Habitats for migratory birds - Lake St. François, Lake St. Louis, Richelieu River (downstream), St. Lawrence River (between Pointe-aux-Trembles and Lake St. Pierre), Lake St. Pierre, Gentilly, Orléans Island, Côte-de-Beaupré, Côte-du-Sud

The subjects of this study – the St. Lawrence (river, estuary and gulf) and the Ottawa and Richelieu rivers – present a range of natural shoreline habitats that are conducive to the flourishing of avian, aquatic and terrestrial fauna. Avian fauna, particularly migratory birds, use wetlands as feeding and resting areas. These wetlands develop primarily in bays that are sheltered from currents and their flora varies depending on water salinity and the presence or absence of tides.

In the lowlands of the St. Lawrence, which are washed by fresh and brackish waters, wetlands contain submerged and emergent aquatic plants in areas unaffected by tidal action and are dominated by the American bulrush in areas where tidal variations uncover muddy sediments. They develop particularly well in areas where water in shallow, as in the bays of the Ottawa River, the shores of the Richelieu, and in the lakes, bays and island shores of the St. Lawrence.

In salt water, they can be found in the fine deposits in the high areas of coves, bays and river mouths sheltered from violent seas. In the St. Lawrence estuary, low wetlands are dominated by Spartina alterniflora communities, while higher wetlands are characterized by the presence of Spartina patens and other halophyte communities. In the Gulf of St. Lawrence, wetland herbaceous species form mosaics of alternating halophyte communities.

Photographic interpretation and mapping (1:20,000) of the shorelines of these waterways provide a means of locating wetlands, determining their size, and identifying disturbances of human origin. The results show that there are 39,000 hectares of these wetlands (submerged and emergent plants) in tideless freshwaters and approximately 3,900 hectares of herbaceous communities dominated by the American bulrush in tidal freshwaters. Identified saltwater wetlands represent a total of 9,000 hectares, 4,000 of which are found in the St. Lawrence estuary, 2,400 of which are distributed sporadically along the north shore of the Gulf of St. Lawrence and Gaspé Peninsula, and 2,200 of which are located in the Îles-de-la-Madeleine.

Finally, an analysis of “control sectors” (La Prairie Basins, Gentilly and Kamouraska) along the St. Lawrence shows that the impact of major human interventions on the shorelines of these waterways has increased significantly over the past 30 years.