Abstract
BackgroundEcological replacement involves the introduction of non-native species to habitats beyond their historical range, a factor identified as increasing the risk of failure for translocations. Yet the effectiveness and success of ecological replacement rely in part on the ability of translocatees to adapt, survive and potentially reproduce in a novel environment. We discuss the welfare aspects of translocating captive-reared non-native tortoises, Aldabrachelys gigantea and Astrochelys radiata, to two offshore Mauritian islands, and the costs and success of the projects to date.Methodology/Principal FindingsBecause tortoises are long-lived, late-maturing reptiles, we assessed the progress of the translocation by monitoring the survival, health, growth, and breeding by the founders. Between 2000 and 2011, a total of 26 A. gigantea were introduced to Ile aux Aigrettes, and in 2007 twelve sexually immature A. gigantea and twelve male A. radiata were introduced to Round Island, Mauritius. Annual mortality rates were low, with most animals either maintaining or gaining weight. A minimum of 529 hatchlings were produced on Ile aux Aigrettes in 11 years; there was no potential for breeding on Round Island. Project costs were low. We attribute the success of these introductions to the tortoises’ generalist diet, habitat requirements, and innate behaviour.Conclusions/SignificanceFeasibility analyses for ecological replacement and assisted colonisation projects should consider the candidate species’ welfare during translocation and in its recipient environment. Our study provides a useful model for how this should be done. In addition to serving as ecological replacements for extinct Mauritian tortoises, we found that releasing small numbers of captive-reared A. gigantea and A. radiata is cost-effective and successful in the short term. The ability to release small numbers of animals is a particularly important attribute for ecological replacement projects since it reduces the potential risk and controversy associated with introducing non-native species.
Highlights
Conservation introductions such as ecological replacement or assisted colonisation, which are defined as the intentional movement and release of an organism outside its indigenous range [1], are increasingly being explored as potential remedies for dysfunctional ecosystems and to reduce extinction risk [2], [3], [4], [5], [6], [7]
In addition to serving as ecological replacements for extinct Mauritian tortoises, we found that releasing small numbers of captive-reared A. gigantea and A. radiata is cost-effective and successful in the short term
Ecological replacements are effectively alien species introduced to resurrect ecosystem functions once performed by extinct species, whereas assisted colonisation is primarily undertaken to ensure species survival as protection from current or likely future threats is deemed less feasible in its current range than at alternative sites
Summary
Conservation introductions such as ecological replacement or assisted colonisation, which are defined as the intentional movement and release of an organism outside its indigenous range [1], are increasingly being explored as potential remedies for dysfunctional ecosystems and to reduce extinction risk [2], [3], [4], [5], [6], [7]. Ecological replacements are effectively alien species introduced to resurrect ecosystem functions once performed by extinct species, whereas assisted colonisation is primarily undertaken to ensure species survival as protection from current or likely future threats is deemed less feasible in its current range than at alternative sites. Much debate about these controversial strategies has focussed on the impact that the deliberate movement of species to novel ecosystems will have on the recipient environment [8], [9] rather than on the welfare of the animals themselves. We discuss the welfare aspects of translocating captive-reared non-native tortoises, Aldabrachelys gigantea and Astrochelys radiata, to two offshore Mauritian islands, and the costs and success of the projects to date
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