In New Zealand, they are a prized delicacy, and harvested from March to August from the Foveaux Strait oyster fishery based around the town of Bluff (hence the local name). From the early 1980s, the fishery went into serious decline, due to the outbreak of an oyster parasite, Bonamia exitiosa, with the disease killing an estimated billion oysters between 2000 and 2003. The population has been recovering since 2003, with fishermen voluntarily limiting the catch to half the allowable to aid the revival.
Changes in river flows in Southland, due to farming and especially power generation, carrying less limestone deposits into the Strait, is therefore believed to have caused an increase in susceptibility to Bonamia, as well as lower growth rates for some seasons in the past, but little evidence supports this and it seems only coincidental.
^H.J. Cranfield, A. Dunn, I.J. Doonan and K.P. Michael 2005. Bonamia exitiosa epizootic in Ostrea chilensis from Foveaux Strait, southern New Zealand between 1986 and 1992. ICES J. Mar. Sci. (2005) 62 (1): 3-13 doi:10.1016/j.icesjms.2004.06.021