Narwhals: Adapting to the cold
What are Narwhals?
Narwhals are warm blooded air breathing marine vertebrates belonging to the cetacean group of whales. Narwhals are typically found around the arctic circle and around north-east Canada in the northern hemisphere. They are not found in the southern hemisphere. The arctic environment can be a very dangerous place for animals to live with ice completely covering the sea in winter months, extremely low temperatures, generally between -1 and -3 degrees Celsius, and food often being scarcely available due to the “pack ice” covering large percentages of the ocean in winter months.
What is pack ice?
Icebergs form from areas ice sheets and glaciers such as Greenland in the arctic. The ice sheets formed from Greenland eventually grow and reach the coasts, due to snow accumulation, and can spread over thousands of square kilometres of ocean as they are less dense than seawater. However, unlike glaciers, Pack ice is formed by the freezing of seawater itself. This takes place in autumn as the surface of the water is cooled to -1.8 degrees Celsius, the freezing point of seawater (eicken 1992). This results in ice crystals being formed and they aggregate into grease ice and eventually form ice pancakes, 5-10cm thick, as more ice coagulates to the growing sea ice patches.
How do Narwhals survive this harsh environment?
Narwhals have developed many adaptations that allow them to thrive in the arctic environment. While many whales migrate south during the autumn months, Thousands of Narwhals migrate north towards the rapidly cooling temperatures and ice. Narwhals can do this as they possess many adaptations that allow them not only to survive but to thrive in the harsh conditions of the arctic seas.
Keeping warm: adaptations allowing the Narwhals to maintain body temperature
One of the Narwhals major adaptations is they have a very low surface area to volume ratio enabling them to stay warm by retaining more heat generated from metabolism. Another major adaptation of the Narwhal is their thick layer of blubber. Blubber contributes to 40% of the Narwhals body mass and provides the Narwhals with many benefits, not just staying warm. Firstly, the blubber provides the Narwhals with an excellent source of insulation allowing them to remain in freezing waters year-round without any risk of hypothermia. Blubber also provides the Narwhals a place to store fat or energy when feeding is plentiful, this provides the Narwhals with almost a safety blanket for when prey is scarce as they can draw energy from their fat reserves in the blubber. Finally, the blubber also provides buoyancy for Narwhals as the fat is less dense than the surrounding seawater.
The counter current heat exchange system plays a vital role in maintaining the body temperature of Narwhals. Like other wales and even penguins found in cold environments the counter current system is found in the flippers of Narwhals. The counter current system is made up of a close arrangement of arteries entering the flippers and veins leaving them. This allows blood coming into the flippers, in the arteries, to be cooled down by the blood leaving the flippers in the veins. This allows the Narwhals to lose a lot less heat as the blood entering the flippers is cooler. This means that significantly less heat is lost through the high surface area to volume ratio of the flippers and allows the Narwhals to maintain its body temperature more effectively its main body.
As Narwhals can dive to over 1500 metres and stay submerged for as long as 25 minutes it is important that they possess adaptations that allow them to dive deep and for long periods of time. The lungs of the Narwhals are collapsed before diving to incredible depths. This prevents any air that has been retained from entering the blood due to the immense pressure of the deep sea and then coming out again as the Narwhal reaches the surface. When diving Narwhals also considerably slow down their heart rate only allowing blood to reach vital organs and organs used to swim and catch prey. This allows the Narwhals to dive for longer periods of time as oxygenated blood is not being used where it isn’t needed.
Large amounts of myoglobin are found in the Narwhals blood. Like haemoglobin, myoglobin is an oxygen carrying molecule found in the blood. Having large amounts of myoglobin is important for diving as, unlike haemoglobin, it retains oxygen for longer periods of time allowing to blood to be oxygenated for longer. The large concentration of myoglobin, along with the slow heart rate, allows the Narwhal to dive for longer periods of time.
Narwhals have a very streamlined body that enables them to move through the water with little drag. This is important as an adaptation for diving as it allows the Narwhal to move faster through the water and to dive to deeper.
Threats to the Narwhals
As temperatures in the arctic are getting warmer each year the threat of Narwhals losing a suitable habitat is very sever. The Narwhals often depend on pack ice to provide a shield from large oceanic predators such as Orca. As the temperatures increase each year less pack ice is being formed and Narwhals are losing their protection, becoming more vulnerable. Another threat of the melting ice is that it opens more shipping lanes. The noise from industrial sized ships can cause the Narwhals to become stressed out and often mask their communication. This can cause a big threat to Narwhal populations as their communications will become masked and the melting ice bring a large increase in threat from predators.
Are the Narwhals suited to live in the arctic environment?
Narwhals possess many adaptations that allow them to survive the freezing temperatures of the arctic seas such as blubber and counter current heat exchange systems. Narwhals also possess diving adaptations allowing them to effectively dive in search of prey in the arctic. Due to these characteristics Narwhals are perfectly adapted to not just survive but thrive in the arctic conditions. However, as a result of increasing sea temperatures in the arctic every year, Narwhals are becoming increasingly threatened and may not be able to survive in the arctic for much longer.