Bad moves: Pros and cons of moving oysters - A case study of global translocations of Ostrea edulis Linnaeus, 1758 (Mollusca: Bivalvia)

The study was aimed at learning lessons from historical translocations of the European native oyster, Ostrea edulis and contributing to the debate on best practice for restoration projects. An extensive literature review of over 100 documents spanning 200 years was conducted to look at translocations of Ostrea edulis and investigate temperature related reproduction. Differences among geographical locations were assessed by multivariate analysis of reproductive data. Translocations of hundreds to millions of Ostrea edulis have taken place over the past 200 years, mainly for commercial purposes. Movements were either single actions or regular events over many years. Whilst 75 separate records of Ostrea edulis movements from within European waters were documented, it is likely that many more took place. Introductions have also been made outside Europe for aquaculture; translocations back to European waters, have led to the introduction of pathogens. The timing and duration of reproductive periods and spawning temperature thresholds of Ostrea edulis in the middle region of its distribution range were similar. Cluster analysis of documented periods of reproduction indicated that introduced and restocked populations clustered with their putative donor populations. Whilst the Irish production areas clustered together, reproductive cycles in Lough Foyle in the northwest of the island of Ireland showed greater similarity to the now extinct deeper water English Channel beds. Historically, the ability of oysters to breed after translocation was not considered important. Successful reproduction and recruitment is however fundamental to conserving the species. Where translocation of stock is used to restore Ostrea edulis in areas where it has been extirpated, this study suggests that restocking should be at high densities and carried out over several years and that harvesting should be restricted to increase the chances of establishing self-sustaining populations.