Tusklessness and tusk fractures in free-ranging African savanna elephants (Loxodonta africana)

Steenkamp, Gerhard; Ferreira, Sam M.; Bester, Marthán N

doi:10.4102/jsava.v78i2.294

Cited by 19 publications

(42 citation statements)

References 12 publications

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“…This is very far from our sustainable harvest estimates (Figure 4). These estimates do not account for population variance in tusk size and tusklessness [16], indirect social effects of the harvest [17] and abiotic effects on demography [11]. Climate predictions show that droughts will intensify and become more frequent [18] hence the population trajectory we simulated is liberal (note how we are not capturing extreme changes, Figure 1C).…”

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confidence: 99%

Can We Sustainably Harvest Ivory?

Lusseau

Lee

2016

Current Biology

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SUMMARYDespite 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 to develop a legal ivory trade [1,2]. The proposal relies on three assumptions: i) harvest regulation will cease all illegal activities; ii) defined sustainable quotas can be enforced; iii) we can define meaningful sustainable quotas that come close to the current demand. We know that regulating harvest does not stop illegal takes. Despite whaling regulation after WWII, illegal whaling continued for decades [3]. The introduction of wolf culls in the USA actually increased poaching activities [4] while 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 agestructured 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 150kg of ivory could be removed from a reference population of 1360 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. RESULTS AND DISCUSSIONHarvest model development In order to develop a harvest model, we must first understand the process by which ivory is obtained. We can apply one of the many approaches used in wildlife management to define these sustainable quotas. However, much of the debate surrounding the sustainability of ivory harvest overlooks one key point: hunters do not want to kill elephants; they want to harvest ivory. Yet, we attempt to inform this harvest using one of two approaches, neither suited to the challenge. It is misguided to use classical population models to try and predict what level of elephant removal population(s) can sustain so as to provide the ivory needed for the market because ivory requires selective harvesting from a sexually dimorphic trait [7]. It is also misguided to use classical resource extraction models, which the current CITES "Decision-Making Mechanism for a Process of Trade in Ivory" is considering, because ivory is a renewable resource made by elephants which increases in mass as elephants age [2]. If the take does not match the demographic pace of elephant populations, a given amount of ivory harvested by removing a few large elephants from the population will require killing more, smaller, elephants the next year. We faced a similar hurdle in the early 20 th century when trying to manage whaling by reducing the harvest to the amount of whale oil produced when that oil was extracted from different age-se...

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confidence: 99%

Can We Sustainably Harvest Ivory?

Lusseau

Lee

2016

Current Biology

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“…Based on this interpretation, the current results would establish that the right tusk is preferentially used over the left in this species. Previous research has shown that tusk fractures in African elephants are strongly correlated with annual rainfall (Steenkamp et al ., ), which may be linked to increased stress while digging in soil and debarking trees. Although we did not have the age of the individuals, as previously noted, tusk weight is a good proxy for age in African elephants (Laws, ), and tusk fractures are higher in adults than subadults (Steenkamp et al ., ).…”

Section: Discussionmentioning

confidence: 99%

Tuskedness in African elephants – an anatomical investigation of laterality

2017

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Evidence for brain and behavioral laterality is ubiquitous across the animal kingdom, ranging from invertebrates to humans. The elephant (Elephas maximus, Loxodonta africana and Loxodonta cyclotis) serves as an interesting model for the study of lateralization given its unique morphology and behavioral repertoire in foraging, and previous reports have documented side preferences in the use of the trunk among Asian elephants (E. maximus). Some authors have even discussed the potential laterality of tusk use among elephants; yet, there are no empirical studies of actual tusk use or appropriate tusk measurements. Here, we undertake an anatomical investigation of laterality in the tusk weights from 683 African elephants (L. africana and L. cyclotis). The vast majority of individuals (94.29%) showed asymmetries in tusk weight, with the left tusk being significantly heavier than the right on average (30.65 vs. 30.24 kg; P < 0.05). Although the age of the individuals in our sample was unknown, the tusks of African elephants continue to grow throughout life and thus individuals with larger tusks should experience greater opportunities for disproportionate wear. Consistent with the view that the reported asymmetries result from behavioral lateralization, that is, side preferences in tusk use in rooting, stripping bark and during agonist interactions, we show that individuals with larger overall tusk pairs had a higher degree of tusk laterality (P < 0.001). The restricted nature of the dataset limited a number of questions that could be examined, but follow‐up research in this area could study differential tusk use in the wild and how this relates to trunk side preferences.

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“…Elephants in different regions of Africa break tusks to different degrees, depending on annual rainfall variations that affect competitive feeding and drinking behavior (Steenkamp et al, 2007). In Zimbabwe, the breaks do not result from the use of tusks in digging or lifting, but from direct percussive impact of the tips against the bodies or tusks of other individuals.…”

Section: Tusk-breakagementioning

confidence: 99%