More surveys of Bonamia in Foveaux Strait oysters
Science Centres: Fisheries
NIWA is working with the Ministry of Fisheries and the Bluff Oyster Management Company to survey parts of Foveaux Strait to collect information on the impact of the current outbreak of Bonamia exitiosus on the oyster population. This is the third such survey this summer.
Between 1986 and 1992 Bonamia reduced the Foveaux Strait oyster population to 9% of its pre- disease size. A survey in March 2000 showed that infection was not widespread and high prevalence was limited to the area of the original outbreak, but by October 2001 Bonamia was widespread over the whole population. A survey of a sub-sample of stations in January 2002 showed a high prevalence of infection and some patches with many infected oysters in all areas that had high densities of recruited oysters.
Most sites showed a decreased density of live recruits in January 2002 and the density of shells of oysters that had died in the previous 6 months (new “clocks”) was higher than in October 2001. The estimated size of the commercial population in January 2002 suggests a reduction to about 60–86% of that estimated in October 2001. The increase in prevalence and intensity of infection from Bonamia found in the January survey suggests that there will be a further reduction in the commercial population size before the beginning of the fishing season in March 2002.
The current survey will be carried out before commercial fishing begins on 24 March. It will provide another data point for the development of a management model for the Foveaux Strait oyster fishery, including the impact of Bonamia on oyster population dynamics.