Harbor Porpoise and Beluga Whale Habitat Use in the Saguenay‐St. Lawrence Marine Park (Canada) Revealed by a Combination of Visual and Acoustic Survey

Abstract

Studying habitat use of cetaceans that spend most of their lives underwater poses challenges, prompting the use of complementary methods. Non‐invasive methods, land‐based surveys (LBS) and passive acoustic monitoring (PAM), were used to characterize occurrence patterns of beluga whales, harbor porpoises, and vessels in the Saguenay–St. Lawrence Marine Park. Between 2020 and 2023, LBS totaled 512 h, while PAM recorded 1591 h in 2023, with 78 h concurrent. LBS results indicate a high occurrence of porpoises and whales (43.3%) and vessels (76.2%), and the presence of calves for both cetacean species. PAM indicates regular use of the area with higher occurrence during periods of reduced vessel traffic (e.g., 2020 for belugas and nighttime for both). During concurrent periods, PAM detections of belugas and porpoises were higher (2.8 and 1.5 times respectively). However, PAM performance was constrained for belugas as their communication band was susceptible to vessel masking. While LBS were limited by weather, they provided supplementary data including detection range, group composition, relative abundance and activity. Combined, the methods improved detection and offset individual limitations. Results support including this portion of the estuary within the beluga critical habitat while highlighting its importance for harbor porpoise foraging and mother‐calf pairs.

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