FAIRBANKS (AP) -- The Fortymile Caribou Herd has reached the point where Alaska isn't big enough.
Thousands of Fortymile caribou forded the Yukon River for the first time in decades earlier this week, crossing into Canada. It's another sign that the growing herd is returning to its past stomping grounds.
As far as biologists who study the herd know, it's the first time the herd has crossed the Yukon River since the early 1960s, said wildlife biologist Craig Gardner with the Alaska Department of Fish and Game in Tok.
''This is a real big deal,'' he said. ''If you read the papers from Dawson City in the early 1900s, this is how it used to be. This is what was common.''
The caribou crossed the river near the mouth of the Fortymile River where it flows into the Yukon. Some trappers who live in the area reported seeing caribou, said Dorothy Cooley, a wildlife biologist with the Yukon Department of Renewable Resources.
''They saw caribou swimming the river,'' she said.
The Fortymile herd has more than doubled in size since biologists began a recovery plan in 1995. The herd numbered only 21,000 in 1995 and the latest population estimate compiled by biologists this fall puts the herd at approximately 46,000. It is the Interior's largest caribou herd.
''We knew it was going to be a density-related move but we never knew what density it would be,'' Gardner said of the herd crossing the Yukon River. ''You can't keep growing a caribou herd and have it staying in the same range.''
Caribou were discovered on the north side of the Yukon on Tuesday during a telemetry tracking flight by pilot Paul Zaczkowski, who picked up signals from five radio-collared caribou that had crossed the river. Based on the five radio signals, Gardner figures there are probably at least 2,000 or 3,000 caribou that have crossed the Yukon River and there are more on the way, judging from reports by Yukoners.
A conservation ranger in Dawson reported hundreds of caribou crossing the Top of the World Highway outside Dawson en route to the Sixtymile River, which empties into the Yukon.
''There's probably at least 20,000 animals in the Yukon (Territory) heading east,'' Gardner said.
The Fortymile herd's move into Canada was cause for celebration among Yukoners, who haven't seen the Fortymile herd for decades. A press conference was scheduled in Whitehorse, Yukon Territory on Thursday afternoon to announce the news.
''It's very exciting,'' said Cooley, the Yukon biologist. ''We have elders who still remember thousands of caribou over here. It's quite a celebration story.''
The Fortymile Herd was once the largest caribou herd in Alaska, numbering an estimated 568,000 animals in 1920. At that time, the herd ranged from Whitehorse in the Yukon Territory to the White Mountains, north of Fairbanks.
Renowned biologist Olaus Murie, who studied the herd in the early 1900s, once spent 20 days watching the herd as it migrated across the Steese Highway. But the herd declined dramatically in the next decade, most likely because of loss of winter habitat due to fires, food limitations and overharvest.
In the 1930s, the herd fell to an estimated 10,000 to 20,000 caribou. The Fortymile herd recovered somewhat in the 1950s, numbering between 40,000 and 60,000 until the early 1960s. The population then plummeted. The herd fell to just over 6,500 in 1973, mainly due to overharvesting by hunters, harsh winters and predation.
The herd rarely crossed into the Yukon after 1973. The herd grew to about 22,000 by 1990 but bad winters and high wolf numbers kept the herd in check until biologists in both the Yukon and Alaska began working to rebuild the herd in 1995.
The state sterilized the breeding pairs in more than a dozen wolf packs that hunted on the herd's calving grounds each spring and moved more than 100 wolves from the Fortymile region to other parts of the state in an attempt to boost calf survival. In addition, private trappers harvested more than 200 wolves from the herd's range and hunting restrictions were put in place to allow the harvest of only 150 bulls a year for five years to give the herd a chance to grow.
The herd responded by growing at a rate of 10-plus percent a year. As the herd expanded, so did its range. A small portion of the herd -- about 5,000 caribou -- made a brief foray into the Yukon Territory last year but they didn't cross the Yukon River, said Gardner. ''You could have blinked and missed them.''
The move into Canada isn't necessarily good news for Alaska hunters who were hoping to bag a caribou during the winter hunt that opens on Dec. 1. With most of the herd in the Yukon, there probably won't be many caribou near the Steese Highway north of Fairbanks or along the Taylor Highway east of Tok. The quota for this winter's hunt is 235.
''This is definitely going to reduce the number of animals around (for the winter hunt),'' Gardner said. ''Most of the herd is in the Yukon and we know they're heading east. ''By the end of November and early December caribou have pretty much chosen their wintering area,'' he said.
''The next three weeks is going to dictate where they winter. If they're still in the Yukon they'll winter there and we won't see them come back in mass numbers until next April.''
The resident hunting season for caribou in Canada is closed and although the Trondek Hwechian First Nation could hunt the herd, Gardner said the Native tribe has supported the recovery plan in the past and has already agreed not to hunt.
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