Four bighorn sheep spotted in the center of the Hanford site on Tuesday were killed by the Washington state Department of Fish and Wildlife.
The 580-square-mile nuclear reservation just north of the Tri-Cities in Eastern Washington is not near any existing bighorn sheep range, and they likely would have continue to move through the area until they found other bighorns or more appropriate habitat, according to Fish and Wildlife.
State officials made the decision to kill the animals, all younger males between 2 and 3 years old that were near the Hanford tank farms, due to the risk of pneumonia.
Bighorn sheep are highly susceptible to respiratory disease and are known to contract pneumonia from domestic sheep and transmit it to each other.
Pneumonia outbreaks contributed to the historical extinction of bighorn sheep in Washington and continue to take a toll on them. Sheep that survive outbreaks of the disease continue to experience long-term impacts to lamb survival.
The pathogen most closely associated with pneumonia in bighorns is not native to North America, and so bighorns have not had evolutionary time to adapt to it.
Officials do not know where they traveled from, but suspect it was a long distance and there was a good chance they came in contact with domestic sheep. Hanford also is close to areas where sheep graze.
" No one at the department enjoys lethally removing any species but unfortunately sometimes it is part of the fine balancing act that is required for wildlife management," said Staci Lehman, spokesman for the Department of Fish and Wildlife.
Pneumonia outbreaks have killed bighorn sheep in other western states and in some Washington herds for decades, according to the department.
Herds in the Hells Canyon and Blue Mountains areas have been affected since the early 1990s and infected bighorns were found in late 2009 and early 2010 in the Umtanum herd in the Yakima River Valley.
In early 2013, a separate disease outbreak occurred in the Tieton Herd, near Naches, and the animals that survived were killed to prevent the spread of the disease to the nearby Cleman Mountain herd.
