Toxic Algae Bloom in the St. Lawrence Estuary: Experts’ Findings

September 2008

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Experts at Fisheries and Oceans Canada and other organizations who joined forces to monitor the “red tide” observed in the St. Lawrence Estuary in August 2008 have concluded that the unusually large toxic algae bloom caused most of the fish, bird and marine mammal mortalities reported in the same period.

The red tide was caused by Alexandrium tamarense, a microscopic alga that occurs naturally in the Estuary and the Gulf of St. Lawrence. Heavy rainfall at the end of July likely caused the extensive bloom, which began at the mouth of the Saguenay Fjord and then drifted with the current to the south shore of the St. Lawrence Estuary up to the Sainte-Anne-des-Monts area. The red tide was probably broken up by the strong winds that blew over the north shore of the Gaspé Peninsula in the week of August 18. During the bloom period, an unusual number of fish, bird and marine mammal mortalities, including those of nine belugas, was recorded. The findings of analyses on the carcasses washed up on shore support the theory that the marine food chain was poisoned by the algae responsible for the red tide.

Since the toxin can cause transitory neurological symptoms and, in extreme cases, death, Fisheries and Oceans Canada closed all the shellfish harvesting areas in the St. Lawrence Estuary because of the risk to human health. Some harvesting areas on the North Shore have since reopened based on the recommendation of the Canadian Food Inspection Agency. 

As a precaution, Health Canada and the Canadian Food Inspection Agency advise against eating the livers and viscera of fish and molluscs caught in the area where the red tide occurred. This recommendation is valid for a few weeks, which is the time required by the organisms to cleanse themselves naturally of their toxins. The agencies also recommend not eating the viscera of any waterfowl caught in the St. Lawrence Estuary this fall. However, eating waterfowl flesh is not a cause of poisoning in humans and is therefore considered safe, as the toxins tend to accumulate in the digestive system (liver and hepatopancreas) of contaminated organisms, not in the flesh.

A significant collaborative effort was made during these events by the members of the Réseau québécois d’urgences pour les mammifères marins, namely Fisheries and Oceans Canada, Parks Canada, the University of Montreal’s Faculty of Veterinary Medicine in St. Hyacinthe, the Group for Research and Education on Marine Mammals and the St. Lawrence National Institute of Ecotoxicology. They were joined by Environment Canada, the Canadian Food Inspection Agency and the National Research Council’s Institute for Marine Biosciences in Halifax.