Fairbanks-- The Interior's largest caribou herd has stopped growing, and state wildlife officials say wolves are to blame.
A multi-pronged recovery plan may have helped the Fortymile caribou herd nearly double in size over the past eight years. But now the herd's size has plateaued around 43,000.
"The growth of that herd has stopped, and the reason is more animals are dying," said information officer Cathie Harms with the Alaska Department of Fish and Game in Fairbanks. "We're relatively confident that the increase in mortality is due to predation."
In response, the state is proposing to expand its aerial wolf-control program to cover the Fortymile herd's entire range, Harms said. The department submitted a proposal outlining such a program to the Alaska Board of Game earlier this month during a meeting in Fairbanks, but the Game Board tabled it and all other predator control proposals until a special meeting next month.
The department is proposing to expand existing aerial wolf control in Units 12 and 20E and annex parts of Units 20B, 20D and 25C into the plan.
The Department of Fish and Game's goal is to build the herd to between 50,000 and 100,000 animals with a harvest of 1,000 to 15,000 caribou a year. The harvest is now capped at 850 animals.
The Fortymile herd, one of only a few Alaska caribou herds accessible by road, has been the focus of a recovery plan for 10 years.
The Fortymile herd is believed to have numbered as many as 500,000 animals during the 1920s and at least 50,000 during the 1950s and early 1960s before plummeting to a low of about 5,000 caribou by the early 1970s. The herd grew to about 23,000 over the next 20 years and remained at that level until the recovery plan was put in place.
The plan included sterilizing 15 pairs of breeding wolves, relocating more than 100 other animals, mounting trapping efforts and establishing hunting restrictions.
The plan worked. The herd grew to 43,000 by 2003 and has fluctuated between 41,000 and 43,000 since.
"The population in the last couple years seems to have plateaued," said state wildlife biologist Jeff Gross with the Department of Fish and Game in Tok.
The sterilized wolves did their jobs, defending their territories from intruders without reproducing, which resulted in fewer wolves over a period of several years. While the herd reaped the temporary benefits of fewer predators on its range, it was just a matter of time before other wolves replaced the wolves that were sterilized or moved, Gross said.
"They're moving in and repopulating," he said. "We're seeing pack sizes of six to eight wolves or better. We're probably approaching pre-control levels, but I don't know if we're there yet."
The wolf population in the new proposed control area is estimated at 210 to 225, and Fish and Game is proposing to reduce the population to no less than 50 wolves.
"All the information available indicates that wolves are the primary predator and the primary factor limiting herd growth," Gross said.
That information comes mainly from mortality studies. The department studies the deaths of individual animals fitted with radio collars to figure out why caribou are dying.
"We try to examine each kill site," Gross said.
The 30 sterilized wolves are gone, likely either killed by other wolves or trapped.
"We don't have any confirmation that there are any sterilized wolves left alive," Gross said. "Our (radio) collars have all gone off the air."
The sterilized wolves would have been at least 10 years old at this point, which is old for wolves, Gross said.
"They've been around quite a while," Gross said. "They were dominant adults when they were sterilized."
Retired state wildlife biologist Bud Burris, who has kept a close eye on the Fortymile herd's progress as a member of the Fairbanks Fish and Game Advisory Committee, said it was inevitable that predator populations would increase, but it happened sooner than expected because of dry summer conditions the past two years that have resulted in lower pregnancy rates and limited herd growth.
"Environmental conditions are a major influence on caribou," Burris said. "You can't order up a better environmental climate. You have to do whatever you can.
"It became clear if we wanted to see any growth back in that herd that we have to establish some kind of predator control," he said, noting that hunters account for about 5 percent of the herd's mortality while wolves are responsible for more than 50 percent.
The predator control program in Units 12 and 20E is designed to benefit moose, not the Fortymile herd, though the herd has benefited from some spillover effect on the western edge of Unit 20E as a result of increased wolf harvest, Gross said. Aerial gunners killed several wolves on the herd's calving grounds last winter, which should have boosted calf survival.
Hunters can access the Fortymile here by road along the Steese and Taylor highways. Other road-accessible Alaska caribou herds include:
* The Nelchina caribou herd (Denali and Richardson highways);
* The Central Arctic caribou herd (Dalton Highway).
Unlike the Nelchina herd, which is limited to a Tier II hunt, and the Central Arctic herd, which caters to bow hunters, the Fortymile herd is open to hunting by registration permit and anybody can get a permit.
Biologists also count the herd by taking aerial photographs and counting individual caribou, but that hasn't been possible the past two years because of heavy smoke from wildfires.