How do whales go months without eating?

In mammals, an organism deprived of food first reacts by tapping into its reserves of glucose (sugar) called “glycogen”. But this strategy is as effective as it is ephemeral: the energy contained in the glucose is exhausted in just a few days. The body then resorts to other energy reserves that break down more slowly: lipids and proteins.

Fasting allows the humpback to dedicate all of its energy to its marathon migration and its reproductive activities. While the warm Caribbean waters are ideal for breeding or calving, the food they contain is not as rich as the krill or capelin found in the St. Lawrence. Feeding in this region is therefore not worth the effort for the humpback: the energy expended foraging would be greater than the yield of its intake!

After giving birth, females continue their fast. This is believed to allow them to prioritize nursing their calf, thereby allowing the latter to grow very quickly in a short period.  Furthermore, fasting is thought to be conducive to converting their fat reserves into fats more easily digested by their offspring.

Thanks to a hormone called leptin, it would seem that the answer is “No”! This element plays a key role in species that fast for long periods: it acts as an appetite suppressant and helps break down fat. In 2017, researchers reportedly detected leptin in one of the deepest layers of blubber of bowhead whales and belugas. They observed the highest levels of leptin in fall, when the members of these two Arctic species were getting ready to migrate, and therefore to fast. Conversely, leptin levels were very low in those times of the year that the animals actively fed. Researchers even believe that this hormone might even be a signal to the whales that it is time to migrate. Even if this mechanism has yet to be demonstrated in humpbacks, it is probably safe to say that they, too, experience this hormonal boost!