acoustical oceanography and whales
In 1992, the navy made hydrophones,underwater microphones, available to scientists. The purpose of these hydrophones was to track Soviet subs, but the navy heard more than just ships and subs. The hydrophones picked up the sounds of everything from rain to earthquakes, including the songs of the great whales. Acoustical oceanography is dedicated to the science of discovering the ocean by listening.
For the first time scientists could listen
to the ocean depths that were filled with the songs of the whales.
The animals could be heard hundreds and even thousands of miles
away. Instead of observing the ocean and hoping for a whale to
pop up within the mile of a research ship, scientists were now
able to study whales thousands of miles away.
The whales songs travel so far because of their low frequency. The melody the whales sing is a slow pattern. A blue whale sings one note every two minutes. The song is sped up by a factor of 60, and only then the melody is heard. Some have theorized that whales use the deep sound channel as a way of echolocating and thus navigating the vast oceans. With the use of the hydrophones it is possible to follow a single whale for days and days at a time. It has been observed that the whales
a blue whale (http://www.marinemultimedia.com/)
"slalom" from one underwater mountain to the next. It has been suggested that the whales might catch an echo off these mountains and hence use them as "markers on a map."
There are only eleven species of large whales and each has a very distinctive song. Humpback Whales are known for their melodious songs, while the blue whale has a rather haunting owl-like song. Sperm whales, on the other hand, have a tapping pattern that is highly rhythmic. The deep water whales seem to have songs that are highly rhythmic, whereas whales that prefer shallower waters tend to sing complex melodies. Perhaps these difference are related to the depths at which they live. Whales like birds sing throughout the year but are most active during the breeding system.
It is uncertain exactly what frequencies are audible to certain whales. Bottlenose dolphins have been tested to have a hearing range from 200 to 150,000 Hz.