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Test Advances Fight Against Bonamia

Test Advances Fight Against Bonamia

A new tool has been developed to detect low levels of the Bluff oyster killer bonamia.

National Institute of Water and Atmospheric Research (NIWA) and a molecular diagnostic company dnature have developed a DNA test that is more sensitive, and can detect lower levels of infection, than using a microscope.

Bonamia is a microscopic disease of oysters. Although not harmful to humans or animals it kills large numbers of oysters. It has been, and we expect it will continue to be, a recurrent problem in the fishery, says NIWA scientist Keith Michael.

“The great advantage of the new method is that it can detect small amounts of bonamia in an oyster. This means we can detect the disease in a bed early before the infection becomes fatal and the oysters are lost to the fishery.”

Mr Michael says this new test takes less time, is more cost-effective and can detect a number of different species of bonamia.

“We can detect fatal and non-fatal infections and more accurately predict the total summer mortality of oysters before the season begins. We can test 96 samples at one time instead of examining one at a time under the microscope.”

"This new research will help the Bluff Oyster Management Company to develop new ways of minimising the losses of oysters and reducing the spread of bonamia.”

The total Bluff oyster population is continuing to grow steadily since bonamia severely reduced the population to 408 million oysters in 2005. The population has steadily rebuilt from 720 in 2009 to 918 million in 2012.

Now there is a wealth of information from research and extensive hands-on knowledge from skippers, oyster population models can reliably predict trends, with research to estimate the total population size carried out every three years.

Consequently, with the growth in numbers, oyster harvests have also grown from the 2005 low of 7.5 million to a harvest of 12 million last year. Harvesting is expected to be higher again this year, closer to the 15 million limit set by the Ministry for Primary Industries (MPI). The oyster season runs from, 1 March and closes 31 August.

The mortality of oysters from diseases has been between 6 and 12 per cent of the population of legal-sized oysters, while the harvest has been close to 1 per cent.

In 2000, NIWA, Bluff Oyster Management Company, MPI and boat skippers started working together to gain a better understanding about the disease.

The oyster industry review pre-season survey information and research before each oyster season to establish an initial harvest level. Oyster skippers meet early in the season to discuss whether their catch observations match the survey results – and they consistently do. Any changes to harvest limits are discussed by the wider management group.

Because there is a long history of research on Bluff oysters providing a good time series of information, NIWA has been able to reliably predict future trends in the oyster population using assessment models developed for the fishery.

NIWA, the oyster industry, and the MPI undertake a number of other research programmes including research to:

-develop tools to better detect disease in oysters, and to understand bonamia and its interaction with the oyster population.

-monitor the abundance of newly settled, small oysters to help predict future trends in the commercial fishery.

-record extensive and detailed information from the fishery in a fishers’ logbook programme.

-improve dredge performance and fishing procedures, as oysters can only be harvested by dredging.

-investigate what drives oyster production in different regions of the fishery.

-develop methods to enhance the oyster population, if required, during disease events.

The oyster festival is held this Saturday in Bluff, for more information:

To view a video about the Bluff oyster industry go to:

Bluff OysterFishery Information:


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