Bivalve shellfish can be affected by paralytic shellfish poison (PSP, also known as “red tide”) and sanitary contamination. Eating shellfish that has been contaminated by PSP can result in serious illness or death. Cooking the shellfish prior to consuming it does not destroy PSP or eliminate this risk.
Harvesters and consumers of bivalve shellfish should also be aware of Vibrio parahaemolyticus (Vp), which can cause symptoms such as diarrhea, cramps, nausea and vomiting if shellfish is not properly stored or cooked prior to consumption. Vp occurs naturally in our coastal waters. The levels of these bacteria rise with warmer water and can concentrate in bivalve shellfish. Immediately after harvesting bivalve shellfish, freeze or refrigerate, and then cook the shellfish as a generally effective way of preventing illness from the Vibrio bacteria. None of these methods, however, destroy PSP.
Bivalve shellfish have a hinged, two-part shell. They include oysters, clams, scallops, mussels and cockles. Other shellfish, such as shrimp, prawns and crabs, are not affected by PSP or Vp.
“Closures can happen quickly in-season, therefore it is essential for public health and safety that harvesters of bivalve shellfish, before fishing, always check to ensure that areas are open and approved for harvesting,” said Kerry Marcus of DFO’s Resource Management team. “To reduce the risk of illness from Vp, we strongly recommend not consuming raw bivalve shellfish, especially during the warm summer months.”
Water and shellfish sampling programs are undertaken by Environment Canada and the Canadian Food Inspection Agency to ensure that fishing areas are safe for bivalve shellfish harvesting. Areas that exceed allowable limits for PSP and sanitary contamination are closed by DFO. It is illegal to harvest shellfish from a closed area.
People buying bivalve shellfish should only purchase them from retailers who can confirm the source of the shellfish and that it was harvested from an open area. Shellfish that have been legally commercially harvested are safe to eat. Proper documentation must accompany commercially-harvested shellfish to demonstrate that it has been harvested legally and has been through the necessary inspections.
