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Marais de Gros-Cacouna (QC043)


Marais de Gros-Cacouna (QC043)

Cacouna, Québec

Latitude 47.946°N
Longitude 69.498°W
Altitude 0 - 65m
Area 45.91km²

Site Description

Marais (marsh) de Gros-Cacouna is on the south shore of the St. Lawrence River, about 10 km east of Rivière-du-Loup, Québec. The site encompasses a 10 km stretch of shoreline, that includes mudflats that are up to 1 km wide, and a 2 km wide strip of open water. The site also includes Cacouna Rock, Gros-Cacouna Island and a small bay east of the island. Other habitat types include cultivated fields, dykes and the Cacouna Port.


An aquatic bird survey in 1988, recorded 115,000 waterbirds in spring and 45,000 in fall, both globally significant numbers. The difference between seasons is mainly because of the larger number of Greater Snow Geese in spring, and also because of the presence of hunters scaring birds in the fall. Up to 100,000 Greater Snow Geese can be present in spring, representing 15% of the North American population. The majority of possible waterfowl species have been seen here, but two species stand out. As many as 3,000 American Black Ducks (1% of the global population) were recorded in fall 1979, and 50 Barrow's Goldeneyes (2% of the species' eastern population) were recorded in spring 1993. Species that are typically present in numbers exceeding 1,000 individuals include Northern Pintail and American Green-winged Teal. Species present in numbers ranging from 100 to 600 individuals include Brant, Oldsquaw, Gadwall, Blue-winged Teal, American Wigeon, Red-breasted Merganser and all three scoter species.

This site is considered one of the three most important shorebird sites on the river's south shore, between La Pocatière and Matane. An incredible 10,000 Black-bellied Plovers were seen here in 1977, which represents 7% of the present North American population. In 1978, 1,000 each of Semipalmated Plovers and Short-billed Dowitchers were seen, representing 2% and 1% of their global populations, respectively. The numbers of Short-billed Dowitchers represents a high percentage of the population stopping in the St-Lawrence flyway and breeding in the northeastern part of the continent (mainly in Québec).

In spring 1994, 120 Black-crowned Night-Herons were present, which is more than 1% of the Canadian population. The birds were local breeders and used the deciduous forest southwest of Gros-Cacouna Island for roosting.

In the marshy area east of Cacouna port, nine male Yellow Rails were recorded in 1993, making this the third most important breeding site in Québec. Also breeding within the site are several species with restricted numbers or ranges in Québec, such as Nelson's Sharp-tailed Sparrow, Wilson's Phalarope, Le Conte's Sparrow and Marsh Wren. Five species at risk nationally have been reported during migration or summer: Harlequin Duck, Red-shouldered Hawk, Least Bittern, Peregrine Falcon and Short-eared Owl.

The cliffs on the northwest side of Gros-Cacouna Island support a small colony of Black Guillemots (16 birds in 1990). In addition, Herring Gulls (peak number 670 pairs in 1989), Great Black-backed Gulls (peak number 75 pairs in 1990), and Common Eider (peak number 349 pairs in 1990) nest on Cacouna Rock. The number of eiders has dropped significantly in the last decade; only 49 pairs were recorded in 1996.

Conservation Issues

The Gros-Cacouna marsh area is at risk from oil spills; a threat facing all of the IBAs situated along the St. Lawrence River. The harbour expansion may also adversely affect habitats. Trails, observation towers, and artificial ponds have been built with the financial assistance of partners such as Hydro-Québec and Transport Canada. In spring 2012, floating islands were installed in the Étang de la Montagne to provide nesting and staging areas for waterfowl. The IBA is now included in the Kiskotuk coastal park created in November 2012.

Fish Habitat

The landscape of the are is made out of Spartina marsh, eelgrass beds, rocky shores and gravel or pebbles beaches. Some rivers are hosting rainbow smelt spawning runs (the south shore population of the St. Lawrence middle estuary). At the beginning of the summer, it is possbile to observe capelin rolling on the beaches during spawning. The downstream migration of American eel toward their breeding sites in the Atlantic, which takes place in the fall, allows the capture of migraing adults using fishing weirs. Two other species commercially exploited are also roaming in the open waters of the estuary: the Atlantic sturgeon and Atlantic herring.

Loss of fish habitat remains a major problem in the region. The dikes, for example, reduce the number of spawning habitats, while agricultural along the coast, the residential development and the presence of resorts together with coastal erosion are resulting in the destruction of several riparian ecosystems.

Major species present:
American eel
American shad
Atlantic herring
Atlantic sturgeon
Rainbow smelt (population of south shore of the St. Lawrence middle estuary)


The landscape of the coastal region is punctuated with salt marshes. Plant species that grow are especially well adapted to survive the rigors of the environment. They occupy different parts of the marsh according to their tolerance to salinity and immersion (tides). We found there mainly cordgrass, saltmeadow cordgrass and glasswort. The tight formation of stems and the large roots network of cordgrass promote the deposition and retention of sediments, reducing coastal erosion. In areas with weak currents, eelgrass colonizes silty soils, while seaweeds attach and inhabit rocky substrates.

The destruction and loss of habitats (shoreline fill, draining wetlands, urbanization) are the main threats affecting the ecosystems of the area. Water pollution and risks of oil spills remain issues of concern. The spread of invasive species need to be monitored. It should be noted that the region is home to 18 endemic plant species, including two endangered species in Québec.

Major species present :
Cordgrass – main species
Saltmeadow cordgrass
Marine eelgrass

IBA Criteria Habitats Land Uses Potential or Ongoing Threats Conservation Status
Black-bellied Plover
Number Year Season
521 - 2,0001994Spring
500 - 1,0001979Fall
Number Year Season
8,000 - 10,0002012Spring
Snow Goose
Number Year Season
5,000 - 50,0001997Spring
5,000 - 12,0001995Spring
6,000 - 15,0001994Spring
5,000 - 10,0001992Spring
5,000 - 20,0001991Spring
5,000 - 34,0001990Spring
5,000 - 11,0001989Spring
5,000 - 15,0001988Spring
5,000 - 10,0001987Spring
5,000 - 10,0001986Spring
5,000 - 6,0001981Spring
Barrow's Goldeneye
Number Year Season
30 - 501993Fall
21 - 301991Fall
Red-throated Loon
Number Year Season