Authorities in Ireland and New Zealand have issued warnings about consumption of collected shellfish in the past week.

The Marine Institute in Ireland detected amounts of naturally occurring compounds in shellfish that can cause illness in consumers. Increased levels have been found in recent weeks during a routine nationwide shellfish monitoring program along the South West and West coasts.

Toxins are diarrheic shellfish poisoning (DSP) which can lead to temporary gastroenteritis-like illness and a less common Paralytic Shellfish Poisoning (PSP), which can cause serious illness. Shellfish with toxic levels of PSP don’t look or taste any different from those that are safe to eat.

Occurrence of the compounds is normal at this time of year and is due to microscopic phytoplankton species, common in coastal waters during summer because of longer day length and warmer temperatures. Toxins they produce can accumulate in filter feeding shellfish and make people ill.

Avoid public harvesting
The problem has led to temporary closure of some commercial shellfish production areas. All commercial harvesting in affected areas has ceased, and safe product from other parts of the country is available through approved suppliers to retailers and restaurants.

The Institute, the National Reference Laboratory (NRL) for marine biotoxins, jointly manages the monitoring program with the Food Safety Authority of Ireland and Sea Fishery Protection Authority.

Dave Clarke, manager of the Marine Institute’s Shellfish Safety program, said the monitoring program is designed to protect the consumer and ensure high quality Irish shellfish on international and domestic markets.

“This summer, so far, has seen high levels of toxic phytoplankton and toxins in shellfish requiring temporary closures until the problem abates. We would strongly advise the public to avoid picking their own shellfish along the shoreline, and to only source shellfish from an approved retail establishment,” Clarke said.

As people begin to go back to the coast, risk of public harvesting of shellfish such as mussels, clams, cockles or oysters for their own consumption will increase. However, it is not advised and only shellfish from approved retailers should be consumed, according to the Marine Institute.

New Zealand and previous warnings
The Ministry for Primary Industries (MPI) issued a health warning advising the public not to collect or consume shellfish harvested from Cape Kidnappers to the Mohaka River mouth.

Routine tests on shellfish samples from this region have shown levels of PSP toxins above the safe limit of 0.8 milligrams per kilogram set by MPI. There are no commercial shellfish farms in the affected region.

The agency warned that mussels, oysters, tuatua, pipi, toheroa, cockles, scallops, catseyes, kina (sea urchin) and all other bivalve shellfish should not be eaten. Pāua, crab and crayfish may be eaten if the guts have been removed prior to cooking.

PSP symptoms typically appear between 10 minutes and three hours after ingestion and may include numbness and a tingling prickly feeling around the mouth, face, hands and feet, difficulty swallowing or breathing, dizziness, headache, nausea, vomiting, diarrhea, paralysis and respiratory failure. It can be fatal within 12 hours.

DSP symptoms usually start within 30 minutes of ingestion and last for about a day. They include diarrhea, vomiting, nausea and abdominal cramps.

In June, Highland Council’s environmental health team identified higher levels of bivalve shellfish biotoxins following routine monitoring at Kyles of Scalpay, off the east coast of the Isle of Skye.

Eating items such as mussels, cockles, oysters or razor fish from these areas may pose a health risk. Cooking or freezing does not remove the toxin.

Monitoring work on behalf of Food Standards Scotland also continued to identify raised levels of shellfish toxins in Traigh Mhor in Barra, according to Comhairle nan Eilean Siar (Western Isles Council).

Notices to warn the public were posted at various locations on the shore. Commercial shellfish harvesters in these areas have been contacted and steps taken to postpone harvesting until algae levels subside.