Scientists discover link between government cull and poaching of wolves

A long-held belief that sanctioned culls of predators would reduce poaching just got shot out of the water.

“To prevent illegal uses of natural resources, such as poaching endangered species, governments have advocated granting policy flexibility to local authorities by liberalizing culling or hunting of large carnivores,” wrote Drs. Guillaume Chapron and Adrian Treves in their study published in the journal Proceedings of The Royal Society B this week.

The duo, through the Carnivore Coexistence Lab at the Nelson Institute for Environmental Studies in the University of Wisconsin-Madison, were contracted to determine what impact such a cull – a popular management tool throughout North America – had on wolves in Michigan and Wisconsin.

The results were rather conclusive.

“We found that it was much more likely that culling would increase poaching,” Dr. Treves told Defender Radio today. How, exactly, the plethora of variables were identified, measured, and analyzed played out almost like a detective novel – and Dr. Treves graciously took the time to explain the methodology involved in his ground breaking study for The Fur-Bearers.

“There’s only three possible explanations for the slowdown in wolf population growth we saw in both the states of Wisconsin and Michigan.

Dr. Treves explains the conclusion

“The three possible explanations are that wolves left those two states, namely emigration. We rejected that possibility because the correlation with the policy signal, that is the announcement of the culling authority or delisting, those policy signals, there’s no known biological mechanism. It’s simply inconceivable that wolves would leave the state when a policy was announced.

“The second possibility is a much more plausible explanation which is density dependence, a phenomenon that’s fairly common in many wildlife where as the population becomes more abundant and densely populated its growth slows, and we therefore tested for that very carefully. But we found the opposite as have other researchers examining the Wisconsin wolf population. Namely, we found that the proportion of packs breeding every year increased as the population became more dense. We looked at other elements of density dependence, but likewise they did not explain it. If anything we should have found an increase in population growth rate, so our estimates probably underestimate poaching.

“The third explanation, the only other one, is that wolves died unreported. Now, we have other evidence here, very few mortality sources destroy radio collars, so some of the wolves in the two states were radio collared and the radio collars disappeared. Poaching is pretty much the only source of mortality that can consistently destroy radio collars and lead to the disappearance of wolf carcasses. That was our primary bit of evidence.

"Secondly, we needed a source of mortality that was new and could respond to a policy signal. As mentioned earlier the policy signal was the declaration of authority for culling, and the length of time that authority was in place independent of the number of wolves culled. So poachers can potentially respond to a policy signal.

"And finally, we had corroborating evidence from attitudinal research we’ve been doing repeatedly for the last 15 years here in Wisconsin, showing that tolerance for wolves and inclination to poach wolves had been changing over the time period indicated. Namely that inclination to poach wolves had increased over time despite culling being in place, and that tolerance for wolves had declined and continued to decline even after the public trapping and hunting season of 2012. That’s not considered in the current paper.

“So we had these corroborating sources of evidence that suggested a new causes of mortality had appeared, that it responded to a policy signal, that it destroys radio collars. And we know from studies of other populations that unreported poaching is usually the most significant source of mortality for large carnivores; therefore we inferred that the slowdown in population growth we measured was caused by a surge in poaching, triggered by the length of time the government had authority to cull wolves, but independent of the implementation, i.e., independent of the wolves killed in culling operations.”

The implications of this study are clear: poaching is playing a significant role in populations of carnivores, but not being recognized for its vast impact in ongoingwildlife management policy discussions.

“We’re looking forward to a policy that’s based on evidence, not presumptions or stories that are repeated often without basis,” Treves noted. “In this case, we believe the management of large carnivores needs to enter 21st century being evidence-based and not driven by narrow interest groups but by the broad public interest.”

We couldn’t agree more. The Fur-Bearers will continue to follow this fascinating work and include it within our own advocacy for modernizing wildlife policy in Canada.

The full interview with Dr. Adrian Treves will be available on Defender Radio next week.

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