Science Centres: Fisheries

The voluntary closure of Whangaroa Harbour, Northland, for oyster harvest has been lifted thanks to innovative thinking, smart technology, and months of concentrated sampling by NIWA, in association with a consortium of oyster farmers.

Over the past few years, oyster farmers in Whangaroa Harbour have been frustrated by finding oysters with elevated levels of bacteria while the harbour was open for harvest. The harvest criteria, based on rainfall and a floating salinity buoy, were not accurately predicting when run-off would pollute the harbour. That led to the voluntary closure, causing some hardship in the oyster fishery.

NIWA was called in, and we recommended developing a new probe to measure changes in salinity at the same tidal level that oysters were feeding in. We began a rigorous sampling programme to compare rainfall with changes in salinity and bacteria levels in the water and oyster flesh.

In October, we had enough data to allow us to predict when oysters would be contaminated. Northland Health and the Food Safety Authority reviewed our new relationship between salinity and contamination and accepted the new harvest criteria, allowing the harbour to open again for commercial harvest.

Peter Harris, chairman of the Whangaroa Delivery Centre, commented, ‘We have tried other service providers in the past without success. Once we got NIWA on board we got it sorted.’

The salinity probe records values and sends the data via cellphone to NIWA’s office in Nelson every 15 minutes. There the data are compared against the criteria and a report is generated to show whether the harbour is open or closed for harvest. Oyster farmers have access to this information on demand at any time of the day or night, and are informed by pager or fax of any change in conditions. This allows them to manage harvesting with information received in near real-time, while ensuring consumers get a safe product.