The animal of choice for marine sound study is the bottlenose dolphin. This marine animal is the most common type of dolphin in our part of the world. It can be found year round off the coast of Florida and is known for swimming around the bows of boats and ships at sea. Usually, dolphins can only be found within 100 miles of the shoreline, but may be found in the open sea as well. They use sound for two main purposes, communication, and echolocation. While there is no dolphin "language" they make a signature sound that can be used to tell one dolphin from the other. Mother dolphins will make this whistling sound for several days just after giving birth to imprint on the calf who its mother is. The sounds for identifying each other are made through the larynx of the blowhole. This sound is in the 40 KHz range, and can travel up to 200 meters. .
The other use of sound is for echolocation. Sounds made for echolocation are made in the nasal cavities and are focused through a sac of fat known as the melon. This rounded projection at the front of the head focuses the sound into a beam that can then be directed in the direction of travel. This sound is produced in the 40 to 150 KHz range and is effective between 5 and 200 meters depending on the frequency of sound and the intensity that it is produced at. .
Humans can hear the lower frequency sounds produced, but most are out of the range of human hearing. All sounds are made either in the air, or more commonly in seawater. The speed of sound in seawater varies from the speed of sound in the air. Sounds made in seawater move in the 1500 meters per second range at 25 degrees Celsius, while the speed of sound in air is 346 meters per second at the same temperature. This means that the sound produced moves 5 times faster in the water than it would if it were made in the air, therefore the sound would still be distorted even if we could hear it.
