Deep Diving
All whales are mammals that need air to be able to circulate oxygen throughout their bodies. They come to the surface to breathe in through their blowhole that is located at the top of the head. The amount of time a whale can hold its breath underwater ranges from species to species with 60 minutes being average; however, in 2014 the Curvier beaked whale broke records with a dive lasting 2 hours and 17 minutes. Curvier beaked whales have more extreme adaptations that allow them to dive longer than any other mammal. They have more lean mass than other whales and their muscle fibers have a larger diameter with increased levels of myoglobin and a decreased density of mitochondria. Their unique muscle fibers are thought to protect them against ischemia, or lack of oxygen, that may occur during longer dives. They also do not seem to suffer injury when blood flow is restored to their tissue or organs after a period of lacking oxygen. Their muscles are capable of functioning anaerobically for prolonged periods of time thanks to some of the most efficient acid buffering capabilities amongst all whales. Furthermore, they have a low metabolic rate and are capable of storing more oxygen than other whales, with increased levels of hemoglobin. When they dive a series of adaptations are triggered like decreased heart rate, a delay in digestion, reduced function of the kidney and liver, and vasoconstriction.(Quick 2020) All these factors help the Curvier beaked whale hold the record for the longest diving mammal.
Extreme Divers
General Adaptation
All whales have made some amazing adaptations to life underwater. Though not all can dive recording breaking lengths, all whales can hold their breath a lot longer than most mammals. They have a large blood volume with 3 to 4 times the amount of milliliters of blood per kilogram of body mass than other mammals. Their blood contains about 60% hemoglobin, while a human’s contains about 30%, this allows them to store more oxygen throughout their bodies. The concentration of the protein myoglobin is around 30% higher than other mammals, allowing them to also store oxygen directly in their muscles. Whales also have control over their heart rate and can reduce it to about half its normal output while diving. Slowing of the heart means less blood flow to certain muscles that have their own oxygen supply and to non essential organs.
Whales are also a lot more efficient at gas exchange than humans. They take conscious, thoughtful breaths that begin with an exhale, releasing the built up CO2, then taking a deep breath in. This allows them to exchange between 80-90% of the air in their lungs. Humans on the other hand breathe subconsciously inhaling before exhaling and only exchange about 10-15% of the air in our lungs. Having huge lungs is of course also quite helpful. Blue whales have a 5,000 L lung capacity and can exhale with such great force that the speed of the air being pushed out can reach 600 km/h. The large surface area helps gas exchange occur more rapidly within the alveoli. However, it turns out whale lungs are not quite as massive as one might think. A whale's lungs only take up about 3% of their body size while a human's take up about 7%, so their main form of oxygen storage occurs in the blood and muscles. (Berry 2012)
Withstanding the Pressure
The pressure experienced underwater, known as hydrostatic pressure, increases with depth. At 20 m the pressure is 3 ATM, which is three times the normal atmospheric pressure we experience. When you reach the deepest known point of the ocean, the Mariana Trench, the pressure is over 1000 ATM. The deepest dive that’s been recorded comes again from the record holding Cuvier's beaked whale with a depth of 2,992 m, though sperm whales are also expert divers that have been known to go past the 2,000 m mark. At this depth the pressure is immense and any gas filled space in the body becomes dangerous. Luckily whales have a venous plexus, which is a structure that lines the middle ear cavity and expands at greater depths, removing the air space. Furthermore, whales have vasculature, which is a structure thought to maintain an equilibrium air pressure within the pterygoid sinus of the head and tympanic cavity of the ear. (Ponganis 2006) However, the best trick up their fluke may be their lung adaptations. Not only do their smaller collapsible lungs help avoid buoyancy issues, they also protect them from nitrogen narcosis. As the whale descends deeper below the surface their flexible rib cage compresses the lungs and causes them to collapse,forcing gas out of the alveoli where gas exchange occurs, and into cavities that are reinforced by cartilage. This is extremely important since 78% of air is nitrogen and gas becomes more soluble with increased pressure it prevents large amounts of nitrogen from dissolving into the bloodstream. When the whales resurface the pressure decreases making compounds like nitrogen and carbon dioxide less soluble. If the whales surface too quickly bubbles of these compounds could start to occur and cause damage like paralysis or death. (Blix, Walloe, Messelt 2013)
Though whales have mechanisms in place to avoid decompression sickness there have still been many instances of mass strandings where the dead whales have been found with embolisms caused by nitrogen bubbles. It’s thought that a rapid increase in CO2, through a burst of activity, may initiate the growth of these bubbles. When N2 becomes supersaturated in the blood from surfacing too quickly the gas escapes the liquid phase with the already forming carbon dioxide bubble. More research needs to be done on this topic, but it is likely that these animals all quickly surfaced in order to escape disturbingly loud noise made by military sonar. (Fahlman 2014) With unusually high numbers of strandings recorded throughout the years worldwide it’s imperative to understand the effect sonar has on cetaceans.
