After decades of stagnation, Idaho’s Hells Canyon bighorn herd is growing. How high can it go?
Thu., Dec. 29, 2022
Biologists and wildlife officials from the Washington Department of Fish and Wildlife take biological samples from a bighorn ram and prepare to fit it with a tracking collar. (Eric Barker/Lewiston Tribune)
BOGGANS – How many bighorn sheep can the greater Hells Canyon region support?
Not too many years ago, that question might have seemed absurd to wildlife managers. Bighorn numbers were stagnant at best. A disease they had spent decades trying to figure out continued to cull each new crop of lambs.
The canyon, with about 1,200 bighorns, is far from overpopulated, and wild sheep have plenty of room to expand. But things are different now. Most of the herds are growing. Some have doubled or tripled in size. How high can they go?
“I don’t know if we can answer that, but that is probably something we are going to have to think about,” said Paul Wik, a district biologist with the Washington Department of Fish and Wildlife.
Wik was standing Dec. 21 alongside the Grande Ronde River with a team of other biologists and wildlife technicians as he contemplated the question. They were waiting for the wap and whirl of Jim Pope’s helicopter, signaling the imminent arrival of captured bighorn sheep.
The big red bird arrived in short order, dangling three hobbled and blindfolded wild sheep. Pope gently set the animals down and then lifted off to find more.
The ground team, carrying stretchers, retrieved the sheep, toted them to a makeshift processing area and began to extract data. Blood was drawn, weights taken, temperatures monitored and the animals’ noses swabbed.
That last test was key to the day’s operation and to the recovery of bighorns that live in the steep basalt canyons of the Snake River in Hells Canyon and tributaries like the Salmon and Grande Ronde rivers and Asotin Creek. The swabs will be tested for the presence of mycoplasma ovipneumoniae – m.ovi for short. It’s the bacteria that causes the pneumonia that has throttled bighorn herds for decades. The bacteria and resulting illness have hammered many herds throughout the American West. The disease, carried by domestic sheep and goats, causes all-age die-offs when first introduced to wild sheep populations. After the first devastating sweeps through newly infected herds, surviving animals develop some immunity but the disease continues to pick off lambs, generation after generation.
Wildlife managers, field biologists and university researchers spent decades trying to find a treatment, cure or vaccine – anything that would allow more sheep to survive. The Hells Canyon Initiative was formed. The partnership between the Idaho Department of Fish and Game, Washington and Oregon departments of fish and wildlife, Washington State University and other institutes of higher education plus federal agencies sought answers. They were joined by the Nez Perce and Umatilla tribes and assisted by the Wild Sheep Foundation and its state chapters across the Pacific Northwest.
In 2015, they started an experimental new strategy – test and remove. It is built on the premise that while most survivors develop immunity, some adult sheep become carriers of the disease and they infect each new crop of lambs. Young sheep are more vulnerable to the illness. Under the strategy, wildlife managers began routine testing of ewes and removed animals that repeatedly tested positive.
It worked. Most of the herds are now healthy and growing. For example, Frances Cassirer, a wildlife researcher for the Idaho Department of Fish and Game at Lewiston and Washington State University at Pullman, said the ratio of lambs to ewes in the Mountain View Herd that lives along the Grande Ronde River between Boggan’s Oasis and Troy, Ore., has doubled.
“That is pretty representative (of all the herds),” she said. “Most of the populations were stable to slightly declining before and now they are increasing at about 12% a year.”
People are noticing. Rafters, jetboaters, hikers, hunters and others are reporting seeing more sheep and more lambs. Bighorns are crowd-pleasers.
“They are very charismatic and they don’t just run away,” she said. “You get to watch them and they are very social so you get to see them interacting and playing. I think they are good wildlife ambassadors.”
The results aren’t uniform across all herds, but Cassirer estimates the number of sheep in the region has doubled. That may lead to more hunting opportunities. Mature rams are highly sought after and hunting is tightly regulated. Cassirer said Idaho is considering increasing the number of tags offered in Unit 11 south of Lewiston from one per year to two per year.
But growth presents challenges. Learning how to deal with expanding bighorn numbers is a new problem and one that recent capture operations like the one along the Grande Ronde aim to tackle. A wandering bighorn could come in contact with domestic animals and carry the disease back to the herd.
Wik said since 2015 the test-and-remove program has concentrated on ewes. Now the wildlife agencies are looking at rams to ensure they are not carrying the disease but also to see how they move about the canyons. Each captured bighorn is fitted with a satellite tracking collar.
“We want to look at how these rams use the landscape as the population grows, because the biggest risk to these animals is recontacting some animal with the disease and bringing it back,” he said.
They are also placing collars on lambs to learn more about the movements of young animals as they mature.
“We think when they get to about a year old they start exploring and are pioneering new areas,” said Cassirer. “We are really interested to see that and they are also moving between populations – they are going to new areas that don’t currently have sheep and they are also going to different populations than the one they grew up in.”
She believes the Idaho population in Hells Canyon, estimated at about 300 animals, can grow by tenfold. With help from a Wild Sheep Foundation grant, wildlife managers are also exporting the test-and-remove strategy to new areas. Idaho is now doing it along the Salmon River, Oregon along the Burnt River and Washington in the Yakima Canyon. The strategy has also been implemented in Montana, South Dakota and Nevada.
Wik and Cassirer said test-and-remove, as important as it is, can’t succeed on its own. Wildlife managers are working with willing landowners in bighorn country to educate them about the disease and steps they can take to help prevent the transfer of disease from domestic sheep and goats to bighorns. Continued growth of bighorn herds depends on such programs.
“It’s really up to whether people want them,” Cassirer said. “It’s not that the department can keep them healthy. We can work toward it, but it’s also the community making sure they are doing whatever they can to prevent new spillover of m.ovi from domestic sheep and goats.”
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