Mesoscale habitat use by St. Lawrence estuary beluga over the annual cycle from an acoustic recording network.

The spatial-temporal distribution pattern of St. Lawrence Estuary (SLE) beluga is examined with a passive acoustic monitoring network of 13 stations from June 2018 to October 2021. A beluga calling index, correlated with beluga density, is used as a proxy for habitat use by the population at weekly, monthly, and yearly scales. The seasonal pattern along SLE upstream-downstream axis was repeated annually. In summer, beluga habitat was confined to a 150 km segment of the SLE, with higher occurrences in its ∼20 km central portion, including the head of the Laurentian Channel and Saguenay Fjord mouth. During fall, the distribution gradually shifted to the downstream portion of the SLE and into the Northwestern Gulf, leaving low to no occurrences upstream in winter, until the spring return, characterized by the highest upstream occurrences. Occurrences off Ste. Marguerite Bay, 25 km upstream in Saguenay Fjord, were essentially from June to October. This multi-year continuous habitat use pattern provides a baseline for year-round SLE beluga distribution dynamics for assessing and mitigating anthropogenic threats to this endangered population, such as shipping noise. It also provides insights for optimizing the assessments of population size from aerial line transect surveys.