THERMOREGULATION
Narwhals have the most northerly geographic range of any mammal, almost entirely above the Arctic Circle, the northern region where the sun does not appear on Dec. 21 and does not set on June 21. According to "ECOVIEWS: Mysterious narwhals are the unicorn of Arctic Ocean," as if the surface in the Arctic seas isn’t cold enough for narwhals, radiotelemetry studies have revealed that narwhals commonly dive to ocean depths of more than 800 feet. Narwhals have been known to remain underwater for more than 15 minutes, but like any mammal, they must eventually surface to breathe.
Narwhals are able to shut down all functions that are not needed while diving. This allows them to stay warm and maximize their ability to hold their breath for extended periods of time. As a result, it protects narwhals from injury from sharp rocks, acts as a sort of bed, and serves as food and energy storage. Even in the coolest of temperatures, narwhals thermoregulate by using their energy to sustain life and to sustain a regular temperature. Through the metabolization of their food, narwhals are able to produce heat as a byproduct and maintain it to survive the extreme cold. They are known to be endothermic creatures that are capable of generating internal heat to regulate their body temperature that is independent of the atmospheric temperature. One-third of a narwhal's body weight is blubber, which serves as an insulator and a source of energy. It also works as a sort of cushion from hard or sharp surfaces and objects.
As explained in "The impact of rising sea temperatures on an Arctic top predator, the narwhal" by Chambault et al., the thick subcutaneous fat deposit (blubber) prevents excessive heat loss and functions as thermal insulation and energy reserve. Cetaceans dispose of excess heat from poorly insulated peripheral areas, such as fins and tail flukes, that are utilized as thermal windows through which heat can be exchanged via conduction and convection. By maintaining this thick blubber layer, it serves as a thermal window for dissipating excess heat. As oceanic temperatures rise, these extreme adaptations that enable polar living may serve as a liability for narwhals, especially as the ice cover becomes more unpredictable, and preferred prey move to new areas or depths. Their limited physiological flexibility also prevents them from adjusting their swimming and diving behavior to climate change via shifts in habitats and prey selections.
Figure 2. Histograms of (a) sea surface temperature and (b) sea ice concentration extracted at each narwhal location for CAA (in blue), West (in green), and East (in red) in summer.
Homeostasis
A narwhal uses counter-current circulation and blubber to maintain homeostasis. When blood flows from the core of the body to the outer parts of the body such as the pectoral fins, the blood cools because of the temperature of the water. To keep the cooled blood from going back into the body core and cooling the animal entirely, the blood vessels are organized very close to each other. This is so, blood flowing back into the body core is warmed by the blood flowing into the outer limb as it comes from the body core.
Even if securing core body temperature to avoid hypothermia is essential for all aquatic mammals, the ability to lose excess heat in connection with exercise is equally important. Bursts of high levels of exercise by narwhals that are built for slow-speed swimming may constrain their ability to remove excess heat, especially in a warming ocean (Chambault et al., 2020; Heide-Jørgensen et al., 2020).