Shellfish gathering is a very popular pursuit in Quebec. There are over 300 harvesting areas, or shellfish beds, scattered along Quebec’s shores. Each year, thousands of people flock to them to either eat or sell the shellfish they collect.
Sadly, not everyone takes the trouble to check whether the shellfish taken are safe to eat.
Yet the risks are very real!
The quality of the shellfish depends on that of the water
There are two main families of shellfish that pose potential risks:
Bivalves, including clams, mussels and scallops, feed by filtering plankton from the water. The plankton may contain microscopic toxic algae.
Gastropods may be carnivores, like whelks, or herbivores, like the common Periwinkle. The carnivorous species that often prey on bivalves are the ones of interest here.
The quality of the marine environment has a direct impact on the quality of the shellfish. If the water in which they live is contaminated with bacteria, toxic algae or chemical pollutants, these substances and micro-organisms will accumulate in their flesh and make them hazardous to human health.
Two toxins are particularly dangerous: paralysing shellfish poison (PSP) and, a recent discovery occasionally reported in our waters, domoic acid. These two toxins are natural products of microscopic algae living in the plankton, and the shellfish that eat these algae accumulate the toxins in their tissues.
Eating shellfish containing these toxins can lead to disorders of the human nervous system that can be fatal. Though not lethal, other biotoxins produced by the algae of the St. Lawrence can cause serious digestive and intestinal problems.