Adaptation is the modification in the physiology, structure, development and behaviour of an organism so it can better live a certain way of life in a certain environment. The sperm whale's ancestor was a mammal, probably a wolf-like omnivore, that lived on land and eventually returned to the sea. However, it didn't become a fish but continued as a mammal, which required drastic adaptations to the animal's physiology and way of life.
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The Sperm Whale
The sperm whale is a toothed whale that can grow to 69 feet, with males much larger than females. It has undergone the same basic evolutionary adaptations to marine life as other whales: Its nostrils are now at the top of its head to make breathing easier, its forelimbs have become flippers, its hind legs have been absorbed into its body, it now has tail flukes to power it through the water. The sperm whale is found in both the Atlantic and Pacific oceans. It mostly eats squid, and many of its adaptations arose so it could more effectively pursue this favourite, deep-diving prey.
The sperm whale's huge head has two reservoirs of fluid that sit inside its skull. The upper holds the spermaceti organ, or case, a barrel-shaped structure that has a network of tissues soaked in oil. Below it is the second chamber, or junk, also filled with oil. Some scientists believe that the head helps the whale's buoyancy. The oil's density and viscosity change with the temperature, as when the whale takes in cold water through its right nasal passage. The water cools the oil, which becomes like wax, which then allows the whale to rise and fall in the water. Other people believe the oil is used to help the whale amplify sounds. Either way, this adaptation helps the whale hunt.
Water is a better conductor of sound than air, and at the depths the sperm whale visits there's very little light to see. This resulted in the development of the adaptation of echolocation. The sperm whale uses echolocation to find its family, which can be spread out over hundreds of miles, and its prey. The clicks it makes are produced by the expansion and contraction of structures in its nasal sacs. Two nasal passages come from the blowhole. One goes to the lungs, but another goes to an air sac through a valve known as the monkey muzzle. Sound is created by the air's being forced through this valve. Sound waves pass through the animal's spermaceti case and then bounce off another air sac at the back of the skull. Then the sound is redirected and broadcast through a series of acoustic lenses in the junk. The bigger the whale and its head, the louder its sounds.
Diving in Cold Water
The sperm whale routinely dives to a depth of 800 meters (2624.67) feet in its pursuit of squid, so another of its adaptations is a flexible ribcage that lets the lungs collapse under increased water pressure without harm to the animal. Also, the sperm whale has a large blood volume that is high in oxygen-carrying haemoglobin and myoglobin, a protein that stores high levels of oxygen in the muscles. Its body can also redirect oxygenated blood to the brain and other critical organs. The blubber of a sperm whale is about six to 12 inches thick as well, which lets it dive down to very cold water while retaining its core body heat.
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- MarineBio.org; Sperm Whales, Physeter catodon
- NOAA Fisheries Office of Protected Resources; Sperm Whales
- Aquarium of the Pacific Online Learning Center: Sperm Whale
- "The Audubon Society Field Guide to North American Fishes, Whales & Dolphins"; Herbert T. Boschung, Jr., et. al.; 1983
- "The Whale"; Philip Hoare; 2010