Biologists find 'concerning' decline in Dall sheep numbers in Yukon's Kluane region

Wildlife surveys in southwest Yukon have shown a "concerning" decline in the number of Dall sheep — and biologists say recent snowy winters may be to blame.

"The fact that populations are decreasing and increasing is not in and of itself novel. I think what is concerning for us is the degree of the decline," said Kyle Russell, sheep program biologist with the Yukon government.

"We wouldn't necessarily expect populations, and multiple populations like this, to all be declining at the same time and to this degree."

The surveys, done early this summer, focused on six defined "sheep management units" in the Kluane region. The last time sheep were counted in some of those areas was in 2015 and 2016. One unit was last surveyed in 2011, and two were done last year.

Researchers found the number of sheep has declined in all those management units since the 2015/2016 surveys. For some areas, the population dropped by between 49 and 63 per cent. The others saw declines of 16 and 24 per cent since the last surveys.

The population in the Donjek unit — northwest of Burwash Landing, Yukon — is now down to just 30 adult sheep. That particular population has historically been relatively small, but biologists are calling its current status "especially concerning."

Two management units were surveyed last year and the population declines observed there sparked the broader survey this year. Those two areas saw a slight population increase since last year, which Russell says is a good sign — though he warns that "one year in and of itself doesn't mark a turnaround."

A survey of Dall sheep populations in 6 management units in southwest Yukon found that all have declined since 2015/2016. (Government of Yukon)

The survey also looked at the ratio of lambs to adult female sheep, as a measure of each population's stability. It found relatively few lambs in two of the management units, suggesting those populations were in decline. The other units had ratios that suggested a more stable population.

Biologists don't believe that the sheep are being over-hunted. Rather, they attribute the population declines to "environmental factors," like snowfall.

The region has seen more snow than normal in recent years. Early-season snowfalls, heavier snowpacks and late spring thaws can take a toll on sheep, Russell said.

"That's a lot of what we think is driving this. So when you get deep, heavy snows like that, you know, it costs [sheep] a lot more energy to dig down through there to actually get at food during the winter," Russell said.

When there's snow in the mountains later into the spring, sheep can also be forced to lower elevations to find food. That makes them more vulnerable to predators, Russell said.

"So it's a compounding number of reasons that are probably driving this."

He said the government will continue to work with local First Nations to monitor the populations, and "potentially begin kind of a sheep management planning regime for the southwest Yukon."

That could mean changing hunting regulations for the area, he said.