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Discussion
Our review of mountain lion mortality records obtained from state wildlife agencies found that during an 8-year period from 1997 to 2004, nearly 30,000 mountain lions were reported killed in the 11 western U.S. states of Arizona, California, Colorado, Idaho, Montana, New Mexico, Nevada, Oregon, Utah, Washington and Wyoming. The number of lions killed each year averaged more than 3,600, with an all-time peak of nearly 4,000 lions killed in 2000.
These levels of human-caused lion mortality are unprecedented at least since records were first maintained in the beginning of the 20th century, and surpass even those levels observed when mountain lions were subject to bounties and government sponsored extermination programs (Torres et al. 2004).
The number of mountain lions killed varied widely among the different western states, with the highest concentrations of mountain lions killed in the Northern Rocky Mountains of northern Idaho, western Montana and northeastern Washington, and in Utah. Overall, the states of Idaho, Montana, Utah and Colorado accounted for 56 percent of all the mountain lions killed from 1997 to 2004.
 Exploitation by humans can have an effect on mountain lion populations in a number of ways, though scientists still have little understanding as to the extent or duration of these changes (Murphy et al. 1999). Extensive removals can reduce mountain lion populations until the habitat is re-colonized by individuals dispersing from surrounding habitat (provided there is connectivity with surrounding populations), which can create a population “sink” effect (Lindzey et al. 1992, Sweanor et al. 2000, Stoner 2004).
In areas where mountain lion populations assume a metapopulation structure—a group of populations connected loosely by dispersing individuals—due to demographic features such as in the Southwest (Sweanor et al. 2000), or human development as in Southern California (Beier 1993;1996), reduction or extinction of mountain lions in one population may destabilize the metapopulation (Sweanor et al. 2000). Killing or removing adult resident mountain lions, particularly females, may affect the dynamics of mountain lion populations and social relations among surviving adults and sub-adults (Murphy et al. 1999). Heavily exploited lion populations also become younger, less productive and socially unstable (Stoner 2004).
Sport hunting is the primary form of exploitation of mountain lions in the West, and the leading cause of all mountain lion mortalities (natural or human-caused) in states where it is permitted (Logan and Sweanor 2001). Eighty five percent of all human-caused mortalities reported from 1997 to 2004 were due to sport hunting.
Over the past several decades a number of state agencies have increasingly liberalized hunting seasons for mountain lions, resulting in a significant rise in the number of mountain lions killed by sport hunters (Dawn 2002). These changes were precipitated by increased interest in mountain lions as a trophy game animal and by the belief that sport hunting addresses reduces the risk of mountain lion attacks on humans and predation on pets, livestock, and big game species desired by human hunters, such as deer, elk and bighorn sheep. However, to date there is no evidence that it accomplishes these goals (Cougar Management Guidelines Working Group 2005, Papouchis 2006).
Ostensibly, hunting management strategies are designed using the best available science to protect hunted mountain lion populations from overexploitation. However, Dawn (2002) analyzed mountain lion sport hunting programs in the American West and concluded that current strategies do not adequately protect populations from overkill and “in some states, may be testing the limits of a population’s ability to withstand it.”
In fact, intensive sport hunting and predator control over the past decade has caused declines of mountain lion populations in at least four western states. Lambert et al (2006) reported a decline of mountain lion metapopulation spanning northeastern Washington, northwestern Idaho and southern British Columbia due to intensive sport hunting and other predator control activities. Similarly, the Washington Department of Fish and Wildlife acknowledged that “the statewide … population appears to have declined at this time due to increased female harvest and objectives to address public safety and protection of property” (Beausoleil et al. 2003). Mountain lion populations have also declined in Idaho and Montana after years of heavy and sustained hunting pressure (Nadeau 2003, DeSimone, Montana Fish, Wildlife and Parks, personal communication). Furthermore, in Utah, according to the state’s Division of Wildlife Resources, mountain lions populations were intentionally reduced through years of intensive sport hunting and predator control efforts (UDWR 2005).
Logan and Sweanor (2001) described the state of hunting management in most western states as “a far cry from science.” They considered that hunting strategies used by wildlife agencies were analogous to a “sledgehammer approach.” Under this approach, the number of lions allowed to be killed by sport hunters and predator control agents is increased more and more,
“until population declines affect hunters to the extent that crude population indices based on harvest data-the number, sex, and spatial distribution of pumas killed, hunter success rates, and hunter testimony-suggest that the puma population has declined. When that happens, presumably hunter off-take has “hammered” the population into a decline phase, the amplitude of which managers cannot fully ascertain” (Logan and Sweanor 2001: 373-374).
Because there is no accurate technique for enumerating mountain lion populations over wide areas (Cougar Management Guidelines Working Group 2005), the precise degree to which lion populations in Idaho, Montana, Utah and Washington have declined remains unknown. However, research in Utah suggests the population decline in that state may have exceeded 50 percent (Stoner 2004). Importantly, these findings do not support previous suppositions that mountain lion populations are increasing throughout the American West (Riley and Malecki 2001).
Since even basic information about the size and status of mountain lion populations is often lacking, the setting of hunting quotas is often determined more by local politics rather than sound science (Laundre and Clark 2001). "Game commissions make decisions based on what they hear from their sportsmen constituents," says Greg Tanner, wildlife biologist with the Nevada Department of Wildlife, "We’ve seen recent trends toward the commission opting to establish year-round [hunting] seasons, increase the annual limit, and reduce the cost of the tag to encourage more lion hunting" (quoted in Peterson 2004). The vulnerability of mountain lions to sport hunters will continue to increase as the result of more hunters in the field and the increased accessibility of remote areas via roads and the use of all terrain motorized vehicles and snowmobiles (Laundré and Clark 2003).
 The increasing number of lions killed in response to conflicts with domestic animals and humans also warrants concern. Across the globe, the disappearance of large wild cat species outside of protected areas begins with the loss and fragmentation of their habitat followed by their direct persecution as the result of conflicts with domestic animals or people (Nowell and Jackson 1996). In the American West, as human development continues to expand into mountain lion habitat, the likelihood of negative interactions with mountain lions increases, as does the number of mountain lions killed (Sweanor et al. 2000).
For example, along California’s rapidly developing west slope of Sierra Nevada Mountains, the cumulative effects of habitat fragmentation and killing of mountain lions in response to attacks on pets and hobby livestock could lead to loss of this population by 2050 in the absence of conservation measures (S. Torres, CDFG, personal communication).
Although conservation scientists may view declines in mountain lion populations with concern, wildlife managers may consider declines the inevitable consequence or even a goal of management (Mace and Hudson 1999).
If high levels of exploitation are sustained, mountain lion numbers may drop below what conservation biologist Michael Soulé and his associates have called an “ecologically effective population density,” which they defined as “the population level that prevents undesired changes in a defined ecological setting” (Soulé et al. 2005). For example, research in Venezuela (Terborgh et al. 2001) and Zion National Park, Utah (Ripple and Beschta 2006), found that the elimination or absence of mountain lions from an area led to an overabundance of browsing species that denuded vegetation, causing significant ecological changes and rapid declines in biodiversity. In essence, the removal of mountain lions and other large carnivores “appears to lead inexorably to ecosystem simplification accompanied by a rush of extinctions” (Terborgh et al. 1999). Conservation scientists believe “the available evidence clearly suggests that the precautionary principle should be front and center in conservation action dealing with large carnivorous animals (Ray et al. 2005:421). Or as Miller et al. (2002) explained:
“Scientific data increasingly indicate that carnivores play an important role in ecological health. Yet, [lethal] carnivore control has been the center of our management solutions, and it even has been institutionalized by several government agencies. When control is used, there typically is little consideration of the circumstances, season, behavior, or other conditions that affect a carnivore’s role in its system. . . . [A]s long as we fail to think in terms of an ecosystem, we will continue to lose diversity despite good intentions, higher budgets, and increasing human effort. In short, management policies based on reducing carnivore numbers has caused, and will continue to cause, severe harm to many other organisms.”
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