•A harvest model is developed to estimate sustainable ivory yield from elephants
•Even in the best-case scenario, the sustainable yield is well below the current demand
•Any overexploitation quickly leads to population extirpation
Summary
Despite the 1989 ivory trade ban, elephants continue to be killed to harvest their tusks for ivory. Since 2008, this poaching has increased to unprecedented levels driven by consumer demand for ivory products. CITES is now considering the development of a legal ivory trade [ 1, 2 ]. The proposal relies on three assumptions: (1) harvest regulation will cease all illegal activities, (2) defined sustainable quotas can be enforced, and (3) we can define meaningful sustainable quotas that come close to the current demand. We know that regulation of harvest does not stop illegal takes. Despite whaling regulation after World War II, illegal whaling continued for decades [ 3 ]. The introduction of wolf culls in the US actually increased poaching activities [ 4 ], and one-off ivory sales in 1999 and 2008 did nothing to halt elephant poaching. Governance issues over the ivory supply chains, including stockpiling, make enforcing quotas challenging, if not impossible [ 5, 6 ]. We have not yet adequately assessed what could be a sustainable ivory yield. To do so, we develop a compartmental model composed of a two-sex age-structured demographic model and an ivory production and harvest model. We applied several offtake and quota strategies to define how much ivory could be sustainably harvested. We found that the sustainability space is very small. Only 100 to 150 kg of ivory could be removed from a reference population of 1,360 elephants, levels well below the current demand. Our study shows that lifting the ivory ban will not address the current poaching challenge. We should instead focus on reducing consumer demand.
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