North Atlantic right whale Eubalaena glacialis summer habitat in the southern Gulf of St. Lawrence, Canada: 2017-2019

The distribution of North Atlantic right whales (hereafter ‘right whales’) has shifted since ~2010, as exemplified by the decreased use of several habitats in the Gulf of Maine, lower Bay of Fundy, and Scotian Shelf, and increased occupancy of the southern Gulf of St. Lawrence (sGSL). The goal of this study was to characterize right whale feeding habitat in the sGSL region. We conducted opportunistic oceanographic sampling in the presence and absence of right whales in July and August over 3 yr (2017-2019). Each oceanographic station was typically comprised of a depth-integrated ring net tow and 2 vertical profiles with a conductivity-temperature-depth instrument and optical plankton counter. Of the calanoid copepod taxa, small copepods (e.g. Centropages spp., Pseudocalanus spp.) were numerically dominant at all stations where data were available, but Calanus finmarchicus was also abundant, while C. hyperboreus comprised most of the biomass. Net-derived abundance of late-stage C. hyperboreus and total biomass were significantly greater at stations where right whales were detected. Logistic regression analysis suggested that a higher probability of right whale detection was associated with a thicker bottom mixed layer and abundant patches of late-stage C. hyperboreus near the seafloor. These results offer insights into the vertical distribution and quantity of prey, the quality of the sGSL as a right whale foraging habitat, and the associated implications for right whale recovery.