New Zealand Journal of Marine and Freshwater Research abstracts
Catastrophic reduction of the oyster, Tiostrea chilensis (Bivalvia:
Ostreidae), in Foveaux Strait, New Zealand, due to infestation by the protistan
Bonamia sp.
I. J. DOONAN
H. J. CRANFIELD
K. P. MICHAEL
Fisheries Research Centre
Ministry of Agriculture and Fisheries
P.O. Box 297
Wellington, New Zealand
Abstract Between 1985 and 1992, mortality due to infestation by the
protistan
Bonamia sp. severely reduced the numbers of the oyster,
Tiostrea chilensis in Foveaux Strait, New Zealand. In 1990, two
dredge surveys gave relative estimates, and a dive survey an absolute estimate,
of the size of this oyster population; this allowed us to estimate dredge
efficiency precisely. This estimate was used to re-evaluate the dredge survey
of 1975-76 and relate the size of the population in 1990 to that in 1975. By
1990 the population density had declined by 67% while a dredge survey in 1992
showed that the population density had declined by 91% from 1975. A dredge
survey in 1993 showed that the population had increased slightly (but not
significantly) over the 1992 level. By 1992 the population had probably been
reduced below 10% of the virgin level. The fishery was closed in 1993 to allow
the population to rebuild. The population surveys have followed stratified
random and grid pattern sampling designs and the merits of the designs and
methodology are discussed.
Keywords oyster fisheries; Tiostrea chilensis; Foveaux Strait;
New Zealand; protistan disease; Bonamia sp.; shellfish kill; depleted
stocks; stock assessment; fishery surveys; diving surveys; dredge surveys
New Zealand Journal of Marine and Freshwater Research, 1994: Vol. 28:
335-344
0028-8330/94/2804-0335 $2.50/0 (c) The Royal Society of New Zealand
1994
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