Deep Diving in Wild, Free-Ranging Beluga Whales, Delphinapterus leucas

Abstract

Three adult female beluga whales, Delphinapterus leucas, were captured during summer in the Canadian high Arctic and equipped with satellite-linked radio transmitters that measured and recorded ambient pressure every 20 s. Diving behaviour was divisible into three distinct categories: (1) near-surface, (2) "spike" dives to 20–150 m depth, and (3) prolonged, flat-bottomed dives to a maximum depth of 350 m. The duration of these prolonged dives was 9.3–13.7 min, but the upper bound is known to be underestimated. Average descent rates varied between dives in the range 1.43–2.20 m/s and ascent rates between 1.23 and 1.84 m/s. Within periods of 20 s duration, maximum descent and ascent rates were 2.55 and 2.35 m/s, respectively. After most prolonged dives the rate of ascent declined progressively as the surface was approached, particularly in the final 100 m. Such dives were usually to, or near to, the seabed and were probably for foraging. Up to 42% of an animal's time could be spent at depths of 8 m or more.