It doesn't bode well for shellfish gatherers this summer. Biotoxin alerts warn of paralytic shellfish poisoning in the Bay of Plenty, from Waihi Beach to Opape, east of Opotiki, while the warning on the

West Coast extends from Oakura to the Hokianga. It means grabbing a few tuatua for a summer barbecue may be more hazardous than usual. But if shellfish remain on the menu, here are a few tips from MPI:

CLEAN AND CHILLL

Looking after your shellfish properly means they stay fresher for longer, reducing the risk of illness from bacteria. Only take shellfish from areas with clean water. Refrigerate shellfish within four hours after gathering, and if transporting shellfish in a chilly bin, store them on ice. But wrap the ice in a towel, as freezing will kill shellfish.

Do not eat broken shellfish or those that have died during storage. Prepare shellfish carefully, wash your hands to avoid cross contamination with other foods or utensils.

COVER

Keep shellfish in the shade during the gathering/collecting process to keep them moist and cool. Cover live shellfish with a clean wet towel and store in the fridge. Don't use airtight containers or bags.

COOK

Bacteria and viruses, chemicals or biotoxins aren't removed if shellfish are eaten raw or lightly steamed. Shellfish are best cooked thoroughly for three-to-five minutes after the shells open. Cooking doesn't remove biotoxins like paralytic shellfish poisoning.

Keep leftovers refrigerated and covered. Thoroughly reheat leftover seafood to a minimum core temperature of 80ºC for at least three minutes.

Bivalves are filter feeders and pose a greater health risk than other seafood. Mussels, oysters, tuatua, pipi, toheroa, cockles and scallops normally feed on phytoplankton, which are tiny algae.

If their water is contaminated, they can pick up and store bacteria, viruses, biotoxins and other contaminants which can make people ill. Mussels can filter up to 360 litres a day, so they can concentrate a lot of contaminants in a short time.

Grazing shellfish such as paua and pupu (cat's eyes) pose a much lower health risk because they are not filter feeders.

Other seafood where the guts (hua) are discarded before being cooked and eaten is also considered lower risk, such as kina, crayfish, crabs and fish.

Pathogens (harmful bacteria, viruses and parasites) such as E. coli, salmonella, norovirus or hepatitis, can accumulate in shellfish, especially when they are collected around outfall pipes or near rivers.

Pathogens may result in vomiting and diarrhoea within a few hours or may result in longer-term complications.

Chemical contamination can be caused by heavy metals, fuel, paints and solvents. Dangerous levels of chemical contamination are very rare in New Zealand shellfish. The areas most likely to be contaminated are in harbours near wharves, industry, marinas and near sewage and storm water outlet pipes.

Biotoxins are toxic chemicals which can cause serious illness if you eat affected shellfish. They are produced by a few types of phytoplankton and become concentrated in shellfish when algae bloom.

Symptoms may include tingling around the mouth and limbs, dizziness, headache, vomiting, diarrhoea and paralysis. You cannot tell if shellfish are toxic by looking at them or smelling them.

MPI tests shellfish for biotoxins around New Zealand at popular recreational gathering sites. If shellfish become contaminated with high levels of biotoxins, warning signs are put up at affected beaches and media releases are issued.

Check out: www.mpi.govt.nz/shellfish website before gathering shellfish in your area to see if there are any biotoxin warnings in place.