Herd composition and behaviour of white whales (Delphinapterus leucas) in two Canadian arctic estuaries

Abstract

White whales occupy the Nastapoka River and Cunningham Inlet estuaries in northeastern Canada each summer. They arrive at the Nastapoka in late June and at Cunningham in mid-July, where numbers build to maxima of 260 and 1750, respectively. Distribution of whales in both estuaries is influenced mainly by the state of the mixed semi-diurnal tides and, to a certain extent, by river outflow and date. Few adult males appear to be present in the estuaries, the herd being composed mainly of females with calves and weaned juveniles. Limited evidence suggests that the basic social units of herds are matrilines consisting of adult nursing females accompanied by older female offspring. The age structure of the herd changes seasonally with an increasing proportion of nursing pairs. Behaviour was grouped into four activity classes. These are descriptive and are not intended to imply functions, which remain somewhat obscure. Much of the nearshore behaviour appears to be related to the processes of shedding old skin and growing of new epidermis. Strong philopatry and physiological dependence of white whales on estuaries indicate that these are important habitats which must be managed and preserved in order to conserve the species.