Gathering shellfish in Nelson

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  • Gathering shellfish in Nelson

Shellfish are filter feeders. They take their food from the surrounding water. In doing so they can also take in various types of contamination from the surrounding water. Contaminants tend to accumulate in the shellfish often to levels greater than that of the surrounding water.

Contamination

There are many potential sources of contamination from human activities and from animals within urban areas. During periods of heavy rain, contaminants such as animal droppings are washed into rivers, streams and stormwater systems and from there into the sea. Where an urban area is located at the head of a bay or within an estuary (like Nelson) contaminants released to the coast do not dilute as quickly and tend to stay in shore for longer periods. This leads to a greater likelihood of the contaminants being picked up and accumulated by shellfish in the area.

Shellfish advice

For these reasons it is accepted wisdom that shellfish should not be taken from enclosed waters adjoining urban areas. Where in the past members of the public have asked Council or Health Board officers if shellfish within the Waimea Inlet or Haven are safe to eat they have been advised that it is not a good idea.

In the past, Council in association with Nelson Marlborough Health Board, collected and analysed a small number of water quality and shellfish flesh samples for faecal coliform, the indicator organisms for microbiological contamination. The samples were collected from three sites within the Waimea Inlet and the Nelson Haven. Some elevated faecal coliform levels were detected in both the water and shellfish flesh samples but the results were inconsistent and difficult to interpret.

Testing continues

Council intends to undertake more comprehensive sampling of shellfish water quality and, on the basis of that work, decide if the expense of a more comprehensive programme of shellfish flesh testing is warranted.

In the meantime the Council confirms its earlier advice that shellfish within the enclosed waters of the Waimea Inlet and the Nelson Haven may from time to time exceed maximum microbiological guideline levels and should not be taken for human consumption.