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SOURCE Université de Sherbrooke
SHERBROOKE, QC, Dec. 10, 2013 /CNW Telbec/ - Sheep "as large as a horse with horns so big that it was a marvel to see." That's how explorers described bighorn sheep 500 years ago. Today, biologist Marco Festa-Bianchet fears that hunting will erode the legendary majesty of the "lord of the Rockies." A native of the Italian Alps, Marco Festa-Bianchet lived for 13 years in Alberta's Rocky Mountains. He's quite familiar with snowy, rugged landscapes. "Few species are as well adapted to the mountains as bighorn sheep," points out Marco Festa-Bianchet. The male, called a ram, has long been one of the trophies most coveted by hunters because of its impressive curved horns. But for how much longer?
"The animal's horn size has been shrinking as evidenced by harvested animals," indicates the biologist, who has studied these ungulates for more than 30 years. In a study recently published in the Journal of Wildlife Management, he examined data collected on more than 7000 rams killed over the last 37 years in Alberta. The investigation was conducted with his colleague Fanie Pelletier, from the Department of Biology in the Faculty of Science, and wildlife managers with the Alberta government. "Of even greater concern," states Festa-Bianchet, "is that harvested rams are now older than those taken 30 years ago. That suggests that the horns are growing more slowly."
From 1980 to 2010, the average age of harvested rams rose from 6.8 to 7.5 years. The research team also noted a decline in the proportion of the harvest made up by males aged 4 to 5 years: from 25% in 1980 to fewer than 10% today. Average horn length has shortened by about 3 cm, representing a 3.5% loss. The researchers suggest that this apparently small reduction is most likely an underestimate, since it is illegal to kill rams with short horns. Small-horned rams are excluded from the harvest sample, as demonstrated by a 2012 study by the same team published in Biology Letters.
In Alberta, bighorn hunting is governed by the "4/5-curl" rule, which requires that the horns of harvested animals form at least 4/5 of a curl. Any Alberta resident can buy a permit to kill one ram. Successful hunters must wait a year before becoming eligible for another hunt. The season starts in late August / early September and closes at the end of October. Rams meeting the 4/5 curl criterion are rare; only 5% to 8% of hunters annually manage to get their ram.
In addition, about 80 permits are issued annually to out-of-province hunters. The law restricts these hunters to specific areas and they must hire the services of a guide, at a cost of $25,000 to $30,000. "Nonresident hunters covet the best trophies and that's understandable," explains the biologist, who hunted bighorn sheep when he lived in Alberta. They have a success rate of about 50%. Surprisingly, however, these hunters do not harvest rams with horns larger than those taken by Alberta residents. "That flies in the face of popular belief," claims Festa-Bianchet. There is no difference between the size of the horns taken by residents and those taken by tourists who spend huge sums to be able to hunt here."
While his study doesn't confirm his hypothesis beyond all doubt, Festa-Bianchet maintains that selective hunting has acted to the detriment of the individuals best equipped to maintain a vigorous population. "There are practically no more large-horned mature individuals," said the researcher, "who have achieved their full reproductive potential with well-developed horns." Under normal conditions, natural selection favors mature, robust individuals, who have strong genes and are highly successful reproductively. These superbreeders have offspring that are larger than average, incuding mothers-to-be with robust constitutions. "These are the physiological characteristics that tend to be eliminated by selective hunting," said Festa-Bianchet.
In addition, the number of rams harvested annually has dropped by 35% in comparison to the cohorts born between 1975 and 1982, while the total bighorn population in Alberta remained relatively stable. "That suggests that there are now fewer rams with large horns," added the biologist, who chairs the expert group on mountain ungulates for the International Union for Conservation of Nature.
Rams whose horns develop rapidly suffer under the current system. Their horns reach legal length by summer's end, just in time to make them legal for the hunt when the season opens a few weeks later. "Our data show that rams whose horns grow quickly have a short life expectancy and low reproductive success, because most are harvested." Fortunately, bighorn sheep are not endangered in Alberta, with a population that has hovered around 6000 in recent decades.
Marco Festa-Bianchet is convinced that the pressure caused by hunting must be reduced in order to extend the life expectancy of bighorns that can pass on their genetic heritage. One solution is to close the hunting season two weeks earlier, so that rams that live in protected areas will not be at risk of harvest. "When rutting around mid-October," explained Festa-Bianchet, "these rams cover long distances, moving outside of national parks, looking for females." These travels often come at the cost of their lives, since the hunting season runs until the end of October. "Shortening the hunting season would give these well-developed rams a chance to reproduce and pass on their DNA to future generations of bighorns," explains Festa-Bianchet.
Another solution could be to increase the minimum legal horn size to full curl. "That could add a year or two to the lives of reproductive males," indicates the biologist. What is most needed, he added, is for hunters and wildlife managers to understand that hunting, as it is currently practised, has a selective impact on the bighorn population. There will be a price to pay to rectify this situation.
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