Project number: 2016-804
Project Status:
Completed
Budget expenditure: $694,773.00
Principal Investigator: Christine D. Crawford
Organisation: University of Tasmania (UTAS)
Project start/end date: 2 Jan 2017 - 29 Jun 2019
Contact:
FRDC
SPECIES
Pacific Oyster

Need

The OsHv-1 virus was first detected in Tasmanian oysters in January 2016 with massive mortality of oysters on farms in several major oyster growing areas, including Pittwater, Pipeclay Lagoon, Blackman Bay and Little Swanport. In other regions such as Bruny Island and Great Swanport the virus was found in oysters but mortalities were low. Reasons for these differences between oyster growing areas are unknown and there is an urgent need for Tasmanian oyster farmers to have region and site specific information on the period of infection of the virus in Tasmania and to better understand the POMS virus dynamics, leading to the development of a predictive framework and early warning for oyster farmers of POMS disease outbreaks. Oyster farmers in Tasmania also desperately need support to develop farm management techniques that enable them to operate successfully in POMS infected areas, especially during the next few years while selective breeding for POMS resistance is being developed.

Objectives

1. To determine i) the periodicity of infection of OsHV-1 virus in Tasmania, ii) advance the understanding of the drivers of POMS disease outbreaks, and iii) develop a predictive framework that allows the Tasmanian oyster industry to forecast danger periods for POMS.
2. To develop farm husbandry and handling protocols to maximise oyster production in POMS infected growing areas by investigating oyster survival in relation to: i) subtidal versus intertidal culture, ii) high water flow areas compared with low flow, iii) reduced handling, iv) size and timing of spat onto growout farms, and v) stocking density.
3. To enhance commercial production of Pacific oysters in a POMS infected area through analysis of past farm production and management records, and a contemporary study of farm production systems and oyster survival.

Final report

ISBN: Print: 978-1-922352-09-5 Electronic: 978-1-922352-10-1
Authors: Christine Crawford Sarah Ugalde
Final Report • 2019-08-01 • 4.07 MB
2016-804-DLD.pdf

Summary

The objectives of our research have been to determine the high-risk periods for POMS infection and to develop a predictive framework so that the farmers can forecast danger periods for POMS. This includes developing a better understanding of where the virus exists in the environment and the factors that drive POMS disease outbreaks. We also aimed to work with the oyster industry to develop farm husbandry and handling protocols that maximise oyster production in POMS infected growing areas. Additionally, we surveyed the oyster farmers affected by POMS to get an overall view of the impact of POMS, especially socio-economic aspects.
 
Our research supports other studies that warm water temperature is a major driver of POMS outbreaks, with temperatures in south-eastern Tasmanian growing areas of 19 °C and above for around one week providing a high risk for a disease event to occur. The risk period for POMS disease outbreaks ranges from mid-November to late March. Other environmental factors likely to be important include water movements and density of infected oysters in a water body. Growing areas with extensive intertidal flats and poor water circulation, such as Pittwater, or with a high biomass of farmed and feral oysters in a relatively small area, such as Pipe Clay Lagoon, have shown to be more susceptible to POMS disease than the other farming areas. As feral oysters in Pipe Clay had a relatively high prevalence of OsHV-1, they may be contributing to the reservoir host of the virus.
 
Studies on farming practices conducted in close collaboration with oyster growers suggest that density of oysters in culture containers has limited effect on mortality rates, and that some
handling is required during the POMS season to reduce biofouling and maintain stocking densities conducive to good growth and survival. Younger and smaller oysters are more susceptible to infection that larger and older juvenile and adult oysters. For oysters of the same age cohort, fast growers had higher mortalities than slow growers.
 
The surveys of oyster growers on the impacts of POMS on their farming operations has shown that mortalities from POMS have rapidly declined from an average of 67% of stock in 2016 to 9% in 2018/19. Changes to farming practices that have occurred during this time include a large increase in stock selectively bred for POMS disease resistance, reduced and more careful handling of oysters during the summer POMS season, selling a higher percentage of stock before the POMS high risk period, and purchasing spat when temperatures are declining.

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