2 Foveaux Strait oyster sampling programme

In 1985, the population of takeable (legal size >=58mm) Foveaux Strait oysters (Tiostrea chilensis) was estimated to have been 1140 million. An epidemic of the protistan parasite Bonamia sp.

Probably began in 1985 and was diagnosed from samples taken after high oyster mortalities in 1986. In response to this outbreak, a series of surveys was undertaken, starting in 1990, to monitor the distribution and intensity of the outbreak. These surveys showed that the infection and subsequent mortality spread through the population in the following years reducing the population to 771 million by July 1990, and 319 million by February 1992, by which time infection had reached the periphery of oyster distribution. In 1992, the population in the area surveyed in 1975 was less than 10% of that present in 1975 and recruitment was considered to be at risk. The fishery was partially closed to fishing in 1992 and fully closed in 1993 to allow the population to rebuild.

Changes in the distribution of Bonamia sp. In Foveaux Strait between 1990 and 1995 had indicated that the prevalence and intensity of infection had waned and that mortality of oysters in the future is unlikely to be as great as it has been in the immediate past. The size of the oyster population estimated in 1992 and 1993 suggested that the population was increasing though the increase was not statistically significant. The population has been surveyed several times since 1995 to monitor further changes.

In 1997, the survey also allowed for the opportunity to examine the effect of different dredge methods on the damage sustained by oysters at harvesting.