Killer whale formation swimming: spatial positions within a group, energetics, and interactions with a declining prey

Swimming in formation is known to provide locomotion energetic advantages; however, these potential benefits are poorly investigated in cetaceans due to the difficulties of studying groups of free-ranging whales. For cetaceans this gregarious behavior could also be influenced by bonds with the conspecifics given the strong sociality which characterizes whale populations. The use of recent technologies such as drones and the observation of a model population such as the Southern Resident killer whales (Orcinus orca), allowed for an optimal focus on whale formations in the wild. The drone-based observation of Southern Residents also allowed for the analysis of their prey chase sequences focusing on their main prey, the Chinook salmon (Oncorhynchus tshawytscha), which is becoming scarce and shrinking in size, hence representing a highly elusive prey. This scarcity of food is likely to influence group travel for killer whales, given the energetic implications of swimming in formation. My research highlighted that killer whale formations can bring energetic and social benefits and provide advantages to the various classes of individuals which characterized the Southern Resident killer whale population. Formation swimming may affect killer whale energetics when considering both whale physical characteristics and relative positioning within the group. The latter appeared to be strongly influenced by the Southern Residents’ intra-population social ties. My thesis study also highlighted differences in prey chase capabilities dictated by killer whale sexual dimorphism: the maneuvering capability of males, due to their large size, was lower than that of females at any given age.