Some scientists warn growing levels of human-caused noise in the oceans from military sonar, ships, oil exploration and drilling, offshore construction, motor boats, and jetskis is disrupting and/or killing whales, dolphins, and other marine life. In 2001, 16 whales and a dolphin were stranded on the northern coast of the Bahamas. Six of the whales and the dolphin died; autopsies showed that they had severe brain hemorrhaging. It is suspected that both the stranding and the bleeding were caused by sonar transmissions from U.S. Navy ships engaged in anti-submarine exercises nearby. There are growing fears that the ocean has become a booming, buzzing, and confusing place for whales, dolphins and other marine mammals. Sound is their principal sensory medium. They use it to communicate, navigate, hunt and find each other in the vastness of the ocean. Blue whales are known to carry out “conversations” with each other over distances of up to 1,000 kilometers (600 miles).
Scientists are focusing on three types of noises: Loud bangs, sonar pings, and explosions that can injure a marine mammal’s ears, droning noises from motorboats, and combined noises from commercial shipping that increase the background sound preventing marine animals from communicating. The biggest source of noise is commercial shipping. These sounds travel far and bounce all around the ocean, and they persist for a long time. To get a handle on how much noise is unusual, scientists are comparing the quieter southern oceans with the more heavily traveled northern ones. Scientists and government officials are also debating exactly what is harmful to marine mammals. For example, do loud sounds that drive away dolphins constitute a minor inconvenience or real harm? It’s an important question. The national Marine Mammal Act states that the animals can’t be harassed. If scientists determine whales are harassed by certain noises, laws could be created to lower the underwater racket. One of the questions in need of answering is what is loud or soft to these animals.
Now, turn on your volume, and compare the sounds of beluga whales and an ice breaker. Click on beluga calls to hear their vocalizations in Beaufort Sea. Click on ice breaker to hear propeller-cavitation noise.
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