How do whales keep warm in frigid waters?

To understand the functions of these particular adaptations, we must first look at how cetacean metabolism works. Thermoregulation is the set of processes that allow an organism to maintain a constant body temperature. In whales, as in humans, this temperature is around 37℃. All mammals are endothermic organisms, meaning they regulate their body temperature through metabolic processes that allow them to produce, retain, or release heat. Thermoregulation is based on this balance between heat gains and losses.

The metabolic pathway for producing internal heat, thermogenesis, makes use of the energy released by muscular contractions (during movement, for example) and from the metabolic activities of the organs to maintain a constant body temperature.

However, energy spent warming the body to compensate for heat loss is energy that cannot be dedicated to other tasks such as swimming, gestation or parental care. These energy expenditures can be life-threatening if an individual or its offspring is not well suited to its environment. In whales, the challenge is even greater since water, with a heat-conducting capacity 25 times higher than air, is a much more efficient thermal conductor! In marine mammals, body heat therefore diffuses much more easily toward the water, which is often substantially colder than their body temperature. This is why they had to develop numerous adaptations to minimize excessive heat loss.

However, cetaceans that live in cold waters year-round (e.g. belugas) do not use their blubber in exactly the same way. They use it more as a genuine protection against freezing temperatures. As they do not fast for any prolonged period, these northern whales do not need to draw from their fat reserves.

The adipose cells that compose blubber fill up with fatty material as a function of the body’s energy needs and food availability. The thicker the layer of blubber, the more the body can tolerate low temperatures without having to expend additional energy to stay warm.

In addition to their coat of blubber, cetaceans have in their extremities a complex labyrinth of arteries and veins called the rete mirabile that enables them to balance the heat distribution throughout their bodies via countercurrent heat exchanges (article in French). If this were not the case, whales’ pectoral, dorsal and caudal fins – the only parts of their body that do not have insulating blubber – would generate significant heat loss.

Under the coat of blubber there is also a tangle of bridges connecting arteries and veins to keep the blood warm. Furthermore, some cetaceans have few or no valves along their veins to regulate blood flow. This absence facilitates blood circulation and allows blood to be rapidly channelled to the organs whenever necessary.

For whales, energy is an invaluable resource for thriving in such an inhospitable environment. The true key to their success therefore lies in conserving this precious energy by optimizing their energy expenditures.