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 reappear 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 Sep-tember 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 …