Predator versus prey
Dr. Tom Stephenson
… with DFG playing the referee between lions, sheep
Dr. Tom Stephenson knew he was walking into a potentially confrontational situation when he stepped inside the Green Church at Benton Crossing last Tuesday night to present his SNARL (Sierra Nevada Aquatic Research Laboratory) lecture, and he seemed to try and face the subject matter head on.
“I’m here to present the science tonight, and to give a flavor of what we’re doing on the [sheep] recovery program,” Stephenson explained, “even amid the controversial press that the program has been receiving.”
Stephenson is the California Department of Fish and Game’s (DFG) Program Leader for the Sierra Nevada Bighorn Sheep Recovery Program (SNBSRP). He was referring to the scrutiny that his predator control protocol has received over the last five months.
In February, The Sheet reported that the Public Employees for Environmental Protection group, otherwise known as PEER, had raised concerns about the treatment of mountain lions within the SNBSRP. After hearing from a concerned employee of Stephenson’s, PEER began to look into the way DFG was treating mountain lions in its efforts to grow the Sierra Nevada Bighorn Sheep population. The goal of recovery programs such as the SNBSRP is to grow the population of an endangered species while protecting an intact ecosystem, according to PEER. The issue continues to remain on the table today.
PEER, a national alliance of local, state and federal resource professionals working for environmental enforcement, is arguing that the predator control protocol is acting as a shoot-on-sight management plan targeting mountain lions. Stephenson argues that it’s not so cut and dried.
“It’s really on a case-by-case basis,” he told The Sheet after giving his lecture. “But if a lion is in sheep habitat and intermingling, then it is considered an imminent threat.”
Lions posing an imminent threat to humans, livestock or Sierra Nevada Bighorn Sheep are the only exceptions to Proposition 117, passed by Californians in 1990, which made it illegal to kill a mountain lion.
One problem, which became apparent during Stephenson’s lecture, is the overlap between Sierra Nevada Bighorn Sheep, and the local mule deer populations. For the most part, mountain lions tend to prey on the mule deer in the Round Valley area. Since the mule deer population is healthy, scientists don’t interfere. The issues arise between December and April when the mule deer herds and the Sierra Nevada Bighorn Sheep herds head to their winter ranges. The ranges of the two species are extremely close together and can even overlap, whereas the summer ranges of the two species are farther apart, with the sheep staying up high in the mountains and the deer coming down into the valley.
Since the mountain lions are preying on the deer, they follow them to their winter ranges. With the close proximity, it seems impossible for the mountain lions to avoid stepping over the imaginary line from deer habitat to sheep habitat when they are hunting.
Since the goal of Stephenson and his team is to grow the population of the sheep and have enough for translocation to other areas, they take predation very seriously. The Southern Recovery Unit, which includes Mt. Baxter and Wheeler Ridge, is doing well on its sheep quota so that is the area where DFG likes to pull sheep for translocation to allotments, like Lundy Canyon that still need to be populated. This area, however, is also the spot where the deer and the sheep overlap the most in the winter, meaning that a lot of mountain lions winter in the Southern Recovery Unit, too.
“We need to be able to pull animals out of the Baxter area where mountain lions are high,” Stephenson explained. “If we could implement more translocations we could reach our numbers in the next decade. Predator removal is the most effective management strategy.”
Stephenson explained that in the early 2000s, during the first several years that the Sierra Nevada Bighorn Sheep were on the endangered species list, DFG didn’t do a lot of predator management.
“We waited for the lions to kill a sheep before taking action,” he said. “The problem was that you can’t collect the GPS data until you get the collar back, so a lion could be out there killing sheep and we wouldn’t know.” The DFG tries to collar every mountain lion adjacent to the sheep recovery units.
The process of wait and see wasn’t working, according to Stephenson.
“Disease is what made the sheep endangered but it’s not what is keeping them down,” he said, “lions are. We need to manage predation for as short of time as possible to get the [sheep] numbers up and make translocation possible.”
Stephenson added that killing lions doesn’t make an impact on the lion population.
“After removing them, they just repopulate the area,” he explained. But not before giving the sheep at least a six month lag time in between. Stephenson estimated that there are approximately 4,000-6,000 mountain lions in California.
“Their entire habitat is occupied,” he concluded.
