Publications: Research reports and publications

Review of disease risks for New Zealand shellfish aquaculture: Perspectives for management

17 January, 2014
Cawthron Report 2297. Prepared for Ministry for Business, Innovation and Employment.

EXECUTIVE SUMMARY

The Cawthron Institute (Cawthron) conducted a review of aquatic disease agents with the potential to adversely affect aquaculture of Greenshell™ mussels (GSM; Perna canaliculus), Pacific oysters (Crassostrea gigas) and flat oysters (Ostrea chilensis) in New Zealand. This report evaluates a subset of the infectious diseases presented in a broader Cawthron review of aquatic diseases by Webb (2013)

*We consider potential threats to mussel and oysterculture, discuss the complexities associated with prediction of spread and impacts, and recommend some generic approaches that the shellfish industry could implement to reduce risk.

Our assessment identified 28 organisms/groups (pathogens and diseases) with the potential to be problematic to GSM and oyster aquaculture in New Zealand. Of these, 11 have already been recorded here, of which by far the most significant for the industry has been the ostreid herpes virus type 1 microvar (OsHV-1) in Pacific oysters. Of the 17 pathogens or groups not yet reported from New Zealand (although there is no official disease surveillance in place), most are associated with Pacific oysters and some occur in both Pacific and flat oysters). We identified three risk organisms that cause problems in mussel aquaculture overseas, including Marteilia refringens, a pathogen that occurs in both oyster and mussel species.Farmed Perna species overseas appear to have few significant diseases and GSM (whichare endemic to New Zealand) have historically been viewed as resilient to diseases in general. However, Pacific oyster aquaculture was also largely unaffected by diseases until mortalities associated with the presence of the OsHV-1 microvar emerged in Northland in 2010. As GSM are not farmed overseas (where they could be exposed to various infectious diseases), it is not possible to rule out the potential susceptibility of GSM to pathogens of blue mussels, of exotic Perna species or of other bivalves, should it be the case that these pathogens arrive or emerge in New Zealand.

There are already measures in place (or being developed) to mitigate the introduction of aquatic pests and diseases into New Zealand. However, there remain significant risks and substantial knowledge gaps; for example, the role of biofouling species on international vessels as hosts for exotic pathogens is poorly understood. Additionally, the establishment and spread of new or existing pathogens, and the associated impacts on bivalve aquaculture, are virtually impossible to reliably predict. The establishment of a pathogen in a new area depends on multiple dynamic factors. For example, environmental changes (e.g. in seawater temperature) may lead to new ecological compatibilities and alter existing host pathogen interactions, contributing to the emergence of significant diseases.

*A first report by Webb (2013) discussed in detail a number of pathology threats of actual or potential concern toindustry, across a wide range of shellfish hosts found in New Zealand. This provided a starting point based on intuitive expert opinion and experience in pathology.

The lack of awareness and experience with diseases and their management makes the New Zealand aquaculture industry vulnerable to incursions of new pathogens, and to disease outbreaks caused by those already present. The industry would benefit from having a generic disease risk management framework in place, developed with support from government and research providers. Fundamental principles such as pathway management, monitoring and reporting should form the basis of good practices, and generic approaches for responding to any future crises would ideally be developed in advance.

Based on our assessment, our specific recommendations to the mussel and oyster aquaculture industry are as follows:

1. Develop and implement effective biosecurity risk management practices that would include the following basic principles applicable at the farm level:

  • Record and report stock and gear movements, to assist with traceability in the event of a disease outbreak.
  • Record and report animal production data (e.g. baseline and abnormal mortalities).
  • Consider whether there are any on-farm biosecurity procedures that might assist in reducing disease risk, recognising that some of the typical management approaches for disease prevention may not be practical for the shellfish industry.

2. Lead the development of generic biosecurity response plans for managing key types of shellfish pathogens or diseases (e.g. Marteilia refringens and Bonamia ostreae, orhatchery-specific diseases like oyster velar virus disease [OVVD]). This should include an appraisal of industry risk pathways and practices, the extent to which existing management approaches would mitigate risk, and identification of the need for additional measures.

3. Ensure risk management approaches are consistent with measures implemented by other stakeholders, including future approaches by MPI and regional councils in terms of managing domestic biosecurity risk pathways.