Adaptations For An Aquatic Environment
- Killer whales are among the fastest swimming marine mammals.
- Killer whales can swim at speeds of up to 45 kph (28 mph), but probably only for a few seconds at a time.
- Killer whales usually cruise at much slower speeds, less than 13 kph (8 mph). They can cruise slowly for long periods of time.
- Killer whales are agile and maneuverable in the water.
Killer whales are amazingly agile.
- When swimming near the surface, a killer whale usually stays below water for 30 seconds or less.
- Swimming energetics.
- Blubber smooths the contour of a killer whale and contributes to its characteristic fusiform shape, which is quite energy efficient for swimming. Compared to other body shapes, this body shape creates less drag (the opposing force an object generates as it travels through water).
- Killer whales and many other toothed whales sometimes "porpoise" at the surface: they swim fast enough to break free of the water, soaring briefly up and out and then back under in one continuous movement, which they generally repeat. Porpoising uses less energy than swimming fast at the surface.
- Wave-riding also saves energy. Killer whales and many other toothed whales sometimes ride ocean swells or a boat’s bow wave or stern wake. Riding a wave or a wake, a killer whale can go almost twice as fast using the same energy cost.
- A killer whale calf swims close to its mother and can be carried in the mother's "slip stream," a type of hydrodynamic wake that develops as the mother swims. This helps the calf swim with less energy and enables the mother and calf to keep up with the pod.
- Dive depth.
- Although not generally deep divers, foraging killer whales can dive to at least 100 m (328 ft.) or more.
- The deepest dive known for a killer whale, performed under experimental conditions, was 259 m (850 ft.)
The deepest dive known for a killer whale was performed
under experimental conditions and was 259 m (850 ft.)
- A study of southern resident killer whales in the North Pacific recorded an animal diving up to 264m (866 ft.)
- Researchers believe that at least some killer whales can dive to at least 350 m (1,148 ft.) Adult males killer whales dive more often and deeper than adult females.
- Dive duration.
- In the eastern North Pacific, resident killer whales usually make three or four 15-second dives and then a dive that lasts about 3 to 4 minutes, repeating this pattern.
- Average dive duration for resident killer whales is approximately 2.3 minutes.
- Transient killer whales have been recorded diving for up to 11.2 minutes. Transient whales in the eastern North Pacific often stay submerged for more than 5 minutes and occasionally for more than 15 minutes in a single dive.
- All marine mammals have physiological responses for diving. These responses enable a killer whale to conserve oxygen while under water.
- Killer whales, like other mammals, have a slower heart rate while diving. One study indicated that a killer whale's heart rate at the surface of the water is approximately 60 beats per minute, but while diving the rate fell to 30 beats per minute.
- When diving, blood is shunted away from tissues tolerant of low oxygen levels toward the heart, lungs, and brain, where oxygen is needed most.
- Certain protein molecules—hemoglobin and myoglobin—store oxygen in body tissues. Hemoglobin occurs in red blood cells. Marine mammals have a higher blood volume and more hemoglobin than comparatively sized land mammals. Myoglobin occurs in muscle tissue. The muscle of whales has a higher myoglobin concentration than the muscle of land mammals.
- Both humans and cetaceans can experience negative physiological impacts from diving.
- As pressure increases with depth, the amount of gas that goes into solution in a diver’s blood and body tissues also increases. At about two atmospheres of pressure (about 60 ft.), tissues are saturated. If a human diver returns to the surface too quickly, the gases, especially nitrogen, come out of solution and form bubbles in the muscles and blood. This painful and sometimes fatal condition is called “the bends.”
- The “bends” is most common in scuba divers, but human breath-hold divers can also get the bends from deep diving. Human breath-hold divers dive on fully inflated lungs. Under pressure, a human’s bronchioles collapse. Lung air is forced into the alveoli: the numerous tiny areas of the lungs where gas exchange takes place. Here gases are absorbed under pressure.
- Unlike human scuba divers, a whale doesn’t breathe air under pressure. It inhales only at the surface and exhales just before diving. Furthermore, in diving mammals, the alveoli collapse at about 3 atmospheres of pressure, forcing air into the rigid peripheral airways where gases are not exchanged.
- A killer whale breathes through a single blowhole on top of its head.
- The visible spout of water that rises from a killer whale’s blowhole is not coming from the lungs, which (like ours) do not tolerate water.
- Water that is on top of the blowhole when the powerful exhale begins is forced up with the exhaled respiratory gases.
- Especially in cool air, a mist may form; it is water vapor condensing as the respiratory gases expand in the open air.
When a whale breathes, the visible blow that appears to be
water is really water vapor condensing in the respiratory
gases as they expand in the cooler ambient air.
- In comparison to a human, a killer whale can hold its breath longer and exchange more lung air with each breath.
- The resting respiratory rate of killer whales at SeaWorld is about three to seven breaths every five minutes.
- Like all mammals, killer whales are warm-blooded. A killer whale’s core body temperature is about 36.4º to 38ºC (97.5º–100.4ºF)—close to that of a human. Living in the sea poses a particular challenge to marine mammals, because water conducts heat about 25 times faster than same-temperature air.
- The large size of a killer whale helps minimize heat loss.
- In general, as an animal increases in size, its surface area decreases relative to volume. A whale's fusiform body shape and reduced limb size further decrease this surface-to-volume ratio.
- A low surface-to-volume ratio helps an animal retain body heat: the large body core produces metabolic heat. Only through the relatively smaller surface area exposed to the external environment (the skin) is that heat lost.
- Just under a killer whale’s skin lies a thick layer of blubber, composed of fat cells and fibrous connective tissue. Blubber helps insulate a whale from heat loss. There is a heat gradient from the body core, through the blubber, to the skin.
- In general, killer whales have a higher metabolic rate than land mammals of similar size. This increased metabolism generates a great deal of body heat.
- Mammals lose body heat when they exhale. Because they breathe less frequently than land mammals, killer whales conserve a considerable amount of heat.
- A killer whale’s circulatory system helps maintain body temperature; it adjusts to conserve or dissipate body heat.
- Some arteries of the flippers, flukes, and dorsal fin are surrounded by veins. Thus, some heat from the blood traveling through arteries is transferred to venous blood rather than the environment. This phenomenon is called countercurrent heat exchange.
- When a killer whale dives, circulation decreases at the skin, shunting blood to the insulated body core.
- During prolonged exercise or in warm water a whale may need to dissipate body heat. In this case, circulation increases near the surface of the flippers, flukes, and dorsal fin. Excess heat is shed to the external environment.
- In male killer whales, a countercurrent heat exchange system cools arterial blood that is flowing to the testes. Another countercurrent heat exchange system regulates the temperature of a developing fetus in gestating females.
A countercurrent heat exchange system exists in
the flippers, flukes, and dorsal fin of a killer whale.
- Several species of cetaceans, including the bottlenose dolphin and beluga whales, have been shown to engage in unihemispheric slow wave sleep (USWS) during which one half of the brain goes into a sleep state, while the other maintains visual and auditory awareness of the environment and allows the animal to resurface for respiration. This ability may help to avoid predators as well as maintain visual contact with cohorts/offspring. Dolphins have one eye closed during USWS.
- Observers note that killer whales typically rest, motionless, at various times throughout the day and night for short periods of time or for as long as eight hours straight. While resting, killer whales may swim slowly or make a series of three to seven short dives of less than a minute before making a long dive for up to three minutes. Resident killer whales often rest in a group, lined up alongside each other.
- When sleep researchers studied two newborn killer whale calves and their mothers at SeaWorld San Diego, they discovered that the mothers and calves didn't appear to sleep or rest at all for the first month of a calf's life. Over the next several months, the whales gradually increased the amount of time they spent resting to normal adult levels. Four bottlenose dolphin calf-mother pairs showed the same sleep-behavior pattern. Staying active and responsive after birth may be an adaptation for avoiding predators and maintaining body temperature while the calf builds up a layer of blubber.