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Shellfish

Shellfish are a high risk food because they may grow in contaminated water, and accumulate any bacteria, viruses, protozoa, biotoxins or pollution present. Disease-causing bugs can survive for weeks, and sometimes months. Diarrhoea and vomiting may result.

In the Auckland region there is no ongoing recreational monitoring of shellfish for possible contaminants, except for marine biotoxins. Therefore, shellfish may not be safe to eat after collection from Auckland beaches and harbours.

As a general principle, Auckland Regional Public Health Service (ARPHS) advises against any consumption of shellfish gathered in urban areas as there is too great a risk from illegally-dumped contaminants, animal waste, road runoff, industrial discharges, leachate from buried materials and sewage overflows.

 ARPHS recommends:

  • Do not gather shellfish where any warning signs are present.
  • Do not gather shellfish within 28 days of a nearby sewage overflow.
  • Do not gather shellfish from beaches with a history of poor water quality.
  • Do not gather shellfish after heavy rain and storms, as rain may flush sewage overflow or farm run-off into water.
  • Only gather shellfish from areas where the seawater is visibly clean and there are no obvious sources of contamination such as;
    - sewage outfall pipes
    - farm animals, especially at dairy farms
    - stormwater outlets, pipes or culverts
    - industrial areas
    - homes – particularly if they are on septic tanks
    - where boats may discharge on-board toilets
  • Thorough cooking at boiling point for several minutes will destroy most harmful bacteria and viruses. However, it is not practical for all types of shellfish as this may affect the texture and flavour, and biotoxins will not be made safe.
People should also read the information produced by the Ministry for Primary Industries (MPI) on foodsmart.govt.nz:

General questions on environments at a particular beach can be directed to Auckland Council’s Environmental Health Officers for the particular area (Ph: 09 3010101).

Marine Biotoxins

Biotoxins are toxins or poisons produced by algae which live in water. Scientists have tried to identify the triggers for the algae that cause the toxic shellfish poisoning, but haven't yet identified the key factors. Marine biotoxins are one potential hazard related to shellfish.

The Ministry for Primary Industries runs a recreational marine biotoxin monitoring programme across New Zealand. Shellfish and seawater samples are tested each week to check if they are contaminated with biotoxins from algal blooms. If marine biotoxin levels in shellfish are found to be unsafe in the Auckland region, ARPHS will implement an appropriate public health response. In co-operation with the council for the affected area, ARPHS will advise against collecting and eating shellfish from the affected area.

Visit Marine Biotoxin Alerts for more information on alerts currently in force around New Zealand.

Remember, before eating shellfish gathered  in the Auckland region always check that the area  is currently safe from toxic shellfish poisoning.

Please phone ARPHS on 09 623 4600 and ask for the duty Health Protection Officer in the Environmental Health Team if you require further advice on this matter.

Toxic Shellfish Poisoning

There are four main kinds of toxic shellfish poisoning. The chemicals that cause toxic shellfish poisoning are produced by certain species of toxic algae and released into the shellfish when they eat the algae. One of these types of toxic shellfish poisoning is paralytic shellfish poisoning.

What is Paralytic Shellfish Poisoning (PSP)?

Paralytic shellfish poisoning is caused by a group of chemicals called the saxitoxins and gonyautoxins. These chemicals are produced by algae and released into the shellfish when the algae are eaten. The chemicals all differ in their toxicity to humans, and can be changed depending on the species of shellfish. Stomach acids in animals and humans can also alter the toxicity.

The toxins can also be released into the sea from the algae but there are no known problems from recreational contact with water (e.g. swimming).

What are the symptoms of Paralytic Shellfish Poisoning (PSP)?

Symptoms of PSP usually occur within 12 hours of consuming shellfish and include:
  • Numbness and tingling around the mouth, face or extremities
  • Difficulties in swallowing or breathing
  • Dizziness, double vision
  • In severe cases, paralysis and respiratory failure

At what levels of toxicity are people at risk of illness and death?

The risk of illness depends on many factors, for example:
  • The toxins present in the shellfish
  • Type of toxins present in shellfish
  • A person's state of health
  • A person's genetic make-up

Remember, these toxins remain even when the shellfish is cooked.

Monitoring and Testing

Shellfish and seawater samples around New Zealand are tested each week to ensure they are not contaminated with biotoxin. Public warnings are issued when shellfish are not safe to eat. Monitoring of toxin levels will continue in the region and the public will be notified of any changes.

For more information on shellfish, please contact Auckland Regional Public Health Service on (09) 623 4600.

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