Seasonal variation in distribution and habitat use of St. Lawrence Estuary Beluga ‪(Delphinapterus leucas)‬ estimated from systematic photographic and visual line-transect aerial surveys

Abstract

Observations from 64 systematic photographic and visual aerial surveys conducted during the summers of 1990 – 2022, and 34 visual surveys conducted in fall, winter and spring of 2012 – 2023 were used to update and quantify the seasonal distribution of St. Lawrence Estuary (SLE) beluga, and to identify their areas of concentration. Kernel density analyses indicate that a large portion of the population (43 – 55%) is present year-round between Kamouraska/La Malbaie and Rimouski/Colombier. A seasonal shift in distribution is observed during the fall and winter, with an easterly movement from the Upper SLE to the Lower SLE and northwestern Gulf of St. Lawrence (nwGSL), followed by a reversed, westerly movement in the spring. In summer, the 50% and 95% kernel contours show that beluga occupy the entire SLE between Battures aux Loups Marins and Rimouski/Colombier. However, an increased use of the Lower SLE habitats between Saint-Simon/Les Escoumins and Rimouski/Forestville has been observed in recent year (2014 – 2022) compared to the earlier period (1990 – 2009). In the fall, distribution generally extends from La Malbaie in the Upper SLE, to the nwGSL, with most of the population occupying the Lower SLE between the mouth of the Saguenay River and Rimouski/Colombier. During winter, only a small portion (5%) of the population appears to remain in the Upper SLE; most of the population (63% on average) occupy the Lower SLE, with approximately one-third (32%) moving into the nwGSL. The beluga range is at its smallest during spring, although the number of spring surveys is small. High concentrations of beluga were observed in the most upstream part of the Upper SLE. Beluga are present in the Saguenay River year-round, mainly downstream of Ile Saint-Louis/Baie-Sainte-Marguerite in summer, and downstream of Cap de la Boule in fall, winter, and spring. Core areas of use (50% kernel) were identified throughout a wide extent of the SLE and nwGSL, and were characterized by a high degree of interconnection (75% kernel). Identifying the vital functions associated with these core areas might help mitigate potential threats, and improve our understanding of the drivers influencing the seasonal movements and distribution of this population.