Right whale, wrong place: modeling endangered species' distribution to identify critical areas in the Estuary and Gulf of St. Lawrence

The North Atlantic right whale Eubalaena glacialis (NARW), once abundant across the North Atlantic, is now primarily found along the eastern USA and Atlantic Canada, with an estimated population of only 372 individuals. Over the past decade, around 40% of the population has shifted from traditional summer feeding grounds in the Gulf of Maine and southeastern Canada to the more northerly Gulf of St. Lawrence (GSL). Following high mortality events in this region in 2017 and 2019, Fisheries and Oceans Canada launched a monitoring program to detect whales, trigger protective management actions, and gather distribution data. Using observation data collected between August 2017 and November 2022, combined with environmental variables, we developed generalized additive mixed models to identify factors influencing NARW distribution in the GSL and to predict their likelihood of occurrence. Models were trained with 2017-2020 data, considering 2 mo periods, half-seasons, or the entire season (global model). Period-specific models outperformed the global model when tested on the training data set (2017-2020), while the global model showed higher accuracy when tested against independent 2021-2022 observations. The best model identified key factors influencing NARW occurrence, including depth, sea surface temperature, salinity, and chlorophyll a. Additional variables, such as sea level anomalies, thermal fronts, current speed, and bottom topography, were likely included due to their role in prey aggregation. Predicted probability maps highlight important areas in the GSL and provide insights into seasonal distribution patterns. These maps will contribute to the ongoing critical habitat designation process for the species in eastern Canadian waters and will inform management strategies to mitigate risks from shipping and fishing activities to this endangered species.