Fluctuations in distribution and patterns of individual range use of northern bottlenose whales

This study investigated the pattern and scale of distribution, movements and range use of the northern bottlenose whale Hyperoodon ampullatus above a submarine canyon, the Gully, off eastern Canada between 1988 and 1998. Locations and individual identification photographs were collected during encounters with whales. Whales showed a discrete distribution within the canyon associated with water depth (500 to 1500 m) and relatively steep topography. Encounter rate and distribution showed some variation between years. Changes in distribution were observed toward the north or south of the canyon, probably a consequence of changes in prey distribution. Individual whales within the canyon displaced 4 to 5 km over 24 h, with negligible further increase in displacement over time scales up to 20 d (their approximate residency period). Short-term VHF radio-tracking of 5 individuals provided an independent source of movement data, showing displacements of approximately 2 km in 1 h and 5 to 10 km in 1 d. The relative lack of movement observed for these whales supports the hypothesis that the canyon contains a profitable and localized food source. Movements of whales best fit a model of short-term residence within ranges of approximately 25 km2, although the range size of mature males was smaller than that of females and immature males. Photo-resightings were also used to investigate variation in the positions of individual whales within the Gully. Within years, individuals showed some separation of ranges associated with periods of high whale abundance, but there was no separation between different age-sex classes. Between years, mature males showed consistent spatial orientations relative to each other, suggesting preferred locations possibly related to mating opportunities