St. Lawrence Estuary IMMA

Criterion A – Species or Population Vulnerability

The St. Lawrence Estuary IMMA is focused on a relict and isolated subpopulation of Beluga whales (Delphinapterus leucas) that is considered of Least Concern globally, but Endangered in Canada (Lowry et al. 2017; COSEWIC 2014).

Criterion B: Distribution and Abundance

Sub-criterion B2: Aggregations

The Lower St. Lawrence Estuary (SLE) is characterized by the upwelling of cold mineral-rich waters caused by local bathymetry, water mass movements and oceanic fronts (Saucier et al. 2009), which enhance local productivity (Savenkoff et al. 2017) that provides prey for St. Lawrence Estuary (SLE) beluga whales. The more estuarine and brackish waters in the Upper St. Lawrence Estuary and Saguenay Fjord, and seasonal sea-ice cover also provide characteristics typical of beluga seasonal habitat in the Arctic (O’Corry-Crowe 2018). Abundance for SLE belugas has been estimated at 1,850 individuals (95% CI: 1,500 – 2,200) in 2022 (Tinker et al. 2024). The IMMA sustains on average 68% of the population year-round, including the entire summer range of the population, and most of its range for other seasons (Lesage et al. 2024). During winter, on average 32% of the population on average moves into the northwestern Gulf of St. Lawrence, aggregating in the waters of the St. Lawrence Estuary between the Battures aux Loups Marins and Pointe-des-Monts / Les Méchins, including the Saguenay River up to Ile St-Louis.

Harbor seals (Phoca vitulina) also form aggregations throughout the IMMA. According to a recent survey, the IMMA supports nearly 22% of the eastern Canadian population (DFO 2024; Figure 1), or 6.4% of the population from the western North Atlantic (DFO 2024; Sigourney et al. 2022).

Criterion C: Key Life Cycle Activities

Sub-criterion C1: Reproductive Areas

Belugas from the St. Lawrence Estuary mate in the spring (Hill et al. 2024) and give birth mainly from late June to August (Sergeant 1986; Michaud 2007). Given that the population’s entire summer range is encompassed in the IMMA, the area provides important habitat for reproduction for this population (Lesage et al. 2024). Herds with neonates are reported throughout the belugas’ summer range, except in the deeper waters of the Laurentian Channel along the north shore of the Lower Estuary (Michaud 1993; Ouellet et al. 2021; Harvey et al. in review).

Harbor seals give birth in late May and June, weaning their pups after 3-4 weeks (Dubé et al. 2003; Muelbert and Bowen 1993). Harbor seals mate shortly after weaning pups.   Given the species’ year-round presence in the IMMA, this area also provides important habitat for mating, parturition and rearing of young for both species.

Sub-criterion C2: Feeding Areas

The enhanced local productivity makes the St. Lawrence Estuary a particularly attractive area for several marine mammal species for feeding, including belugas and harbor seals (reviewed in Savenkoff et al. 2017; see also Lesage et al. 2007; Lesage et al. 2018; Lacroix Lepage 2018; Mosnier et al. 2023; Ramp et al. 2024).

There is no evidence that beluga go through a fast and feast cycle, suggesting they feed year-round, although not necessarily at the same intensity at all times (Vladykov 1946; Lesage et al. 2020). In the St. Lawrence Estuary, they feed on a variety of prey ranging from invertebrates to small and larger fish species as evidenced by digestive tracts analyses (Vladykov 1946; Lesage et al. 2020). The occurrence of at least 68% of the population in the IMMA throughout the year, and of 100% of the population during summer, is indirect evidence that the IMMA supports feeding. While direct evidence linking specific habitat to foraging are still scarce, archival tag data indicate that area-restricted-search, a behaviour often related to foraging, occurs in several areas of the beluga range (Lemieux-Lefebvre et al. 2012; 2018; Barreau et al. in review).

Satellite tracking and archival tag data, as well as stomach temperature pills, stomach contents and stable isotope analyses indicate that harbor seals are feeding in the IMMA throughout the year (Lesage et al. 1999; Lesage et al. 2001; Lesage et al. 2004).

Criterion D: Special Attributes

Sub-criterion D1 – Distinctiveness

The SLE beluga subpopulation is significantly differentiated and the most genetically divergent group of Belugas in Canada (Brown Gladden et al. 1999; de March and Postma 2003; Postma 2017; Montana et al. in press). This subpopulation is at the southernmost limit of the species’ distribution, and is geographically separated by thousands of kilometres from other beluga subpopulations. This isolation from other subpopulations could lead to local adaptations to both a year-round estuarine habitat existence and to a warmer southern location (COSEWIC 2016).