EMERGING CONCERNS - Marine Pollution: What Everyone Needs to Know - page 132

from natural sources such as the clicks and songs of whales,
and the grunts, croaks, and drumming of fishes named after
their sounds. Many marine species have acute hearing, echo-
location, and communication abilities. Time was when a blue
whale call could be heard by others of its species many miles
away, but since the advent of the propeller engine 150 years
ago, that has changed. An increase in boats, commercial ship-
ping traffic, exploration and extraction of oil and minerals,
air guns used for seismic exploration, sonar, and even jet skis
contribute to the increased level of underwater noise. Sound
travels four times faster in water than in air so it travels farther
under water. High intensity sound can travel for thousands
of miles. Since water is denser than air, sound waves travel
though water at higher energy levels and are therefore louder.
What types of noise occur in the ocean?
Underwater noise has been divided into two main
types: (1) impulsive—loud, intermittent or infrequent noises,
such as those generated by pile driving and seismic surveys;
and (2) continuous—lower-level constant noises, such as those
generated by ship engines and wind turbines. These two types
of noise have different impacts on marine life. The frequency
or pitch of the noise is also important, as animals are sensi-
tive to different frequencies. For instance, most of the noise
produced by pleasure boats is low frequency, below 1.5 kilo-
hertz (kHz). Although most sensitive to sounds above 15 kHz,
bottlenose dolphins could be disturbed by these boat noises
because they hear in the wider range 0.075-150 kHz and some
of their calls are below 2 kHz.
One new noise source having immediate and obvious
negative effects has been the development and testing of
low-frequency active (LFA) sonar that has a potential world-
wide deployment by the US Navy. Several tests of this sonar
have resulted in deaths of many marine animals. The oil and
gas industry uses arrays of airguns which release intense