Littlehorn Sheep — The 'Alarming Results' of Trophy Hunting

Despite minimum size requirements and increasing license fees, it seems trophy hunting of bighorn sheep may have some rather alarming, and unintended consequences.

David Coltman, a professor of biological sciences at the University of Alberta, alongside his colleagues from the University of Sherbrooke, has been studying data collected on bighorn sheep on Ram Mountain, near Nordegg, Alberta. The impressive data collection dates back 39 years, including 23 years where bighorn sheep were subject to intense trophy hunting. And it seems, over that time, selective hunting actually led to evolutionary change, and a reduction in horn length.

“What you have here is clearly artificial selection,” said Coltman. “It doesn’t take a big stretch as an evolutionary biologist to recognize that this is strong selection pressure.”

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David Coltman joins RealAgriculture’s Debra Murphy to talk about the results of a study looking into evolution by trophy hunting.

In Alberta, legal age for trophy hunting is currently a “four-fifths” curl, or, as the 2015 Alberta Guide to Trapping Regulations puts it, when a “straight line drawn from the most anterior point of the base of the horn to the tip of the horn extends beyond the anterior edge of the eye when viewed in profile.”

Many hunters argue that the minimum size guidelines ensure rams have the opportunity to reproduce, but it turns out dominant rams can reach legal trophy hunting age long before their peak reproductive years, at 8-10.

According to the 2015 Bighorn Sheep Management Plan, rams as young as 4 years old can be legal to hunt, though the average age of those harvested in 2014 was 7.6 years. 

“You can’t imagine a stronger selection pressure than hunting based on a measurable morphometric trait,” Coltman said in a release. “What we have here is a very hard-edged selection. We simply need to reduce the selective edge by taking fewer rams or re-examining size requirements. If we stop hunting based on horn size, the horn size will increase, albeit slowly. We have to be more evolutionarily enlightened about how we manage and conserve animal populations.”

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