Energy & metabolism of cetaceans: kcal/day, expenditure, intake

The most efficient biological machines

A blue whale consumes 600,000 kcal a day, the equivalent of 240 humans. Relative to its weight, though, its metabolism is remarkably economical, one of the consequences of the hydrodynamic efficiency of cetaceans. This comparator presents documented daily energy requirements and how they are divided between hunting, migration, breeding and resting.

Basal metabolism: being large to stay warm

The basal metabolic rate (BMR) of cetaceans follows Kleiber‘s law: it rises as mass to the power 0.75. A 100-tonne blue whale burns ~3 million kcal/day; a 200 kg common bottlenose dolphin, ~10,000 kcal/day. This outlay of energy is imposed by endothermy in a cold medium: water carries heat away 25 times faster than air.

Cetaceans answer it with fat (blubber) reaching 50% of body mass in rorquals and the bowhead whale, and with the rete mirabile, networks of small vessels working as a thermal counter-current that limit losses at the fins. The grey whale fasts for nearly 4 months during its migration from the Arctic to Baja California, losing up to 30% of its body mass.

Also worth exploring

Metabolism governs survival: see hydrodynamics, diets, diving physiology and swimming performance.