Geographic Variation in Diving Behaviour and Skin Isotope Ratios of Northern Bottlenose Whales, <i>Hyperoodon ampullatus</i>

ABSTRACT Geographic variation in the diving behaviour of oceanic mammals is a major component of their biodiversity with far‐reaching relevance for ecology and conservation. Here we compared high‐resolution multi‐sensor tag data from northern bottlenose whales in Jan Mayen, Norway ( n = 15, 127.2 h) and the Gully, Scotian Shelf, Canada ( n = 6, 45.8 h) to compare diving and foraging behaviours. K ‐means clustering identified short‐shallow and long‐deep dive types in both locations but showed a propensity for mid‐depth dives in Jan Mayen. Foraging dives (defined by high roll variance corroborated by active clicking) included long‐deep dives (Jan Mayen = 967 ± 394 m SD, n = 26; Gully = 1247 ± 411 m, n = 14) but also these mid‐depth dives (537 ± 135 m, n = 105). Time budgets varied substantially between locations with whales in the Gully spending 15% less time foraging ( Z = 2.1, p = 0.03) and twice as much time near‐surface resting ( Z = −3.8, p &lt; 0.001). Movement parameters further showed enigmatic gyrations during dives, more common in Jan Mayen. Skin biopsy stable isotopes revealed small regional differences, likely reflecting both diet and ecoregion (Jan Mayen n = 18: δ 15 N 15.03‰ ± 0.35‰, Gully n = 41: δ 15 N 15.41‰ ± 0.44‰). These population differences suggest unequal susceptibility to stressors and unequal likelihood of detection, with consequences for population management and abundance estimation.