People along the top of the South Island have been told to stop gathering shellfish from a stretch of the Marlborough Sounds after routine testing turned up a dangerous natural toxin in wild mussels. New Zealand Food Safety issued the public health warning on Friday afternoon and it covers the coastline from Tennyson Inlet through to Fitzroy Bay, taking in some of the most popular gathering spots in the outer Sounds.
The warning follows tests on mussels pulled from Canoe Bay, where the results came back above the level regulators consider safe to eat. New Zealand Food Safety acting deputy director-general Mike Inglis said the readings left no room for doubt. Speaking to RNZ, he said “routine tests on mussels from Canoe Bay have shown levels of paralytic shellfish toxin over the safe limit.” Because of that, anyone gathering and eating shellfish from the affected coast risks getting sick.
The toxin comes from a bloom of a tiny marine algae called Gymnodinium catenatum. It is a naturally occurring plankton that drifts through New Zealand coastal waters, and in the right conditions it multiplies quickly. Shellfish are filter feeders, meaning they draw seawater through their bodies and strain out the plankton they live on. When a toxic bloom is present, the poison builds up in the gut and flesh of the shellfish and can reach levels that are harmful to people long before there is any obvious change in how the shellfish look or smell.
That is the part of these warnings that catches people out. A mussel or a pipi carrying a heavy dose of paralytic shellfish toxin looks exactly the same as a clean one. There is no taste, no smell and no discolouration to warn a gatherer off, and cooking does not help. Boiling, steaming, frying or smoking the shellfish will not break the toxin down, so a feed that looks and tastes fine can still make someone very unwell.
The warning applies to the shellfish most people go out for. That means mussels, oysters, tuatua, pipi, toheroa, cockles and scallops, along with pūpū, the small sea snails many people know as cat’s eyes, and the larger Cook’s turban. New Zealand Food Safety says pāua, crab and crayfish can still be eaten from the area as long as the gut is removed completely before cooking, because the toxin concentrates in the gut rather than the flesh. Kina and finfish caught in the zone are not affected by this particular warning, although the agency’s standing advice is to gut fish and throw the liver away before cooking.
Paralytic shellfish poisoning is not a mild stomach upset. The first signs usually show up within ten minutes to three hours of eating contaminated shellfish and start with numbness and a tingling feeling around the mouth, face, hands and feet. From there it can move to difficulty swallowing or breathing, dizziness, headache, nausea, vomiting and diarrhoea. In the most serious cases the toxin can cause paralysis and respiratory failure, and it can be fatal. Anyone who feels unwell after eating shellfish from an area under a warning has been told to call Healthline on 0800 61 11 16 or seek medical help straight away, and to keep any leftover shellfish so it can be tested.
Commercially sold shellfish are not caught up in this. Mussels, oysters and other seafood bought from a shop, supermarket or fish retailer come through operations that are monitored under a separate and continuous testing programme, so a bag of mussels off the shelf is not part of the warning. The alert is aimed squarely at recreational and customary gatherers heading out to collect their own kai from the affected coast.
These warnings are a regular feature of the New Zealand calendar, particularly through the cooler months, and the Marlborough Sounds sees them more than most stretches of coast. The sheltered inlets and slow-moving water that make the Sounds such a rich place for shellfish also make them prone to algal blooms building up and lingering. New Zealand Food Safety keeps a running national list of every active shellfish biotoxin alert on the Ministry for Primary Industries website, and the agency tests shellfish at sites around the country week in and week out to catch blooms like this one early.
A warning stays in place until follow-up testing shows the toxin has dropped back below the safe limit and stayed there, which can take weeks depending on how long the bloom hangs around and how quickly the shellfish flush the poison out of their systems. Lifting a warning too soon carries its own risk, so the agency waits for a clear run of clean results before it gives an area the all clear. Until then, the simplest and safest approach for anyone in the Tennyson Inlet to Fitzroy Bay area is to leave the wild shellfish where they are.
For gatherers who want to check before they head out, the biotoxin alert map is updated as new results come in and as warnings are added or lifted, and it is worth a look before any trip because the boundaries of these zones can shift as blooms move along the coast. A spot that was fine last month can be under warning today, and the only way to know is to check the current list rather than rely on past experience.
Have you had to change your shellfish gathering plans because of a biotoxin warning this winter? Share your experience in the comments below.
This article was written by AI, briefed to report the facts, hopefully without some of the bias people bring to the job 🙂
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