Modeling blue whale (Balaenoptera musculus) habitat use and relative abundance; conservation implications in the Gulf of St-Lawrence, Canada

The Gulf of St. Lawrence (GSL), Canada, is an important feeding and socializing ground for endangered blue whales (Balaenoptera musculus). This region is frequented by blue whales throughout the year, predominantly during the months of August and September, and is one of the few places in the world where they can be found in close proximity to the coast. Consequently, they are increasingly susceptible to anthropogenic impacts due to coastal development, recreational boating, shipping traffic, and an expanding whale-watching industry. Until now, the distribution and habitat use of blue whales in this region was relatively unknown, limiting the effectiveness of conservation initiatives that depend on spatiotemporal distribution information. Nine years of non-systematic survey data were used to investigate blue whale distribution and relative abundance in relation to environmental variables including sea bed depth and slope, distance to shore, sea surface temperature (SST), distance to a thermal front, and chlorophyll-a (chl-a) concentration. The relative abundance of blue whales was modeled with generalized additive models and model selection was based on generalized cross-validation scores. Blue whales were strongly associated with bathymetric features, time-lagged chl-a, SST, and proximity to thermal fronts, suggesting that they prefer features that not only drive biological activity, but also those that aggregate prey. The final model identified the north shore of the lower St. Lawrence Estuary and the easternmost tip of the Gaspé Peninsula as important habitat for blue whales. This study provides valuable information for the development of a conservation management plan for this species in the GSL and presents a scientific foundation for the implementation of the ‘Recovery Strategy for the Blue Whale, Northwest Atlantic Population, in Canada’ under the Canadian Species at Risk Act.

Key words: Blue whale, distribution, Gulf of St. Lawrence, habitat model, relative abundance, thermal front