The blue whale, the largest animal known to have ever existed, can reach lengths of over 30 meters and weigh up to 190 metric tons. As mammals, these ocean giants must periodically return to the surface to breathe air. Their immense size requires a tremendous amount of energy, which drives them to undertake deep, sustained dives into the ocean’s depths. The primary behaviors that necessitate this underwater existence are directly linked to locating and consuming their microscopic prey.
Observed Depth and Duration Metrics
Blue whales exhibit a range of diving behaviors, with the depth and duration largely determined by their activity. Foraging dives, where the whale is actively feeding, are generally deeper and longer than traveling or resting dives. In the Eastern North Pacific, for example, studies using tracking tags show that feeding dives average around 201 meters and last for about 9.8 minutes.
Typical feeding dives generally range between 10 to 20 minutes, allowing the whale to efficiently pursue prey patches before needing to resurface for air. The maximum confirmed dive duration recorded for a blue whale is approximately 15.2 minutes, which is significantly shorter than their theoretical aerobic dive limit of about 31.2 minutes. This suggests the whales prioritize energy efficiency and consistent oxygen access over maximizing time submerged.
While blue whales are not the deepest-diving cetaceans, they can descend to impressive depths when necessary. Tagging studies have recorded maximum dive depths reaching 315 meters for the common blue whale and up to 506 meters for the smaller pygmy blue whale subspecies. These deeper excursions are often linked to following krill swarms that descend lower in the water column during daylight hours.
Diving Purpose: Tracking Krill Swarms
The overwhelming purpose for the blue whale’s deep dives is to feed almost exclusively on krill, which are small, shrimp-like crustaceans. Blue whales are “lunge feeders,” a highly energetically demanding feeding strategy that involves accelerating into dense krill aggregations with their mouths open. They then engulf a massive volume of water and prey, which they filter out using baleen plates.
Because lunge feeding is costly in terms of energy expenditure, the whales must target extremely concentrated patches of krill to ensure a net energy gain. A krill patch must contain a minimum density, often measured at over 100 krill per cubic meter, to be worth the effort of a single lunge. Their massive bodies require consuming an estimated 1,120 kilograms of krill per day during feeding season.
The need to find these profitable prey patches drives the whale’s vertical movements throughout the day. Krill often exhibit diel vertical migration, moving deeper into the water column during the day to avoid visual predators and migrating toward the surface at night to feed. Blue whales track this migration, diving deeper in daylight hours to intercept the swarms and feeding in shallower waters when the krill rise toward the surface.
Targeting these deep, dense swarms allows the whale to maximize its caloric intake, which is essential for building blubber reserves needed for migration and reproduction. The dive depth is therefore a direct consequence of the krill’s distribution, with the whale only diving as deep as required to access the most concentrated food source. When disturbed by vessels, blue whales reduce their dive depth and duration, which can significantly cut into their energy intake by preventing them from reaching the optimal feeding layers.
Biological Adaptations for Extreme Dives
The ability of the blue whale to undertake prolonged, deep dives is supported by several specialized physiological mechanisms. One significant adaptation is the high concentration of myoglobin within their muscle tissues. Myoglobin functions as an oxygen storage unit, giving the muscles an independent supply of oxygen during submersion.
The whale’s cardiovascular system also features a dive response that conserves oxygen for vital organs. This response includes bradycardia, a dramatic slowing of the heart rate that can drop to as low as two beats per minute at maximum depth. Simultaneously, blood flow is rerouted away from non-essential tissues, such as the digestive tract and skin, to maintain oxygen delivery solely to the heart and brain.
The blue whale manages the effects of increasing hydrostatic pressure and nitrogen buildup by allowing its lungs to safely collapse as it descends. This mechanism forces the remaining air away from the alveoli, the tiny air sacs where gas exchange occurs, preventing excessive nitrogen from dissolving into the bloodstream. By exhaling approximately 90% of the air in their lungs before a deep dive, the whales also reduce their buoyancy, saving energy that would otherwise be spent fighting to descend.