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Dall Sheep Research in Southcentral Alaska
This has been an ambitious year for Tom Lohuis, Southcentral Alaska’s new Dall sheep biologist. This spring Lohuis was helicopter net-gunning ewes for examination and radiocollaring, and in May and June he was chasing down and collaring newborn lambs. Summer found him scrambling down cliffs to retrieve collars and flying hundreds of hours in the Chugach Mountains monitoring his collared animals.
The work paid off. He’s gained a wealth of data on Southcentral Alaska’s Dall sheep, and encountered a few surprises. He now has 49 collared lambs and ewes that he hopes will continue to provide insights in the year to come.
The VHF radio collars allow Lohuis to identify and track individual animals. Samples were taken from the sheep for a variety of tests. “Right now pregnancy, disease and survival rates are the focus,” he said.
Lohuis captured 37 adult ewes in the Chugach Mountains north of Anchorage, between Tazlina Lake and the Matanuska Glacier. Blood was taken for a variety of tests, including viral diseases; nasal and throat swabs were taken to look for bacteria associated with respiratory diseases, and fecal samples were taken to look for parasites.
Disease is an important issue with Dall sheep. Bacteria and viruses cause respiratory illnesses, almost always pneumonia, and these illnesses have profoundly affected some populations in the Lower 48.
“We have not yet had a documented large scale die-off in sheep populations in Alaska,” Lohuis said. “There have been some small localized things but never a large-scale event that’s been documented. Down south such events have killed 80 percent of populations in some areas. They have literally wiped populations out.”
“We identified some bacteria species in these sheep that had not previously been indentified in Alaska,” Lohuis said. “We’re still awaiting results. We’re looking at different strains of bacteria, called biovariants. There are some that are really bad and some that are benign, and we don’t know what biovariants of the species (of bacteria) we have.”
Lohuis found some indication of viruses that have been associated with sheep in the Lower 48, but he found them at very low levels. “It’s not uncommon for wild sheep to have been exposed to these viruses. Whether they have a pathogenic effect or not is dependent on a lot of different things.”
“It may not be a problem,” he added. “Just because we have it doesn’t mean it’s a bad thing. The low pregnancy rate is biggest deal for me.”
Blood tests revealed that only 22 of the 37 ewes captured were pregnant, which surprised Lohuis.
“We have a much lower pregnancy rate than I would’ve expected for these animals,” Lohuis said. “It’s about 65 percent.”
Lohuis said state wildlife biologist Steve Arthur conducted a similar sheep research project in the Alaska Range between 1999 and 2005 and found pregnancy rates of 75 percent in a low year and 85 to 95 percent in high years.
“The caveat is we don’t know if we just had a bad year,” Lohuis said. Weather conditions in the winter, poor weather the previous summer, and poor forage could all account for the relatively low rate. Further study in the future will reveal a better picture, he said.
Three of the collared ewes died during late winter. One was killed by a wolverine, one died in an avalanche, and one died of unknown causes.
In May, Lohuis flew into the mountains almost daily to monitor the sheep, eagerly awaiting the birth of the lambs. The first lamb was observed on May 11, and the median lambing date was May 27. He captured and collared lambs as they appeared, and by early July, eight lambs born to uncollared ewes were also captured and radiocollared to comprise an initial sample of 24 lambs.
Lambs were captured by hand after an approach on foot. Handling time was typically less than two minutes. Lambs were weighed, sexed, a cheek swab taken to obtain a DNA sample, and they were collared with an expandable VHF radio collar designed to detach at about one year of age. Lohuis said it was interesting to learn that 17 out of the 24 lambs were female.
The first weeks of a lamb’s life are precarious. “The bulk of the mortality is in first 30 to 45 days of life, when the lambs are most vulnerable,” Lohuis said. By mid-July, nine of 24 lambs died, but Lohuis said he expected an even higher mortality.
“Compared to some other Alaska Dall sheep studies, in some years the mortality was 70 to 85 percent of the total number of lambs born,” Lohuis said. “Right now we're sitting at roughly 30 percent, but it’s October and we don’t know what winter conditions will bring.”
Two lambs were killed by golden eagles, one by a grizzly bear, one by an unknown predator, one drowned, one died of pneumonia, and one starved. That particular lamb was found dead at three days of age, and its empty stomach was confirmed by necropsy. The ewe was present when lamb carcass recovered, suggesting that the ewe might not have been able to produce milk.
Lohuis considered two additional deaths to be capture related. Although no lambs were killed or injured during actual capture or handling, two were killed by golden eagles after release but before they reunited with the ewe. These were both older lambs that had left the sheltered birthing site and were captured in the open. After collaring, they attempted to follow the ewe across an open slope which made them extremely vulnerable to eagle predation. These two deaths are attributed to capture/handling mortality, Lohuis said, as they would not have happened if the lambs were not interfered with.
It was a valuable lesson. Lohuis said this type of loss can be limited by capturing lambs less than 48 hours old that appear to be less able to follow the ewe and instead remain protected by cover at the lambing site during the brief interval between the departure of the capture crew and the return of the ewe to the lamb.
As of October 2009, Lohuis has 15 lambs and 34 ewes collared. Lohuis will fly into the mountains every two weeks in winter to check on the animals. The collars are strictly VHF, which helps researchers find the animal and get a visual, and which also a mortality sensor. “If an animal is dead we’ll get the carcass,” Lohuis said.
Down the road, Lohuis hopes to equip some sheep with GPS collars, which can pinpoint an animal’s location at frequent predetermined intervals. Detailed maps can then be created showing the animals movements over time. “GPS provides more insight into movement patterns, home range size, and potential effects of weather – what are they doing in response to storms and icing,” Lohuis said.
Riley Woodford is the editor of Alaska Fish and Wildlife News and produces the "Sounds Wild" radio program.
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