The rediscovery of the Aldabra banded snail, Rhachistia aldabrae

In 2007, we published an article by Justin Gerlach reporting that the population of the Aldabra banded snail, Rhachistia aldabrae, had declined during the latter part of the twentieth century and had become extinct in the late 1990s [1]. This conclusion was based on the analysis of data from a range of shell collections made across the different islands of the Aldabra atoll from 1895 through to 2006. Gerlach noted that no juveniles had been collected since 1976, and no live adults since 1996, despite systematic surveys aimed specifically at finding the snail in 2005 and 2006. After examining the data, Gerlach discounted changes in habitat, predator pressure or diet as reasons for the population change. He argued, on the basis of a correlation between snail numbers and rainfall, that its decline and proposed extinction was due to a change in climate, namely decreased rainfall, claiming that juveniles were unable to tolerate extended dry periods. Shortly after the publication of the Gerlach paper, we received a comment article from Clive Hambler and co-authors (as reported in The Times on Saturday 20 September 2014 [2]) that contested Gerlach's findings. After independent peer review, the paper was rejected. However, among the concerns expressed in the comment article submitted by Hambler et al. was doubt that the snail was extinct. The authors predicted that the snail would re-appear in due course. In August 2014, the snail did reappear. Its rediscovery was announced by the Seychelles Island Foundation after it had been spotted by a member of a team exploring dense scrub in a remote part of Malabar Island, one of the largest islands in the Aldabra atoll [3]. In the light of this news, we were contacted by Clive Hambler in early September 2014 who requested that Gerlach's original article be retracted and the comment article he had submitted in 2007 be published. While in full agreement of the need for an update to the scientific record, we declined to retract Gerlach's paper and invited Hambler instead to resubmit his 2007 comment article updated with evidence of the snail's rediscovery, an invitation he has until now declined. Does the rediscovery of R. aldabrae justify retraction? It is a normal part of the scientific method that findings published in good faith, based on the evidence available at the time, may later prove to be incorrect. In such a situation, journals have a range of options for alerting the scientific community. Some of the options are outlined on our website [4]. According to the Committee on Publication Ethics, journal editors should consider retracting a publication if “they have clear evidence that the findings are unreliable, either as a result of misconduct (e.g. data fabrication) or honest error (e.g. miscalculation or experimental error)” [5; p. 1]. Our considered view is that, while the report of extinction in the Gerlach paper has lately been revealed to be incorrect, neither misconduct nor honest error have been the cause. In this case, we believe the most appropriate action is for this new evidence to be published, thus updating the scientific record. The principal purpose of this Editorial therefore is to make this update to the scientific record clear, prior to the possible publication of such evidence, by publicizing the rediscovery and acknowledging that the claim by Gerlach in Biology Letters [1] that R. aldabrae was extinct was incorrect. In this Editorial, I also want most strongly to counter views expressed in the wider media about the integrity of our reviewing process and about the relationship between Biology Letters and the Royal Society. First, I can confirm that all papers published in Biology Letters are subjected to most careful, independent peer review, and second, I can re-affirm that the journal has complete editorial independence from any policy position adopted by the Royal Society. Biology Letters, like all peer-reviewed journals, has a responsibility to ensure the continuing debate about scientific findings and theories, including those surrounding climate change. We believe the role of Biology Letters in this case is to ensure that discussion continues around the causes and possible impacts of climate change informed by the most accurate science possible. In this case, Gerlach's proposed extinction of R. aldabrae was cited by Cahill et al. [6] which was referenced by the Intergovernmental Panel on Climate Change (IPCC) in its latest report [7] as one of the few convincing examples of species extinctions as a result of climate change. The IPCC consequently need to be made aware of the rediscovery of R. aldabrae and the rediscovery needs to be brought to the attention of the wider public, not least to those seeking to question the relationship between greenhouse gas emissions and climate. However, in so doing, it is also incumbent on us to point out that the rediscovery does not necessarily invalidate Gerlach's claim that decreased rainfall was and is the principal cause of the snail's apparent decline. Where does this leave us? First, it leaves us with the need to have a renewed debate about the methods used to assess extinction probability, especially for small organisms. To that extent we have commissioned an article to review this field of science. Second, it leaves us with the continuing need to encourage research, including the potential role of climate change, to explain the striking patterns of biodiversity change that have occurred over recent decades throughout the world. And finally it leaves us with the knowledge, and good news, that R. aldabrae is not extinct and that there is a renewed opportunity for conservation biologists to devise a strategy for its future protection.