An aerial count of the Aishihik wood bison herd was conducted Tuesday in an attempt to gain the best estimate of population size in eight years.

Bison biologist Tom Jung of the Department of the Environment explained Monday that three helicopter crews were involved in the count.

One crew will come in from Braeburn on the northeast border of the herd's range, while a crew from Whitehorse surveys the southern portion and a crew from Haines Junction looks at after the northwestern portion.

'This is an actual census of the herd where we should be able to tell you was the estimated size of the herd is, plus or minus, with some degree of confidence,' Jung said.

He expects the confidence level will be in the neighbourhood of plus or minus 15 per cent.

The intent was to fly the entire 9,000-square-kilometre range in one day, over a period of about five hours, Jung explained.

'There are hunters out there that we do not want to disturb too much, and two, just from our knowledge of bison, they can move quite a big distance over one day.'

Keeping the count to one day will minimize or eliminate the risk of counting individual groups twice, Jung said.

He said while the herd is still considered to be a single herd, it's comprised of several different groups, some as large as 100 animals.

Radio collars on bison roaming with the different groups will help the helicopter crews locate the animals, he said.

The wood bison were re-introduced to the Yukon in the mid-1980s. It was decided in the late 1990s that a hunt was necessary to control growth, as there were no predators to help keep the population in check.

Evidence from re-introduction programs in other regions has suggested it can take wolves up to 20 years to figure out how to include the huge animals as part of their menu.

Without some means of controlling the population, it was feared the bison population would become so large that it would chase caribou and moose and other species away from their home range. There's also been documented concerns of bison causing property damage.

Jung noted the goal has always been to maintain the bison herd at 500 animals, after the annual hunt that runs from Dec. 1 to March 31.

But with no recent comprehensive count, there is uncertainty about its size, he said.

What he described as the last reasonable survey in 2003 put the population at 530.

Jung added, however, that some have suggested there may be up to 1,000 bison in the herd, while hunters who have experienced trouble locating the animals suspect numbers are actually shrinking.

'So you have the whole gamut, that there is not many out there anymore to there is a lot more than we think.'

Jung expects the count will come in at somewhere between 550 and 620 animals.

Results of Tuesday's work should be available by the end of the week, he said.

Meanwhile, Jung pointed out, the radio collars fitted with GPS transmitters are helping to track the movement of individual groups.

At this point, the herd is still considered as one, as there does not appear to be a splinter group establishing what would be considered a second herd, he said.

Most of the bison generally come together in July for the calving season, he added.

The first experimental hunt of six bison occurred in the spring of 1998, when the herd's size was pegged at 500 animals.

Jung said 45 bison were harvested in 1999; 74 animals from the target harvest of 80 were taken in 2000; 62 bison from the target harvest of 80 were taken in 2001; 74 from the target harvest of 70 were taken in 2002; 40 from the target harvest of 70 were taken in 2003; 67 from the target harvest of 63 were taken in 2004; and 59 from the target harvest of 81 were taken last year.

Conservation officer Dan Drummond of the Haines Junction Environment office said Tuesday the known harvest so far this season is 40 bison, though the compulsory reporting deadline for the December-January segment of the hunt isn't until Friday.

The reporting deadline for the February-March segment of the hunt isn't until April 10, he said.

But there is no question the bison are quite a bit more wily since the days of the late '90s, Drummond said, adding they've become sensitized to the sound of snowmachines.

'So it has become more of a hunt, which is good.'