On paper, telling the difference between woodland caribou from the Hart River herd and their barrenground cousins from the Porcupine Herd seems as though it should be easy enough.

After all, woodland caribou are typically bigger than barrenground caribou, they do not migrate as much, and they usually are found in different places.

But drive along the Dempster Highway this time of year, and you might have only a 50/50 chance of guessing whether that animal grazing on the tundra is a woodland or a barrenground caribou.

Caribou from the Hart River herd are spending more time in the western part of their range, where they overlap with the Porcupine herd, and wildlife managers are concerned that this mixing could hurt the herd.

Here's the problem: when the hunting season for woodland caribou ends on October 31, Hart River caribou will probably still be in the Blackstone uplands, mingling with animals from the Porcupine herd.

As it is difficult to tell the two subspecies of caribou apart by looking at them, hunters could mistakenly shoot Hart River caribou, assuming that they are barrenground animals.

"Caribou are very diverse and variable," explains Dorothy Cooley, the regional biologist for the Dawson area. "There can be large Porcupine caribou and there can be quite small Hart River caribou, so you cannot look at a caribou, or any particular group of caribou, and know for sure which herd they are from."

At 123,000 animals, the Porcupine herd is more than 100 times larger than the Hart River herd, and differences in population size are reflected in hunting regulations. The hunting season for barrenground caribou is six months long, compared to three months for woodland caribou.

Also, hunters are allowed to take two barrenground caribou per year, but only one woodland caribou. "The Porcupine Caribou Herd can withstand much more hunting pressure than the smaller woodland herds," says Cooley.

When the size of the Hart River herd was last estimated in the late 1970s, its numbers were put at about 1,200 animals. At this population size, hunters could safely take 30 bull caribou from the herd each year.

"On average there is a reported harvest of 26 Hart River caribou, and on top of that 26, there is an unknown number that are harvested along the Dempster Highway when the Porcupine caribou are there," says Cooley. "In some years as many as 90 caribou have been harvested in the overlap areas."

In the past, management of the Hart River herd was based on the assumption that these caribou would have moved east by the time that the Porcupine caribou showed up along the Dempster. But now biologists know that this is not always the case.

Radio collars were put on about 20 of the Hart River caribou in 1999, and the following November one of these animals was shot in the overlap area after the herd should have moved out. Last year, two of these radio-collared caribou spent the winter west of the highway instead of moving deep into the Hart River basin.

Local people believe that the herd has increased in size since the last census, and Cooley says that an increase in numbers could help explain why the Hart River herd is spending more time in the western part of its range. Also, the snowpack on the uplands has been lower over the last few years, which could be making it easier for the caribou to stay there through the winter.

If the Hart River herd continues this pattern, biologists are facing a management challenge. "The problem is, how do we conservatively manage the Hart River herd without limiting access to the Porcupine Caribou herd? That is the dilemma. The Dempster is an extremely popular hunting area," says Cooley.

Cooperating with the Renewable Resources Councils in Mayo and Dawson, the Porcupine Caribou Management Board will address this issue next year.

In the meantime, biologists are tracking the overlap in ranges to see whether the herds continue to intermingle, or whether it is just a short-term problem. They also want to conduct another census; a difficult task as the herds overlap in winter, which is also the best season for counting the animals.

They also are asking hunters that harvest caribou in the Blackstone uplands to contribute meat samples for genetic testing. Right now the samples are being kept on ice as standard laboratory tests cannot distinguish between Porcupine and Hart River caribou. But Cooley has asked the lab to come up with a different technique, and hopes that soon such tests will confirm exactly how many Hart River caribou are being shot in the overlap areas.

For more information on the Hart River Caribou Herd contact Dorothy Cooley at dorothy.cooley@gov.yk.ca or Mark O'Donoghue, the regional biologist for Mayo, at mark.odonoghue@gov.yk.ca.