Bonamia Response 2015: Report from the Technical Advisory Group on Resilience Breeding in Flat Oysters

Abstract

Bonamia ostreae is an unwanted and notifiable organism that was first detected in New Zealand in flat oysters (Ostrea chilensis) collected in 2014 from the Marlborough Sounds. It is not known how B. ostreae entered New Zealand. Evidence indicates that it is a recent introduction. A Controlled Area Notice was issued as a measure to prevent the spread of B. ostreae from the known infected area to valuable wild oyster populations and farmed oysters in Big Glory Bay (Stewart Island). In May 2017, MPI’s surveillance programme detected B. ostreae in farmed oysters from Big Glory Bay. The decision was made to depopulate all oyster farms in Big Glory Bay and the Marlborough Sounds to protect the wild flat oyster population in Foveaux Strait and contain the spread of infection to other areas. The aquaculture industry requested that MPI consider retaining some stock from the Marlborough Sounds farms for the purpose of breeding B. ostreae resilient oysters. The oysters to be retained were stock that had survived B. ostreae mortality events and were considered by some oyster farmers and Cawthron scientists to be B. ostreae resilient. The premise for the proposal was that a “selective breeding programme could potentially future-proof and rebuild wild oyster fisheries by increasing the resilience of the populations even in the absence of the parasite, so that in the event of future incursions flat oysters would be more able to survive infections”. The proposed programme was also put forward as a way to future-proof and support the reestablishment of O. chilensis aquaculture. In response to this proposal a Technical Advisory Group (TAG) was assembled by MPI to provide independent, expert scientific and technical advice on Bonamia spp. resilience breeding in flat oysters. The TAGs discussions were conducted in the context of Bonamia ostreae being an unwanted organism in New Zealand, with a distribution of infection that is highly localised. The understanding of the TAG was that the highest priorities were the ongoing containment of B. ostreae and the protection of wild populations of O. chilensis from B. ostreae infection.