The challenges of a small population exposed to multiple anthropogenic stressors and a changing climate: the St. Lawrence Estuary beluga

The beluga (Dephinapterus leucas) has a discontinuous circumpolar distribution in the Arctic and Subarctic regions, with eight populations occurring in Canadian waters (Stewart & Stewart 1989; COSEWIC 2016). The lack of a dorsal fin and a relatively thick dermis (5–12 mm) make the species particularly well adapted to environments with seasonal and extensive ice cover. The population in the SLE, Canada, is at the southern limit of the species’ global distribution and probably established itself thereafter the Wisconsin glaciation (Harington 1977, 2008). The beluga persistence in the SLE is probably largely due to the combination of an extensive and seasonal seaice cover and the cold and productive environmental conditions that are maintained in this region in part from the influx and upwelling of Arctic waters of the Labrador Current (El-Sabh & Silverberg 1990). The SLE beluga, like several other populations, undertakes seasonal movements, but its extent appears limited to a few tens or hundreds of kilometres (Mosnier et al. 2010). The core of its distribution remains in the SLE year-round, but an unknown and likely variable proportion of the population moves eastward each fall to winter in the western Gulf of St. Lawrence (Fig. 1). While immigration from other populations might have been notable a century ago (Vladykov 1944), the SLE beluga population now has the lowest haplotype diversity of all beluga populations and shares none with other populations (Postma 2017; Skovring et al. 2019). Abstract