The IBA is part of the Île-aux-Grues archipelago which comprises 21 islands and islets situated in the lower estuary of the St. Lawrence River, north of the town of Montmagny. The island is 7 km long and 2 km wide and is connected to Île-aux-Oies by marshes which the islands' residents call “la batture”. These are the largest insular high marshes remaining along the St. Lawrence River. This IBA includes the land portion, the high marshes and all surrounding intertidal zones, thus containing a diversity of habitats ranging from wetlands to woodlands to agricultural lands. The high marshes and the intertidal habitats are of particular importance to birds. Île-aux-Grues has been inhabited since 1679 and is now home to about 240 permanent residents (excludes vacationers).
This site supports large numbers of Greater Snow Goose (124,000 individuals have been observed) during spring and fall migration. Other dominant species include American Black Duck (high count of 8,000 individuals in 1996), Mallard, Northern Pintail and Green-winged Teal. In addition, numerous migrating shorebirds use this site, including Semipalmated Sandpiper which has been recorded here in nationally significant numbers.
The high marshes are home to several species listed as being at risk of extinction (by the Committee on the Status of Endangered Wildlife in Canada – COSEWIC) including Yellow Rail, Short-eared Owl, and Peregrine Falcon. Nesting passerines include Savannah Sparrow, Swamp Sparrow, Le Conte's Sparrow, and Nelson's Sharp-tailed Sparrow (the latter two are identified as species at risk in Quebec).
Farming activities on Île aux Grues and Île aux Oies, such as the mowing and burning of reeds used as livestock feed, pose a threat to the Yellow Rail which breeds in tidal marshes. However, reed mowing and burning offer some advantages since it prevents further degradation of the Yellow Rail's and Short-eared Owl's nesting habitat caused by invading plants species. Erosion of the marsh caused by ice, wave action and boating activities is particularly concerning; several cubic metres of soil are washed away by the river each year. Finally, the increasing numbers of Snow Geese is causing damage to the vegetation and may also have a negative impact. The IBA is also especially vulnerable to oil spills because of the numerous ships using the St. Lawrence Seaway and the presence of an oil refinery a few kilometers upstream. An oil spill occurred on the islands with the sinking of the Xantoria in the late '80s. Moreover, it appears that the quality of the habitats is at risk from other sources of pollution: elevated concentrations of copper and chromium were recorded in the sediments west of the wharf. Certain sections of the IBA are provincially designated as Wildlife Habitat - Aquatic Birds Concentration Area and as such, any harmful activities or habitat alterations are prohibited. However, the increase in the number of visitors and the related expansion of tourist activities, notably hunting, constitute a source of disturbance for shorebirds using the IBA during migration. In 2013, Nature Conservancy Canada organized birdwatching activities and bird surveys, including a conference on biodiversity, in cooperation with the Imperial Oil Foundation, the Corporation de développement touristique de l'île aux Grues and the municipality of Saint-Antoine-de-l'Isle-aux-Grues.
The bulrush marsh is the typical coastal habitat in the region. While the water has in this region a low salinity, tides are still present and reshape continuously the river landscape. Several species, such as the rainbow smelt (population of south shore of the St. Lawrence middle estuary) and Atlantic tomcod exploit the shallow waters of the area. Many migratory species (anadromous and catadromous) are also found in the area. In addition to the two species mentioned above, we found also the American shad, the Atlantic sturgeon and the American eel, all three species being prized for their tasteful flesh.
However, several sources of pressures are threatening both the quality and the availability of aquatic habitats. The expansion of agriculture, the residential development, the creation of new resorts and artificialization of the shoreline represent significant habitat losses. The presence of major obstacles may impede the movement of fish toward their breeding site. Finally, the maintenance of the Seaway for commercial navigation (dredging and the discharge of sediments) reduces the water quality and may cause the destruction of spawning sites. The decrease of the Atlantic sturgeon population of in the St. Lawrence can be assign to this aspect. Because of habitat alteration, high exploitation of commercial and recreational fisheries and non-compliance, the population of striped bass in the estuary of the St. Lawrence disappeared around 1968. In 2002, Quebec government has established an important reintroduction program to rehabilitate the specie. Between 2002 and 2007, more than 6 300 striped bass and 6,5 millions larvae were introduced into the St. Lawrence river. A network monitoring incidental captures has been implemented in 2004, allowing to document the evolution of the population.
30,000 fry and more than a thousand individual larger than 35 cm were introduced into the St. Lawrence. In early summer 2006, over one million . From 2008, up to 50 000 fry are introduced annually over a period of 10 years. The objective of this program is to rehabilitate the striped bass population of the St. Lawrence.
Major species present:
Rainbow smelt (population of south shore of the St. Lawrence middle estuary)
Coastal habitats of this area are soaked by generally turbid and lightly salted water. We found mostly brackish marshes, dominated by American bulrush, sessilefruit arrowhead and broad-leafed arrowhead. With there large root system, theses plants retain the soil in place, helping to protect the banks against coastal erosion. In addition, the underground parts are used as a food source by the snow geese during their migrations.
The destruction and loss of habitat (shoreline fill, draining wetlands, urbanization) are the main threats affecting this ecosystem. Water pollution and the risks of oil spills are issues of concern. The spread of invasive species is to be monitored. This region is hosting 18 endemic plant species, including three endangered species in Québec.
Major species present :
|American Black Duck|
|5,000 - 8,000||1996||Fall|
|5,000 - 10,000||1996||Fall|
|5,000 - 10,000||1996||Spring|
|5,000 - 10,000||1995||Fall|
|5,000 - 11,111||1995||Spring|
|8,000 - 60,000||1986||Fall|
|8,000 - 30,000||1982||Spring|