Whitehorse.

It's not uncommon for Environment Yukon to close hunting along the Dempster to protect the Hart River woodland caribou herd when Porcupine caribou begin mixing with the Hart River herd during their fall migration.

The Hart River herd is estimated at 2,200 animals, and is not able to withstand the same pressure from hunters as the much larger Porcupine herd, so when the herds mix, the area is closed.

Campbell said the Porcupine barren-land herd, estimated at 169,000 animals, has essentially split into two groups this fall.

There is a group near Arctic Village in Alaska and another group is sort of spread out between Old Crow and the Miner River in the Ogilive Mountains about 100 kilometres east of the Dempster, she explained.

Historical records show the Fortymile herd fed thousands and thousands of miners in the Gold Rush era of the late 1800s and early 1900s in the Yukon and Alaska.

It was thought to have been fully recovered by the early 1920s when one biologist recalls it took 10 days for the 500,000 animals to cross the Yukon River.

With an expanding network of roads on both sides of the border, along with growing populations in the North, the Fortymile herd plummeted in just 20 years, until it bottomed out at about 15,000 animals in the early 1940s.

The historical account of one game officer in 1941 recalls counting 146 vehicles on Alaska's Eagle Summit in two hours, with quite a few caribou being killed and wounded.

The next year, another game officer recalled seeing more Fortymile caribou being wounded than killed, with hunters shooting blindly into the herd.

"Most people are content to believe that the animals are in countless numbers that cannot be exhausted,” the officer wrote in 1942, as it was reported in a Yukon government publication about the Fortymile herd and its recovery program.

The herd bounced back to about 50,000 animals in the early '60s, but nose-dived again to just 5,000 or so by the mid-1970s, largely due to over-hunting and wolf predation.

Hunting restrictions and intensive wolf-kill programs in Yukon and Alaska are being credited for the herd's rebound.

It was in October 2002 that the Fortymile caribou crossed into the Yukon in great numbers for the first time in 50 years.

It was estimated that 20,000 caribou crossed over the border in 2002.

They've been part of the fall landscape ever since, though they've never migrated so far north along the Dempster in recent memory.