Archived – Toxic Algae Bloom in the St. Lawrence Estuary

August 14, 2008

Mont-Joli – A bloom of toxic algae, known as a red tide, has been present in the St. Lawrence Estuary for several days, with large algae concentrations being observed particularly at the mouth of the Saguenay Fjord and on the south shore of the Estuary between Rivière-du-Loup and Rimouski. Fisheries and Oceans Canada has closed all of the shellfish harvesting areas in the affected zone and reminded the public that shellfish harvesting is prohibited in all closed areas. Although many dead birds, fish and marine mammals have been sighted over the past several days, a link has not been established between the mortalities and the toxic algae bloom. Field and laboratory work is currently being carried out to determine the cause of the mortalities.

This red tide is caused by Alexandrium tamarense, a microscopic algae that occurs naturally in the Estuary and the Gulf of St. Lawrence. Heavy rainfall creates conditions favouring the rapid growth, or bloom, of populations of this algae. The increased freshwater inputs can cause a rise in water temperature and a drop in salinity in the surface layer, initiating a bloom event. Alexandrium tamarense produces toxins that can affect the nervous system of fish, birds and mammals. People who eat shellfish contaminated with the toxin may experience adverse health effects. The toxin can cause transitory neurological symptoms and, in extreme cases, death. According to Health Canada, although fish can be affected, they are not considered to be a cause of toxin-induced poisoning in humans. The toxins tend to accumulate in the digestive system of fish, including the liver, rather than in the flesh. As a precaution, the liver and viscera of fish caught in closed shellfish areas should not be eaten.

The Réseau québécois d’urgence pour les mammifères marins has received a large number of reports about dead animals, which include numerous seabird and marine mammal species. Nine belugas died last week, which stands in contrast to the average annual mortality of 15 belugas recorded in the St. Lawrence River. No link has as yet been established between the large number of mortalities and the toxic algae bloom. Teams of scientists are currently in the field collecting water samples and animal carcasses so they can be analyzed at Fisheries and Oceans Canada’s Maurice Lamontagne Institute in Mont Joli and at the Veterinary Medicine Faculty of the Université de Montréal in Saint-Hyacinthe. The results of the analyses will become available within the next few weeks.

A Notice to Shipping was issued on August 12 asking mariners to be vigilant. Toxic algae can affect marine mammals and make them more vulnerable to collisions with ships.

Backgrounder:

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

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