Harbour oysters need Otago wash
Parts of Bluff Harbour are so polluted from sewage, discharge from vessels and farmland runoff that oysters and other shellfish grown there cannot be sold for human consumption.
New Zealand's Bluff Oyster Co is one of two companies with a resource consent to farm oysters in Bluff Harbour but it cannot "finish" the oysters in the harbour because of the poor water quality.
The company is working with Southern Clams and the Otago Regional Council to finish Bluff oysters in Otago Harbour to ensure its oysters meet consumer safety standards.
Ministry for Primary Industries specialist seafood adviser Brian Roughan said oysters were grown in a section of Bluff Harbour that was "restricted", which meant the shellfish could not be harvested for direct human consumption.
Bluff Harbour was classified as restricted after 30 microbiological and flesh samples were taken in a year.
The ongoing requirement was to conduct five samples annually, plus tests for heavy metals every three years. Marine biotoxins were sampled each harvest. Any risks to consumers were mitigated by the requirements of the control scheme.
"The water quality is such that the pollution events cannot be reliably predicted," Mr Roughan said.
"The shellfish need to be either relayed to better classified waters and grown for a period of time to cleanse, or sent to a land-based premises and go through an approved depuration process."
A sanitary survey "could not allay" concerns with Bluff's sewage infrastructure and discharges from large vessels in the port, Mr Roughan said.
The pollution impacted on the faecal coliform bacteria levels in the shellfish.
The waters are classified according to the Animal Products Act and the Bivalve Molluscan Shellfish Regulated Control Scheme.
"Because confidence could not be gained about the predictability of the pollution events, a restricted classification was the outcome," he said.
Run-off from farmland does cause pollution but has a "predictable" impact on the growing area because rainfall is monitored.
Environment Southland senior resource planner Kylie Galbraith said there were seven marine farm resource consents issued for Bluff Harbour, two of which were for farming oysters or had Bluff dredge stock.
When it asked in emailed questions why oysters could not be finished in Bluff Harbour, why the harbour was not considered certified waters, and who monitored the water quality in the harbour, The Southland Times was told "not our jurisdiction".
However, Environment Southland had "lots" of initiatives to improve water quality in Southland under the Water and Land 2020 and Beyond initiative, she said.
The Ministry for Primary Industries said it was unaware of any aquaculture activities in Bluff Harbour.
- © Fairfax NZ News
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