In go-go Alberta, it seems one of the few things that is becoming smaller, slower and older is the provincial animal.

Newly published research suggests that the Rocky Mountain bighorn sheep, with its iconic curling horns that adorn many a sportsman's rec-room, is starting to show the effects of generations of trophy hunting.

"The hunt is actually selecting in a direction that is opposite to what natural selection would be," said biologist Marco Festa-Bianchet from the University of Sherbrooke in Quebec. "Normally, a large-horned ram would do very well, but in a hunted population he is more likely to get shot."

'The hunt is actually selecting in a direction that is opposite to what natural selection would be.' - Marco Festa-Biachet, University of Sherbrooke

He said Alberta should consider changes to its hunting regulations for the animal — an important quarry for professional guides to offer clients, who may pay many thousands of dollars for the right to shoot one.

Festa-Bianchet, whose paper was recently published in the Journal of Wildlife Management, examined records of 7,000 Alberta bighorn rams taken between 1974 and 2010.

In Alberta, rams may only be legally shot once their horns form four-fifths of a complete circle on either side of their heads, which generally takes four or five years. However, rams don't reach their reproductive peak until a couple of years after that.

That means a disproportionate number of young adults that grow quickly or even at just an average rate are taken before they've had a chance to breed much. It also means that rams who grow slowly and stay relatively small are less likely to wind up at the taxidermist's and more likely to sire more lambs.

The result?

"The rams are getting smaller because the big ones are getting shot," said Festa-Bianchet.

Horn length down 3 cm since 1980

He found that between 1980 and 2010, the average horn length of a six-year-old bighorn decreased by about three centimetres. That result held whether the horns were taken by a resident hunter on his own or a non-resident led by a professional guide, suggesting the outcome isn't affected by the skill of the hunter.

The age makeup of herds has also changed.

In 1980, a herd would be about 25 per cent rams between four and five years old. After 30 years of hunters picking off males as soon as their horns curled enough, that proportion is down to about 10 per cent.

The size changes don't threaten the species' health. Bighorn sheep are abundant in Alberta and coexist quite well with humans.

But the changes could threaten the province's reputation as the place to go for a trophy bighorn. Non-resident hunters pay guides up to $35,000, said Festa-Bianchet, who has hunted the animals himself.

There is, he said, only one way to stop the slow diminishing of Alberta's mighty bighorn.

"There's no way out of the problem than reducing the size of the harvest."

The province could change its policy of issuing ram tags to every hunter who asks for one. Or it could trim a couple of weeks off the hunting season to give young males a chance to breed without getting shot.

Festa-Bianchet's study was done with scientists from Alberta Environment.

"I think the government is looking at this very seriously," he said. "I know there was a proposal that was floated to shorten the hunting season.

"Obviously, they have to weigh it against pressure that they get from hunting groups and outfitters. It's never just biology that goes into hunting regulations."