Foraging habitat associations of North Atlantic right whales (Eubalaena glacialis) measured using ocean gliders

Kimberley Davies1,2, Hansen Johnson2,3, Delphine Durette-Morin2, Mark Baumgartner3, Richard F. Davis4, Adam Comeau5, Frederick Gilbert Whoriskey6 and Christopher T. Taggart2, (1)University of New Brunswick, Dept. of Biological Sciences, Saint John, NB, Canada, (2)Dalhousie University, Oceanography Department, Halifax, NS, Canada, (3)Woods Hole Oceanographic Institution, Biology Department, Woods Hole, MA, United States, (4)Ocean Frontiers Institute, Halifax, NS, Canada, (5)Coastal Environmental, Observation, Technology and Research (CEOTR) group, Halifax, NS, Canada, (6)Ocean Tracking Network, Halifax, NS, Canada
North Atlantic right whales (Eubalaena glacialis) migrate seasonally into several temperate North Atlantic habitats to feed on dense aggregations of planktonic copepods. Recently a previously unknown foraging area was discovered within the Gulf of St. Lawrence (GSL), a body of water that lies several hundred kilometers north of the known right whale foraging range. Key feeding habitat characteristics, such as dominant prey species, water mass hydrography and tidal current amplitude, appear strikingly different in the GSL relative to other described habitats. This study is the first description of regional environmental associations of right whales in the newly discovered habitat. Between 2016 and 2018 profiling gliders were equipped with hydrophones and conductivity-temperature-depth sensors and deployed continuously between 2 and 6 months per year to measure physical habitat associations of right whales in the GSL. Binary multivariate regression models were applied to these data to explain right whale acoustic presence-absence as a function of variables describing water mass characteristics. Preliminary models containing the main effects of temperature, salinity and stratification were selected over a null model containing only static explanatory variables such as bathymetric depth. This demonstrates that dynamic oceanographic processes are important for explaining regional right whale occurrence. The odds of acoustically detecting a right whale each day were twenty times higher in stratified summer conditions than well-mixed conditions typical of the windy autumn period, suggesting a preference for certain seasonally-varying physical processes that affect prey energy density and availability. After accounting for the seasonal effect, right whales were ten times less likely to be detected in warm, fresh water that signifies the regional coastal current, suggesting that right whales target offshore species of copepods such as Calanus spp., as opposed to coastal species, in this habitat. This study identifies key spatiotemporal constraints on right whale occurrence and demonstrates the use of gliders as tools to study whale-habitat associations.