Dive behavior and estimated energy expenditure of foraging humpback whales in southeast Alaska

Abstract

The ventilatory and dive behaviors of humpback whales were studied during July–September 1982–1984 in the area of Frederick Sound, Alaska. Oxygen utilization and energy expenditure were estimated based upon observed blow rates and calculated tidal volume during foraging at identified depths between 0 and 120 m. Duration of dive, duration of surfacing, and number of blows per surfacing were all strongly correlated with depth of dive. Dives tended to be short (57.4% were less than 2.8 min in duration) and shallow (84.6% were to depths of less than 60 m). Humpback whales dived and returned to the surface directly, which allowed for calculation of the time spent at depth in different diving situations. The percent of time spent at the surface tended to increase with increasing depth of dive and exhibited a marked increase at depths surpassing 60 m. The lowest oxygen utilization rate was found during dives 41–60 m in depth. Oxygen utilization per ventilation–dive cycle was strongly and positively correlated with depth of dive. It is postulated that dives to depths of 41–60 m (4–6 min in duration) represent the aerobic limit of humpback whales. Dives exceeding these limits result in anaerobic metabolism and, consequently, an inefficient use of time and energy resources.