Evaluating how lethal management affects poaching of Mexican wolves

Abstract

Despite illegal killing (poaching) being the major cause of death among large carnivores globally, little is known about the effect of implementing lethal management policies on poaching. Two opposing hypotheses have been proposed in the literature: implementing lethal management may decrease poaching incidence ( killing for tolerance) or increase it ( facilitated illegal killing). Here, we report a test of the two opposed hypotheses that poaching (reported and unreported) of Mexican grey wolves (Canis lupus baileyi) in Arizona and New Mexico, USA, responded to changes in policy that reduced protections to allow more wolf-killing. We employ advanced biostatistical survival and competing-risk methods to data on individual resightings, mortality and disappearances of collared Mexican wolves, supplemented with Bayes Factors to assess strength of evidence. We find inconclusive evidence for any decreases in reported poaching. We also find strong evidence that Mexican wolves were 121% more likely to disappear during periods of reduced protections than during periods of stricter protections, with only slight changes in legal removals by the agency. Therefore, we find strong support for the facilitated illegal killing hypothesis and none for the killing for tolerance hypothesis. We provide recommendations for improving the effectiveness of US policy on environmental crimes, endangered species, and protections for wild animals. Our results have implications beyond the USA or wolves because the results suggest transformations of decades-old management interventions against human-caused mortality among wild animals subject to high rates of poaching.