With a “significant mortality event happening,” bighorn sheep west of Naches, Wash., area will have to be killed over the next few weeks in an attempt to curb the spread of a pneumonia outbreak.
WDFW and Wildlife Services, a branch of USDA, will team up on the grim operation that will lead to the euthanization of most of the Tieton herd, according to a state press release.
“A majority of the live bighorn sheep spotted during recent surveys looked to be in poor condition, with about a third of those animals coughing or showing other signs of the disease,” WDFW special-species manager Rich Harris said in a press release. “We hate to have to take this action, but we believe it’s necessary to stop the spread of a disease that could devastate adjacent herds of wild bighorn sheep in the area.”
UPDATE APRIL 2, 2013: Scott Sandsberry, outdoors reporter at the Yakima Herald-Republic, has an article on the situation here.
It’s not the first time the disease has hit the herd, down to only three to four dozen individuals from as many as 200 in recent years, or other groups.
So far, 25 dead bighorns have been found this year in the Tieton herd. The latest outbreak began in late January or February, according to WDFW.
Carcasses were sent to a lab at WSU which found pneumonia caused by Mycoplasma bacteria, often fatal to sheep in the wild and which, according to WDFW, can affect lambs born to survivors. The state says there is no treatment or vaccines.
The disease is linked to contact with domestic goats and sheep that carry the bacteria but are unaffected. WDFW says there’s no evidence of contact between the Tieton herd and local livestock.
In 2010, similar steps were taken to stop the spread of the illness in the Yakima River canyon.
Overall, there are about 700 bighorn in four herds in Central Washington, including Umtanum, Cleman Mountain and Quilomene.
The agency’s 2012 Game Status and Trends Report offers a little bit more information on the Tieton sheep:
The Tieton herd was established with the release of 54 sheep from 1998-2002. Radio telemetry indicates relatively low mortality. The rams in the herd have been difficult to survey, due to heavy cover. However, very reliable hunters drew tags in recent years and have provided excellent data that supported population estimates.
Lamb production has been very high. An aerial survey in 2008 confirmed the population was over objective. Sixty animals have been removed for translocation since 2009. During the capture, crews also confirmed population estimates. The area has a lot of suitable habitat. The production of 54 lambs from 81 ewes (67 lambs per 100 ewes) in 2008 was the highest ever recorded within the district. Since ewes do not typically breed until 2.5 year old and twinning is rare, nearly every ewe >2.5 was productive in 2008. Such high productivity indicates the herd is below carrying capacity and initial population goals were low.
One problem has been that translocations focused on ewes, leaving a potentially large surplus of rams (Table 2). The rams were seen in fall 2009 and September 2010, but then adult rams could not be found later in 2010 by biologists, volunteers, or hunters. During the 2011 hunts, only 2 of the 8 harvested sheep were >3.5 years old and none were >6.5 years old. Additional sheep were first noticed on Cleman Mountain during the winter of 2010-2011 and a large increase in adult rams noted in 2011-2012. Harvest and translocation have removed 76 bighorns the last 3 in an attempt keep the population near stated objectives.
The history of bighorn sheep in Region 3 has been one of boom and bust. The declines have likely been associated with disease outbreaks, similar to that documented in the Yakima River Canyon in 2009-2010. Disease outbreak is not unexpected as domestic sheep and/or goats have been documented in close proximity to bighorns in every herd in the Region. In 2009 – 2011, a small but growing group of bighorns were seen within a USFS domestic sheep allotment a few miles west of the Cleman Mountain core herd. Domestic goat ranching has increased dramatically within the region in the last 10 years and contact with bighorns is likely. Radioing sheep in herds near USFS grazing allotments is currently underway and should continue, to document disease risk.
A concern the last 3-4 years has been Cleman Mountain and Tieton bighorn sheep licking highways. It is not uncommon for 40-60 animals to be on the pavement. The content of the de-icing materials is very attractive to bighorns. Center lines have had pits ground into the pavement in recent years. Those pits seem to concentrate the minerals and bighorns are often observed on the centerline. The highways also have many blind corners making accidents likely. Mineral blocks have been placed up away from the highways in attempts to attract bighorns away from traffic. Options are being explored to minimize the number of sheep on highways.