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.