Bimodal vertical distribution of right whales Eubalaena glacialis in the Gulf of St. Lawrence

ABSTRACT: Critically endangered North Atlantic right whales Eubalaena glacialis have recently shifted their summer distribution from the Bay of Fundy to the Gulf of St. Lawrence (GSL), Canada. Entanglement in fishing gear and vessel strikes remain the main lethal threats. Foraging on deep aggregations of Calanus prey in the Bay of Fundy involves stereotyped deep ‘flat-bottom’ (U-shaped) dives, while foraging on sub-surface Calanus aggregations on the winter feeding grounds of Cape Cod Bay involves surface feeding. To explore North Atlantic right whale feeding behaviour in the GSL, 5 acoustic and biologging tags (DTAGs) were deployed using suction cups in 2019 and 2020. One whale knocked off the tag after 14 min. Diving behaviour of the other 4 whales with 2.0 to 4.7 h of data was mostly split between flat-bottom foraging dives at, or very close to, the sea floor, and near-surface activities, including logging, respirations, and potentially also sleeping. This biphasic vertical distribution not only places the whales at risk of being hit by vessels, but it may also put them at risk of coming into contact with groundlines used in various fishing industries in the GSL. Although additional research is needed as this limited dataset was restricted to hours of daylight, these results provide new information about right whale behaviour in the GSL that can help inform management actions to reduce human impacts on this endangered species.