Agencies Joining To Study Shellfish Quality

MEDIA RELEASE 9 October 2007

Agencies Joining To Study Shellfish Quality in Estuaries

A study to assess the microbiological quality of shellfish in estuaries begins this week.

Medical Officer of Health Dr Phil Shoemack says recent monitoring of shellfish has shown an increase in bacterial levels in some shellfish beds in estuarine areas. “Unfortunately we do not know with confidence whether these results represent a long term problem or if they result from one-off contamination. Testing of recreational water has also confirmed occasional elevation of bacterial levels. Shellfish get their own food by filtering relatively large volumes of water and they therefore tend to concentrate any contaminants, including microbes that are in the water. This is why shellfish are seen as high-risk foods for causing diarrhoeal illnesses, especially if eaten raw” says Dr Shoemack.

The agencies funding the study include the New Zealand Food Safety Authority (NZFSA), Toi Te Ora – Public Health (Toi Te Ora), Environment Bay of Plenty (EBOP), Tauranga City Council (TCC), and Western Bay of Plenty District Council (WBOPDC). They’ve identified that they need better information about the bacterial and viral quality of shellfish stocks so the public have better information about the possible risk of eating shellfish from local beds.

The NZFSA has been funding the Institute of Environmental Science and Research (ESR) to develop norovirus testing for shellfish. Both organisations are now interested in proving the test method in a field situation and to confirm whether the use of viral rather than bacterial indicators is useful. The local study supports similar international scientific work and will gather data so that viral contamination of similar estuarine areas can be predicted without having to necessarily test shellfish samples. The organisations involved have agreed to jointly fund the study in order to fill an information gap relating to contamination of estuaries and shellfish within them.

Microbial contamination can enter waterways through storm water, rural and urban runoff, leaky sewer pipes, septic tanks and inadequately treated sewage discharges. There is also an increased risk of faecal contamination where there are stock crossings or any other direct access by stock to a waterway.

Impacts of contamination through sewage discharges and rainfall, together with tidal flows will determine if or when and for how long shellfish remain contaminated. The study aims to assess the shellfish quality against recommended guideline values for human consumption. It hopes to ultimately limit illness from shellfish gathered in estuarine areas.

At this stage there is funding to carry out monthly sampling of shellfish at six locations and water sampling at 13 sites in Tauranga Harbour and Little Waihi Estuary for a year. Additional, and more comprehensive, sampling will also be carried out following an event such as heavy rainfall or a sewer break which could cause contamination.

ESR will carry out the virus testing component of the study in Wellington and EBOP will carry out the bacteria testing at their laboratory in Whakatane. Water and shellfish samples will be collected by EBOP, WBOPDC and TCC, and Toi Te Ora will manage the project with the aid of the other agencies.

The shellfish species to be sampled includes Cockles, Oysters, Pipi and Horse Mussel. Locations include Pios Beach, two locations in the Te Puna area, Fergusson Park, Pilot Bay and Little Waihi Estuary. If more funding became available other sites could be included as the work progresses.

The study will help EBOP ensure the water quality of the Bay of Plenty’s harbours, estuaries and beaches is suitable for contact recreation and shellfish gathering. TCC hopes to be able to establish baseline data for water and shellfish quality in Tauranga Harbour which will then allow Council to measure any changes in quality after a contamination incident. WBOPDC hopes the study will provide information to help protect, maintain and enhance their district’s natural environment.

Depending on the findings it is hoped that this study will be a stepping stone to further work on shellfish quality. Dr Shoemack adds “the study will confirm the quality of the shellfish in the harbour. It’s also great to see the multi-agency co-operation with this work.”

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