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...interferes marine mammals, especially cetaceans, which use sound as their prime mechanism to learn about their environment, as well as communicate, navigate, and forage. Here I review the various effects of anthropogenic noise on cetaceans. Conservation biologists need to explore how cetaceans are responding to this increase in noise pollution and determine what further research needs to be done in order to protect these animals and their habitat.
Introduction
Cetaceans are divided into two suborders: Mysticeti (baleen whales) and Odontoceti (toothed whales, which include dolphins and porpoises). The toothed whales use their teeth for catching fish, squid or other marine life that they then swallow whole (Rice 1998). Baleen whales do not have teeth, but have plates made of keratin that act as a giant filter, straining small animals from the seawater. Not all Mysticeti feed on plankton: the larger whales tend to eat small shoaling fish, such as herrings and sardine. One species of Mysticeti, the Gray Whale (Eschrichtius robustus), is a benthic feeder, primarily eating sea floor crustaceans (Rice 1998).
Uses of Sounds
Cetaceans may be especially sensitive to anthropogenic noise because some species of toothed whales have developed a special sense called echolocation that allows them to hunt and gather information about their environment in turbid and deep water where no light penetrates (Richardson et al. 1995). They send out a sound into the water and then use the returning echo to identify the objects that have reflected the sound. The differences in the returning echo provide the animal with information about the size, shape, orientation, direction, speed, and composition of the object or landscape.
Baleen whales live throughout the world's oceans and produce acoustic signals at low to moderate frequencies from 12 Hz-8 kHz (Ridgway and Harrison 1985; Richardson et al. 1995). These cetaceans lack an echolocation system. Toothed whales live in oceans around the world and in some rivers (Jefferson et al. 1993). They signal at moderate to high frequencies from 1-20 kHz and use echolocation at high frequencies from 20-150 kHz (Richardson et al. 1995). Cetaceans have inner ears that are so well developed that they can not only hear sounds tens of miles away, but are also able to discern the direction from which the sound comes.
Cetaceans not only use sound for navigation and feeding, but also to communicate, through methods such as groans, moans, whistles, clicks, or complex singing (Caldwell 1972). Communication is a behavior by one individual which causes a change in behavior or state of another individual, the receiver, through conveying information (Alcock 2005). Cetaceans use sound to communicate information about the location and identity of individuals or groups, reproductive status, food sources, predation risk, and dominance (Tyack 1999). For example, humpback whale males compete with other males through complex songs that can last for several hours, and females choose between males based on these vocalizations (Gaskin 1982).
Cetaceans communicate with each other using individualized vocalizations. Bottlenose dolphins, for example, have signature whistles used in communication (Tyack 1999). This whistle not only sends information on location, but also gives the identity of the individual vocalizing.
Sound is also important for marine mammals because it allows them to locate food sources. Echolocation is typically used by toothed whales to capture single prey items such as...
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