Oyster mortalities in Ireland are slowing down

Samples from seven bays have shown the presence of herpes virus, OsHV1. Further analysis is being carried out to identify if there are any other pathogens present. Analysis is ongoing on samples from a further six bays affected by oyster losses.  

Mortalities have affected principally seed and juvenile oysters brought into Ireland in 2009. Mortalities in this stock have ranged from 15 to 95 percent. There have also been mortalities in half grown and adult oysters in a small number of bays. The mortality in these stocks has been much less severe with reported levels of around 30 percent in half-grown oysters and even lower in adult oysters.

Different bays have experience varying ranges of mortalities -  in some bays there was a small peak of mortality in seed, which stopped relatively quickly, whilst in others the mortality was more severe and persisted for longer, sometimes affecting the majority of stock in the bay.  

The role of OsHV1 in the mortality is unclear as a number of parameters remain to be explored, the Marine Institute said.  

It is however, probable that the herpes virus has played some part in mortalities, possibly in conjunction with certain bacterial pathogens and probably in conjunction with other environmental parameters.